FOOD CHEMISTRY
FSTC 605
 Instructor: Dr.
Steve Talcott
 Office: 220F Centeq A
 Phone: 862-4056
 E-mail: stalcott@tamu.edu

Course website:
http://nfscfaculty.tamu.edu/talcott
Recommended Text
Food Chemistry, 3rd Edition
Owen Fennema ed.
 Classes
 My
Meet: Mon, Wed, and Fri
office is open at all times
www.ift.org
IFT Definition of Food Science
Food science is the discipline in which biology,
chemistry, physical sciences and engineering are
used to study:
The nature of foods
The causes of their deterioration
The principles underlying food processing.
Food Science: An Interdisciplinary
Field of Study
Microbiology
Biology
Chemistry
Food Science
Physics
Engineering
Nutrition
Food Chemistry
 Basis
of food science
 Water
 Carbohydrates
 Proteins
 Lipids
 Micronutrients
 Phytochemicals
 Others
Food Chemistry Examples
Lipids in Peanuts
 Opened
jar peanut butter: chemical reaction
in the oil phase
 Oxidation of the unsaturated fatty acids in
the peanut oil results in production of a
rancid odor.
 Peanut butter represents a special food
system called an emulsion
H
C
H
oxygen
H
C
H
C
H
C
H
Hydrocarbon chain
Solutions and Emulsions
Solutions are homogeneous mixtures in which solute
particles are small enough to dissolve within solvent
Solute examples: salt, sugar, vitamin C, other small solid particles
Solute liquid examples: water, ethanol; gas examples: CO2
Droplets of dispersed phase
within the continuous phase
Examples of colloids
MILK
Dispersions (colloidal dispersions) are mixtures in which
solutes do not dissolve (too large)
milk protein (casein)
egg white protein (albumen)
gelatin protein
pectin polysaccharide
Ca and Mg (minerals)
What is an emulsion?
Mixture of two immiscible liquids
oil
Surface tension acts to keep the liquids
from mixing
H2O
Result: oil “sits” on
top of the water phase
Stable food emulsions = addition of emulsifiers
lecithin, sucrose esters, MAG, DAG, etc
O/W
emulsion
milk
ice cream
mayo
W/O
emulsion
Margarine
butter
Common Chemical Bonds in Foods

Covalent




Ionic



Sharing 1 or more pairs of electrons
Very strong bonds, not easily broken in foods
C-C or C=C bonds
Filling of orbitals through the transfer of electrons
Cations (+) and Anions (-); Na+ + Cl- => NaCl
Hydrogen


Compounds containing O or N with bound hydrogen
Very weak bonds; C-H or N-H
Functional Groups in Foods
The “Basics” of Food Chemistry
SOME FOOD MOLECULES
important in food chemistry
H–O–H
Na H CO3
CH3 – COOH
C6H12O6
NH2 – CH2 - COOH
O=C=O
NaCl
CH3 – (CH2)n - COOH
SOME FOOD MOLECULES
important in food chemistry
WATER
sodium bicarbonate
The amino acid
“glycine”
acetic acid
glucose
carbon dioxide
sodium chloride
general
structure of a
fatty acid
A Few Food Functional Groups:
ACID GROUP: “carboxylic acid” COOH
acids donate (lose) protons
COOH  COO(-) + H(+)
This means acids form ions (charged species)
anion has (-) charge
cation has (+) charge
Vinegar contains acetic acid CH3COOH
Tartaric acid found in grapes is a di-carboxylic acid –
what does this mean?
Citric acid is tri-carboxylic acid.
AMINO GROUP: NH2
Derived from ammonia (NH3)
Amines are “basic” – means they gain protons
methyl amine: CH3 – NH2
trimethylamine is found in fish, and is responsible for
“fishy odor”
CH3 – CH – COOH
NH2
Alanine, an amino acid
Alcohol group - OH “hydroxyl group”
Methyl alcohol = methanol: CH3- OH
Ethanol C2H5OH is produced during the fermentation
of sugars; it is water-soluble and is called “grain alcohol”
because it is obtained from corn, wheat, rice, barley,
and fruits.
Yeasts use sugars for food – they ferment
simple carbohydrates and produce ethanol and CO2:
STARCH hydrolysis  C6H12O6  2 C2H5OH + 2 CO2
Glucose
Ethanol
Carbon
Dioxide
Other food molecules that contain OH groups: cholesterol (a lipid),
tocopherol (a vitamin), retinol (a vitamin), & calciferol (a vitamin)
Aldehyde group - CHO
There is actually a double bond between two atoms
in this group:
formaldehyde HCHO:
H–C–H
O
Aldehydes can be formed from lipid oxidation, and
generally have very low sensory thresholds.
For example, fresh pumpkin has the smell of
acetaldehyde; fresh cut grass the small of hexenal.
Covalent: Sharing of electrons, strong bonds, C-C or C=C bonds
Ionic: Transfer of electrons, NaCl
Hydrogen: Weak bonds with O or N with bound hydrogen
There are 3 other important bonds in foods:
(1) An ester bond (linkage) in lipids
(2) A peptide bond (linkage) in proteins
(3) A glycosidic bond (linkage) in sugars
An ester bond (linkage) in lipids:
In food fats, fatty acids are attached to glycerol molecules, through
what is called an ester linkage
O
Glycerol
C
O
Ester linkage
fatty acid
Glycerol is a small molecule, containing only 3 carbons
But, to each carbon atom of glycerol, one fatty acid
can attach, via an ester bond.
A mono-, di-, or tri-esterified fatty acid to a glycerol is:
A MONOACYLGLYCEROL. A fat molecule that
has ONE fatty acid attached (“esterified”) to glycerol.
A DIACYLGLYCEROL. A fat molecule that
has TWO fatty acids esterified to glycerol.
A TRIACYLGLYCEROL. A fat molecule that
has THREE fatty acids esterified to glycerol.
H
H
H–C–OH
H–C–OH
H–C–OH
O
H – C – O – C - (CH2)n – CH3
H–C–OH
Fatty acid chain
H–C–OH
H
H
a monoglyceride
Glycerol
What do peptide bonds (linkages) in proteins look like?
In food proteins, or “polypeptides”, individual amino acids are
attached to each other through what is called a peptide linkage
Amino acid
Peptide linkage
Amino acid. . . repeat
AMINO ACIDS contain both the amino (NH2)
and the acid (COOH) group in their structure.
In the formation of a peptide bond, one of the amino
acids loses one H atom, and the other loses O and H.
H
O
H
O
NH2 C – C - O – H ------------- NH2 C – C - O – H
R is any
Side chain
“R”
Acid group of the amino acid
“R”
Amino group
The formation of peptide bond
N-C-C-N
A glycosidic linkage in sugars connects
sugar units into larger structures
Glycosidic linkage
glucose
O
glucose
MALTOSE, a disaccharide composed of 2 glucose units
Structures of sugar disaccharides
Alpha 1,4 glycosidic
bond
Beta 1,4 glycosidic
bond
Alpha 1,4 glycosidic
bond
Polymeric Linkages
CH 2 OH
O
O OH
CH 2 OH
O
O
OH
OH
OH
Amylose
Cellulose
Alpha 1,4 Linkage
Digestible
Beta 1,4 Linkage
Indigestible
Organic Acids in Foods
Application of functional groups
Acids in Foods
Organic acids
 Citric (lemons), Malic (apples), Tartaric
(grapes), Lactic (yogurt), Acetic (vinegar)
 Food acids come in many forms, however:
 Proteins
are made of amino acids
 Fats are made from fatty acids
 Fruits and vegetables contain phenolic acids
 Organic
acids are characterized by carboxylic
acid group (R-COOH); not present in “mineral
acids” such as HCl and H3PO4
Chemical
Structures
of
Common
Organic
Acids
Acids in Foods
 Add
flavor, tartness
 Aid in food preservation by lowering pH
 Acids donate protons (H+) when dissociated
 Strong acids have a lot of dissociated ions
 Weak acids have a small dissociation constant
 Acids dissociate based on pH
 As the pH increases, acid will dissociate
 pKa is the pH equilibrium between assoc/dissoc
Titration Curve for Acetic Acid
Acids in Foods
 Weak
acids are commonly added to foods
 Citric acid is the most common
 When we eat a food containing citric acid, the
higher pH of our mouth (pH 7) will dissociate
the acid, and giving a characteristics sour flavor
pH and Titratable Acidity
 pH measures the amount of dissociated ions
 TA measures total acidity (assoc and dissoc)
 The type of food process is largely based on pH
They also have other roles in food

