KOFORIDUA TECHNICAL UNIVERSITY
FACULTY OF APPLIED SCIENCE AND TECHNOLOGY
DEPARTMENT OF FOOD AND POSTHARVEST TECHNOLOGY
A RESEARCH ON THE DEVELOPMENT OF LOW FAT ICE CREAM FLAVOURED
WITH AVOCADO (PERSEA AMERICANA) FRUIT PULP.
BY
OPARE JEMIMA ADUBEA
(04/2018/3951D)
A PROJECT WORK SUBMITTED TO THE DEPARTMENT OF FOOD AND
POSTHARVEST TECHNOLOGY, KOFORIDUA TECHNICAL UNIVERSITY IN
PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF HIGHER
NATIONAL DIPLOMA IN FOOD TECHNOLOGY.
DECEMBER, 2021
STUDENTS' DECLARATION
I hereby declare that this project work is the outcome of my own research and that no part has been
presented for the award of any other certificate in this University or elsewhere.
OPARE JEMIMA ADUBEA
(04/2018/3951D)
………………………….
………………………….
DATE
SIGNATURE
i
SUPERVISOR’S CERTIFICATION
I hereby certify that this project work was supervised in accordance with the University’s
guidelines for supervision of project work.
MS. DHAILLY ARABA ARKORFUL
………………………….
(SUPERVISOR)
DATE
ii
………………………….
SIGNATURE
ACKNOWLEDGEMENTS
My most sincere gratitude goes to God Almighty who has brought me this far in my academic
career. I give Him all the thanks for the wisdom and knowledge in putting these scripts together
for the successful completion of this project work. My hearty gratitude also goes to my project
supervisor Ms. Dhailly Araba Arkorful for her unending devotion, time and attention towards me,
that greatly helped me in accomplishing this work. My gratitude also goes to my family and love
ones for their support, both financially, morally and their advice during my trying times in the
course of this project work. It is my prayer that God meets you all at your various points of need.
iii
ABSTRACT
Consumer preferences towards plant-based foods have shifted significantly due to sustainable and
healthy reasons. Dairy products consist of high saturated fatty acid (SFA) and overconsumption
of SFA could lead to cardiovascular diseases. Avocado contains high levels of fat dominated by
monounsaturated fatty acid (MUFA) and phytosterol that have the potential as plant-based fat to
substitute dairy fat in ice cream. The objective of this study was to analyze the physiochemical,
rheological and sensorial properties of ice cream substituted with different concentrations of
avocado paste ranging from 20%, 30%, 40%, 50% and 60% respectively against dairy fat to
produce non-dairy fat ice cream. The physiochemical properties and total fat were determined.
Sensorial quality and hedonic attributes of the ice cream were investigated using 30 semi-trained
panelists. There were significant differences (p<0.05) for some parameters of the ice cream
substituted with avocado paste while the sensorial attributes for taste, colour, flavour, aroma and
overall acceptance also had some significant differences (p<0.05). The addition of 20% (T2) of
the avocado paste was the most preferred amongst the panelists. Avocado could provide a potential
substitution for dairy fat in ice cream.
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TABLE OF CONTENTS
CONTENT
PAGES
STUDENTS' DECLARATION ....................................................................................................... i
SUPERVISOR’S CERTIFICATION ............................................................................................. ii
ACKNOWLEDGEMENTS ........................................................................................................... iii
ABSTRACT ................................................................................................................................... iv
TABLE OF CONTENTS ................................................................................................................ v
LIST OF TABLES ....................................................................................................................... viii
LIST OF FIGURES ....................................................................................................................... ix
CHAPTER ONE ........................................................................................................................... 1
1.0 INTRODUCTION .................................................................................................................... 1
1.1 BACKGROUND OF STUDY .................................................................................................. 1
1.2 PROBLEM STATEMENT ....................................................................................................... 3
1.3 JUSTIFICATION ..................................................................................................................... 4
1.4 SCOPE OF STUDY.................................................................................................................. 4
1.5 OBJECTIVE OF STUDY ......................................................................................................... 4
1.6 ORGANIZATION OF STUDY ................................................................................................ 5
CHAPTER TWO .......................................................................................................................... 6
LITERATURE REVIEW ............................................................................................................ 6
2.0 INTRODUCTION .................................................................................................................... 6
2.1 LITERATURE REVIEW ON LOW FAT ICE CREAM USING AVOCADO FRUIT PULP 6
CHAPTER THREE .................................................................................................................... 20
RESEARCH METHODOLOGY .............................................................................................. 20
3.0 MATERIALS .......................................................................................................................... 20
3.1 STUDY LOCATION .............................................................................................................. 20
3.2 PREPARATION OF SAMPLES ............................................................................................ 20
3.2.1 Preparation of Avocado Fruit Pulp ...................................................................................... 21
v
3.2.2 Preparation of Ice cream; ..................................................................................................... 21
3.3 PROXIMATE AND PHYSIOCHEMICAL ANALYSIS ON AVOCADO ICE CREAM. ... 29
3.3.1 Moisture Content Determination ......................................................................................... 29
3.3.2 Ash Content Determination ................................................................................................. 30
3.3.3 Crude Protein Determination ............................................................................................... 30
3.3.5 Crude Fat Determination...................................................................................................... 31
3.3.6 Free Fatty Acid Determination. ........................................................................................... 32
3.3.7 Determination Of pH ........................................................................................................... 32
3.4 Determination of Total Soluble Solids. .................................................................................. 32
3.5 Overrun ................................................................................................................................... 33
3.6 Melting Rate............................................................................................................................ 33
CHAPTER FOUR ....................................................................................................................... 37
RESULTS AND DISCUSSION ................................................................................................. 37
4.0 INTRODUCTION .................................................................................................................. 37
4.1 CHEMICAL COMPOSITION AND ANTIOXIDANT ACTIVITY OF THE AVOCADO
FRUIT PULP. ............................................................................................................................... 37
4.1.1 SENSORY EVALUATION ................................................................................................ 38
4.2. PHYSIOCHEMICAL PROPERTIES OF THE VARIOUS ICE CREAM SAMPLES ........ 46
4.2.1 pH......................................................................................................................................... 47
4.3 Total Soluble Solids ................................................................................................................ 48
4.4 NUTRITIONAL COMPOSITION OF THE VARIOUS ICE CREAM SAMPLES .............. 49
4.4.1 MOISTURE CONTENT ..................................................................................................... 49
4.5 TOTAL FAT DETERMINATION ......................................................................................... 51
4.5.1 FREE FATTY ACID DETERMINATION ......................................................................... 52
4.6 ANTIOXIDANT ACTIVITY ................................................................................................. 54
4.6.1 PROTEIN DETERMINATION........................................................................................... 55
4.7 PHYSIOCHEMICAL PROPERTIES (OVERRUN AND MELTING RATE) OF THE
VARIOUS ICE CREAM SAMPLE. ............................................................................................ 56
4.8 MELTING RATE ................................................................................................................... 58
vi
CHAPTER FIVE ........................................................................................................................ 60
5.0 CONCLUSION AND RECOMMENDATION ...................................................................... 60
5.1 RECOMMENDATION .......................................................................................................... 61
REFERENCES ............................................................................................................................ 62
vii
LIST OF TABLES
TABLE
PAGES
Table 3.1 Specifications of different ice cream mixes. ................................................................ 20
Table 4.1 Chemical composition and antioxidant activity of Avocado ....................................... 37
Table 4.2 Results of samples in relation to the attribute taste ..................................................... 38
Table 4.3 Results of samples in relation to the attribute colour................................................... 40
Table 4.4 Results of samples in relation to the attribute flavour ................................................. 41
Table 4.5 Results of samples in relation to the attribute aroma ................................................... 42
Table 4.6 Results of samples in relation to the attribute mouthfeel............................................. 44
Table 4.7 Results of samples in relation to the overall acceptability........................................... 45
Table 4.8 Physiochemical properties (pH and TSS) of the various ice cream samples............... 46
Table 4.9 Nutritional composition (moisture, total fat%, FFA, Antioxidant activity and protein%)
....................................................................................................................................................... 49
Table 4.10 Overrun percentage. ................................................................................................... 56
viii
LIST OF FIGURES
FIGURES
PAGES
Figure 4.1 Antioxidant capacity standard calibration curve. ........................................................ 54
Figure 4.2 Results of melting rate. ................................................................................................ 58
ix
CHAPTER ONE
1.0 INTRODUCTION
This chapter is the introduction part of the study that entails the background of the study, problem
statement, aims and objectives of the study, research methodology, research questions, scope of
study, organization of study and justification.
1.1 BACKGROUND OF STUDY
Ice cream is a complex colloidal system, containing fat globules, air bubbles and ice crystals
dispersion/solution of proteins, salts, polysaccharide sugars and different flavors. Milk fat has been
recognized as a critical factor for the formation and support of structural characteristics of ice
cream as well as for the formation and support of structural characteristics of ice cream as well as
for the perceived texture of quality. The avocado (Persea Americana), a tree likely originated from
south-central Mexico, is classified as a member of the flowering plant family Lauraceae (Royal
Botanic Gardens et al., 2010) The fruits of the plant also called an avocado (or avocado pear or
alligator pear), is botanically a large berry containing a single large seed (Wegier et al., 2017). The
avocado may be originated in southern Mexico but was cultivated from the Rio Grande to central
Peru long before the arrival of the Europeans. Thereafter, it was carried not only to West Indies,
but also to nearly all parts of the tropical and subtropical world with suitable environmental
conditions. Now avocado is grown commercially in most parts of the world. (Morton, 1987).
Ghanaian avocados range in size, shape, color and flavor thanks to a large gene pool in the country.
There are many local varieties and hybrids that offer unique fruit and fruiting qualities, from early
bearing to late season, and from green-skinned to dark purple-black fruit at maturity. The peel may
be thick and pebbled, as found in the Guatemalan race of avocados, thin and delicate, typical of
1
the Mexican race, or smooth, leathery, and thin-to-medium in thickness, characteristics of the West
Indian race. Hass is the most common type of avocado that is available in all parts of Ghana and
even the world at large. Ghanaian avocados vary from pear-shaped to rounded, and can weigh as
much as a pound or more. The pale green or yellow flesh can be more watery, fibrous, dry or
buttery, depending on the variety and oil content. The flavor of avocado varies from mild to rih,
and offers hints of sweetness or nuttiness. Ghanaian avocados are available year-round in the local
markets (Tobón et al., 2017). Avocados are most well known for being a good source of mono
saturated, second only to olives amongst other fruits and vegetables so it is the most suitable fruit
that can be used for mayonnaise unlike the other forms of mayonnaise on the local markets.
Avocado can be used in its raw state or cooked by the application of a little heat although avocados
are mostly used or eaten in its raw state.
Good nutrition is one of the keys to a healthy life. You can improve your health by keeping a
balance diet. It is important to eat foods that contain vitamins and minerals because it all
contributes to the fitness of the human immune system. In Ghana, ice cream made from avocado
fruit pulp is not as common and well known as compared to the regular ice creams on the local
market, it is very healthy, nutritious and easy to make in our various homes as compared to other
forms of ice creams. Avocado ice cream is made from real avocados, which gives it a brilliant
green color. Avocado ice cream has the highest source of protein of all fruits, and have more
potassium than other plant-base crops. They also contain dietary fiber, folate, vitamin C, vitamin
K, and vitamin E. They are considered a ‘nutrient booster’ because they enable the body to absorb
more fat-soluble nutrient. Avocado ice cream contains a good source of monounsaturated fat (most
of which are oleic acid) which is good for your heart, fight inflammation, and may have anticancer
properties and can help absorb other fat-soluble nutrients (Lauren, 2019). Furthermore, avocado is
2
full of fiber, which is an important nutrient lacking in most Western diets. Studies have shown that
people who consume avocado tend to weigh less, perhaps due to the fruits’ high content of fiber
and healthy fat as well as its low glycemic index (Lauren, 2019). It also contains antioxidants that
are good for your eyes and brain, such as lutein and zeaxanthin. These antioxidants may lower
your risk of metabolic syndrome.
