FOOD CHEMISTRYFSTC 312/313, 3+1 Credits

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

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

Dimensions of Food Science and Technology

•Food processing and manufacture

•Food preservation and packaging

•Food wholesomeness and safety

•Food quality evaluation

•Food distribution

•Consumer food preparation and use

Other Components

Growing/HarvestingPackagingMarketing/RetailFood ServiceConsumer Services

Components of Food ScienceFood ChemistryFood MicrobiologyFood ProcessingRegulationsNutritionOthers

Food ChemistryBasis of food science

Water Carbohydrates Proteins Lipids Micronutrients Phytochemicals Others

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 are “amphiphiles”

O/Wemulsion

W/Oemulsion

milkice creammayo

Margarinebutter

Foods Are Made of ChemicalsSingle elementsChemically bonded elements (compounds)

Electrons Distributed via Energy Layers

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

Exams and Grading 3 hourly exams Material is not “cumulative”, but material will build

upon itself. Multiple choice, short answer, short essay format

2 class assignments Short term paper Literature review Topic of special interest etc

Several announced or unannounced quizzes Beginning or end of class University excused absence policy will be followed

The “Basics” of Food Chemistry

Functional Groups in Foods

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:

- C – H formaldehyde HCHO: H – C – H

O 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.

We have already talked generally about covalent, ionic, and hydrogen bonds:

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“Acyl” 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

“I’m a 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 precipitiation 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)

Functional Groups and Bonds Acids Amino Alcohol Aldehydes

Ester Peptide Glycosidic

Application: Organic Acids 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)

Acidity is important chemically

Denaturation and precipitiation 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 ther are are several enzyme categories

Enzyme Class Characterizations

1. Oxidoreductase1. Oxidation/reduction reactions

2. Transferase1. Transfer of one molecule to another (i.e. functional groups)

3. Hydrolase1. Catalyze bond breaking using water (ie. protease, lipase)

4. Lyase1. Catalyze the formation of double bonds, often in

dehydration reations5. Isomerase

1. Catalyze intramolecular rearrangement of molecules6. Ligase

1. 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 in Foods

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

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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

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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

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

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-Speeding it Up 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.

The application of pressure lowers the melting point of ice.

About 0.55ºC per 80 atm of pressure down to about -22ºC at 2,700 atm.

Pressure (and friction) help ice to melt under the blades of ice skates.

Potential applications in cryonics

Increase pressure to 2,000 atm (get really cold)

Suddenly increase pressure to >20,000 atm

Results: Frozen so fast that ice crystals will not form

Pressure (Atm) Freezing Pt (C)

1 0

1,000 -10

2,045 -22

3,420 -17

6,160 0

7,390 10

9,800 25

13,970 50

23,000 100

36,500 175

Freezing Foods Freezing can be damaging to food systems 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

HP freezing generally involves cooling an unfrozen sample to -21C under high pressures (300MPa) causing ice formation to occur. 1 MPa ~ 145 psi or ~10 atm

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.

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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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

Methods of Drying

Air drying methods Cabinet Tunnel

Concurrent flow Countercurrent flow

Continuous Fluidized bed Spray Drum

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)

Aldose (aldehyde) and Ketose (ketone)

Properties of GlucoseC1 of glucose is the carbonyl carbonGlucose has 4 chiral centers

Non-super-imposable on its mirror imageCarbons 2, 3, 4, 5 are chiral carbons

The carbonyl carbon (C1) is also the site of many reactions involving glucose They have two enantiomeric forms, D and

L, depending on the location of the hydroxyl group at the chiral carbons.

Sugar Reactions

Reduction of Monosaccharide

In this reaction the carbonyl group is reduced to an alcohol by a metal catalyzed reaction of hydrogen gas under pressure.

Sugar Alcohols

Not commonly found in nature Generally lower in calories (2 to 3 kcal/g) A CHO for labeling purposes Not digested by oral bacteria “does not promote tooth decay”

– Xylitol (from xylose) – Sorbitol (from glucose) – Mannitol (from mannose) – Lactitol (from lactose) – Maltitol (from maltose)

Sugar Sweetness

Fructose 173

Sucrose 100

Xylitol 100

Glucose 74

Sorbitol 55

Mannitol 50

Maltose 32

Lactose 15

Sweetness is but one of a varietyof functional characteristics ofimportance in food chemistry,food product development, and product quality

Functionality

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)

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 varous amounts of frutose. 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

Carbohydrates in Foods

Gums GUAR (Guran Gum)

Most used, Cold water soluble, Stable, Thickening agent

XANTHAN Polysaccharide from Xanthomonas campestris

Popular, inexpensive Thick gels

LOCUST BEAN Hot water to soluble Jellies, ice cream, mayonnaise

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

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 fragments and condensation/dehydration products. diacetyl, formic acid, hydroxy dimethylfuranone

Artificial andAlternative Sweeteners

Sweeteners Non-nutritive (no calories) Cyclamate (banned in 1969) Saccharin (Sweet ‘N Low, 300-fold) Aspartame (warning label) = aspartic acid and

phenylalanine (180-fold) Acesulfame-K (Sunette, 200-fold)

Alitame (Aclame, 2,000-fold) Sucralose (Splenda, 600-fold)

Sucralose

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, 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 sweetener with zero calories.

