Advance Journal of Food Science and Technology 2(5): 286-290, 2010
ISSN: 2042-4876
© M axwell Scientific Organization, 2010
Submitted Date: August 19, 2010
Accepted Date: September 13, 2010
Published Date: September 25, 2010
Comparison of Chemical and Microbiological Parameters of Charcoal
Versus Gas and Solar Energy Treated Milk
M.O.M . Abdalla and M .S. Daffalla
Department of Dairy Production, Faculty of Animal Production, University of Khartoum,
Shambat, Postal Code 13314, Khartoum North, Sudan
Abstract: The effect of heat treatment using different sources of heat on the chemical composition and
microbial quality of milk was studied. Raw cow, goat and sh eep m ilk were heated w ith charcoal, gas and solar
energy at 99ºC for 12 min, cooled to 20ºC and chem ical (fat, protein, total so lids, ash, titratable ac idity, vitam in
C) composition as well as microbiolog ical exa mination (total viable bacteria c ount) were carried out. Results
showed that fat, total solids and ash con tents w ere high in cow m ilk heated w ith solar energy, while protein
content was high when m ilk wa s heated w ith gas, and the titratable ac idity w as high in milk heated w ith
charcoal and gas. The fat, total solids and ash conten ts of goat milk w ere high when milk was heated w ith gas,
while the protein content and titratab le acidity were high when m ilk was heated with solar energy. The fat
contents of sheep milk was high when milk was heated w ith gas, while the protein and total solids con tents were
high in milk h eated with solar energy, and ash content and titratable acidity were high in milk h eated with
charc oal. Vitamin C content was high for all milks when heated w ith solar energy, while the total viable
bacteria count was high in milks of all species when heated with charcoal. Solar energy was shown to be
suitable for heating milk from chemical view point, while heat treatment of milk with gas was found to be better
microbiologically.
Key w ords: Chemical, charcoal, gas, milk, solar energy
INTRODUCTION
The main objective of milk heat treatment is to
eliminate pathogenic microorganisms, or reduc e them to
a level safe for human consumption and to increase the
shelf-life by inactivating spoilage microorganisms without
affecting the nutritive value of milk. In modern da iry
industry, milk heat treatm ent is the major method for milk
preservation and extending the shelf life. Heat treatment
methods include thermization, low temperature long time,
high temperature short time, sterilization and ultra high
temperature (Gedam et al., 2007). However, in many
rural areas traditional methods such as boiling are the
methods o f choice.
Recently, many methods other than heat treatment
were used to impro ve the quality of fresh milk
including ultraviolet treatment (Reinemann et al., 2006;
Matak et al., 2007); microwave (Clare et al., 2005),
membrane processing (Eckner and Zottola, 1991) and
microfiltration (Elwell and Barban o, 2006). The effect of
heat treatment on major vitamins and minerals has been
studied and it w as indicated that the major nu trients are
left unchanged by pasteurization and that thiamin, folate,
B12 and riboflavin experienced losses from zero to 10%
(Haddad and Loewenstein, 1983; Gills, 2005). The value
of non-casein nitrogen was reduced to 58% when cow 's
milk was heated to 65-90ºC, and to 33% for camel milk,
while the am ount of non -protein nitrogen was not affected
by heat treatment, and the amount of denatured whey
protein nitrogen was reduced to 80% in cow milk and
46% in camel milk (Farah, 1986). The Maillard reaction
is initiated during UHT treatment of milk and continued
during storage to cause degradation in protein qua lity
leading to losses of 14% in available lysine after six
mon ths of storage (G ills, 2005 ).
Mo st liquid foods are processed by pasteurization
(HTST) and UHT processing, and pasteurization is the
practice of cho ice in m any coun tries arou nd the world
since it removes 95-99% of bacteria present in milk
significa ntly extending the shelf life (Pereira et al., 2006;
Gills, 2005). However, the U V trea tment leads to
reduction of Log10 3 cfu/mL of milk measured as
standard plate co unt, psychrotrophic, coliforms and
thermoduric counts (Reinemann et al., 2006 ).