Although avocado ice cream has many nutritional benefits to the human system, it has its
disadvantages when it comes to its shelf life and color. The one caveat to making this avocado ice
cream is that, avocado undergo enzymatic browning when exposed to oxygen and this tends to
give an undesirable color to the blend (Christous et al., 2009).
Almost everyone can benefit from cutting back on unhealthy fat. If you currently eat many of the
regular ice creams, commit to cutting back and changing your habits by adopting to the use of
avocado ice cream that contains more healthy fats and other nutrients that is good for the body’s
immune system (Baars et al., 2004).
1.2 PROBLEM STATEMENT
Ice cream is high in sugar and fat, which makes up the majority of its carbohydrate and fat content
(Bower et al.,2004). The consumption of too much sugar and fat has contributed to health problems
such as weight gain, cavities and increased levels of blood triglycerides, another unhealthy type of
fat (Ranganathan et al., 2004). To lower the risk for high cholesterol and sugar-related problems,
there has been the need to produce a low-fat, low-sugar ice cream making use of the avocado fruit
pulp in order to solve health problems associated with the consumption of a full fat ice cream
(Christous et al., 2009).
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1.3 JUSTIFICATION
Using avocado ice cream ensures that the cream is filled with what is considered good, healthy
fats (monosaturated fats) (Bower et al., 2004). It is also high in oleic acid (an omega-9 fatty acid),
which is taught to have anti-inflammatory and immune-boosting properties (Brian, 2014). Also,
storing the ice cream in a container with a tight fitting lid prevents oxygen ingression. Ice creams
cannot be stored under normal room temperature so it must be kept frozen (Owni et al., 2009). In
order to maintain this physical property, avocado ice cream must be stored in a freezer at an
ambient temperature in relation to time (Dello et al., 2004).
1.4 SCOPE OF STUDY

Determination of the nutritional composition of the avocado ice cream.

Consumer acceptability of avocado ice cream using different percentage of avocado fruit
pulp.
1.5 OBJECTIVE OF STUDY
MAIN OBJECTIVE
The main objective of this work is to produce a low fat ice cream with the use of avocado fruit
pulp.
SPECIFIC OBJECTIVES
The specific objectives are outlined below;

To produce low fat ice cream using avocado fruit pulp in different proportions (20, 30, 40,
50 and 60%).
4

To analyze the physiochemical properties of the ice cream using different proportions of
the avocado fruit pulp.

To analyze the nutritional composition of the ice cream produce.

To analyze the sensory properties of the ice cream produce.
1.6 ORGANIZATION OF STUDY
The study has been organized into five chapters. The first chapter gives a background of the study,
problem statement, main aim and specific objectives of the study. The second chapter takes care
of the literature review related to the research topic under study. Chapter three explains how the
study was conducted and the method employed. It comprises of the research design, equipment
used, and data collection procedure as well as data analysis. Finally, chapter four and five presents
the findings of the study that is used to draw conclusions and recommendations on the research
topic under study.
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CHAPTER TWO
LITERATURE REVIEW
2.0 INTRODUCTION
This chapter contains the literature review on avocado ice cream, materials and method which
would be adopted to conduct the research.
2.1 LITERATURE REVIEW ON LOW FAT ICE CREAM USING AVOCADO FRUIT
PULP
Consumer preferences towards plant-based food have shifted significantly due to sustainable and
healthy reasons (Ranganathan, 2016). Dairy products consist of high Saturated Fatty Acids (SFA)
and overconsumption of SFA could lead to cardiovascular diseases. The preference towards plantbased diets has significantly increased (Granato et al., 2010), with the rise of millennial generation
who are increasingly adopting vegan and free-lactose diets (Flavera et al., 2008). Ice cream is a
complex colloidal system, containing fat globules, air bubbles and ice cream crystals dispersed in
a freeze-concentrated dispersion/solution of proteins, salts, polysaccharides, sugars and different
flavours. Milk fat has been recognized as a critical factor for the formation and support of structural
characteristics of ice cream as well as for the perceived textural quality example, lubrication of
tongue, richness of mouth feel, enhancement of creaminess, thickness and flavor perception
(Turgut and Cakmacki, 2009). However, several chronic diseases found to be correlated with fat
rich foods such as obesity, cardiovascular diseases and cancer (Fenelon and Guinee, 2000).
Therefore, there is a growing demand for low fat products which retain the desirable characteristics
of the full- fat product (Romeih et al., 2002). Reduction of fat content of ice cream makes a product
of lost textural properties and mouth feel as compared to full fat ice cream (Aime et al., 2001). It
6
has been reported that dairy milk sales have decreased globally by 7% in 2015 due to the negative
health perception of diary-based product consumption. Plant-based food diets however have
become more inclusive within personalized nutrition plans for more than 70% of consumers (FMI,
2017).
The avocado (Persea Americana), a tree likely originated from southcentral Mexico, is classified
as a member of the flowering plant family Lauraceae (RBG et al., 2010) The fruits of the plant
also called an avocado (or avocado pear or alligator pear), is botanically a large berry containing
a single large seed. The avocado may be originated in southern Mexico but was cultivated from
the Rio Grande to central Peru long before the arrival of the Europeans. Thereafter, it was carried
not only to West Indies, but to nearly all parts of the tropical and subtropical world with suitable
environmental conditions. Now avocado is grown commercially in most parts of the world.
(Morton, 1987).
Ghanaian avocados range in size, shape, color and flavor thanks to a large gene pool in the
country. There are many local varieties and hybrids that offer unique fruit and fruiting qualities,
from early bearing to late season, and from green-skinned to dark purple-black fruit at maturity
(Baars et al., 2004). The peel may be thick and pebbled, as found in the Guatemalan race of
avocados, thin and delicate, typical of the Mexican race, or smooth, leathery, and thin-to-medium
in thickness, characteristics of the West Indian race (Christous et al., 2008). Hass is the most
common type of avocado which is available in all parts of Ghana and even the world at large.
Ghanaian avocados vary from pear-shaped to rounded, and can weigh as much as a pound or more
(Peter et al., 2012). The pale green or yellow flesh can be more watery, fibrous, dry or buttery,
depending on the variety and oil content. The flavor of avocado varies from mild to rich, and offers
hints of sweetness or nuttiness. Ghanaian avocados are available year-round in the local markets
7
(Bhandari et al., 2005). Avocado is a highly caloric fruit with a good source of reliable and
insoluble fibre, vitamin C, E, K, B complex, folate and phytochemicals such as phytosterol and
carotenoids which possess antioxidant and radical scavenging activities (Lee et al., 2004).
Avocados are good sources of potassium, carbohydrates and sugar (Slater et al., 1975).
Furthermore, it is rich in monounsaturated fatty acids, especially oleic and palmitoleic acids, which
is related to decrease risk of cardiovascular diseases because these fatty acids preserve levels of
high –density lipoproteins and act as antioxidants (Richard et al., 2008). Thus, avocado can be
considered as highly desirable additive to a healthy diet. According to the American Heart
Association (Dietary Guidelines, 2008) reports that avocados can help consumers to meet the
dietary guidelines which involves eating a diet of low fat content, rich in unsaturated fatty acids
with lower cholesterol because avocados are the only fruits that contain monou saturated fats.
Although avocado ice cream contains a lot of nutrients which is good for our health, the fruit
avocado, used for making this snack is prone to bacterium specifically listeria which causes food
borne illness (Catherine, 2019). The potential issue is that when you cut through the avocado’s
pebbly skin, bacteria could be transferred to the knife. And then the knife could contaminate the
avocado flesh. Before peeling off the produce before use, make sure that the skin is thoroughly
washed and gently scrubbed under clean water to get rid of these bacteria and prevent crosscontamination from occurring. In addition, avocado easily undergoes enzymatic browning. This is
because, avocado contains an enzyme called polyphenol oxidase, which causes the flesh brown
when exposed to air or more specifically, when it is exposed to oxygen. So, in order to maintain
that gorgeous green color, seal in an air tight container to maintain its color for some period of
time before it is ready to be used (Racheal, 2019). Although the browning part of the avocado
might look unappetizing and can taste bitter, it is still safe to consume (Nathaniel et al., 2020).
8
Consumers prefer plant-based diets (Ranganathan, 2016), which are more sustainable (Salonen,
2003) and able to provide better health benefits. The preference towards plant-based diets has
significantly increased (Granato et al., 2010) with the rise of millennial generation who are
increasingly adopting vegan and free-lactose diets (Flavera et al., 2008). It also has been reported
that diary milk sales have decreased globally by 7% in 2015 due to the negative health perception
of diary-based product consumption. It has been reported that people who consumed avocado
regularly tend to have a sufficient nutrient supply of dietary fibre, vitamin K, vitamin E, potassium,
magnesium as well as vitamin B complex (Fulgoni et al., 2010). The functions and importance of
these nutrients in avocado to the human system are;
DIETARY FIBRE
The dietary fibre in avocado helps increase the weight and size of your stool and softens it. Hence,
decreasing the chances of getting constipation. In case of releasing loose, watery stools, the fiber
may help to solidify the stool because it absorbs water and adds bulk to stool which helps maintain
bowel health (Fulgoni et al., 2010).
Vitamin K helps to make various proteins that are needed for blood clotting and the building of
strong bones (Fulgoni et al., 2010).
VITAMIN E
Vitamin E is a fat soluble nutrient, which acts as an antioxidant, capable of helping to protect the
body cells from the damage caused by free radicals. Free radicals are compounds formed when
our bodies convert the food we eat into energy (Fulgoni et al., 2010).
9
POTASSIUM
Potassium helps your nerves to function and muscles to contract. It helps your heartbeat to stay
regular and also helps to move nutrients into the cells and waste products out of the cell (Fulgoni
et al., 2010).
MAGNESIUM
Magnesium helps to maintain normal nerve and muscle function, supports a healthy immune
system, keeps the heartbeat steady and maintain strong bones. Magnesium also helps to adjust
blood glucose levels and acids in the production of energy and protein (Fulgoni et al., 2010)
VITAMIN B COMPLEX
Vitamin B complex play a vital role in maintaining good health and well-being. As the building
blocks of a healthy body, B vitamins have a direct impact on your energy levels, brain function
and cell metabolism. Vitamin B complex helps prevent infections and helps support or promote
cell health (Fulgoni et al., 2010)
These nutrients provide a wide range of potential health benefits such as preventing
hyperchostrolemia (Salonen et al., 2003), vascular damage (Jacobs et al., 2007), and reduce the
risk of antherosclerosis (Dwyer et al., 2004). The consumption of avocado has been investigated
to have positive effects on lipid profiles (Carranza et al., 1997) by increasing HDL cholesterol
levels, reducing lipid serum peroxidation, and promoting cardiovascular health (Wu X et al.,2007).
Furthermore, phytosterol has also been proven to be an effective compound against type-2-diabetis
mellitus, lowering the risk of cardiovascular diseases, and preventing cancer (Jones et al., 2009).