Control pH
 Preserve food (pH 4.6 is a critical value)
 Provide leavening (chemical leavening)
 Aid in gel formation (i.e. pectin gels)
 Help prevent non-enzymatic browning
 Help prevent enzymatic browning
 Synergists for antioxidants (for some, low pH is good)
 Chelate metal ions (i.e. citric acid)
 Enhance flavor (balance sweetness)
Acids in Foods
 In
product development you can use one acid
or a combinations of acids
 -flavor
 -functionality
-
synergy
 - naturally occurring blends
 - food additives
Acidity is important chemically
 -Denaturation and
precipitation of proteins
 -Modify
carbohydrates and hydrolysis of
complex sugars
 -Hydrolysis of
 Generally
fatty acids from TAG’s
under alkaline conditions
 Inversion of
sugars (sucrose to glu + fru)
Chemical Reactions in Foods
(1) Enzymatic
(2) Non-enzymatic
Generically applied to:
Carbohydrates
Lipids
Proteins
CARBOHYDRATE
chemical reactions:
 Enzymatic
browning
 Non-enzymatic browning
 Hydrolysis
 Fermentation
 Oxidation/reduction
 Starch gelatinization
PROTEIN
chemical reactions:
 Buffering
 Non-enzymatic browning
 Hydrolysis
 Condensation
 Oxidation
 Denaturation
 Coagulation
LIPID
chemical reactions
 Oxidation
 Hydrolysis
 Hydrogenation
Chemical Bonds to Chemical Rxns
Chemical Reactions in Foods
 Enzymatic
 Enzymes
are proteins that occur in every living system
 Enzymes can have beneficial and detrimental effects
Bacterial fermentations in cheese, pickles, yogurt
 Adverse color, texture, flavor, and odor

 High
degree of specificity (Enzyme – Substrate)
 Non-enzymatic
 Those
reactions that do not require enzymes
 Addition, redox, condensation, hydrolysis
The Active Site of the ES Complex
Enzyme Reactions
 Enzymatic
reactions can occur from enzymes
naturally present in a food
 Or as part of food processing, enzymes are
added to foods to enable a desired effect
 Enzymes speed up chemical reactions (good
or bad) and must be controlled by
monitoring time and temperature.
 Typically we think of enzymes as “breaking
apart” lipids, proteins, or carbs; but there
are several enzyme categories
sucrase
sucrose
“invertase”
glucose + fructose
Enzyme Class Characterizations
1.
Oxidoreductase
Oxidation/reduction reactions
2.
Transferase
Transfer of one molecule to another (i.e. functional groups)
3.
Hydrolase
Catalyze bond breaking using water (ie. protease, lipase)
4.
Lyase
Catalyze the formation of double bonds, often in dehydration
reactions, during bond breaking
5.
Isomerase
Catalyze intramolecular rearrangement of molecules
6.
Ligase
Catalyze covalent attachment of two substrate molecules
Common Enzyme Reactions
(some reactions can also occur without enzymes)
HYDROLYSIS
 Food molecules split into smaller products, due to the
action of enzymes, or other catalysts (heat, acid) in the
presence of water
OXIDATION / REDUCTION:
 Reactions that cause changes in a food’s chemical
structures through the addition or removal of an
electron (hydrogen).


Oxidation is the removal of an electron
Reduction is the addition of an electron
Oxidation vs Oxidized

The removal of an electron is oxidation (redox reactions).
 When a food system is oxidized, oxygen is added to an active
binding site
 For example, the result of lipid oxidation is that the lipid may
become oxidized.


In the food industry, we common speak of “oxidizing agents”
versus “reducing agents”. Both are used in foods.
Reducing agents are compounds that can donate an electron in the
event of an oxidation reaction.