Sucralose

Developers found that selective halogenations changed the perceived sweetness of a sucrose molecule, with chlorine and bromine being the most effective.

Chlorine tends to have a higher water solubility, so chlorine was picked as the ideal halogen for substitution. 

Sucrose portion

Fructose portion

Sucralose Splenda 1998, approved for table-top sweetener and use

in various foods Approved already in UK, Canada before US Only one “made from sugar”

There was a law suit last year of this claim Splenda lost….not a natural compound and not really

made from sugar….a bit of a deceptive marketing.

Clean, sweet taste and no undesirable off-flavor

Saccharin Sweet’n Low, The 1st artificial sweetener Accidentally found in 1879 by Remsen and Fahlberg Saccharin use increased during wars due to sugar

rationing By 1917, common table-top sweetener in America Banned in 1977 due to safety issue 1991, withdrawal banning, but remained warning

label 2000, removed warning label Intensely sweet, but bitter aftertaste

Aspartame Nutrasweet, Equal Discovered in 1965 by J. Schlatter Composed of aspartic acid and phenylalanine 4 kcal/g, but 200 times sweeter Approved in 1981 for table-top sweetener and

powdered mixes Safety debating 1996, approved for use in all foods and beverage Short shelf life, not stable at high temperature

Acesulfame K Sunette, Sweet One Discovered in 1967 by Hoechst 1992, approved for gum and dry foods 1998, approved for liquid use Blending with Aspartame due to synergistic effect Stable at high temperature and long shelf life (3-4

years) Bitter aftertaste

Neotame Brand new approved sweetener (Jan. 2000) 7,000 ~ 13,000 times sweeter than sugar Dipeptide methyl ester derivative structurally

similar to Aspartame Enhance sweetness and flavor Baked goods, non-alcoholic beverages

(including soft drinks), chewing gum, confections and frostings, frozen desserts, processed fruits and fruit juices, toppings and syrups.

Safe for human consumption

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

Proteins

From the Greek “proteios” or primary.

ProteinsMany important functions

Functional Nutritional Biological

EnzymesStructurally complex and large compoundsMajor source of nitrogen in the diet

By weight, proteins are about 16% nitrogen

Protein Content of Foods Beef -- 16.5% Pork -- 10% Chicken -- 23.5% Milk -- 3.6% Eggs -- 13% Bread -- 8.5% Cooked beans -- 8% Potato -- 2%

Proteins

Proteins are polymers of amino acids joined together by peptide bonds

Structure, arrangement, and functionality of a protein is based on amino acid composition

All amino acids contain nitrogen, but also C, H, O, and S

Protein Structure

The formation of peptide bond

N-C-C-N

Proteins are composed of amino acids which are carboxylic acids also containing an amine functional group.

The amino acids are linked together by peptide bonds (amide bonds) forming long chains

Short chains of amino acids are commonly called polypeptides (eg. dipeptide, tripeptide, hexapeptide, etc)

Longer chains of amino acids normally called proteins.

Proteins

Proteins

Peptide bonds are strong covalent bonds that connect 2 amino acids

Dipeptide- 2 amino acids joined together by a peptide bond

Polypeptide- 3 or more amino acids joined together by peptide bonds in a specific sequence

20 Amino Acids Alanine (Ala) Arginine (Arg) Asparagine (Asn) Aspartic acid (Asp) Cysteine (Cys) Glutamine (Gln) Glutamic acid (Glu) Glycine (Gly) Histidine (His) Isoleucie (Ile)

Leucine (Leu) Lysine (Lys) Methinine (Met) Phenylalanine (Phe) Proline (Pro) Serine (Ser) Threonine (Thr) Tryptophan (Trp) Tyrosine (Try) Valine (Val)

Proteins Composed of amino acids 20 common amino acids Polymerize via peptide bonds Essential vs. non-essential amino acids Essential must come from diet Essential amino acids:

"Pvt. T.M. Hill” phenylalanine, valine, threonine, tryptophan,

methionine, histidine, isoleucine, leucine, lysine

Properties of Amino AcidsAliphatic chains: Gly, Ala, Val, Leucine, IleHydroxy or sulfur side chains: Ser, Thr, Cys, MetAromatic: Phe, Trp, TryBasic: His, Lys, ArgAcidic and their amides: Asp, Asn, Glu, Gln

Properties of Amino Acids:

Aliphatic Side Chains

Aromatic Side Chains

Acidic Side Chains

SulfurSideChains

Properties of Amino Acids:Zwitterions are electrically neutral, but carry a

“formal” positive or negative charge.Give proteins their water solubility

The Zwitterion Nature Zwitterions make amino acids good acid-base buffers.

For proteins and amino acids, the pH at which they have no net charge in solution is called the Isoelectric Point of pI (i.e. IEP).

The solubility of a protein depends on the pH of the solution.

Similar to amino acids, proteins can be either positively or negatively charged due to the terminal amine -NH2 and carboxyl (-COOH) groups.

Proteins are positively charged at low pH and negatively charged at high pH. When the net charge is zero, we are at the IEP.

A charged protein helps interactions with water and increases its solubility.

As a result, protein is the least soluble when the pH of the solution is at its isoelectric point.

Physical Nature of Proteins

Protein StructuresPrimary = sequence of amino acidsSecondary = alpha helix, beta pleated sheetsTertiary = 3-D folding of chainQuaternary = “association” of subunits and

other internal linkages

Primary Sequence

Secondary protein structureThe spatial structure the protein assumes along

its axis (its “native conformation” or min. free energy)

This gives a protein functional properties such as flexibility and strength

Tertiary Structure of Proteins3-D organization of a polypeptide chainCompacts proteins Interior is mostly devoid of water or charge groups

3-D folding of chain

Quaternary Structure of ProteinsNon-covalent associations of protein units

Shape Interactions of Proteins

Protein Structure

Globular - polypeptide folded upon itself in a spherical structure

Fibrous – polypeptide is arranged along a common straight axis

Classification of simple proteins Composed of amino acids and based on solubility. Every food has

a mixture of these protein types in different ratios. Albumins – soluble in pure water Globulins – Soluble in salt solutions at pH 7.0, but

insoluble in pure water Glutelins – soluble in dilute acid or base, but insoluble in

pure water Prolamins – soluble in 50-90% ethanol, but insoluble in

pure water Scleroproteins – insoluble in neutral solvents and

resistant to enzymatic hydrolysis Histones – soluble in pure water and precipitated by

ammonia; typically basic proteins Protamines – extremely basic proteins of low molecular

weight

Classification of complex proteins

A protein with a non-protein functional group attached

Glycoproteins- carbohydrate attached to protein Lipoproteins – lipid material attached to proteins Phosphoproteins- phosphate groups attached Chromoprotein- prosthetic groups associated

with colored compounds (i.e. hemoglobin)

Emulsoids and Suspensiods

Proteins should be thought of as solids Not in true solution, but bond to a lot of water

Can be described in 2 ways:

Emulsoids- have close to the same surface charge with many shells of bound water

Suspensoids- colloidal particles that are suspended by charge alone

Functional Properties of Proteins3 major categories Hydration properties

Protein to water interactions Dispersibility, solubility, adhesion, Water holding capacity, viscosity

Structure formation Protein to protein interactions Gel formation, precipitation, Aggregation

Surface properties Protein to interface interactions Foaming, emulsification

Proteins and peptide chains are “directional”. That means the chain has a free alpha amino group and a free carboxyl group.

The Amino Terminus (N-Terminus) is the end of the chain containing the free alpha amino function. The Carboxy Terminus (C-Terminus) is the end of the chain containing the free carboxyl group.

NH3

HOOC

N

C

Proteins: more than just energy

“Functional” propertiesEmulsifierFoaming = egg whitesGel formation = jelloWater binding or thickeningParticipation in browning reactions

Enzymes (more on this next week)

Enzymes Proteins that act as catalysts

Can be good or bad

Ripening of fruits, vegetables Meat tenderization Destruction of color, flavor Heat preservation, inactivates

Blanching, cooking

ProteinsChanges in structure Denaturation

Breaking of any structure except primary Reversible or irreversible, depending on severity of the

denaturation process Examples:

Heat - frying an egg High salt content High alcohol content Low or High pH Extreme physical agitation Enzyme action (proteases)

Protein Structure (part of the tertiary structure)

Globular - polypeptide folded upon itself in a spherical structure

Fibrous – polypeptide is arranged along a common straight axis (beta-pleated sheet)