10
Avocado has high fat content (USDA, 2011) which is a good source for substituting the milk fat
in frozen diary desserts (Goff and Richard, 2013). Ice cream is one of the most widely consumed
foods in frozen dairy desserts category (Goff and Richard, 2013). A series of different types of
non-diary based ice cream have been developed due to rise of health concerns associated with milk
consumption (Peter and Keigan, 2012), milk fat consumption that is dominated by SFA, and clean
label issues (Barrs et al., 2004). A non-diary fat source derived from avocado could be a potential
alternative in order to create an option for free-diary fat ice cream as well as provide better health
benefits to the consumers. Plant-baseed fat sources in the ice cream formulation. Furthermore,
plant-based replacement for diary-based fat sources is generally less expensive compared to diary
fat (Goff and Richard, 2013) and provide advantages towards health (Salonen et al., 2003, Wu X
et al., 2007). The objective of this study is to analyze the physiochemical, rheological and sensorial
properties of ice cream that have been substituted with different concentrations of avocado paste.
SKIMMED MILK POWDER
Skimmed powdered milk, also called milk powder or historically dried milk, is a manufactured
dairy product made by evaporating milk to dryness. Skim Milk Powder is obtained by removing
water from pasteurized skim milk. It contains 5% or less moisture (by weight) and 1.5% or less
milkfat (by weight) and a minimum milk protein content of 34% (Filomena et. al., 2010). One
purpose of drying milk is to preserve it; milk powder has a far longer shelf life than liquid milk
and does not need to be refrigerated, due to its low moisture content. Another purpose is to reduce
its bulk for the economy of transportation. Powdered milk and dairy products include such items
as dry whole milk, nonfat (skimmed) dry milk, dry buttermilk, dry whey products and dry dairy
blends. Many exported dairy products conform to standards laid out in Codex Alimentarius.
11
USES AND BENEFITS DEEIVED FROM SKIMMED MILK POWDER CONSUMPTION
Skimmed powdered milk is frequently used in the manufacture of infant formula, confectionery
such as ice cream, chocolate and caramel candy, and in recipes for baked goods where adding
liquid milk would render the product too thin. Powdered milk is also widely used in various sweets
such as the famous Indian milk balls known as gulab jamun and a popular Indian sweet delicacy
(sprinkled with desiccated coconut) known as chum chum (made with skim milk powder). Many
no-cook recipes that use nut butters use powdered milk to prevent the nut butter from turning liquid
by absorbing the oil (Tucker et al., 2013).
Powdered milk is also a common item in UN food aid supplies, fallout shelters, warehouses, and
wherever fresh milk is not a viable option. It is widely used in many developing countries
because of reduced transport and storage costs (reduced bulk and weight, no refrigerated
vehicles). Like other dry foods, it is considered nonperishable and is favored by survivalists,
hikers, and others requiring nonperishable, easy-to-prepare food. Because of its resemblance to
cocaine and other drugs, powdered milk is sometimes used in filmmaking as a non-toxic prop
that may be insufflated (Wayne, 2009).
NUTRITIONAL COMPOSITION AND SOME HEALTH IMPLICATIONS RELATED
TO SKIMMED MILK POWDER
Skimmed milk powders contain all 21 standard amino acids, the building blocks of proteins, and
are high in soluble vitamins and minerals (MPNI, 2013). According to USAID, (USAID, 2006)
the typical average amounts of major nutrients in the reconstituted nonfat dry milk are (by weight)
36% protein, 52% carbohydrates (predominantly lactose), calcium 1.3%, potassium 1.8%. Whole
milk powder, on the other hand, contains an average of 25-27% protein, 36-38% carbohydrates,
12
26-40% fat, and 5-7% ash (minerals). In Canada, powdered skim milk must contain added vitamin
D in an amount such that a reasonable daily intake of the milk will provide between 300 and 400
International Units (IU) of vitamin D (F.D.R, 2019). However, inappropriate storage conditions,
such as high relative humidity and high ambient temperature, can significantly degrade the
nutritive value of the skimmed milk powder (M. Okamato et al., 2020).
Commercial skimmed milk powders are reported to contain oxysterols (oxidized cholesterol) (P.F
Fox et al., 2006) in higher amounts than in fresh milk (up to 30 μg/g, versus trace amounts in fresh
milk) (Dabrowski et al., 2016). Oxysterols are derivatives of cholesterol that are produced either
by free radicals or by enzymes. Some free radicals-derived oxysterols have been suspected of being
initiators of atherosclerotic plaques (PIFNS, 2019). For comparison, powdered eggs contain even
more oxysterols, up to 200 μg/g (Dabdowski et al., 2006).
SUGAR
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in
food. Table sugar, granulated sugar, or regular sugar, refers to sucrose, a disaccharide composed
of glucose and fructose (FAO, 2019). Simple sugars, also called monosaccharides, include glucose,
fructose, and galactose. Compound sugars, also called disaccharides or double sugars, are
molecules composed of two monosaccharides joined by a glycosidic bond. Common examples are
sucrose (table sugar) (glucose + fructose), lactose (glucose + galactose), and maltose (two
molecules of glucose). In the body, compound sugars are hydrolysed into simple sugars (WHO,
2015).
Longer chains of monosaccharides are not regarded as sugars, and are called oligosaccharides or
polysaccharides. Starch is a glucose polymer found in plants, and is the most abundant source of
13
energy in human food. Some other chemical substances, such as glycerol and sugar alcohols, may
have a sweet taste, but are not classified as sugar. Sucrose is used in prepared foods (e.g., cookies
and cakes), is sometimes added to commercially available processed food and beverages, and may
be used by people as a sweetener for foods (e.g., toast and cereal) and beverages (e.g., coffee and
tea). The average person consumes about 24 kilograms (53 lb) of sugar each year, with North and
South Americans consuming up to 50 kilograms (110 lb) and Africans consuming under 20
kilograms (44 lb) (FAO, 2020). As sugar consumption grew in the latter part of the 20th century,
researchers began to examine whether a diet high in sugar, especially refined sugar, was damaging
to human health. Excessive consumption of sugar has been implicated in the onset of obesity,
diabetes, cardiovascular disease, dementia, and tooth decay. Numerous studies have tried to clarify
those implications, but with varying results, mainly because of the difficulty of finding populations
for use as controls that consume little or no sugar. In 2015, the World Health Organization
recommended that adults and children reduce their intake of free sugars to less than 10%, and
encouraged a reduction to below 5%, of their total energy intake (WHO, 2015).
TYPES OF SUGAR
Monosaccharides
Fructose, galactose, and glucose are all simple sugars, monosaccharides, with the general formula
C6H12O6. They have five hydroxyl groups (−OH) and a carbonyl group (C=O) and are cyclic when
dissolved in water. They each exist as several isomers with dextro- and laevo-rotatory forms that
cause polarized light to diverge to the right or the left (David et al., 2020).
14
Fructose
Fructose, or fruit sugar, occurs naturally in fruits, some root vegetables, cane sugar and honey and
is the sweetest of the sugars. It is one of the components of sucrose or table sugar. It is used as a
high-fructose syrup, which is manufactured from hydrolyzed corn starch that has been processed
to yield corn syrup, with enzymes then added to convert part of the glucose into fructose
(Kretchmer et al., 2018).
Galactose
Galactose generally does not occur in the free state but is a constituent with glucose of the
disaccharide lactose or milk sugar. It is less sweet than glucose. It is a component of the antigens
found on the surface of red blood cells that determine blood groups (Raven et al., 2014).
Glucose
Glucose occurs naturally in fruits and plant juices and is the primary product of photosynthesis.
Starch is converted into glucose during digestion, and glucose is the form of sugar that is
transported around the bodies of animals in the bloodstream. Although in principle there are two
enantiomers of glucose (mirror images one of the other), naturally occurring glucose is D-glucose.
This is also called dextrose, or grape sugar because drying grape juice produces crystals of dextrose
that can be sieved from the other components (George, 2013). Glucose syrup is a liquid form of
glucose that is widely used in the manufacture of foodstuffs. It can be manufactured from starch
by enzymatic hydrolysis (Schenck et al., 2017). For example, corn syrup, which is produced
commercially by breaking down maize starch, is one common source of purified dextrose (CFR,
2020). However, dextrose is naturally present in many unprocessed, whole foods, including honey
and fruits such as grapes (Ireland et al., 2010).
15
Disaccharides
Lactose, maltose, and sucrose are all compound sugars, disaccharides, with the general formula
C12H22O11. They are formed by the combination of two monosaccharide molecules with the
exclusion of a molecule of water (CFR, 2020).
Lactose
Lactose is the naturally occurring sugar found in milk. A molecule of lactose is formed by the
combination of a molecule of galactose with a molecule of glucose. It is broken down when
consumed into its constituent parts by the enzyme lactase during digestion. Children have this
enzyme but some adults no longer form it and they are unable to digest lactose (EBO, 2019)
Maltose
Maltose is formed during the germination of certain grains, the most notable being barley, which
is converted into malt, the source of the sugar's name. A molecule of maltose is formed by the
combination of two molecules of glucose. It is less sweet than glucose, fructose or sucrose (CFA,
2020). It is formed in the body during the digestion of starch by the enzyme amylase and is itself
broken down during digestion by the enzyme maltase (EBO, 2019).
Sucrose
Sucrose is found in the stems of sugarcane and roots of sugar beet. It also occurs naturally
alongside fructose and glucose in other plants, in particular fruits and some roots such as carrots.
The different proportions of sugars found in these foods determines the range of sweetness
experienced when eating them (Buzz et al., 2016). A molecule of sucrose is formed by the
combination of a molecule of glucose with a molecule of fructose. After being eaten, sucrose is
16
split into its constituent parts during digestion by a number of enzymes known as sucrase (EBO,
2019). They have five hydroxyl groups (−OH) and a carbonyl group (C=O) and are cyclic when
dissolved in water. They each exist as several isomers with Dextro and Levo rotatory forms that
cause polarized light to diverge to the right or the left (David et al., 2019).
HEALTH IMPLICATIONS RELATED FO EXCESSIVE INTAKE OF SUGAR
Sugar refiners and manufacturers of sugary foods and drinks have sought to influence medical
research and public health recommendations, (Mozaffarian, 2017) with substantial and largely
clandestine spending documented from the 1960s to 2016 (Aaron et al., 2017) results of research
on the health effects of sugary food and drink differ significantly, depending on whether the
researcher has financial ties to the food and drink industry (Jessica et al., 2016). A 2013 medical
review concluded "unhealthy commodity industries should have no role in the formation of
national or international NCD [non-communicable disease] policy" (Rob et al., 2013). There have
been similar efforts to steer coverage of sugar-related health information in popular media,
including news media and social media (Eric, 2014).
Obesity and Metabolic Syndrome
A 2003 World Health Organization technical report provided evidence that high intake of sugary
drinks (including fruit juice) increased the risk of obesity by adding to overall energy intake
(WHO, 2003). By itself, sugar is not a factor causing obesity and metabolic syndrome, but rather,
when over-consumed, is a component of unhealthy dietary behavior (Alexandra, 2013). Metaanalyses showed that excessive consumption of sugar-sweetened beverages increased the risk of
developing type 2 diabetes and metabolic syndrome including weight gain (Hill et.al, 2019) and
obesity in adults and children (Mallika et al., 2018).
17
Hyperactivity
A 2019 meta-analysis found that sugar consumption does not improve mood, but can lower
alertness and increase fatigue within an hour of consumption (Mantantzis et al., 2019). Some
studies report evidence of causality between high consumption of refined sugar and hyperactivity
(Davis et al., 2010). One review of low-quality studies of children consuming high amounts of
energy drinks showed association with higher rates of unhealthy behaviors, including smoking and
excessive alcohol use, and with hyperactivity and insomnia (Visram et al., 2016).