In most rural areas around the world, the pasteurized
milk is consumed in confined areas, while mos t people
consume milk after boiling on charcoal or gas, a practice
that might either cause quality deterioration of milk when
excessive heat is applied, or microorganisms might not be
killed when the treatment is not efficient. This study was
conducted to evaluate the qu ality of milk treated by
different sources of heat; nam ely charcoa l, gas and solar
Corresponding Author: M.O.M. Abdalla, Department of Dairy Production, Faculty of Animal Production, University of Khartoum,
Shambat, Postal Code 13314, Khartoum North, Sudan
286
Adv. J. Food Sci. Technol., 2(5): 286-290, 2010
Table 1: Ch emic al composition and total viable bacteria count of raw
milk from diffe rent s pec ies of anim als
energy and how the milk is affected chemically and
microbiologically.
Parameter
MATERIALS AND METHODS
Typ e of m ilk
------------------------------------------------------------Cow
Goat
Sheep
F at (% )
4.82±1.08
P ro te in (% )
4.46±1.03
T ota l s olid (% )
14.56±1.43
A sh (% )
0.72±0.053
Titratable acidity
0.22±0.26
(% lactic acid)
V i ta m in C
2.02±0.96
(mg/100 mL)
Total viable bacteria 4.72±0.77
count (Log10 cfu/mL)
This study w as conducted at the D epartmen t of Dairy
Production, Faculty of Animal Production, University of
Khartoum during the period Septem ber-Decemb er, 2001.
Collection and heat treatment of m ilk samples: Fresh
whole cow, goat and sheep milks were obtained from the
University of Khartoum Dairy Farm. Charcoal and gas
were purch ased from the local market, wh ile cooking with
solar energy was done at W omen Group Action
Organization, Khartoum, Sudan. Milk was heat-treated
with charcoal, gas and solar en ergy at 99ºC for 12 min,
then cooled to 20ºC and analyses w ere carried ou t.
3.64±0.59
4.31±0.69
12.08±1.46
0.52±0.09
0.18±0.018
7.75±0.74
8.37±0.64
18 .65±1 .24
0.84±0.10
0.20±0.02
2.22±1.05
2.02±0.96
5.13±1.12
4.78±1.27
Tab le 2: E ffects of so urce of h eat o n the qua lity of c ow milk
Parameter
Source of heat
-------------------------------------------------Charcoal
Gas
Solar energy S.L
F at (% )
3.28±1.90 c
P ro te in (% )
3.89±1.15 c
T ota l s olid (% )
13. 50±1.25 b
A sh (% )
0.72±0.15 a
Titrata ble a cidity
0.21±0.05 a
(% lactic acid)
V i ta m in C
0.01±0. 001 a
(mg/100 mL)
To tal viab le ba cteria 4.31±1.82 a
count (Log10 cfu/mL)
Ch em ical analysis: Milk was analysed for fat, protein,
total solids, ash and titratable acidity according to AOAC
(2000), while vitamin C was determined according to the
method described by Owen and Iggo (1956) as follows:
metaphospho ric acid solution (6.0 mL) was added to each
of five test tubes followed by the addition of milk (4.0
mL) in the first tube; three standard ascorbic solutions in
the second, third and fo urth tub es; and to the last tube,
water (4.0 mL) was added. The mixture in the first tube
was mixed and filtered through Whatman filter paper No.
42. To milk filtrate (2 mL), 5% sodium citrate (0.5 mL)
was adde d. To each of the standard solution (2 mL) and
blank (2 mL), 10% sodium citrate solution (0.5 mL) was
added. To each o f the five tubes 1 mL of 2-6dichlorophenoliodophenol solution was added and mixed.
The optical density at 520 nm was measured using water
or air as reference. Optical densities of the standards and
blank were plotted against the co ncen tration of ascorbic
acid. The optical densities were re-measured and the value
was subtracted from that of milk.
