FOOD CHEMISTRYFSTC 605

Instructor: Dr. Steve TalcottOffice: 220F Centeq APhone: 862-4056E-mail: stalcott@tamu.edu

Course website:

http://nfscfaculty.tamu.edu/talcott

Recommended TextFood Chemistry, 3rd EditionOwen Fennema ed.

Classes Meet: Mon, Wed, and Fri

My office is open at all times

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.

www.ift.org

Food Science: An Interdisciplinary Field of Study

Food Science

Microbiology

Engineering

Biology

Physics

Chemistry

Nutrition

Food ChemistryBasis of food science

Water Carbohydrates Proteins Lipids Micronutrients Phytochemicals Others

Food Chemistry Examples

Lipids in PeanutsOpened 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 H H HC C C CH H

oxygen

Hydrocarbon chain

Solutions and Emulsions

Droplets of dispersed phasewithin the continuous phase

Solutions are homogeneous mixtures in which soluteparticles 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

Dispersions (colloidal dispersions) are mixtures in whichsolutes do not dissolve (too large)

Examples of colloids milk protein (casein)egg white protein (albumen)gelatin proteinpectin polysaccharideCa and Mg (minerals)MILK

What is an emulsion?

Mixture of two immiscible liquids

oil H2OSurface tension acts to keep the liquidsfrom mixing

Result: oil “sits” ontop of the water phase

Stable food emulsions = addition of emulsifierslecithin, sucrose esters, MAG, DAG, etc

O/Wemulsion

W/Oemulsion

milkice creammayo

Margarinebutter

Common Chemical Bonds in Foods

Covalent Sharing 1 or more pairs of electrons Very strong bonds, not easily broken in foods C-C or C=C bonds

Ionic 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 MOLECULESimportant in food chemistry

H – O – H O = C = O CH3 – COOH

Na H CO3 C6H12O6 NaCl

NH2 – CH2 - COOH CH3 – (CH2)n - COOH

SOME FOOD MOLECULESimportant in food chemistry

WATER carbon dioxideacetic acid

sodium bicarbonate glucose sodium chloride

The amino acid“glycine”

generalstructure of a

fatty acid

A Few Food Functional Groups:

ACID GROUP: “carboxylic acid” COOHacids donate (lose) protons

COOH COO(-) + H(+)

This means acids form ions (charged species) anion has (-) chargecation 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 Alanine, an amino acid

NH2

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 CO2Glucose 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.

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

Covalent: Sharing of electrons, strong bonds, C-C or C=C bondsIonic: Transfer of electrons, NaClHydrogen: Weak bonds with O or N with bound hydrogen

An ester bond (linkage) in lipids:

O

Glycerol C O fatty acid

In food fats, fatty acids are attached to glycerol molecules, through what is called an ester linkage

Ester linkage

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.

Glycerol

H

H – C – O H

H – C – O H

H – C – O H

H

H O

H – C – O – C - (CH2)n – CH3

H – C – O H

H – C – O H

H

Ester

Fatty acid chain

a monoglyceride

What do peptide bonds (linkages) in proteins look like?

Amino acid Amino acid. . . repeat

In food proteins, or “polypeptides”, individual amino acids are attached to each other through what is called a peptide linkage

Peptide linkage

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.

Acid group of the amino acid

NH2 NH2C – C - O – H -------------

OH

“R”R is anySide chain

C – C - O – H

H

“R”

O

Amino group

The formation of peptide bond

N-C-C-N

A glycosidic linkage in sugars connects sugar units into larger structures

glucose glucoseO

MALTOSE, a disaccharide composed of 2 glucose units

Glycosidic linkage

Structures of sugar disaccharides

Alpha 1,4 glycosidicbond

Alpha 1,4 glycosidicbond

Beta 1,4 glycosidicbond

Polymeric Linkages

OCH 2 OH

OHO

OH

Cellulose

OCH 2 OH

OHO

OH

Amylose

Beta 1,4 LinkageIndigestible

Alpha 1,4 LinkageDigestible

Organic Acids in Foods

Application of functional groups

Acids in FoodsOrganic acidsCitric (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

ofCommonOrganic

Acids

Acids in FoodsAdd flavor, tartnessAid in food preservation by lowering pHAcids donate protons (H+) when dissociatedStrong acids have a lot of dissociated ionsWeak acids have a small dissociation constantAcids dissociate based on pHAs the pH increases, acid will dissociatepKa is the pH equilibrium between assoc/dissoc

Titration Curve for Acetic Acid

Acids in FoodsWeak acids are commonly added to foodsCitric acid is the most commonWhen 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 AciditypH measures the amount of dissociated ionsTA 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 fatty acids from TAG’s Generally under alkaline conditions

Inversion of sugars (sucrose to glu + fru)