Tooth decay
The 2003 WHO report stated that "Sugars are undoubtedly the most important dietary factor in the
development of dental caries" (WHO, 2003). A review of human studies showed that the incidence
of caries is lower when sugar intake is less than 10% of total energy consumed (Anahad et al.,
2015).
VANILLA ESSENCE
Vanilla essence is a solution made by macerating and percolating vanilla pods in a solution of
ethanol and water. It is considered an essential ingredient in many Western desserts, especially
baked goods like cakes, cookies, brownies, and cupcakes, as well as custards, ice creams, and
puddings (Lior, 2016). Although its primary flavor compound is vanillin, pure vanilla extract
contains several hundred additional flavor compounds, which are responsible for its complex, deep
flavor (Rose, 2017). By contrast, artificial vanilla flavor is solely made up of artificially derived
vanillin, which is frequently made from a by-product of the wood pulp industry (FSM, 2013).
Because of the way that vanilla extract is made (that is, by macerating naturally brown vanilla
18
beans in alcohol), there is no possible way for it to be colorless or clear. Therefore, any clear vanilla
flavoring is artificial (Baking bites, 2014).
19
CHAPTER THREE
RESEARCH METHODOLOGY
3.0 MATERIALS
Fresh full ripped avocado pear (Hass variety) was obtained from Koforidua Central Market. Fresh
skimmed milk powder, cream, sugar and vanilla was purchased in a local market in Koforidua. All
other solvents and chemicals needed for the analysis was obtained from the Department of Food
and Postharvest Chemistry Laboratory.
3.1 STUDY LOCATION
The study was conducted at the Food Product Development and the Chemistry Laboratory of the
Department of Food and Postharvest Technology, Koforidua Technical University, Koforidua
Ghana.
3.2 PREPARATION OF SAMPLES
Table 3.1 Specifications of different ice cream mixes.
Ingredients
T1
T2
T3
T4
T5
T6
100 g
80g
70g
60g
50g
40g
0g
20g
30g
40g
50g
60g
Distilled water
300ml
300ml
300ml
300ml
350ml
350ml
Sugar
100g
100g
100g
100g
100g
100g
0.2g
0.2g
0.2g
0.2g
0.2g
0.2g
(CONTROL)
Skim milk powder
Avocado
Flavour
(vanilla
essence)
20
3.2.1 Preparation of Avocado Fruit Pulp
The ripened avocado fruit was washed, dried, cut opened and flesh removed and mixed through
using blender. The homogenate was packaged in plastic containers and cold stored at 4°C till used.
The fruit pulp was freshly prepared directly before ice cream making.
3.2.2 Preparation of Ice cream;
Ice cream mixes and ice cream was made as described by Charles and Williams (2019). Table one
shows the formulation of different ice cream mixes.
SAMPLE T1
Skim milk powder (100g) was first be mixed with 100g of sugar and 0.2g of flavor to form a
mixture. 300ml distilled water was added to the mixture and stirred vigorously until a uniform
solution was formed. The mixture was then heated at 80°C for 5 minutes. The pasteurized mixture
was then be cooled to a temperature of 40°C. Sample T1 was then refrigerated at a temperature of
5°C between 12-24 hours.
SAMPLE T2
Skim milk powder (80g) was first mixed with 100g of sugar and 0.2g of flavor to form a mixture.
300ml distilled water was added to the mixture and stirred vigorously until a uniform solution was
formed. The mixture would then be heated at 80°C for 5 minutes. The pasteurized mixture was
then cooled to a temperature of 40°C and 20g of the blended avocado fruit pulp was added and
mixed thoroughly. Sample T2 was then refrigerated at a temperature of 5°C between 12-24 hours.
21
SAMPLE T3
Skim milk powder (70g) was first mixed with 100g of sugar and 0.2g of flavor to form a mixture.
300ml of distilled water was added to the mixture and stirred vigorously until a uniform solution
was formed. The mixture was then be heated at 80°C for 5 minutes. The pasteurized mixture was
then cooled to a temperature of 40°C and 30g of the blended avocado fruit pulp was added and
mixed thoroughly. Sample T3 was then refrigerated at a temperature of 5°C between 12-24 hours.
SAMPLE T4
Skim milk powder (60g) was first mixed with 100g of sugar and 0.2g of flavor to form a mixture.
300ml of distilled water was added to the mixture and stirred vigorously until a uniform solution
was formed. The mixture was heated at 80°C for 5 minutes. The pasteurized mixture was then
cooled to a temperature of 40°C and 40g of the blended avocado fruit pulp was added and mixed
thoroughly. Sample T4 was refrigerated at a temperature of 5°C between 12-24 hours.
SAMPLE T5
Skim milk powder (50g) was first mixed with 100g of sugar and 0.2g of flavor to form a mixture.
300ml of distilled water was added to the mixture and stirred vigorously until a uniform solution
was formed. The mixture was heated at 80°C for 5 minutes. The pasteurized mixture was cooled
to a temperature of 40°C and 50g of the blended avocado fruit pulp was added and mixed
thoroughly. Sample T5 was refrigerated at a temperature of 5°C between 12-24 hours.
SAMPLE T6
Skim milk powder (40g) was first mixed with 100g of sugar and 0.2g of flavor to form a mixture.
300ml of distilled water was added to the mixture and stirred vigorously until a uniform solution
22
was formed. The mixture was then heated at 80°C for 5 minutes. The pasteurized mixture was
cooled to a temperature of 40°C and 60g of the blended avocado fruit pulp was added and mixed
thoroughly. Sample T6 was then refrigerated at a temperature of 5°C between 12-24 hours.
The avocado fruit pulp would be used in different proportions that is (T2: T3: T4:T5: T6, 20g, 30g,
40g, 50g and 60g respectively). The frozen mixtures would then be whipped in an ice cream mixer
(Taylormate Model 152, Taylor Company, Blackhawk Blvd, USA). The ice cream would then be
collected into 100 ml plastic cups, covered, hardened and stored at a temperature of -18°C for one
day until analysis.
23
FLOW DIAGRAM OF AVOCADO ICE CREAM PREPARATION.
Washing and cutting of avocado
Scooping and blending of avocado
Packaging and storing of avocado paste in a refrigerator at a temperature
of 4°c
Mixing all measured dried ingredients together for ice cream
preparation
Pasteurize the mixture at a temperature of 80°c for 5 minutes
Cool the pasteurized mixture with cold water to reduce the temperature
to 40°c
Add the cooled avocado paste to the mixture and mix to achieve a
homogeneous mixture.
Refrigerate the mixture at a temperature of 5°c between 12-24 hours.
Whip the mixture in an ice cream maker machine.
Package the ice cream into plastic cups with thight fitting lid.
Store packaged ice cream in the freezer at a temperature of -18°c.
24
PROXIMATE ANALYSIS ON AVOCADO
Moisture Content Determination
The moisture content of the samples was determined using the method as described by AOAC,
(2005). The crucibles were washed and dried in an oven for 20 minutes. It was then cooled in a
desiccator. 4g of the sample was weighed into previously weighed crucibles and was transferred
into an oven set at a temperature of 103°C for 4 hours. At the end of the four hours, the samples
were removed and were placed in a desiccator to cool then weighed.
% Moisture: W2 - W1/W2 - W0 × 100
Where;
WO: weight of empty crucible
W1: weight of crucible sample.
W2 weight of crucible dried sample
Ash Content Determination
Three grams of sample was weighed using an analytical balance (SARTORIUS B120S,
GERMANY). The weight of the crucible and each sample was determined and recorded. The
crucible and its content were placed in the muffle furnace (THERMO SCIENTIFIC) at 600 degree
celcius for 2 hours cooled in desiccators and weighed. The procedure was repeated for each sample
in triplicates (AOAC,2000). The percentage ash was determined using the following formulae.
%Ash = W2 - W1 × 100/W3
25
Where;
W1 = weight of empty crucible
W2 = weight of ashes sample
W3 = weight of sample
Crude protein determination
The crude protein of the ice cream was analyzed using Kjheldah method. 3 grams of the ice cream
sample was weighed using an analytical balance (SARTORIUS B120S, GERMANY) and was
placed in a digested flask. 25ml of concentrated H2SO4 and Kjheldah catalyst was added. Digestion
was carried out in the digestion chamber until a clear solution is obtained. The digested sample
was filtered into a 100ml volumetric flask and made to the mark with 60ml distilled water and
mixed well. 70ml of NaOH and 10ml of the sample were put into the Kjheldah apparatus and be
heated for the distillation of Ammonia. 25ml of 4% boric acid was measured into the conical flask
to receive the liberated ammonia gas.
The nitrogen content was estimated by titrating the ammonium borate formed with standard
0.096N HCL using mixed indicator and titer values recorded. The procedure was repeated for each
sample in the (AOAC 2000). The protein content was calculated using the formula.
Protein % = (A - B) × 14.007 × 6.25/W
Where;
A = volume (ml) of 0.2N HCL used sample titration
B = volume (ml) of 0.2N HCL used in sample titration
26
14.007 = atomic weight of nitrogen
6.25 = the protein-nitrogen conversion factor.
Determination of Total Soluble Solids.
A hand held refractometer (Atagos master series, Japan) was used. The refractometer was
standardized by placing a drop of distilled water on the prism. The refractometer was placed in
such a way that it allowed entry of sunlight into the prism. The refractometer was placed such that
it allowed entry of sunlight into the prism. The eye-piece was used to observe the standardization
after adjusting the coarse and fine adjustment properly. The process was repeated in triplicate and
the results were recorded.
A hand held refractometer (Atagos master series, Japan) was used. The refractometer was
standardized by placing a drop of distilled water on the prism. The refractometer was placed in
such a way that it allowed entry of sunlight into the prism. The
Determination Of pH
The digital bench top Ph meter (Ph/ORP/ISE meters) equipped with an electrode wasused in the
determination. The electrode was washed in distilled water. It was then placed in each sample. The
Ph reading was read from the recorder of the Ph meter (AOAC, 1990).
Fat content determination
2gram avocado fruit pulp sample which the moisture content had been determined was used. The
beakers were weighed using an analytical balance (SARTORIUS B120S, GERMANY). The
samples were transferred into a thimble and placed in a holding chamber of the Goldfish apparatus.
An amount of petroleum ether was poured into each of the beakers. Asbstos was placed on top of
27
each sample in the thimble, the thimbles were then inserted in the gaskets of the condenser. The
beaker containing the solvents was also connected to the gaskets. The tap was then opened to allow
free flow of water through the apparatus to facilitate the condensing of the solvents. The apparatus
was switched on and the sample extracted for 4 hours within a rate of 5 drops per second. The
beakers and its content were dried in an oven (FISHER Isotemp oven SENIOR MODEL) for
30minutes, cooled in a desiccator for 30minutes and weighed on an analytical balance
(SARTORIUS B120S GERMANY) to determine the difference in weight of the flask. This
procedure was repeated for each sample in triplicates (AOAC,2000).The fat content was calculated
using the formula
%Crudefat=W1/W2 × 100
W1 = fat weight
W2 = sample weight
Crude fiber content determination
The sample used for the fat determination will be used for the crude fiber analysis. The defatted
sample was transferred into 500ml Erlenmeyer flask and 0.5g of the asbestos and 200ml of 1.25%
boiling hydrogen sulphate was added and connected to a condenser and set on a hot plate. The
flask boiled for 30minutes, its content was filtered out and washed with boiling water until the
washings are no more acidic. The residues were put into a flask, connected to the condenser and
made to boil with 200ml of 25% NaOH for 30minutes. It was then filtered and washed with bottling
water till filtrate was no longer basic and 1.5ml alcohol was used to do the final washing. Residues
will then be transferred into silica crucible and dried in an electric oven (FISHER Isotemp oven,
SENIOR MODEL) for an hour at 100 degree Celsius. It is then cooled in a desiccator and weighed
28
and loss in weight would be determined. The procedure was repeated for each sample in triplicates
(AOAC,1990).The crude fiber content was calculated using the formula
%Crude fiber = (C1 - C2) × 100/C3
Where;
C1 = weight of dried sample
C2 = weight of ashed sample
C3 = weight of defatted sample
Carbohydrate Determination
The carbohydrate content was determined by the method of difference AOAC (1990). The quantity
of carbohydrate was calculated by the following equation.