Classification of simple proteins Composed of amino acids and based on solubility. Every food has

a mixture of these protein types in different ratios. Albumins – soluble in pure water Globulins – Soluble in salt solutions at pH 7.0, but

insoluble in pure water Glutelins – soluble in dilute acid or base, but insoluble in

pure water Prolamins – soluble in 50-90% ethanol, but insoluble in

pure water Scleroproteins – insoluble in neutral solvents and

resistant to enzymatic hydrolysis Histones – soluble in pure water and precipitated by

ammonia; typically basic proteins Protamines – extremely basic proteins of low molecular

weight

Classification of complex proteins

A protein with a non-protein functional group attached

Glycoproteins- carbohydrate attached to protein (i.e. ovomucin)

Lipoproteins – lipid material attached to proteins (i.e. HDL and LDL)

Phosphoproteins- phosphate groups attached (i.e. casein)

Chromoprotein- prosthetic groups associated with colored compounds (i.e. hemoglobin)

Emulsoids and Suspensiods

Proteins should be thought of as solids Not all in a true solution, but bond to a lot of water

Can be described in 2 ways:

Emulsoids- have close to the same surface charge, with many “shells” of bound water

Suspensoids- colloidal particles that are suspended by charge alone

Functional Properties of Proteins3 major categories Hydration properties

Protein to water interactions Dispersion, solubility, adhesion, viscosity Water holding capacity

Structure formation Protein to protein interactions Gel formation, precipitation, aggregation

Surface properties Protein to interface interactions Foaming and emulsification

1. Hydration Properties (protein to water)

Most foods are hydrated to some extent. Behavior of proteins are influenced by the presence of water and

water activity Dry proteins must be hydrated (food process or human digestion)

Solubility- as a rule of thumb, denatured proteins are less soluble than native proteins

Many proteins (particularly suspensoids) aggregate or precipitate at their isoelectric point (IEP)

Viscosity- viscosity is highly influenced by the size and shape of dispersed proteins Influenced by pH Swelling of proteins Overall solubility of a protein

2. Structure Formation (protein to protein)

Gels - formation of a protein 3-D network is from a balance between attractive and repulsive forces between adjacent polypeptides

Gelation- denatured proteins aggregate and form an ordered protein matrix Plays major role in foods and water control Water absorption and thickening Formation of solid, visco-elastic gels

In most cases, a thermal treatment is required followed by cooling Yet a protein does not have to be soluble to form a gel (emulsoid)

Texturization – Proteins are responsible for the structure and texture of many foods Meat, bread dough, gelatin Proteins can be “texturized” or modified to change their

functional properties (i.e. salts, acid/alkali, oxidants/reductants) Can also be processed to mimic other proteins (i.e. surimi)

3. Surface Properties (protein to interface)

Emulsions- Ability for a protein to unfold (tertiary denaturation) and expose hydrophobic sites that can interact with lipids. Alters viscosity Proteins must be “flexible” Overall net charge and amino acid composition

Foams- dispersion of gas bubbles in a liquid or highly viscous medium Solubility of the protein is critical; concentration Bubble size (smaller is stronger) Duration and intensity of agitation Mild heat improves foaming; excessive heat destroys Salt and lipids reduce foam stability Some metal ions and sugar increase foam stability

Quick Application: Food Protein Systems

Milk- Emulsoid and suspensoid system Classified as whey proteins and caseins Casein - a phosphoprotein in a micelle structure Suspensoid - coagulates at IEP (casein)

Egg (Albumen) – Emulsoid Surface denatures very easily Heating drives off the structural water and creates a

strong protein to protein interaction Cannot make foam from severely denatured egg white,

requires bound water and native conformation

Factors Affecting Changes to Proteins

Denaturation

Aggregation

Salts

Gelation

Changes to Proteins Native State

The natural form of a protein from a food The unique way the polypeptide chain is oriented

There is only 1 native state; but many altered states The native state can be fragile to:

Acids Alkali Salts Heat Alcohol Pressure Mixing (shear) Oxidants (form bonds) and antioxidants (break bonds)

Changes to ProteinsDenaturation

Any modification to the structural state The structure can be re-formed If severe, the denatured state is permanent

Denatured proteins are common in processed foods Decreased water solubility (i.e. cheese, bread) Increased viscosity (fermented dairy products) Altered water-holding capacity Loss of enzyme activity Increased digestibility

Changes to Proteins Temperature is the most common way to denature a

protein Both hot and cold conditions affect proteins

Every tried to freeze milk? Eggs?