Chemical Reactions in Foods

(1) Enzymatic(2) Non-enzymatic

Generically applied to:Carbohydrates

LipidsProteins

CARBOHYDRATE chemical reactions:

Enzymatic browningNon-enzymatic browningHydrolysisFermentationOxidation/reductionStarch gelatinization

PROTEIN chemical reactions:

BufferingNon-enzymatic browningHydrolysisCondensationOxidationDenaturationCoagulation

LIPID chemical reactions

OxidationHydrolysisHydrogenation

Chemical Bonds to Chemical Rxns

Chemical Reactions in FoodsEnzymatic

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

sucrose glucoseglucose + fructosefructosesucrase

“invertase”

Enzyme ReactionsEnzymatic reactions can occur from

enzymes naturally present in a foodOr as part of food processing, enzymes are

added to foods to enable a desired effectEnzymes 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

Enzyme Class Characterizations

1. OxidoreductaseOxidation/reduction reactions

2. TransferaseTransfer of one molecule to another (i.e. functional groups)

3. HydrolaseCatalyze bond breaking using water (ie. protease, lipase)

4. LyaseCatalyze the formation of double bonds, often in dehydration

reactions, during bond breaking5. Isomerase

Catalyze intramolecular rearrangement of molecules6. 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 catalystscatalysts (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 do so through enzyme catalysis A common biological reaction can take place without

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 Enzyme-catalyzed reactions can either enhanceenhance or or deterioratedeteriorate food quality food quality

• Changes in color, texture, sensory propertiesChanges in color, texture, sensory properties

Enzyme Applications in the Food Industry

Carbohydrases: making corn syrup from starchProteases: Meat tenderizersLipases: 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% Meats -- 65-70% Bread -- 35% Honey -- 20% Rice, wheat flour -- 12% Shortening -- 0%

HO H

OHH

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. boundWater activity (Aw)

Measured by vapor pressure of food This value is directly correlated to the growth of

microorganisms and the chemical reactions

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

3 Forms of Water

Water Sorption Isotherm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Type IHydration

Type IIAbsorbed

Type IIIFree

Moi

stur

e C

onte

nt

Water Activity

Moisture

Content Is

otherm

Water Sorption Isotherm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Type IHydration

Type IIAbsorbed

Type IIIFree

Moi

stur

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onte

nt

Rel

ativ

e R

eact

ivit

y

Water Activity

Lipid ox

idatio

n

NEB

Enzyme activity

Molds

Yeast

MO

Moisture

Content Is

otherm

Moisture sorption isotherm (MSI)

How to Use the IsothermMoisture 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 Foods will naturally equilibrate to a point of equilibrium with its environmentenvironment

Therefore, foods can Therefore, foods can adsorbadsorb or or desorbdesorb water from the environment water from the environment DesorptionDesorption 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 environmentAdsorption 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 PracticeBacterial growth and rapid deterioration

High water activity in meat, milk, eggs, fruits/veggies

1.0-0.9Yeast and mold spoilage

Intermediate water activity foods such as bread and cheese

0.75-0.9Analogous 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) Can change the physical nature of the food Alter is color, texture, and/or flavor

Or you can convert the free water to bound water 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 covalentpolar covalent bonds Effects

Boiling point Freezing point Vapor pressure

Easy formation of H bondsH bonds with food molecules

Properties of WaterThe 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 waterChemical and functional properties of water

Solvation, dispersion, hydrationWater activity and moistureWater as a component of emulsionsWater and heat transferWater as an ingredient

Freezing Foods

Controlling Water

FreezingGreatly influenced the way we eatFreezing curvesWater Freezes “Pure”

Frozen FoodsMust be super-cooled to below 0°C Crystal nucleation beginsTemperature 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

0

5

10

15

20

25

30

35

40

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Freezing Time

Tem

pera

ture

Super-cooling

Freezing Point

2060

7090

9598

9999.9

Latent heat of Crystallization

Freezing

Freezing FoodRequire lower temp. to continue freezingLast portion of water is very hard to freezeUnfrozen 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 freezingConcentration effect = small amount of

unfrozen waterExcess solutes may precipitateProteins may denaturepH may decreaseGases may concentrate (i.e. oxygen)

Freezing

Quality changes during freezing Damage from ice crystals

Puncture cell membranes

Large crystals cause more problems

Fast freezing much more desirableLess concentration effectSmaller ice crystals

Freezing

Final storage temperature -18°C is standardSafe microbiologicallyLimits enzyme activityNon-enzymatic changes are slowCan maintain fairly easilyGood overall shelf-life

Freezing

Intermittent thawingPartial thawing, then refreezingComplete thawing does not have to occurGet concentration effectGet larger ice crystals as water re-freezes

Freezing

Factors determining freezing rate:Food compositionFat and air have low thermal conductivity,

slow down freezingThis is a “buffering” effect.