Carbohydrate =100 - (Ash + moisture + protein + fat + fiber).
3.3 PROXIMATE AND PHYSIOCHEMICAL ANALYSIS ON AVOCADO ICE CREAM.
3.3.1 Moisture Content Determination
The moisture content of the sample was determined using the method as described by AOAC,
(2005). The crucibles were washed and dried in an oven for 20 minutes. It was then cooled in a
desiccator. 4g of the sample was weighed into previously weighed crucibles and was transferred
into an oven set at a temperature of 103°C for 4 hours. At the end of the four hours, the samples
were removed and were placed in a desiccator to cool then weighed.
% Moisture: W2-W1/W2-W0×100
29
Where;
WO: weight of empty crucible
W1: weight of crucible+ sample.
W2= weight of crucible + dried sample
3.3.2 Ash Content Determination
The ash content was determined by the methods as described by AOAC (2005). 4g of each sample
was weighed into a weighed crucible, which has been dried in an oven ad cooled in a desiccator.
It was then transferred into an electric furnace set at 550°C for 8 hours. After the 8 hours, the
crucibles with samples were then cooled in the desiccator before it was weighed.
Weight of sample = (wt of sample + wt of crucible)−wt of crucible
Weight of sample= ash − empty crucible
% Ash =weight of ash/weight of sample×100
3.3.3 Crude Protein Determination
The protein content was determined by the Kjeldahl Nitrogen method as described by AOAC
(2005). In brief, 1 liter of the samples were weighed unto a filter paper. The filter paper was folded
into a long protein tube (test tube). 25ml of concentrated H2SO4 was measured onto the sample in
the test tube. One khejedal tablet was added to the mixture in the test tube. The tube was fixed onto
a digester for 90 minutes at a temperature of 400°C to digest all the nitrogen to ammonium
sulphate. After the digestion, the test tubes were fixed onto a digestion machine. 100ml of 40%
NaOH and 150ml of water was added to the samples in distillatory.
30
The mixtures were steam distilled for 2 minutes into 500ml conical flask containing 10ml of 4%
Boric acid with three drops of screened methyl red as indicator and placed at the receiving top of
the condenser. The solution was then titrated against 0.1036N HCL in a 50ml burette.
% Nitrogen=[H+] × titer × (molar mass) ×100÷ sample wt×100
%Nitrogen=[H+] × (titer - blank) ×molar mass ÷ sample wt×10
The %nitrogen was then multiplied by a correction factor to obtain the %crude protein.
Correction factor= 6.25
% Crude protein= (%nitrogen) × (correction factor)
3.3.5 Crude Fat Determination
The fat content was determined using AOAC (2005). In brief, 2g of each sample were weighed
unto a filter paper, cotton was placed inside a thimble, the sample were placed on the cotton and
covered with extra nonabsorbent cotton to create an environment for the extraction. 90ml of
petroleum ether which boils at 40°C was measured. The petroleum ether was poured into the flask
containing the thimble o completely cover the surface. The flask was then fixed onto the soxtherm
apparatus for 3 hours. After the 3 hours the sample was removed from the beaker leaving the
extract at the bottom of the beaker. The extract was then dried in an oven for 1 hour. After 1 hour,
the beaker was removed from the oven and allowed to cool. The sample was then weighed.
Fat content= weight of beaker-weight of dried sample.
%Fat= fat content ÷ weight of sample×100
31
3.3.6 Free Fatty Acid Determination.
The free fatty acid content of the ice creams was determined by a modification of the solvent
extraction procedure. 30 grams of melted ice cream mix were weighed into 250ml centrifuge
bottles. The ice cream was diluted with 10ml of distilled water and titrated with 1N H2SO4. The
titrated mixture was shaken vigorously with 40ml of ethanol for 30 seconds and allowed to stand
for 5 minutes. 60ml of ethyl ether was added and the mixture was swirled for some seconds. The
mixture was then centrifuged for 10 minutes at 2,000 r.p.m. The fat layer of the solvent was then
transferred to a fat dish by siphoning and the extracted fat was freed from solvent by allowing the
pans to stand at room temperature overnight. The last traces of solvent were removed by placing
the fat in a 60°C oven at 50mm mercury for 10 minutes. The free fatty acid content of the extracted
fat was determined by the method of Breazeale and Bird. One gram of the day was dissolved in
5ml of absolute ethanol and 15ml of petroleum ether. Ten drops of phenolphthalein solution were
added and the solution was titrated for the first definite color change with 0.01N KOH using a 5ml
micro-burette.
3.3.7 Determination Of pH
The digital bench top pH meter (pH/ORP/ISE meters) equipped with an electrode was used in the
determination. The electrode was washed in distilled water. It was then placed in each sample. The
pH reading was read from the recorder of the pH meter (AOAC, 1990).
3.4 Determination of Total Soluble Solids.
The total soluble solid (TSS) were determined using a moisture analyzer (MB45 Ohaus).
32
3.5 Overrun
The overrun was determined using an exact measurement of volume and weight of the ice cream
mixture before and after mixing (Hammink, Practical Analysis, 2014). The formula used for
calculating the overrun was;
%Overrun= V2 - V1/V1×100
Where;
V2= volume of ice cream
V1= volume of ice cream mix
3.6 Melting Rate
The melting rate was quantified using the dripping method by which an amount of ice cream (ml)
was dripped over time (ml/min) at room temperature. A funnel was placed on top of a measuring
cylinder (100 ml) and a filter paper was placed inside the funnel. The amount of liquid that was
dripped into the measuring cylinder was recorded after 60 minutes.
Total Antioxidants determination
DPPH radical scavenging activity was determined as described by Okawa et al with slight
modification. Solutions of known Trolux with concentration were used for calibration. Trolux was
mixed with 250ml of methanolic DPPH. The homogenate was shaken vigorously and kept in
darkness for 30minutes. Absorption of the sample was measured on the spectrophotometer at
515πm. Results were expressed as Trolux equivalent per gram of dry weight.
33
SENSORY EVALUATION
Man accepts food on the basis of certain characteristics that he defines and perceives with his
senses. These attributes are described in terms of sensations and are sometimes referred to as
qualitative or sensory qualities. They include perceptions of appearance factors such as color,
shape and flavor factors or sensations combining odor and taste
Appearance: Appearance is the surface characteristics of the food judged by eye or feeling with
hands. Appearance influence food appreciation and quality especially the consumer acceptance. It
includes color, shape and size characteristics of food (Gellynck et al., 2008).
Colour: colour affects our acceptance of food. Color of the food is one which is important to
determine the quality of the food. At the time of observing the food the first impression on the
acceptance of the food is formed. Surface color depends both on the physicochemical
characteristics of the ice cream mixture and on the operating conditions applied during freezing.
Maillard browning caused by the reaction between milk proteins and the added sugar (Akubor and
Obiegbuna, 2002), is the crucial factor that affects the color of ice creams during pasteurization.
The other factor that affects the color of the ice cream product as far as avocado fruit pulp is
concerned is oxidation, which is influenced by the activation of enzyme with the aid of oxygen.
Flavor: The interaction of taste, odor and textural feeling provides an overall sensation which is
best defined by “flavor” Flavor and texture of avocado ice cream are key attributes to the consumer
acceptance (Heinio, 2006). Volatile flavor compounds which found in milk powder are playing a
key role in the perception of the ice cream flavor (Molnar, 2000). However, the perceived ice
cream flavor often relies on the type of band method of production and shelf life (Lior, 2006).
34
Taste: is the gustatory perceptions caused by soluble substance which found in the mouth (Molnar,
2000). For the period of eating or consuming the food the taste receptors (taste buds) are stimulated
and create the taste sensation. It can be described as salty, sweet, bitter and sour (Belitz et al.,
2009). It depends on the chemical composition of the food. Foods containing sugar taste sweet
while those foods which contain salt taste salty. Thus, the taste of foods is one factor which
contributes to the acceptability of food. Tastes may increase the apparent intensity of odors may
also increase the apparent intensity of taste (Gellynck et al., 2008).
The ice cream samples were evaluated using 30 semi-trained sensory panelists who were selected
from Koforidua Technical University. They were asked to evaluate the colour, flavour, taste,
aroma, texture and overall acceptability of each sample. The panelists were properly briefed and
instructed individually on the procedure with emphasis on rinsing their mouth with water in
between sample tasting using a 5 point hedonic scale where 1 is like very much, 2 is like, 3 is
neither like nor dislike, 4 is dislike and 5 is dislike very much. In order to avoid biased evaluation
by panelists, the various ice cream samples were coded. Warm water was given to them to wash
their mouth before tasting and in between tasting session.
QUESTIONNAIRE
The research instrument used in this study was the questionnaire. Questionnaire is a set of
questions that have been specially formulated as a means of collecting information and surveying
opinions on a specified subject or theme. The questionnaire was used to access the sensory qualities
and overall acceptability of the avocado ice cream produced. The questionnaire contained both
open and closed-related questions. In the open-ended questions, respondents were given the
opportunity to express their thoughts about the properties of the avocado fruit pulp used in the
35
preparation of ice cream while with the closed-ended questions using a 5-ponit hedonic scale,
possible answers were provided for respondents to select from.
DATA ANALYSIS
All experiments were conducted in triplicate. One-way Analysis of variance (ANOVA) was
performed on each of the variables. The data obtained from the study was analyzed using statistical
package for social science (SPSS) version 20. The significant differences was determined using
Fisher’s Least Significant Difference (LSD) at p < 0.05. The results was expressed as means and
standard deviations.
36
CHAPTER FOUR
RESULTS AND DISCUSSION
4.0 INTRODUCTION
This chapter presents the results and discussion from the lab. The data was analysed using SPSS
Software to determine the mean and standard deviation of the sensory evaluation for the low fat
ice cream prepared with different percentages of avocado fruit pulp. The statistical analysis was
based on the objective of the study which includes; performing proximate analysis and also
evaluating the consumer acceptability of the various formulations.
4.1 CHEMICAL COMPOSITION AND ANTIOXIDANT ACTIVITY OF THE
AVOCADO FRUIT PULP.
Table (4.1) constitutes the chemical composition and antioxidant activity of the avocado fruit pulp
used in the production of the ice cream without any treatment.
Table 4.1 Chemical composition and antioxidant activity of Avocado
Constituents.
Content
Protein
1.34±0.13
Moisture
6.21±0.03
Ash
1.52±0.05
Fiber
5.14±0.08
Total Soluble Solids
6.21±0.13
pH
6.50±0.03
Fat
12.21±0.18
Antioxidant activity
39.51±0.44
Table (1) shows that the avocado fruit pulp can be considered as a non-acidic fruit, rich in fat
content and moderate percentage of protein (1.34%), moisture (6.51%), ash (1.52%), fibre (5.14%)
37
and total soluble solids (6.21oBrix). The avocado fruit pulp had high antioxidant scavenging
activity (39.15%). The composition of Avocado fruit pulp of used variety (Hass), fall in reported
composition of avocado fruit (Maitera et.al 2014). Also, several bioactive compounds are
beneficial to human health such as liposoluble vitamin E, K and β-carotene (USDA, 2011). In
addition, avocado fruit pulp is characterized by a rich mouthfeel, acceptable flavour, and taste. The
composition and sensory properties of avocado fruit pulp suggest that it can be added as functional
ingredient in low fat dairy products to impart the fat rich taste to these products.