4.32±1.53 b
5.45±1.44 a
14.85±2.22 a
0.71±0.19 a
0.21±0.08 a
5.23±1.07 a
4.97±1.90 b
14.99±0.50 a
0.73±0.08 a
0.19±0.09 a
**
**
***
NS
NS
0.03±0.001 a 0.04±0.002 a N S
3.87±1.29 b
4.21±0.79 a
*
Means in ea ch ro w b earin g the sam e su pers cripts a re no t significantly
different (p>0.05)
*: p< 0.05 , **: p <0 .01, * **: p< 0.00 1, N S = No t sign ifican t,
S.L. = Significance level
was high in cow milk. Vitamin C content and total viable
bacteria count were high in goat milk (Table 1). Results
show that fat (p<0.01) and total solids (p<0.001) contents
of cow milk were high in milk heated with solar energy,
while the protein content w as high (p<0.01) in milk
heated with gas. N o significant difference was observed
in ash content and titratable acidity. Vitamin C content
was high in milk heated with solar energy although the
difference was not significant. The total viable bacteria
count was high (p<0.05) in milk heated with charcoal
(Table 2).
The fat (p<0.001), total solids and ash contents
(p<0.05) of goa t milk were high in milk h eated with gas,
while the protein content was high in milk heated with
solar energy (p<0.01), vitamin C content was high in milk
heated with g as (p< 0.001), total viable bacteria count was
high in milk heated with charcoal (p<0.01) an d titratable
acidity was not significantly affected by the source of heat
(Table 3).
The total solids content of sheep milk was high when
heated with solar energy (p<0.05) and total viable bacteria
count was high in milk heated with charcoal (p<0.01),
while no significant difference w as noted in other milk
com ponents between the three so urces of heat (Table 4).
Microbiological examination: The total viable bacteria
count was determined according to Houghtby et al. (1992)
using standard plate count agar (Scharlawu 01-161). The
plates w ere incubated at 32±1ºC for 48±3 h.
Statistical analyses: Statistical analyses w ere performed
using the Statistical Ana lysis Systems (SAS , ver. 6.12).
General Linear Models (GLM ) were used to determine the
effects of source of heat on the quality of milk (fat,
protein, total solids, ash, titratab le acidity, vitamin C, total
viable bacteria count). Means were separated using
Duncan M ultiple Range Test with an p#0.05.
RESULTS AND DISCUSSION
Fat, protein, total solids and ash contents were high
in sheep milk and low in goat milk, w hile titratable acidity
287
Adv. J. Food Sci. Technol., 2(5): 286-290, 2010
Table 3: Effect of source of heat on the quality of goat milk
Source of heat
-------------------------------------------------Parameter
Charcoal
Gas
Solar energy S.L
F at (% )
3.81±0.28 c
4.25±1.96 a 4.04±0.05 b ***
P ro te in (% )
3.80±0.71 b
3.90±0.92 a b 4.04±1.20 a **
T ota l s olid (% )
12.06±1.56 c 13 .4± 4.1 a
12.75±1.17 b *
A sh (% )
0.4 6± 0.7 c
0.61±0.20 a 0.54±0.032 b *
Titrata ble a cidity
0.17±0.04 a
0.17±0.03 a 0.17±0.02 a
NS
(% lactic acid)
V i ta m in C
0.0 1± 0.0 b
0.10±0.06 a 0.05±0.02 a b ***
(mg/100 mL)
To tal viab le ba cteria 4.9 9± 1.3 a
4.06±0.71 b
4.22±0.53 b **
count (Log10 cfu/mL)
Means in each row bearing the same superscripts are not significantly
different (p>0.05)
*: p<0.05 , **: p <0 .01, * **: p <0 .001 , NS = N ot sig nifica nt,
S.L. = Significance level
Our findings of fat content are in agreement w ith
those reported by Sahan et al. (1996) who found no
significant effect of pasteu rization on fat and protein
contents. Heat treatment with charcoal resulted in a
significant decrease in protein content compared to gas
and solar energy (Table 5). This might be due to the
heating effect of charcoal that resu lted in protein
denaturation
(Alkanal,
2001;
Hassan,
2008 ).