L-ascorbic acid is an excellent reducing agent as are most antioxidants
Oxidizing agents induce the removal of electrons

Benzoyl peroxide is commonly added to “bleached” wheat flour
Lets put Enzymes and Chemical
Reactions into Perspective
Enzymes

Living organisms must be able to carry out chemical reactions
which are thermodynamically very unfavorable




Break and/or form covalent bonds
Alter large structures
Effect three dimensional structure changes
Regulate gene expression
They

A common biological reaction can take place without
enzyme catalysis



do so through enzyme catalysis
…but will take 750,000,000 years
With an enzyme….it takes ~22 milliseconds
Even improvement of a factor of 1,000 would be good


Only 750,000 years
Living system would be impossible
Effect of Enzymes
A
bag of sugar can be stored for years with very little
conversion to CO2 and H2O
 This conversion is basic to life, for energy
 When consumed, it is converted to chemical energy
very fast
 Both enzymatic and non-enzymatic reactions
 Enzymes
are highly specialized class of proteins:
 Specialized
to perform specific chemical reactions
 Specialized to work in specific environments
Enzymes
• Food quality can be changed due to the activity of
enzymes during storage or processing
• Enzymes can also be used as analytical indicators to
follow those changes
• Enzyme-catalyzed reactions can either enhance or
deteriorate food quality
• Changes in color, texture, sensory properties
Enzyme Applications in the Food Industry
Carbohydrases: making corn syrup from starch
Proteases: Meat tenderizers
Lipases: Flavor production in chocolate and cheese
 Pectinases
 Glucose
oxidase
 Flavor enzymes
 Lipoxygenase
 Polyphenol oxidase
 Rennin (chymosin)
Water Content of Foods

Tomatoes, lettuce -- 95%
 Apple juice, milk -- 87%
 Potato -- 78%
H
 Meats -- 65-70%
O
H
 Bread -- 35%
 Honey -- 20%
 Rice, wheat flour -- 12%
 Shortening -- 0%
H
O
H
Water Works

Water must be “available” in foods for the action of
both chemical and enzymatic reactions.

The “available” water represents the degree to which
water in a food is free for:




Chemical reactions
Enzymatic reactions
Microbial growth
Quality characteristics



Related to a simple loss of moisture
Related to gel breakdown
Food texture (gain or loss)
Water Works

Very important (#1 ingredient in many foods)
 Structure

Polar nature, hydrogen bonding

Can occur in many forms (S,L,V)
 Acts as a dispersing medium or solvent


Solubility
Hydration



Emulsions
Gels
Colloids
Water Works
The amount of “free” water, available for these reactions
and changes is represented by Water Activity.
 As the percentage of water in a food is “bound” changing
from its “free” state, the water activity decreases
 Water Activity is represented by the abbreviation: Aw
 Aw = P/ Po




P = Vapor pressure of a food
Po = Vapor pressure of pure water (1.0)
Vapor pressure can be represented as equilibrium RH
 Is based on a scale of 0.0 to 1.0
 Any food substance added to water will lower water
activity….so, all foods have a water activity less than 1.0
Water
Free vs. bound
 Water activity (Aw)
 Measured
by vapor pressure of food
 This value is directly correlated to the growth of
microorganisms and the chemical reactions
3 Forms of Water

Free water (capillary water or Type III)
 Water that can be easily removed from a food
 Water that is responsible for the humidity of a food
 Water from which water activity is measured

Bound water (adsorbed or Type II)
 Water that is tied up by the presense of soluble solids
 Salts, vitamins, carbohydrates, proteins, emsulifiers, etc.

Water of hydration (Structured or Type I)
 Water held in hydrated chemicals
.
 Na2SO4 10H2O
Water Sorption Isotherm
Type I
Hydration
0
0.1
0.2
Type II
Absorbed
0.3
0.4
0.5
0.6
Water Activity
Type III
Free
0.7
0.8
0.9
1
Water Sorption Isotherm
Type I
Hydration
0
0.1
0.2
Type II
Absorbed
0.3
0.4
0.5
0.6
Water Activity
Type III
Free
0.7
0.8
0.9
1
Moisture sorption isotherm (MSI)
How to Use the Isotherm
Moisture sorption isotherms
 Shows the relationship between water activity and moisture at a
given temperature (the two are NOT equivalent)

Represent moisture content at equilibrium for each water activity

Allow for predictions in changes of moisture content and its
potential effect on water activity

If the temperature is altered, then the relationships can not be
compared equivalently

Each reaction is governed by its own temperature-dependence


Acid hydrolysis reactions are faster at high temperatures
Enzyme-catalyzed reactions cease to function at high temperatures
Influences on Water Activity



Foods will naturally equilibrate to a point of equilibrium with its environment
Therefore, foods can adsorb or desorb water from the environment
Desorption is when a “wet” food is placed in a dry environment




Analogous to dehydration; but not the same
Desorption implies that the food is attempting to move into equilibrium (ie. in a
package)
Dehydration is the permanent loss of water from a food
In both cases, the Aw decreases

Desorption is generally a slow process, with moisture gradually decreasing
until it is in equilibrium with its environment.

Adsorption is when a “dry” food is placed in a wet environment
As foods gain moisture, the Aw increases
The term “hygroscopic” is used to describe foods or chemicals that absorb
moisture
A real problem in the food industry (lumping, clumping, increases rxn rates)



Water Activity in Practice
 Bacterial
growth and rapid deterioration
 High
water activity in meat, milk, eggs,
fruits/veggies
 1.0-0.9
 Yeast
and mold spoilage
 Intermediate
water activity foods such as bread
and cheese
 0.75-0.9
 Analogous to
a pH < 4.6, an Aw < 0.6 has the
same preservation effect
Aw in Low Moisture Foods

Water activity and its relationship with moisture content
help to predict and control the shelf life of foods.
 Generally speaking, the growth of most bacteria is
inhibited at water activities lower than 0.9 and yeast and
mold growth prevented between 0.80 and 0.88.
 Aw also controls physiochemical reactions.
 Water activity plays an important role in the
dehydration process. Knowledge of absorption and
desorption behavior is useful for designing drying
processes for foods.
How to “Control” water


The ratio of free to bound water has to be altered
You can either remove water (dehydration or
concentration)