4.1.1 SENSORY EVALUATION
TASTE
Table (4.2) shows the results obtained after the panelists analysed the attribute of the various
samples in relation to the attribute taste.
Table 4.2 Results of samples in relation to the attribute taste
Sample.
Mean.
Standard Deviation
T1
1.87
0.97b
T2
1.57
0.68a
T3
1.77
0.73b
T4
2.27
0.94c
T5
2.20
1.03bc
T6
2.53
1.20ab
Each value is presented as mean ± standard deviation. Means within a row with the same letter
superscript is not significantly different (P>0.05 Tukey’s test) whereas those with different
superscripts are significantly different = (P<0.05 Tukey’s test). A=; B=; C=;The least value in
the samples for each attribute represents the highest accepted attribute for each sample.
38
The mean sensory score for taste of the ice cream samples of different formulation are shown in
Table 2. Statistical analysis showed that the partial substitution of avocado paste in the ice cream
samples had significant effect (p<0.05) on the taste of the different ice cream formulation. Sample
B recorded the highest score of 1.57±0.68 for taste whiles sample F had the lowest value of
2.53±1.20. The taste of the sample with 20% avocado paste (sample B) replacement recorded the
highest rating for taste with a mean value of 1.57 which was not significantly different from sample
with 30% avocado paste (sample C) which recorded mean of 1.77. The sample with 30% avocado
paste replacement was ranked second as far as taste is concerned with a mean value of 1.77;
followed by 0% avocado paste (sample A which is the control) with a mean of 1.87 and the least
was sample with 60% of the avocado paste (sample F) with a mean value of 2.53. The taste ranking
did not increase proportional as the level of avocado paste increased. From the results, there is a
strong indication that, the ice cream sample with 20% replacement of avocado paste gave panelists
the highest and the most preferred taste followed by a 30% (sampl C) and 50% (sample E) avocado
paste replacement if there is a taste preference decision to be taken on only the avocado ice cream
product. There was no significant difference between the control 0% avocado paste, 20% (sample
B) and 30% (sample C) avocado paste replacement but a significant (p<0.05) different as the level
of avocado paste increased above 30% replacement.
39
COLOUR
Table (4.3) shows the results obtained after the panelists analysed the attribute of the various
samples in relation to the attribute colour.
Table 4.3 Results of samples in relation to the attribute colour
Sample.
Mean.
Standard deviation
T1
1.80
0.76b
T2
1.73
0.64a
T3
1.83
0.75b
T4
2.40
0.89a
T5
2.30
0.92ab
T6
2.37
0.96a
Each value is presented as mean ± standard deviation. Means within a row with the same letter
superscript is not significantly different (P>0.05 Tukey’s test) whereas those with different
superscripts are significantly different = (P<0.05 Tukey’s test). A=; B=; The least value in the
samples for each attribute represents the highest accepted attribute for each sample.
Colour is an important parameter to the quality of food products because of its association with
factors such as freshness, ripeness, desirability, and food safety. It is often a primary consideration
for consumers when making purchasing decisions. All ice cream samples containing avocado fruit
pulp exhibited slight green colour of variable intensity according to the avocado fruit pulp ratio
used. The panelists described the colour of the 5 ice cream samples (sample T2, T3, T4, T5, and
T6) as new. From the results the colour for the various samples ranges from a mean of 1.80 to 2.37.
The sample with 20% (sample T2) avocado paste replacement and 0% (sample T1 which is the
control) avocado paste replacement recorded the maximum mean for colour of 1.73 and 1.80
respectively, followed by sample C produce from a 30% substitution of the avocado fruit pulp
40
attained a mean of 1.83. The respond found no significant different in colour between sample with
0%, 20% and 30% (sample T1, T2 and T3 respectively) avocado fruit pulp replacement as well as
sample with 40%, 50% and 60% (sample T4, T5 and T6 respectively) avocado fruit pulp
incorporation. The results showed a colour preference order of sample T2 (1.73±0.64), sample T1
(1.80±0.76), Sample T3 (1.83±0.75), Sample T5 (2.30±0.92), Sample T6 (2.37±0.96) and Sample
T4 (2.40±0.89).
FLAVOUR
Table (4.4) shows the results obtained after the panelists analysed the attribute of the various
samples in relation to the attribute flavour.
Table 4.4 Results of samples in relation to the attribute flavour
Sample.
Mean.
Standard Deviation
T1
1.87
0.86a
T2
1.80
0.55b
T3
2.07
0.94c
T4
2.40
0.93c
T5
2.30
0.92c
T6
2.60
1.13c
Each value is presented as mean ± standard deviation. Means within a row with the same letter
superscript is not significantly different (P>0.05 Tukey’s test) whereas those with different
superscripts are significantly different = (P<0.05 Tukey’s test). A=; B=; C=;The least value in
the samples for each attribute represents the highest accepted attribute for each sample.
Flavour is an important parameter of food, good” flavour from food excites the taste buds, making
the system ready to accept the product. “Poor” flavour may cause outright rejection of food before
they are tasted. A good level of flavour intensity influences taste (Pearson et.al, 2019). From the
41
results of the sensory evaluation of the six products under study, the statistical analysis showed
that the partial substitution of avocado fruit pulp with skimmed milk powder had significant effect
(p< 0.05) on the flavor of the different ice cream formulation. Sample T2 (20% avocado fruit pulp
incorporation) obtain the highest score, giving it a better preference for flavour which was
significantly different from sample T1 (0% avocado fruit pulp incorporation), this shows that,
incorporation of whole milk with avocado fruit pulp has effect on flavor characteristics of ice
cream (Carrari et.al, 2006) product with 30%, 50%, 40% and 60% avocado fruit pulp replacement
was rated second most preferred with respect to flavour with mean of 2.07, 2.30, 2.40 and 2.60
respectively which was not significantly different (p< 0.05) from each other. From the result it
can be concluded that as the amount of avocado fruit pulp incorporated into the mixture increases,
the acceptability on flavor of product goes on decreasing.
AROMA
Table (4.5) shows the results obtained after the panelists analysed the attribute of the various
samples in relation to the attribute aroma.
Table 4.5 Results of samples in relation to the attribute aroma
Sample.
Mean.
Standard deviation
T1
1.80
0.76a
T2
1.77
0.57b
T3
2.03
0.76a
T4
2.47
0.94ab
T5
2.43
0.86b
T6
2.57
1.17ab
Each value is presented as mean ± standard deviation. Means within a row with the same letter
superscript is not significantly different (P>0.05 Tukey’s test) whereas those with different
42
superscripts are significantly different = (P<0.05 Tukey’s test). A=; B=;The least value in the
samples for each attribute represents the highest accepted attribute for each sample.
Statistical analysis showed that the partial substitution of the vanilla essence and avocado paste in
the ice cream samples had significant effect (p<0.05) on the aroma of the different ice cream
formulation. Sample T2 recorded the highest score of 1.77±0.57 for taste whiles sample T6 had
the lowest value of 2.73±1.34. The aroma of the sample with 20% avocado paste replacement
recorded the highest rating for aroma with a mean value of 1.77 which was not significantly
different from sample with 0% avocado paste (sample T1) which recorded mean of 1.80. The
sample with 0% avocado paste replacement was ranked second as far as aroma is concerned with
a mean value of 1.80; followed by 30% avocado paste (sample T3) with a mean of 2.03 and the
least was sample T6 which contained 60% of the avocado paste with a mean value of 2.73. The
aroma ranking did not increase proportional as the level of avocado paste increased. From the
results, there is a strong indication that, the ice cream sample with 20% replacement of avocado
paste gave panelists the highest and the most preferred aroma followed by a 30% of avocado fruit
pulp (sample T3) and 40% (sample T4) avocado paste replacement if there is anaroma preference
decision to be taken on only the avocado ice cream product. There was no significant difference
between the control 0% avocado paste and 20% (sample T2) of the avocado paste replacement but
a significant (p<0.05) different as the level of avocado paste increased above 20% replacement.
43
MOUTHFEEL
Table (4.6) shows the results obtained after the panelists analysed the attribute of the various
samples in relation to the attribute mouthfeel.
Table 4.6 Results of samples in relation to the attribute mouthfeel
Sample.
Mean.
Standard deviation
T1
1.83
0.79a
T2
1.87
0.86b
T3
2.03
0.76bc
T4
2.47
0.97c
T5
2.50
1.11c
T6
2.73
1.34ab
Each value is presented as mean ± standard deviation. Means within a row with the sample letter
superscript is not significantly different (P>0.05 Tukey’s test) whereas those with different
superscripts are significantly different = (P<0.05 Tukey’s test). A=; B=; C=;The least value in
the samples for each attribute represents the highest accepted attribute for each sample.
The product with the 40%, 50% and 60% avocado fruit pulp replacement was rated the least as far
as mouth-feel is concern with mean rating of 2.47 (sample T4), 2.50 (sample T5) and 2.73 (sample
T6) respectively which was not significantly (p< 0.05) different from each other. While the sample
produce from only 100% skimmed milk powder (sample T1) was the highest. The sample with
20% avocado fruit pulp replacement was rated at 1.87 which was the second highest, whiles the
30% replacement was rated with a mean value of 2.03. The control product obtained the highest
mouthfeel. Similarly, to a study by (Emma et al., 2019). Which suggests that when the proportion
of incorporated avocado fruit pulp increased in the ice cream, the mouth feel of ice cream scores
44
decreased significantly, the mouth feel of the ice cream products understudy decreases
significantly with 20%, 30%, 40%, 50% and 60% avocado fruit pulp replacements.
OVERALL ACCEPTABILITY
Table (4.7) shows the results obtained after the panelists analysed the attribute of the various
samples in relation to the overall acceptability.
Table 4.7 Results of samples in relation to the overall acceptability
Sample.
Mean.
Standard deviation
T1.
1.67
0.80a
T2.
1.67
0.55b
T3.
1.90
0.84c
T4.
2.47
0.94ab
T5.
2.30
0.92c
T6.
2.83
1.39abc
Each value is presented as mean ± standard deviation. Means within a row with the same letter
superscript is not significantly different (P>0.05 Tukey’s test) whereas those with different
superscripts are significantly different = (P<0.05 Tukey’s test). A=; B=; C=;The least value in
the samples for each attribute represents the highest accepted attribute for each sample.
The descriptive statistics of the overall satisfaction of panelists have with the entire product. The
overall acceptability of the samples ranged from 1.67±0.80 to 2.83±1.39. Maximum score value
of overall acceptability from five-point hedonic scale was (1.67±0.80) recorded by Sample T1
100% skimmed milk powder with 0% avocado fruit pulp and (1.67±0.35) recorded by Sample T2
which contained 80% of the skimmed milk powder and 20% of the avocado fruit pulp, while the
minimum score value (2.83±1.39) was scored by sample T6 which contained 40% of the skimmed
milk powder and 60% of the avocado fruit pulp. It was noted that, there was no significant
45
difference between sample T1 and sample T2 but there was a significant difference in the overall
acceptability of sample T3, sample T4, sample T5 and sample T6 products. The overall
acceptability of samples was significantly different (p<0.05). It was observed that the increase in
avocado fruit pulp substitution decreased the overall acceptability of the ice cream. The decrease
in overall acceptability may be due to the results of appearance, texture, aroma and taste of the ice
cream with different amounts of skimmed milk powder and avocado fruit pulp or could be because
the panellist was not familiar with the control product. The results on acceptability agreed with
those reported in previous related studies where it was found out that substitution levels of avocado
fruit pulp in ice cream decrease the overall acceptability (Pearson et al., 2019).