Freezing

Ways to speed up freezingThinner foods freeze fasterGreater air velocity More intimate contact with coolantUse 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

Formation of ice crystals (especially large ice crystals) Concentration of soluble solids Concentration of gasses (ie. oxygen) Intermittent thawing (poor temperature control)

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: 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 ratesSurface areaTemperatureAir velocityHumidityPressure (vacuum)Solute concentrationAmount of free and bound water

Drying Curve of a Food

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5 6 7 8 9 10 11 12

Time (Hrs)

Moi

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nt Water that is easily removed

Water that is difficult to remove

Dehydration and Concentration

Quality changesBrowningEnzymes - sulfite will preventCarmelization - lower temps. will limitMaillard reaction - reaction of sugars and

amino acids - lower temps will limit Acrylamide…???

Flavor changes

Carbohydrates in Foods

A general overview

Classifications for the main categories of food carbohydrates are based on their degree of polymerization.

CARBOHYDRATES

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 sugarsGlucose, Galactose, Fructose

Fischer Projection of a-D-Glucose

Haworth Projection of a-D-Glucose

Chair form of a-D-Glucose

Sucrose: prevalent in sugar cane and sugar beets, is composed of glucose and fructose through an α-(1,2) glycosidic bond.

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.

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 composedof 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 amyloseBranched 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 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 enzymeinvertase enzyme glucose + fructose

Where does sucrose come from?

Sucrose

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 enzymeinvertase enzyme glucose + fructose

Corn syrups Corn syrupsCorn 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 (High-fructose corn syrup (HFCSHFCS)) 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 fructosefructose.

PROCESSING OF CORN STARCH HFCS

Corn starch is treated with α-amylaseα-amylase, of bacterial origin, to produce shorter chains of sugars (dextrins) as starch fragments.

Next, an enzyme called glucoamylaseglucoamylase, obtained from the fungus Aspergillus niger, breaks the fragments down even further to yield the simple sugar glucose.

A third enzyme, glucose isomeraseglucose 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 thermostablethermostable.

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 starchstarch

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

STARCHPolymers of glucoseAMYLOSE linear chain of glucose

Glucose polymer linked α-1,4

AMYLOPECTIN branched polymer of glucose

Amylose

Amylopectin

AMYLOSELinear polymer of glucoseα 1 - 4 linkagesDigestable by humans (4 kcal/g)250-350 glucose units on averageCorn, wheat, and potato starch

~10-30% amylose

AMYLOPECTINBranched chain polymer of glucoseα 1 - 4 and α 1 - 6 glycosidic linkagesFully digestable by humans1,000 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

hydrolyzes α (1-4) linkage random attack to make shorter chains

β-Amylase 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 productshydrolysis products ofincompletely 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

DextrDextriinsns = starch fragments (α-1-4) linkages produced by hydrolysis of amylose

DextrDextraansns = polysaccharides made by bacteria and yeast metabolism, fragments with mostly α (1 - 6) linkages

Maltodextrins and enzyme-converted starch:

STARCHSTARCH fermentation SUGARS

ETHANOL

MODIFIED STARCHESMODIFIED STARCHES

GELATINIZED STARCHGELATINIZED 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 DESyrup

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 pH effects

Chain length Longer chains are more viscous

Linear 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

GumsLOCUST BEAN

Branched galactomannan polymer (like guar), but needs hot water to solubilize

Bean from Italy and Spain Jams, jellies, ice cream, mayonnaise

SEAWEED EXTRACTSCarrageenans (from red seaweed)

Kappa (gel) Iota (gel) Lambda (thickener only) Milk, baking, cheese, ice cream

AgarAlginates

“Structural” Polysaccharides

CellulosePolymer of glucose linked ß-1,4

HemicelluloseSimilar to celluloseConsist of glucose and other monosaccharides

Arabinose, xylose, other 5-carbon sugars

PectinPolymer of galacturonic acid

MODIFIED CELLULOSESChemically modified celluloseDo not occur naturally in plantsSimilar to starch, but β-(1,4) glycosidic bondsCarboxymethyl 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

Gels form with degree of methylation of its carboxylic acid groups

Many sources, all natural, apple and citrus pomace

Susceptible to degrading enzymes 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 acidgalacturonic acid.

Composition: polymer of galacturonic acids; may be partially esterifiedesterified.