Or you can convert the free water to bound water


Can change the physical nature of the food
Alter is color, texture, and/or flavor
Addition of sugars, salts, or other water-soluble agents
You can freeze the food



This immobilizes the water (and lowers the Aw)
However, not all foods can be or should be frozen
Frozen foods will eventually thaw, and the problem persists
Water


Water contains intramolecular polar covalent bonds
Effects




Boiling point
Freezing point
Vapor pressure
Easy formation of H bonds with food molecules
Properties of Water
 The
triple point is the temperature and pressure at
which three phases (liquid, ice, and vapor)
coexist at equilibrium, and will transform phases
small changes in temperature or pressure.
 The dashed line is the vapor pressure of
supercooled liquid water.
Chemical and functional properties of water
 Solvation, dispersion, hydration
 Water
activity and moisture
 Water as a component of emulsions
 Water and heat transfer
 Water as an ingredient
Freezing Foods
Controlling Water
Freezing
Greatly influenced the way we eat
 Freezing curves
 Water Freezes “Pure”
Frozen Foods
 Must be super-cooled to below 0°C
 Crystal nucleation begins
 Temperature rises to 0°C as ice forms
Refrigerated and Frozen Foods
The Market
 Meals and entrees
 Meat, poultry, fish
 Dairy, beverage
 Fruits and veggies
 Bakery products
 Snacks, appetizers,
and side dishes
Annual Sales ($Billion)
 $83.7
 69.8
 21.9
 11.6
 16.1
 15.8
Freezing Foods
Temperature
40
35
Freezing Point
20
30
25
60
70
20
15
90
Super-cooling
95
Latent heat of
Crystallization
10
5
0
2
4
6
8
98
99
99.9
10 12 14 16 18 20 22 24 26 28 30
Freezing Time
Freezing
Freezing Food
 Require lower temp. to continue freezing
 Last portion of water is very hard to freeze
 Unfrozen water is a problem
***As long as unfrozen water is present in a
food, the temperature will remain near 0°C
due to the latent heat of crystallization.
Freezing
Quality changes during freezing
 Concentration effect = small amount of
unfrozen water
 Excess solutes may precipitate
 Proteins may denature
 pH may decrease
 Gases may concentrate (i.e. oxygen)
Freezing
Quality changes during freezing
 Damage from ice crystals
 Puncture
 Large
cell membranes
crystals cause more problems
Fast freezing much more desirable
 Less concentration effect
 Smaller ice crystals
Freezing
Final storage temperature
 -18°C is standard
 Safe microbiologically
 Limits enzyme activity
 Non-enzymatic changes are slow
 Can maintain fairly easily
 Good overall shelf-life
Freezing
Intermittent thawing
 Partial thawing, then refreezing
 Complete thawing does not have to occur
 Get concentration effect
 Get larger ice crystals as water re-freezes
Freezing
Factors determining freezing rate:
 Food composition
 Fat and air have low thermal conductivity,
slow down freezing
 This is a “buffering” effect.
Freezing
Ways to speed up freezing
 Thinner foods freeze faster
 Greater air velocity
 More intimate contact with coolant
 Use refrigerant with greater heat capacity
High Pressure Effects
 Freezing
is regarded as one of the best methods
for long term food preservation.
 The benefits of this technique are primarily from
low temperatures rather than ice formation.
Freezing Foods

Freezing can be damaging to food systems due to





To reduce the chemical and mechanical damage to food systems during
freezing, technologies have been developed to freeze foods faster or under high
pressures. Benefits include:







Formation of ice crystals (especially large ice crystals)
Concentration of soluble solids
Concentration of gasses (ie. oxygen)
Intermittent thawing (poor temperature control)
Higher density ice (less “space” between crystals from air or solids)
Increased rate of freezing
Smaller ice crystal formation
Uniform crystal formation
With high-pressure freezing the increasing pressure decreases the temperature
needed to freeze water, thus the ice nucleation rate increases.
HP freezing generally involves cooling an unfrozen sample to -21C under high
pressures (300MPa) causing ice formation to occur.
Another method involves pressure shift freezing where the food is cooled
under high pressures without causing freezing. Once the pressure is released,
the sample freezes instantly.

The Phase diagram shows us the process which takes place as water is
added to a lipid system. It can be seen that the lipid phase transition
temperature falls with increasing water content. So,below that
particular temperature the chains are crystalline and when the
temperature is above it they are melted in a fluid condition. Note: The
phosphatidyl cholines bind a significant amount of water. This is said
to be 'bound' or 'unfreezable' water.





Water content in a food system influences the rate of chemical
reactions by shifting reaction equilibria via LeChatelier's
principle or by the more subtle effect of changing the pH.
Essentially, as water is removed those solutes involved in
degradation reactions are concentrated. These solutes are
responsible for the pH of the system.
Back in 1923, two researchers, Corran and Lewis, showed that
the activity of the hydronium ions (-OH) increased with
increasing sucrose concentration.
Basically the sucrose bound the water resulting in a decrease in
pH, or an increase in the acidity of a given solution.
Recent research has demonstrated that reaction rate of amino
acid degradation reactions are pH dependent.
Dehydration and Concentration
of Foods
Controlling Water
Dehydration and Concentration
Factors affecting drying rates
 Surface area
 Temperature
 Air velocity
 Humidity
 Pressure (vacuum)
 Solute concentration
 Amount of free and bound water
Moisture Content
Drying Curve of a Food
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Water that is easily removed
Water that is difficult to remove
0
1
2
3
4
5
6
7
Time (Hrs)
8
9
10
11
12
Dehydration and Concentration
Quality changes
Browning
 Enzymes - sulfite will prevent
 Carmelization - lower temps. will limit
 Maillard reaction - reaction of sugars and
amino acids - lower temps will limit
 Acrylamide…???
Flavor changes
Carbohydrates in Foods
A general overview
CARBOHYDRATES
Classifications for the main categories of food carbohydrates are
based on their degree of polymerization.
Types of Carbohydrates
CARBOHYDRATES