4.2. PHYSIOCHEMICAL PROPERTIES OF THE VARIOUS ICE CREAM SAMPLES
Table (4.8) shows the physiochemical properties (pH and TSS) of the various ice cream samples.
Table 4.8 Physiochemical properties (pH and TSS) of the various ice cream samples.
Sample.
pH.
TSS
T1.
6.65±0.14a.
0.32±0.004a
T2.
6.56 ±0.00b.
0.33±0.006b
T3.
6.49±0.01b.
0.31±0.016c
T4.
6.52±0.01c
0.33±0.017e
T5.
6.32±0.04ab
0.32±0.014d
T6.
6.50±0.00b.
0.34±0.013b
Each value is presented as mean ± standard deviation. Means within a row with the same letter
superscript is not significantly different (P>0.05 Tukey’s test) whereas those with different
superscripts are significantly different = (P<0.05 Tukey’s test). A=; B=; C=; D=; E=;
46
4.2.1 pH
In chemistry, pH, (historically denoting "potential of hydrogen" or "power of hydrogen") (Jensen
et al., 2004) is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions
(solutions with higher concentrations of hydrogen ions) are measured to have lower pH values
than basic or alkaline solutions. The pH scale is logarithmic and inversely indicates the
concentration of hydrogen ions in the solution. This is because of the formula used to calculate pH
approximates the negative of the base 10 logarithm of the molar concentration of hydrogen ions in
the solution. More precisely, pH is the negative of the base 10 logarithm of the activity of the
hydrogen ion (Bates et al., 2019). At 25°C, solutions with a pH less than 7 are acidic, and solutions
with pH greater than 7 are basic. Solutions with a pH of 7 at this temperature are neutral (example,
pure water). The neutral value of the pH depends on the temperature being lower than 7 if the
temperature increases. The pH value can be less than 0 for a very strong acid or greater than 14 for
very strong bases (Lim et al., 2006). When the pH of a solution is more than 5.9 but less than 7, it
is considered as a weak acid. The pH of aqueous solutions can be measured with a glass of
electrode and a pH meter, or a colour-changing indicator. Measurement of pH are important in
chemistry, agronomy, medicine, food production, water treatment and many other applications.
Table (8) shows the results obtained after analysing the pH of the various samples. pH showed no
significant difference between the formulations. However, the trend showed that, the addition of
avocado paste lowered the acidity level of the ice cream. The acidity level of avocado was between
pH 6.2-6.6 depending on the type of cultivar, ripening stage, and maturity of the fruit. The range
of pH from each formulation of sample T1, sample T2, sample T3, sample T4, sample T5 and
sample T6 demonstrated that they were on the standard acidity level of the ice cream mixtures
47
(Goff et al., 2013). The acidity of ice cream is important because it determines the whipping
capability that contributes to the stability of the ice cream (Goff et al., 2013).
4.3 Total Soluble Solids
Total Soluble Solids measures the sugar solutions which the sugar is the main component using a
refractometer. Total Soluble Solids content of a solution is determined by the index of refraction.
This is measured using a refractometer and it is referred to as the degrees Brix. Brix is the term
used when a refractometer equipped with a scale, based on the relationship between refractive
indices at 20°C and the percentage by mass of total soluble solids of a pure aqueous sucrose
solution. This tests the solids concentration of a sucrose contained solution. Sugar concentration
is expressed in degrees Brix. At 20°C, the Brix is usually considered equivalent to the percentage
of sucrose (sugar) in the solution (Emma et al., 2015). Table (8) shows the results that was derived
after analysing the total soluble solids of the six samples. The total solid measurement
demonstrated that there was no significance difference between sample T1 which is the control,
sample T2 (which had 20% of the avocado fruit pulp), sample T3 (which had 30% of the avocado
fruit pulp), sample T4 (which had 40% of the avocado fruit pulp), sample T5 (which had 50% of
the avocado fruit pulp), and sample T6 (which had 60% of the avocado fruit pulp). And it was
noticed that the temperature of the ice cream was suitable hence, producing accurate results and
met the standard required for the ice cream to be consumed on the market (Carrari et al., 2006).
The suitability of the ice cream was due to the storage treatment given to it. The soluble solids to
titrable acidity ratio was constant throughout the sample test due to the controlled temperature
storage. During the storage, the constant trend of TSS/TA was conducive in MAP than other
treatment although the effects of treatments were insignificant.
48
4.4 NUTRITIONAL COMPOSITION OF THE VARIOUS ICE CREAM SAMPLES
Table (9) shows the nutritional composition (moisture, total fat%, FFA, Antioxidant activity and
protein%)
Table 4.9 Nutritional composition (moisture, total fat%, FFA, Antioxidant activity and protein%)
SAMPLES
MOISTURE
TOTAL
FFA
ANTIOXIDANT PROTEIN%
%
FAT %
T1
65.86±0.14a
12.28±0.06a
2.34±0.06b
0.54±0.08a
3.70±0.07a
T2
65.79±0.01a
11.54±0.04b
2.48±0.06a
33.8±0.52b
3.68±0.06b
T3
65.40±0.06b
10.64±0.01c
3.25±0.07b
67.6±0.70c
3.32±0.02abc
T4
64.37±0.03c
9.76±0.04d
3.27±0.38c
101.4±1.1d
3.61±0.06c
T5
64.37±0.03d
8.68±0.06e
3.64±0.06d
135.2±1.5 e
3.51±0.06e
T6
63.76±0.04 e
8.01±0.07 f
3.83±0.02 e
169±1.89 f
3.50±0.07 f
ACTIVITY
Each value is presented as mean ± standard deviation. Means within a row with the same letter
superscript is not significantly different (P>0.05 Tukey’s test) whereas those with different
superscripts are significantly different = (P<0.05 Tukey’s test). A=; B=; C=;D=; E=; F=.
4.4.1 MOISTURE CONTENT
Moisture content of food is the quantity of water contained in a given sample of food. Even though,
water may be present in every moist substance, moisture content may include other mass losses
such as alcohol and other organic solvents. The moisture content of foods is important to food
manufacturers for a variety of reasons. Moisture is an important factor in food quality, preservation
and resistance to deterioration. Water is a major constituent of most food products. The
49
approximate, expected moisture content of a good can affect the choice and method of
measurement. Determination of the moisture content of food is necessary to calculate the content
of other food constituent on a uniform basis. Moisture content of the food material is important to
consider the food is suitable before the consumption, because moisture content affects the physical,
chemical and biological aspects of food which relates with the freshness and stability. Moisture
content of foods can be determined by a variety of methods, but obtaining accurate and precise
data is commonly a challenge (Emmanuel et al., 2019). Moisture loss from a sample during
analysis is due to the time and temperature factors.
From the above analysis done, the results that was obtained in table (8) for the percentages of
moisture content for the various samples were; sample T1 obtained 65.86% of moisture, sample
T2 obtained 65.79% of moisture, sample T3 obtained 65.49% of moisture, sample T4 obtained
64.37% of moisture, followed by sample T5 which had 64.37% of moisture and lastly, sample T6
obtained a 63.76% of moisture respectively. Based on the results obtained, the weight changed in
drying method are assumed to be due to moisture loss. Ice cream should contain 55-65% water
(Kwang et al., 2014). Ice cream mixture with high water content will result in a low total solid
content in general and proportionately higher water that is available to freeze when hardened at
the same temperature compared to the ice cream mixture with low water content and high total
solids. This condition affected the quality of the ice cream particularly for the texture and hardness.
A knowledge about moisture content is often necessary to predict the background and behavior of
foods during processing example mixing, drying, freezing, flow through a pipe or packaging.
Foods are heterogeneous materials that contain different proportions of chemically bound,
physically bound, capillary, trapped or bulk water. Moisture assay can be one of the most important
analysis performed on food and yet one of the most difficult experiment to get an accurate and
50
precise data. It is therefore important for food scientist to be able to reliably measure moisture
from foods to prolong the shelf life of foods (Pearson et.al., 2019).
4.5 TOTAL FAT DETERMINATION
There was a significance difference (p<0.05) in total fat content for each formulation. The data
showed that the highest fat content was obtained by sample T1 (12.28%), followed by sample T2
(11.54%), sample T3 (10.64%), sample T4 (9.76%), sample T5 (8.68%) and sample T6 (8.01%).
Skimmed milk powder act as one of the base ingredients in the ice cream production and
contributed up to 35.1% (w/w) of total fat content while avocado fruit contributed around 12.21%
(w/w) of total fat including MUFA and the phytosterol (USDA, 2011). The differences in fat
content of each formulation are due to the reducing fat source from the skimmed milk powder that
has subsequently substituted with avocado paste. This fat content contributes to the fat
crystallization and was able to influence the textural properties of the ice cream (Pelan et al., 1997).
Ice cream contains at least 10% of dairy fat, 20% of total milk solid and able to establish a certain
percentage of overrun, which is increasing vin volume by whipping air into the ice cream mixture
(Goff et al., 2013), (Brian, 2014), (Karaman et al., 2012). The percentage of fat, total solids and
overrun are important factors in ice cream quality (Goff et al., 2013). It has been demonstrated that
the increase in dairy fat and total solid lead to higher costs in ice cream products, since dairy fat is
considered as an expensive ingredient. However, this ingredient is the main structure in
constructing sensorial properties and determines quality of the ice cream (Hui Y et al., 2004). The
role of fat, particularly milk fat in ice cream is important to act as an air stabilizer during the
freezing process which creates a dispersed phase of air bubbles (Goff et al., 2013). During the
freezing process the crystalized fat and partially coalesced fat globule stabilize the air bubbles of
the ice cream mixture and provide the desired foamy texture which contributes to the hardness
51
quality of the ice cream (Goff et al., 2013). Milk fat acts as a thermal insulator which affects the
melting properties of the ice cream (Newton et al., 2014), (Li Z et al., 1997). Ice cream with high
milk fat can retain its shape and take longer time to melt. In this experiment, the substitution of
milk fat with avocado paste proportionally at 0%, 20%, 30%, 40%, 50% and 60% resulted in
reducing the amount of total fat content and retained the melting rate. This substitution of dairy fat
into plant-based fat from avocado was able to lower the total fat content of the ice cream mixture.
This might be due to the fibre content in avocado paste that has the ability to lower the water
mobility in the ice cream (Dello et al., 2004), (Gelrath et al., 2001).
4.5.1 FREE FATTY ACID DETERMINATION
Free fatty acids are long chain acids that are not conjugated or attached to anything else and they
are free and not bonded to any atom (Emma et al., 2019). Much attention has been given to the
action of normal milk lipase in milk, and investigations have been conducted with the view of
establishing the fatty acid threshold level (Dunkley et al., 1938). Also, the concentration of free
acids in butter and cheese has been related to flavour characteristics of these products (Gould et
al., 2018). Lipase action in relationship to ice cream quality has not been given specific attention.