Villamiel et al. (1996) reported that heat denaturation of
whey protein was observed when m ilk was heatd at 70ºC
for 10, 20 and 30 m in, being higher after microwave
heating than conv entional heating. Löker et al. (2003)
reported that pasteurization of milk resulted in increase in
fat content by 94%, protein by 1.19%. H assan (2008)
reported that as heat treatmen t increased from low
pasteurization (85ºC/40 min) to ultra high temperature
(UHT ), fat, protein and total solids contents decreased,
while ash conten t increased. The results of total solids
content followed that of protein, with the highest
reduction being in milk h eated with charcoal. This might
be attributed to the effect of moisture rem oved from milk
during heat treatment. Löker et al. (2003) reported that
pasteurization resulted in 95% loss in moisture content of
milk. Pereira et al. (2006) found that the total solids
content of goat’s milk slightly increased when treated
with Ohmic heating, wh ile slightly decreased by
conventional heating as compared to unprocessed milk.
The ash content of cow and sheep milk was not
significa ntly affected by the method of heating, w hile in
goat milk it slightly increased when milk was heated with
gas and solar energy. These findings are in agreement
with those of Lö ker et al. (2003) who found that
pasteurization resulted in an increase in ash content of
milk by 12.73%.The titratable acidity of milk decreased
when milk was heated with the three methods, although
the decrease was not significant, but when sheep milk was
heated with charco al, the acidity increased (+ 15% ).
These results are in accord with the findings of
Pereira et al. (2006) who found the titratable acidity of
goat milk to d ecrease w hen milk w as heated w ith Oh mic
heating, while that of conventional heating increased.
Hassan et al. (2009) reported that titratable acidity of low
pasteurized milk (85ºC/40 min), high pasteurized milk
(98ºC for 1.87 m in) and UH T milk decreased as the
Tab le 4: E ffect o f sou rce o f hea t on th e qu ality o f she ep m ilk
Source of heat
-------------------------------------------------Parameter
Charcoal
Gas
Solar energy S.L
F at (% )
7.7 5± 2.9 a
8.0 2± 2.4 a
7.5 0± 1.4 a
NS
P ro te in (% )
8.0 4± 2.1 a
8.2 7± 1.2 a
8.3 8± 2.1 a
NS
b
a
a
T ota l s olid (% )
18 .06 ±2 .3
19 .43 ±2 .8
19 .73 ±1 .5
*
A sh (% )
0.84±0.25 a 0.78±0.095 a 0.81±174 a
NS
Titrata ble a cidity
0.23±0.047 a 0.20±0.024 a 0.19±0.034 a N S
(% lactic acid)
V i ta m in C
0.02±0.014 a 0.02±0.014 a 0.03±0.05 a N S
(mg/100 mL)
To tal viab le ba cteria 4.7 7± 1.2 a
3.70±2.23 b 4.6 3± 2.2 a
**
count (Log10 cfu/mL)
Means in each row bearing th e sam e su pers cripts a re no t sign ifican tly
different (p>0.05)
*: p<0.05, **: p<0.01, NS = N ot significant, S.L. = Significance level
It was noted that the losses in fat con tent reached to
31.95% in cow milk heated with charcoal decreased to as
low as 3.23% in sheep milk heated with solar energy,
while the fat content incre ased in goat milk. The pro tein
and total solids contents sh owed gre at losses wh en m ilk
was heated with charcoal. The ash content showed losses
as high as 11.15% in goat milk heated w ith charcoal.
Heat treatme nt of milk decreased the titratable acidity
except for sheep m ilk heated w ith charcoal. Heating milk
resulted in losses in vitamin C content of 95.5-99.55%.
Total viable bacteria count decreased after heating milk
by all methods w ith the decrease being 0.21-22.59%
(Table 5).