Carbohydrates are carbon compounds that contain many
hydroxyl groups.
 The simplest carbohydrates also contain either an aldehyde (these
are termed polyhydroxyaldehydes) or a ketone
(polyhydroxyketones).
 All carbohydrates can be classified as either monosaccharides,
disaccharides, oligosaccharides or polysaccharides.
 An oligosaccharide is anywhere from about two to ten
monosaccharide units, linked by glycosidic bonds.
 Polysaccharides are much larger, containing hundreds of
monosaccharide units.
 The presence of the hydroxyl groups (–OH) allows
carbohydrates to interact with the aqueous environment and to
participate in hydrogen bonding, both within and between chains.
CARBOHYDRATES

SUGARS contain 2 important and very reactive
Functional groups:


-OH (hydroxyl group)
Important for solubility and sweetness

-C=O (carbonyl group)

Important for reducing ability and Maillard browning

GLUCOSE is an ALDOSE sugar with one C atom
external to the 6-membered ring

FRUCTOSE is a KETOSE hexose with two carbon
atoms external to the 6-membered ring
Monosaccharides
 The
monosaccharides commonly found in
foods are classified according to the
number of carbons they contain in their
backbone structures.
 The major food monosaccharides contain
six carbon atoms.
Carbohydrate Classifications
 Hexose = six-carbon sugars
 Glucose, Galactose, Fructose
Fischer Projection of a-D-Glucose
Haworth Projection of a-D-Glucose
Chair form of a-D-Glucose
Disaccharides

Bonds between sugar units are termed glycosidic bonds,
and the resultant molecules are glycosides.
 The linkage of two monosaccharides to form
disaccharides involves a glycosidic bond. The important
food disaccharides are sucrose, lactose, and maltose.
Sucrose: prevalent in sugar cane and sugar beets, is composed
of glucose and fructose through an α-(1,2) glycosidic bond.
Lactose:
is found exclusively in the milk of mammals and consists of
galactose and glucose in a β-(1,4) glycosidic bond.
Maltose:
Is the major degradation product of starch, and is composed
of 2 glucose monomers in an α-(1,4) glycosidic bond.
Polysaccharides

Most of the carbohydrates found in nature occur in the
form of high molecular weight polymers called
polysaccharides.
 The monomeric building blocks used to generate
polysaccharides can be varied; in all cases, however,
the predominant monosaccharide found in
polysaccharides is D-glucose.
 When polysaccharides are composed of a single
monosaccharide building block, they are termed
homopolysaccharides.
Starch
 Starch
is the major form of stored carbohydrate
in plant cells.
 Its structure is identical to glycogen, except for
a much lower degree of branching (about every
20-30 residues).
 Unbranched starch is called amylose
 Branched starch is called amylopectin.
FUNCTIONAL PROPERTIES OF CARBOHYDRATES

Reducing sugars
 Browning reactions (caramelization and Maillard)
 Sweetness and flavors
 Crystallization
 Humectancy
 Inversion
 Oxidation and reduction
 Texturizing
 Viscosity
 Gelling (gums, pectins, other hydrocolloids)
 Gelatinization (Starch)
Invert sugar

Invert sugar is a liquid carbohydrate sweetener in which
all or a portion of the sucrose present has been inverted:

The sucrose molecule is split and converts to an equimolar
mixture of glucose and fructose.

Invert sugars have properties from sucrose; they help
baked goods retain moisture, and prolong shelf-life.
 Candy manufacturers use invert sugar to control
graining.
 Invert sugar is different from high fructose sweeteners

SUCROSE + invertase enzyme  glucose + fructose
Sucrose
Where does sucrose come from?
Invert sugar

Invert sugar is a liquid carbohydrate sweetener in which
all or a portion of the sucrose present has been inverted:

The sucrose molecule is split and converts to an equimolar
mixture of glucose and fructose.

Invert sugars have properties from sucrose; they help
baked goods retain moisture, and prolong shelf-life.
 Candy manufacturers use invert sugar to control
graining.
 Invert sugar is different from high fructose sweeteners

SUCROSE + invertase enzyme  glucose + fructose
Corn syrups

Corn syrups are manufactured by treating corn starch
with acids or enzymes.
 Corn syrups, used extensively by the food industry and
in the home kitchen, contain primarily glucose
(dextrose) but other sugars as well.
 High-fructose corn syrup (HFCS) is made by treating
dextrose-rich corn syrup with enzymes (isomerase).
 The resulting HFCS is a liquid mixture of dextrose and
fructose used by food manufacturers in soft drinks,
canned fruits, jams and other foods.

HFCS contains 42, 55, 90 or 99 percent fructose.
PROCESSING OF CORN STARCH  HFCS

Corn starch is treated with α-amylase, of bacterial origin, to
produce shorter chains of sugars (dextrins) as starch fragments.

Next, an enzyme called glucoamylase, obtained from the fungus
Aspergillus niger, breaks the fragments down even further to
yield the simple sugar glucose.

A third enzyme, glucose isomerase, is expensive, and converts
glucose to various amounts of fructose.



HFCS-55 has the exact same sweetness intensity as sucrose (cola)
HFCS-42 is less sweet, used with fruit-based beverages and for baking
Glucose isomerase is so expensive that it is commonly
immobilized on a solid-based “resin” bead and the glucose syrup
passed over it. Can be used many times over before it slowly
looses its activity.
HFCS

HFCS is selected for different purposes.
Selection is based on specific desired properties:













Retain moisture and/or prevent drying out
Control crystallization
Produce a higher osmotic pressure (more molecules in solution) than
for sucrose
Control microbiological growth
Provide a ready yeast-fermentable substrate
Blend easily with sweeteners, acids, and flavorings
Provide a controllable substrate for browning and Maillard reaction.
Impart a degree of sweetness essentially = to invert liquid sugars
High sweetness
Low viscosity
Reduced tendency toward crystallization
Costs less than liquid sucrose or corn syrup blends
Retain moisture and/or prevent drying out of food product
HFCS





HFCS has the exact same sweetness and taste as an equal
amount of sucrose from cane or beet sugar. Despite being a
more complicated process than the manufacture of sugar, HFCS
is actually less costly.
It is also very easy to transport, being pumped into tanker
trucks.
Two of the enzymes used, α-amylase and glucose-isomerase,
are genetically modified to make them more thermostable.
This involves exchanging specific amino acids in the primary
sequence so that the enzyme is resistant to unfolding or
denaturing.
This allows the industry to use the enzymes at higher
temperatures without loss of activity.
Starch
Starches- #1 Hydrocolloid

Hydrocolloids are substances that will form a gel or
add viscosity on addition of water.
 Most are polysaccharides and all interact with water.