Such consideration seems justified for three reasons. First, rancid and closely related flavours are
found in ice cream. This indicates that under certain conditions of processing and manufacturing,
or through improper control of dairy products used, a sufficient quantity of free fatty acid is
developed to produce the 'off' flavour. This matter becomes increasingly important as greater use
is made of low-heat condensed or concentrated milk products as a source of the milk solids. In
certain of these products, sufficient active lipase may remain to create a flavour problem unless
proper precautions are used in processing. Second, free fatty acids when added to the mix have
been found to be related to shrinkage in ice cream (Dahle et al., 2001). However, no studies have
52
been made of the relationship of shrinkage to the free fatty acid content of ice cream resulting from
normal lipase action. Third, a certain concentration of free fatty acid has been found to be
beneficial in improving the flavour of milk (Hollender et al., 2018). The possibility exists that
controlled lipolysis may be utilized by the ice cream maker in the production of avocado ice cream
with higher consumer acceptance.
On the basis of the data presented, it appears that the FFA content of the various sample’s merits
attention. The fatty acid-rancid flavor threshold in ice cream is more than twice the threshold value
of 2.0 established for milk or cream (Dunkley et al.,1938). This indicates that the other components
in the ice cream obscure the rancidity and made difficult its detection by organoleptic means. The
obscuring effect of sample T6 which contained 60% of the avocado paste was appreciably greater
than that for the other samples most especially sample T1. The acid degree of the strictly fresh ice
cream which is the control (sample T1) appears to be definitely higher than the other samples.
Non-dairy products may contribute to the acid-degree of ice cream under certain conditions. The
fact that the free fatty acid of the various samples was just below the threshold level of rancidity
poses an interesting question as to whether or not the small concentration of free acids may be
beneficial to the flavour of the various samples.
53
4.6 ANTIOXIDANT ACTIVITY
Figure 4.1 Antioxidant capacity standard calibration curve.
Antioxidants are chemical substances that can neutralize and scanvage the free radicals, which are
continuously produced by the body (Yazdanparast et al., 2007). Antioxidant activity or capacity
of dairy products is mainly due to sulfur containing amino acids such as, cysteine, phosphate,
Vitamin A, E, carotenoids, zinc, selenium, enzyme systems, superoxide dismutase, catalase,
glutathione peroxide, milk oligosaccharides and peptides that are produced during fermentation.
Antioxidant activity of dairy products can be enhanced by phytochemicals supplementation while
fermented dairy products have been reported to contain higher antioxidant capacity as compared
to the non-fermented dairy products. Literature review has shown that most dairy products have
54
antioxidant capacity, however, information regarding the antioxidant capacity of milk and its
products have not been previously compiled.
Fig (4.1), shows the results for the antioxidant capacity curve which was obtained after the analysis
on the various samples were tested. Both the table and the figure show change of the antioxidant
activity of the various ice cream samples during frozen storage as affected by using different
percentages of the avocado fruit pulp. The control which is sample T1, had lower antioxidant
activity than those of low fat ice cream which is sample T2, T3, T4, T5 and T6. This may be
attributed to the differences in the mixtures which correlated to its content of protein and nonprotein antioxidants. The protein group includes various kinds of enzymes, and also a number of
proteins and peptides which had phenolic compounds and antioxidant activity power (Lindmark
et al., 2000). Addition of avocado fruit pulp in the 5 samples (T2, T3, T4, T5 and T6) increased
significantly (p<0.01) the antioxidant activity of the low fat ice cream with respect to the
percentages of the avocado fruit pulp added. This may be due to the addition antioxidant activity
of the fruit pulp (Table 1) and also a possible oxidation process for the nutrients of the various
samples. Similar findings reported by (El-Samahy et al., 2015) for low fat ice cream made with
added cactus pear fruit pulp as a natural antioxidant obtained an increase in the antioxidant activity
of the sample during it stored period.
4.6.1 PROTEIN DETERMINATION
Ice cream is a very complex food. The water dissolves the sugars (lactose). There is colloidal
system suspended in the water. The milk proteins constitute the colloids in one suspension, and
the insoluble salts constitute another. Anther system that depends on water is the emulsion phase,
and all systems coexist (Kilara et al., 2002). Therefore, the adsorption of protein is influenced by
the type of fat and the emulsifier used in the ice cream manufacture. According to USDA, the
55
amount of protein contained in an ice cream ranges from 3.5%-4.0%. But there would not be any
negative effect when the protein content in an ice cream increases beyond this range since there
might be other factors involved which may lead to the increment in the protein content. Table (8)
shows the results obtained after the 6 samples were analyzed for protein.
There was no significant different between the various samples (T1, T2, T3, T4, T5 and T6) (p<
0.05) under study. The results obtained after the analysis tally with the protein range (3.5-4.0%) in
any ice cream sample. Sample T1 had the highest protein content of 3.70%, followed by sample
T2, sample T4, sample T5 and sample T6. Sample T3 had the least value for protein and this may
be due to some factors like the freezing temperature and the ingredients used.
4.7 PHYSIOCHEMICAL PROPERTIES (OVERRUN AND MELTING RATE) OF THE
VARIOUS ICE CREAM SAMPLE.
Table (4.10) shows the physiochemical properties (overrun) of the various ice cream samples.
Table 4.10 Overrun percentage.
SAMPLE
OVERRUN
T1
55.48±0.06a
T2
46.77±0.06b.
T3
52.30±0.06c
T4
56.18±0.06d
T5
60.42±0.06e
T6
70.00±0.06 f
Each value is presented as mean ± standard deviation. Means within a row with the same letter
superscript is not significantly different (P>0.05 Tukey’s test) whereas those with different
superscripts are significantly different = (P<0.05 Tukey’s test). A=; B=; C=;D=; E=; F=.
56
The overrun showed significant difference (p<0.05) among the formulations. The data showed that
increasing the avocado paste substitution towards milk fat in the ice cream mixture significantly
reduce the overrun of the ice cream. The highest overrun achieved by sample T1 (55.48%), sample
T2 (46.77%), sample T3 (52.30%), sample T4 (56.18%), sample T5 (60.42%) and sample T6
(70.00%). Based on Duncan test, it showed significant difference between sample T1 and sample
T2 (p<0.05) but no significant difference between sample T4, sample T5 and sample T6 and the
other formulations. The data for the overrun is in line with the melting rate where sample T1 had
the highest overrun ability followed by rapid melting rate properties. The higher overrun
significantly contributed to the higher melting rate in the ice cream (Rosalina et al., 2004), (Brain
R, 2014). High overrun level in ice cream resulted to high melting rate due to instability of air cells
Incorporated in the ice cream mixture (Brain R, 2014). The instability is due to the increase in
temperature levels when ice cream is unfrozen.
Moreover, the overrun also affected the hardness profile of ice cream (Rosalina et al., 2004).
Overrun and air cell distribution becomes critical parameters in the ice cream industry that
continuously needs to be controlled and monitored. There are numerous factors that could
influence the development of air cells and affect overrun in ice cream products such as mixing,
freezing, hardening, the use of stabilizers, homogenization, and ingredients used in the ice cream
mixture (Goff et al., 2013), (Rosalina et al., 2004). Air content in the ice cream mixture contributed
to the physical properties of the ice cream such as texture, hardness, melting properties and other
sensorial characteristics (Rosalina et al., 2004). The amount of air incorporated in the colloidal
system in the ice cream mixture influenced the distribution of the air size that could provide
melting profile and directly affect the sensory quality parameters of the ice cream (Rosalina et al.,
2004).
57
The presence of air cells in the ice cream mixture is important in determining the texture quality
of the ice cream. It has been suggested that the amount of air cells at 70% overrun is enough to
prevent collision among ice crystals and the lower the overrun will subsequently create larger ice
crystals, thus lead to the increase of hardness of the ice cream (Prindiville et al., 1999). Air is one
of the important ingredients that need to be incorporated in the ice cream mixture. It makes up
between 30%-50% of the total volume of the ice cream (Brian, 2014). It has been reported that the
stability of air cells could slow down the melting rate of the ice cream as determined by adding
saturated monoglycerides to the ice cream mixture (Pelan et al., 1997).
4.8 MELTING RATE
Figure 4.2 Results of melting rate.
The melting rate of any substance depends on the temperature and fiber content of that substance.
The melting rate showed significant difference between formulations (p<0.05). It is demonstrated
from figure 2 that sample T2 had the highest melting rate, followed by sample T3, sample T1,
sample T4, sample T5 and sample T6 respectively. The higher concentration of avocado paste in
relation to degree of temperature resulted in the decrease in melting rate of sample T6. The
58
temperature and fiber content in the avocado paste could have affected the melting rate of the
samples been observed. It has been reported that frozen dairy dessert formulated with dietary fibre
could improve the melting quality of an ice cream (Stieven, 2009) depending on the type of fibre
used (Stieven, 2009). Fibre with high soluble fraction capability such as insulin affects the
rheology of the ice cream and could provide potential cryoprotective action (Stieven, 2009). The
result showed that the fibre in insoluble compounds decrease significantly the melting rate of the
samples but due to temperature differences, the control (sample T1), had a decrease in its melting
rate as compared to sample T2 and T3 (Christous et al., 2009).
Fibre has water binding properties that creates a lower melting rate of ice cream mixtures due to a
reduction in water molecule mobility from bulk aqueous phase into the ice crystal surface phase
(Christous et al., 2009), (Stieven, 2009). The addition of fibre from fruits such as avocado in ice
cream mixtures decreases the melting rate of the ice cream (Christous et al., 2009). Fibre can
contribute to the modification and improvement of food texture and sensory characteristics due to
its water-binding capacity, gel forming ability, texturizing, and thickening effects (Dello et al.,
2004), (Gelroth et al., 2001). Dietary fibre could promote an effective control of ice crystalization
and ice crystal growth during freezing and storage as well as improve the melting and viscosity
properties for the ice cream products (Christous et al., 2009), (Dello et al., 2004), (Gelroth et al.,
2001).
59
CHAPTER FIVE
5.0 CONCLUSION
Avocado fruit (Persea Americana) can be used as a functional ingredient in ice cream due to its
flavour, natural antioxidant, fiber content in addition to its essential monounsaturated fatty acids
constituents and related health promoting characteristics. This fruit pulp had unique characteristics
which makes it suitable to be applied in low fat ice cream making. Avocado fruit pulp improved
the rheological characteristics, the antioxidant activity, melting characteristics and total
acceptability of ice cream. Therefore, this fruit pulp can be used successfully in making functional
low fat ice cream of acceptable sensory attributes comparable with that of full fat ice cream. From
the results obtained after analysing the melting rate of the various ice cream samples, it was
observed that sample T6 had the most suitable melting rate as compared to the other samples this
is because it contained a higher percentage of the avocado fruit pulp. The most suitable amount of
Total soluble solids, pH, Total fat, Free fatty acids antioxidant activity, protein and overrun were
observed in sample T2 (0.33±0.006b), sample T1 (6.65±0.14a.), sample T6 (8.01±0.07f), sample
T6 (8.01±0.06f), sample T6, (169±1.89f), sample T2 (3.68±0.06b) and sample T2 (46.77±0.06b)
respectively. Taking into consideration the overall accepted sample based on the various attributes
involved during analysis as far as sensory evaluation is , it can be concluded that, sample T2 was
highly accepted over all the other samples hence, making sample T2 ( which contained 20% of the
avocado paste) highly recommended.
60
5.1 RECOMMENDATION
1. Avocado incorporation in ice cream at the ratio of 20% to 40% can be recommended in the
manufacture of low-fat ice cream with enhanced acceptability comparable to full fat ice cream.
2. Food processors should be encouraged to use avocado fruit pulp in the production of ice cream
since it has a lot of great health benefits.
3. Microbial and shelf life analysis should be conducted to determine and be sure about the safety
and quality of the food product from time to time.
61
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