                                                                                                   

Pectic Acid

                                                                                                                 

Pectin Molecule

Pectins Pectins are important because they form gelsgels

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 cationsdivalent cations

Sugar and acid under certain conditions can contribute to gel structure and formation

LM pectin “low methoxyl pectin”LM pectin “low methoxyl pectin” has DE < 50% ; gelatin is controlled by adding cations (like Ca++ and controlling the pH)

HM pectinHM pectin “high methoxyl pectin” has DE >50% and forms a gel under acidic conditions by hydrophobic interactions and H-bonding with dissolved solids (i.e. sugar)

Hydrophobic attractions between neighboring pectin polymer chainspromote gelation

BETA-GLUCANSExtracts from the bran of barley and oatsLong glucose chains with mixed ß-linkagesVery 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

OthersCHITIN 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

HemicelluloseAll food plants, especially cerealbran

Pectin Mainly fruit

LigninMainly cereals and 'woody'vegetables

Gums and some foodthickeners

Food additives in processedfoods

HYDROCOLLOIDS

A key attribute of gums is to produce viscous dispersionsviscous 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

CARAMELIZATIONCARAMELIZATION 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 colorantcolorant

(+) 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 andAlternative Sweeteners

The perception of sweetnessis proposed to be due to achemical interaction that takes place on the tongueBetween a tastant moleculetastant moleculeand tongue receptor proteintongue receptor protein

THE AH/B THEORY OF SWEETNESS

A sweet tastant molecule (i.e. glucose) is called the AH+/B- “glycophoreglycophore”.It binds to the receptor B-/AH+ site through mechanisms that include H-bondingH-bonding.

AH

B

B

AH

Glycophore

γ

γ

Tongue receptor protein molecule

Hydrophobic interaction

For sweetness to be perceived, a molecule needs to have certain requirements. It must be solublesoluble in the chemical environment of the receptor site on the tongue. It must also have a certain molecular shapeshape 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.

AH+ / B-

Gamma (γ) sites are relatively hydrophobichydrophobic functional groups such as benzene rings, multiple CH2 groups, and CH3

Identifying the AH+ and B- regions of two sweet tastantmolecules: glucose and saccharin.

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 chlorinecreated 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. 

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.

hydrophobic

Area (AH+): This area has hydrogens available to hydrogen bond to chlorine attached to the glucose bottom portion of the molecule.

Area (B -): This area has a partially negative oxygen available to hydrogen bond to the partially positive hydrogen of an alcohol group.

hydrophilic

hydrophilic

In 2005 Coca-Cola released a new formulation of Diet Coke sweetened with sucralose, called “Diet Coke with Splenda”.

WholeWheat

WheatBran

Removed

Corn

Milled,Polished

Rice

CerealsCereals Starch, protein, fiberWater LysineStructure

Husk (inedible) Bran (fiber) Endosperm (starch, protein, oil) Germ (oil)

Wheat Kernel

EndospermStarchProtein

Oil

GermOil

Protein

BranFiber

Cereal Grain

Composition of Cereals

Wheat2 types of wheatHARD = 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 flourCleaned with air (dust, bugs, chaff)Soaked to 17% moisture - optimum for

millingRemove huskCrack seeds - frees germ from endosperm

Wheat

Wheat MillingRollers- two metal wheels turning in opposite

direction of each otherEndosperm is brittle and breaksGerm and bran form flat flakes and are

removed by screens or sievesEndosperm = flour

Less color and less nutrients as milling continuesWhole wheat flour = do not remove all of the

bran and/or germ

Wheat Mill Grinding Rolls

Wheat Milling Sifters

Wheat

Wheat EnrichmentAdd B-vitamins and some minerals to most

white flours (since missing the bran)

Uses of flourCakes, breads, etc.Pasta, noodles, etc.Course flour, not leavened

Rice Processing

Rice

Rice MillingMost rice is "whole grain"Remove husk, bran, germ by rubbing with

abrasive disks or rubber beltsPolish endosperm to glassy finishBrown rice = very little milling

Rice

Rice EnrichmentAdd 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 productsQuick cooking (instant) = precooked, driedRice flourSake (15-20% alcohol)

Advantages/Disadvantages of Milling RiceBrown 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

CornCorn 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 cornGrind 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 starchCan produce corn syrups from starchUse 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 feedBarley = used in beerRye = can not use alone (poor protein quality)Oats = oatmeal, flakes

Breakfast cerealsMade from many different grains

Baking

IngredientsFlour

Starch Protein = gluten; forms elastic dough that will

expand during rising

Baking

Ingredients…Leavening agentRising due to carbon dioxide or airYeast = alcoholic fermentation produces

carbon dioxideBaking 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

…IngredientsShortening

Tenderizes Hold air

Sugar Tenderizes Sweetness Fermentable sugar Helps retain moisture

Baking

Oven bakingGas production and rising continuesDenaturation and coagulation of proteinsDrying and crust formationFlavor developmentColor development = Carmelization and

Maillard reaction

Baking

High altitudesExcessive gas production (less pressure)Weakens and collapses doughNot as bad for bread

Can alter formulaLess baking powderMake 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 acidsProtein complementation with cereals

Legumes and OilseedsSoybeans = used for both oil and proteinPeanuts = whole nut, oil, peanut butter