The most common is starch

Starch is a mixture of amylose and amylopectin.

The size distribution of these hydrocolloids is the most
important factor in the texture and physical features of
foods
STARCH
Polymers of glucose
 AMYLOSE linear chain of glucose

Glucose polymer linked α-1,4
 AMYLOPECTIN
branched polymer of glucose
Amylose
Amylopectin
AMYLOSE
 Linear
polymer of glucose
 α 1 - 4 linkages
 Digestable by humans (4 kcal/g)
 250-350 glucose units on average
 Corn, wheat, and potato starch
 ~10-30%
amylose
AMYLOPECTIN
 Branched
chain polymer of glucose
 α 1 - 4 and α 1 - 6 glycosidic linkages
 Fully digestable by humans
 1,000 glucose units is common
 Branch
points every ~15-25 units
Starch

Amylopectin (black)
 Amylose (blue)
Modified Starches

Gelatinization is the easiest modification

Heated in water then dried.
Acid and/heat will form “dextrins”
 α-Amylase




β-Amylase




hydrolyzes α (1-4) linkage
random attack to make shorter chains
Also attacks α (1 - 4) linkages
Starts at the non-reducing end of the starch chain
Gives short dextrins and maltose
Both enzymes have trouble with α (1 - 6) linkages
DEXTRINS are considered to be hydrolysis products of
incompletely broken down starch fractions
Polysaccharide Breakdown Products
What’s the difference between…?








Maltose
Maltitol
Maltodextrins
Dextrins
Dextrans
Maltose = glucose disaccharide
Maltitol = example of a “polyol”
Maltodextrins = enzyme converted starch fragments

Dextrins = starch fragments (α-1-4) linkages produced by
hydrolysis of amylose

Dextrans = polysaccharides made by bacteria and yeast
metabolism, fragments with mostly α (1 - 6) linkages
Maltodextrins and enzyme-converted starch:
STARCH
fermentation
SUGARS
ETHANOL
MODIFIED STARCHES
GELATINIZED STARCH
alpha amylase
Maltodextrins
Corn Syrups
Sugars
The smaller the size of the products in these reactions, the
higher the dextrose equivalence (DE), and the sweeter
they are
Starch DE = 0
Glucose (dextrose) DE = 100
Maltodextrin (MD) DE is <20
Corn syrup solids (CS) DE is >20
Low DE syrup
alpha amylase
MD
beta amylase
High
DE
Syrup
Hydrocolloids
Binding water with carbohydrates
“Gums”
“Vegetable gum” polysaccharides are substances derived
from plants, including seaweed and various shrubs or trees,
have the ability to hold water, and often act as thickeners,
stabilizers, or gelling agents in various food products.
Plant gums - exudates, seeds
Marine hydrocolloids - extracts from seaweeds
Microbiological polysaccharides - exocellular polysaccharides
Modified, natural polysaccharides
FUNCTIONS IN FOOD

Gelatin
 Viscosity
 Suspension
 Emulsification and stability
 Whipping
 Freeze thaw protection
 Fiber (dietary fiber)


Gut health
Binds cholesterol
STRUCTURAL CONSIDERATIONS
 Electrical
charge, pH sensitive
 Interactions
with oppositely charged molecules
 Salts
 Low
 Chain
pH effects
length
 Longer
 Linear
chains are more viscous
vs Branched chains
 Inter-entangled,
enter-woven molecules
Gums

GUAR (Guran Gum)






Most used, behind starch, low cost
Guar bean from India and Pakistan
Cold water soluble, highly branched galactomannan
Stable over large pH range, heat stable
Thickening agent, not a gel
Often added with xanthan gum (synergistic)

XANTHAN
 Extracellular polysaccharide from Xanthomonas campestris


Very popular, inexpensive from fermentations
Forms very thick gels at very low concentrations
Gums
 LOCUST
BEAN
 Branched
galactomannan polymer (like guar), but
needs hot water to solubilize
 Bean from Italy and Spain
 Jams, jellies, ice cream, mayonnaise
SEAWEED EXTRACTS
 Carrageenans (from
 Kappa
red seaweed)
(gel)
 Iota (gel)
 Lambda (thickener only)
 Milk, baking, cheese, ice cream
 Agar
 Alginates
“Structural” Polysaccharides
Cellulose
 Polymer of glucose linked ß-1,4
Hemicellulose
 Similar to cellulose
 Consist of glucose and other monosaccharides
 Arabinose,
xylose, other 5-carbon sugars
Pectin
 Polymer of galacturonic acid
MODIFIED CELLULOSES
 Chemically
modified cellulose
 Do not occur naturally in plants
 Similar to starch, but β-(1,4) glycosidic bonds
 Carboxymethyl cellulose (CMC) most common
 Acid
treatment to add a methyl group
 Increases water solubility, thickening agent
 Sensitive to salts and low pH
 Fruit
fillings, custards, processed cheeses, high
fiber filler
PECTINS

Linear polymers of galacturonic acid



Susceptible to degrading enzymes



Gels form with degree of methylation of its carboxylic acid
groups
Many sources, all natural, apple and citrus pomace
Polygalacturonase (depolymerize)
Pectin esterases (remove methyl groups)
Longer polymers, higher viscosity
 Lower methylation, lower viscosity
 Increase electrolytes (ie. metal cations), higher viscosity
 pH an soluble solids impact viscosity
PECTIC SUBSTANCES: cell cementing compound; fruits and vegetables;
pectin will form gel with appropriate concentration, amount of sugar and pH.
Basic unit comprised of galacturonic acid.
Composition: polymer of galacturonic acids; may be partially esterified.
Pectic Acid
Pectin Molecule
Pectins

Pectins are important because they form gels

Mechanism of gel formation differs by the degree of esterification
(DE) of the pectin molecules