Tab le 5: Percent increase (+) or decrease (-) in the chemical composition and total viable bacteria count of milk heated by the three methods compared
to raw milk
Parameter
Co w m ilk
Go at milk
Sh eep milk
---------------------------------------------------------------------------------------- ------------------------------------------------Charcoal
Gas
Solar energy
Charcoal
Gas
Solar energy Charcoal
Gas
Solar energy
Fat
- 31.95 - 10.37
- 8.51
+ 4.67
+ 16.76
+ 10.99
0.00
+ 3.48
- 3.23
Pro tein
- 12.78 + 22.20
+ 11.43
- 11.83 - 9.51
- 6.26
- 3.94
- 1.19
+ 0.12
Total solids
- 7.28
+ 1.99
+ 2.95
- 0.17
+ 10.93
+ 5.55
- 3.16
+ 4.18
+ 5.79
Ash
0.00
- 1.39
+ 1.39
- 11.54 + 17.31
+ 3.85
0.00
- 7.14
- 3.57
Titrata ble a cidity
- 4.55
- 4.55
- 13.64
- 5.56
- 5.56
- 5.56
+ 15.00
0.00
- 5.00
Vitamin C
- 99.50 - 98.51
- 98.02
- 99.55 - 95.50
- 97.75
- 99.01
- 99.01
- 98.51
To tal viab le ba cteria
- 8.69
- 18.01
- 10.81
- 2.73
- 20.86
- 17.74
- 0.21
- 22.59
- 3.14
288
Adv. J. Food Sci. Technol., 2(5): 286-290, 2010
heating temperature increased and this decrease continued
throughout the storage period of 30 days.
Losses of 95.5-99.55% in vitamin C occurred during
heating of milk with charco al, gas and so lar energy w ith
the greatest losses being in milk heated w ith charcoal.
These results indicate that heating milk with charcoal has
a detrimental effect on vitamin C. The loss in vitamin C
reported in this stud y is higher than the value reported by
Mehaia (1994) who found a loss in vitamin C content of
27-67% due to heating camel milk at 63, 80, 90 and 100ºC
for 30 m in, and a loss of 18-48% due to heating cow milk
at the same time-temperature conditions. Haddad and
Loewenstein (1983) reported that losses of vitamin C
from milk varied from 16 .55% to 29.695 w ith the ab solute
UHT sterilization treatment (140ºC /3.5 sec), while the
loss from commercial UHT sterilization treatment
(110ºC/3.5 sec) was higher (25.59%) than HTST
pasteurization (16 .55-21.29% ).
Löker et al. (2003) reported a reduc tion in vitamin C
content of 6.25% on heating milk at 75ºC for 16 sec. The
greater loss of vitamin C reported in this study could be
explained by the fact that uncontrolled heating (boiling to
99ºC) for 10 min caused adverse effect on vitamin C
content of m ilk.
The total viable bacteria count decreased with heating
with the decrease rang ing from 0.21 to 22.59 %. It is
expected that heat treatment would eliminate or reduce the
bacterial load of milk; how ever, the decrease in bacterial
count in this study is not within the standards of
pasteurization that would lead to producing safe milk.
These results are in disagreement with the findings of
Clare et al. (2005) who reported that UHT and microwave
processing eliminated all bacterial growth in milk as
evidenced by lack of co lony fo rmation using various
microbiological med ia. How ever, the findings are in line
with Elzubeir et al. (2007) who is reported a total
bacterial count of 10000000 cfu /mL in pasteurized milk
samples collected from Western Cape of South Africa.
M ilk heat treatment (low pasteu rization , high
pasteurization and UHT) did not completely destroy total
viable bacteria in milk, and the number increased with the
progress of storage period till day 30 where the count
reached to 7.17±0.07, 6.41±0.35 and 2.90±0.14 Log10
cfu/mL for LP, HP and UHT , respectively.
adverse effect of direct heating. More research is needed
to study the effect of heat on constituents such as fatty
acids, amino acids and other vitamins besides evaluating
the efficiency in eliminating pathogens.
ACKNOWLEDGMENT
The help of the staff of the Chemistry and
Microbiology laboratory of the D epartmen t of Dairy
Production is acknowledged.
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