Heating affects the tertiary structure Mild heat can activate enzymes

Hydrogen and ionic bonds dissociate Hydrophobic regions are exposed Hydration increases, or entraps water Viscosity increases accordingly

Changes to ProteinsWe discussed protein solubility characteristicsSolubility depends on the nature of the solution

Water-soluble proteins generally have more polar amino acids on their surface.

Less soluble proteins have less polar amino acids and/or functional groups on their surface.

Isoelectric PrecipitationsProteins have no net charge at their IEP

- -

- -- -

- - - -

- -

+ +

+ ++ +

+ ++ +

+ ++ +

+ ++ +

+ ++ +

+ +

- -

- -+ +

+ + - -

+ +

- -

- -- -

- - - -

- -

- -

- -+ +

+ + - -

+ +

Strong Repulsion

(net negative charge)

Strong Repulsion

(net positive charge)

Aggregation

(net neutral charge)

Isoelectric PrecipitationsProteins can be “salted out”, adding charges

- -

- -- -

- - - -

- -+ +

+ ++ +

+ ++ +

+ +Aggregation

(net neutral charge)

Na+Na+ Na+ Cl-Cl- Cl-

Measuring IEP PrecipitationsEmpirical measurements for precipitationA protein is dispersed in a buffered solution

Add salt at various concentrations Add alcohols (disrupt hydrophobic regions) Change the pH Add surfactant detergents (i.e. SDS)

Centrifuge and measure quantitatively The pellet will be insoluble protein The supernatant will be soluble protein

Gel Formation Many foods owe their physical properties to a gel

formation. Influences quality and perception. Cheese, fermented dairy, hotdogs, custards, etc

As little as 1% protein may be needed to form a rigid gel for a food.

Most protein-based gels are thermally-induced Cause water to be entrapped, and a gel-matrix formation

Thermally irreversible gels are most common Gel formed during heating, maintained after cooling Will not reform when re-heated and cooled

Thermally reversible gels Gel formed after heating/cooling. Added heat will melt the gel.

Gel Formation Many foods owe their physical properties to a gel

formation. Influences quality and perception. Cheese, fermented dairy, hotdogs, custards, etc

As little as 1% protein may be needed to form a rigid gel for a food.

Most protein-based gels are thermally-induced Cause water to be entrapped, and a gel-matrix formation

Thermally irreversible gels are most common Gel formed during heating, maintained after cooling Will not reform when re-heated and cooled

Thermally reversible gels Gel formed after heating/cooling. Added heat will melt the gel.

Processing and StorageDecreases spoilage of foods, increases shelf life

Loss of nutritional value in some cases Severity of processing

Loss of functionality Denatured proteins have far fewer functional aspects

Both desirable and undesirable flavor changes

Processing and StorageProteins are affected by

Heat Extremes in pH (remember the freezing example?) Oxidizing conditions

Oxidizing additives, lipid oxidation, pro-oxidants Reactions with reducing sugars in browning rxns

Processing and Storage Mild heat treatments

May slightly reduce protein solubility Cause some denaturation Can inactive some enzyme Improves digestibility of some proteins

Severe heat treatments (for example: >100°C) Some sulfur amino acids are damaged

Release of hydrogen sulfide, etc (stinky)

Deamination can occur Release of ammonia (stinky)

Very high temperatures (>180°C) Some of the roasted smells that occur with peanuts or coffee

Enzyme Influencing Factors Enzymes are proteins that act as biological catalysts They are influenced in foods by:

Temperature pH Water activity Ionic strength (ie. Salt concentrations) Presence of other agents in solution

Meta chelators Reducing agents Other inhibitors

Enzyme Influencing Factors

Temperature-dependence of enzymesEvery enzyme has an optimal temperature for

maximal activityThe effectiveness of an enzyme: Enzyme activityFor most enzymes, it is 30-40°CMany enzymes denature >45°CEach enzyme is different, and vary by isozymes Often an enzyme is at is maximal activity just

before it denatures at its maximum temperature

pHLike temp, enzymes have an optimal pH where

they are maximally activeGenerally between 4 and 8

with many exceptions

Most have a very narrow pH range where they show activity.

This influences their selectivity and activity.

Water ActivityEnzymes need free water to operateLow Aw foods have very slow enzyme reactions

Ionic StrengthSome ions may be needed by active sites on the

protein Ions may be a link between the enzyme and substrate Ions change the surface charge on the enzyme Ions may block, inhibit, or remove an inhibitor Others, enzyme-specific

Common Enzymes in FoodsPolyphenol oxidasePlant cell wall degrading enzymesProteasesLipasesPeroxidase/CatalaseAmylaseAscorbic acid oxidaseLipoxygenase