DE refers to that percentage of pectin units with a methyl group attached

Free COOH groups can crosslink with divalent cations

Sugar and acid under certain conditions can contribute to gel
structure and formation

LM pectin “low methoxyl pectin” has DE < 50% ; gelatin is
controlled by adding cations (like Ca++ and controlling the pH)

HM pectin “high methoxyl pectin” has DE >50% and forms a gel
under acidic conditions by hydrophobic interactions and Hbonding with dissolved solids (i.e. sugar)
Hydrophobic attractions between neighboring pectin polymer chains
promote gelation
BETA-GLUCANS
 Extracts
from the bran of barley and oats
 Long glucose chains with mixed ß-linkages
 Very large (~250,000 glucose units)
 Water
soluble, but have a low viscosity
 Can be used as a fat replacer
 Responsible for the health claims (cholesterol) for
whole oat products
 Formulated to reduce the glycemic index of a food
Others
CHITIN
 Polymer of N-Acetyl-D-glucosamine
 Found in the exoskeleton of insects and shellfish
 Many uses in industry, food and non-food.
INULIN
 Chains of fructose that end in a glucose molecule




Generally a sweet taste
Isolated from Jerusalem artichokes and chicory
Act as a dietary fiber
Potentially a pre-biotic compound
COMPONENTS OF DIETARY FIBER
COMPONENT
SOURCE
Cellulose
All food plants
Hemicellulose
All food plants, especially cereal
bran
Pectin
Mainly fruit
Lignin
Mainly cereals and 'woody'
vegetables
Gums and some food
thickeners
Food additives in processed
foods
HYDROCOLLOIDS

A key attribute of gums is to produce viscous dispersions in water

Viscosity depends on:


Gum type
Temperature
Concentration of gum
Degree of polymerization of gum
Linear or branched polymers
Presence of other substances in the system

Solubility (dispersability in water) varies among gums

Agar is insoluble in cold water; dissolves in boiling water

Methylcellulose is insoluble in hot water, but soluble in cold !




Our First Browning Reaction
Caramelization
BROWNING REACTIONS in CARBOHYDRATES

There are 2 different kinds of browning reactions with carbohydrates:

Caramelization

Maillard (or non-enzymatic) browning

CARAMELIZATION occurs when sucrose is heated >150-170°C (high
heat!) via controlled thermal processing

Dehydration of the sugar, removal of a water molecule

The structure of caramelized sugar is poorly understood but can exist in both
(+) and (-) species

Commonly used as a colorant


(+) charged caramel = promotes brown color in brewing and baking
industries
(-) charged caramel in beverage/ soft drink industry (cola and root beer)
CARAMELIZATION

What is referred to as “caramel pigment” consists of a
complex mixture of polymers and fragments of
indefinite chemical composition

Caramelans (24, 36, or 125 carbon lengths)

Since caramel is a charged molecule, to be compatible
with phosphoric acid in colas the negative form is used

Caramel flavor is also due to these and other fragments,
condensation, and dehydration products.

diacetyl, formic acid, hydroxy dimethylfuranone
Artificial and
Alternative Sweeteners
The perception of sweetness
is proposed to be due to a
chemical interaction that
takes place on the tongue
Between a tastant molecule
and tongue receptor protein
THE AH/B THEORY OF SWEETNESS
A sweet tastant molecule (i.e. glucose) is called the AH+/B“glycophore”.
It binds to the receptor B-/AH+ site through mechanisms
that include H-bonding.
AH+ / B-
γ
B
Glycophore
Hydrophobic interaction
AH
AH
B
γ
Tongue receptor protein molecule
For sweetness to be perceived, a molecule needs to have certain requirements.
It must be soluble in the chemical environment of the receptor site on the
tongue. It must also have a certain molecular shape that will allow it to bond
to the receptor protein.
Lastly, the sugar must have the proper electronic distribution. This electronic
distribution is often referred to as the AH, B system. The present theory of
sweetness is AH-B-X (or gamma). There are three basic components
to a sweetener, and the three sites are often represented as a triangle.
Identifying the AH+ and Bregions of two sweet tastant
molecules: glucose and saccharin.
Gamma (γ) sites are relatively hydrophobic functional groups
such as benzene rings, multiple CH2 groups, and CH3
WHAT IS SUCRALOSE AND HOW IS IT MADE?
Sucralose, an intense sweetener made from sugar,
is approximately 600 times sweeter than sugar.
In a patented multi stage process three of the hydroxyl
groups in the sucrose molecule are selectively substituted
with 3 atoms of chlorine.
This intensifies the sugar like taste while creating a safe,
stable low kcal sweetener with zero calories.
Although its chemical structure is very close to that of sucrose
(table sugar), sucralose is not recognized by the body as a carbohydrate
and has no effect on insulin secretion or overall carbohydrate metabolism
in healthy human beings.
Developers found that selective halogenations changed
the perceived sweetness of a sucrose molecule, with chlorine
and bromine being the most effective.
Chlorine, as a lighter halogen, retains higher water solubility,
so chlorine was picked as the ideal halogen for substitution.
Sucrose portion
Fructose portion
Compared to sucrose, sucralose has three key molecular
differences that make it similar in structure, yet different in
metabolism and function.
These three differences are chlorine. Three chlorine atoms,
in the form of chloride ions, replace three hydroxyl groups in
native sucralose.
It was determined that the tightly bound chlorine
created a stable molecular structure, approximately
600 times sweeter than sugar.
In sucralose, the two chlorine atoms present in the fructose
portion of the molecule comprise the hydrophobic X-site,
which extends over the entire outer region of the fructose
portion of the sucralose molecule.
The hydrophobic and hydrophilic regions are situated on
opposite ends of the molecule, similar to sucrose,
apparently unaffected by the third chlorine on the C4 of
the pyranose ring.
The similar structure of sucralose to native sucrose is
responsible for its remarkably similar taste to sugar.
hydrophobic
Area (AH+): This area has hydrogens available to
hydrogen bond to chlorine attached to the glucose
bottom portion of the molecule.
hydrophilic
Area (B -): This area has a partially negative
oxygen available to hydrogen bond to the
partially positive hydrogen of an alcohol group.
hydrophilic
The drastically increased sweetness of sucralose is due
to the structure of molecule. In sucralose, the two chlorine
atoms present in the fructose portion of the molecule lead
to more hydrophobic properties on the opposite side of the
molecule (upper left), which extends over the entire outer
region of the fructose portion of the sucralose molecule.
In 2005 Coca-Cola released a new formulation of Diet Coke
sweetened with sucralose, called “Diet Coke with Splenda”.
Wheat
Bran
Removed
Whole
Wheat
Corn
Milled,
Polished
Rice
Cereals
Cereals
 Starch, protein, fiber
 Water
 Lysine
 Structure
 Husk
(inedible)
 Bran (fiber)
 Endosperm (starch, protein, oil)
 Germ (oil)
Wheat Kernel
Bran
Bran
Fiber
Endosperm
Endosperm
Starch
Protein
Oil
Germ
Germ
Oil
Protein
Cereal Grain
Composition of Cereals
Grain
Water
Carbo.
Protein
Fat
Fiber
Corn
11
72
10
4
2
Wheat
11
69
13
2
3
Oats
13
58
10
5
10
Sorghum
11
70
12
4
2
Barley
14
63
12
2
6
Rye
11
71
12
2
2
Rice
11
65
8
2
9
Buckwheat
10
64
11
2
11
Wheat
2
types of wheat
 HARD = higher protein (gluten), makes
elastic dough, used for bread-making
 Higher
“quality”
 High water absorption
 SOFT
= lower protein (gluten), make weak
doughs/batters, used for cakes, pastries,
biscuits, cakes, crackers, etc.
 Lower
“quality” due to lower protein content
and useful applications
Wheat
Wheat Milling
To produce flour
 Cleaned with air (dust, bugs, chaff)
 Soaked to 17% moisture - optimum for
milling
 Remove husk
 Crack seeds - frees germ from endosperm
Wheat
Wheat Milling
 Rollers- two metal wheels turning in opposite
direction of each other
 Endosperm is brittle and breaks
 Germ and bran form flat flakes and are
removed by screens or sieves
 Endosperm = flour
 Less
 Whole
color and less nutrients as milling continues
wheat flour = do not remove all of the
bran and/or germ
Wheat Mill Grinding Rolls
Wheat Milling Sifters
Wheat
Wheat Enrichment
 Add B-vitamins and some minerals to most
white flours (since missing the bran)
Uses of flour
 Cakes, breads, etc.
 Pasta, noodles, etc.
 Course flour, not leavened
Rice Processing
Rice
Rice Milling
 Most rice is "whole grain"
 Remove husk, bran, germ by rubbing with
abrasive disks or rubber belts
 Polish endosperm to glassy finish
 Brown rice = very little milling
Rice
Rice Enrichment
 Add some vitamins, minerals
 Coat rice with nutrients (folic acid)
Parboiling or steeping (converted rice)
 Boil rice before milling (~10 hrs, 70°C)
 Nutrients, vitamins and minerals, will
migrate into endosperm (no fortification)
Rice
Rice
Other rice products
 Quick cooking (instant) = precooked, dried
 Rice flour
 Sake (15-20% alcohol)
Advantages/Disadvantages of
Milling Rice
 Brown
Rice
 Minimal
milling
Higher in lipid (shortens shelf-life)
 Higher in minerals (not removed in milling)

 White
(Milled) Rice
 Extreme
milling
Vitamins and minerals removed (Thiamin)
 Fortification to prevent Beriberi disease

Anatomy of Corn
Corn
Corn

Some fresh/frozen/canned corn, but most is milled
 Dry milling (grits, meal, flour)
 Adjust moisture to 21%- optimum for "dry" milling
 Loosen hull (pericarp) and germ by rollers
 Dry to 15% moisture
 Remove husk with air blast; germ and bran by sieving
 Continue grinding endosperm to grits, meal or flour
 Process very similar to wheat milling at this point.



Grits = large particle size
Meal = medium particle size
Flout = small particle size
Grain Processing
Wet milling (corn starch, corn syrups)
 Soak corn
 Grind with water into a wet "paste"
 Slurry is allowed to settle and the germ
and hulls float to top (high in oil)
 Remainder is endosperm (starch/protein)
 Centrifuged or filtered
 to
remove/collect the starch
Grain Processing
Wet milling (cont'd.)
 Dried starch = corn starch
 Can produce corn syrups from starch
 Use enzymes (amylase) to break starch into
glucose (corn syrup)
 Use another enzyme (isomerase) to convert
glucose into fructose (HFCS)
 Can also produce ethanol from corn syrup
Products from Corn
Grain Usage
Other grains- mostly for animal feed
 Barley = used in beer
 Rye = can not use alone (poor protein quality)
 Oats = oatmeal, flakes
Breakfast cereals
 Made from many different grains
Baking
Ingredients
 Flour
 Starch
 Protein
= gluten; forms elastic dough that will
expand during rising
Baking
Ingredients…
 Leavening agent
 Rising due to carbon dioxide or air
 Yeast = alcoholic fermentation produces
carbon dioxide
 Baking powder = chemical reaction that
releases carbon dioxide
Baking
…Ingredients
Leavening
 Air leavening = sponge cake
 Partial leavening = pie crusts, crackers
Eggs
 Add flavorings
 Add color
 Helps holds air when whipped
Baking
…Ingredients
 Shortening
 Tenderizes
 Hold
air
 Sugar
 Tenderizes
 Sweetness
 Fermentable
sugar
 Helps retain moisture
Baking
Oven baking
 Gas production and rising continues
 Denaturation and coagulation of proteins
 Drying and crust formation
 Flavor development
 Color development = Carmelization and
Maillard reaction
Baking
High altitudes
 Excessive gas production (less pressure)
 Weakens and collapses dough
 Not as bad for bread
Can alter formula
 Less baking powder
 Make tougher dough
 Add less tenderizers
Legumes and Oilseeds
Soybeans, peanuts, etc.
 Higher in oil (20-50%) and protein (20%)
 Methionine and/or cysteine are limiting
amino acids
 Protein complementation with cereals
Legumes and Oilseeds
 Soybeans
= used for both oil and protein
 Peanuts = whole nut, oil, peanut butter