Food Chemistry Exam 3

Physiochemical properties thatenable proteins to contribute to thedesirable characteristics of food.

emulsification, water retention

Foaming, gelation

emulsification, coagulation

emulsification, water retention

dough formation, browning

Foaming

1. Hydration properties

– protein-water interactions

2. Protein-protein interactions

3. Surface properties

• Categories not independent of each other

– Gelation: protein-protein and protein-waterinteractions

– Solubility: protein-protein and protein-waterinteractions

Includes the following properties:

– Water absorption/retention

– Swelling

– Solubility

– Viscosity

– Surface amino acids/amino acid comp.

– Protein concentration

• ^ Protein concentration = ^ water absorption– pH

• change in pH = change in protein ionization (net charge)

• at the pI of a protein:

– maximal protein-protein interactions

– minimal protein-water interactions

» ex) beef post-rigor

» ex) production of soy protein isolate

– Ionic Strength

• Low salt ( < 1M) = ^ solubility (“salting in”)

• High salt = decreased solubility (“salting out”)–Temperature

• Extreme ^ Temp = dec, solubility

• Extreme ^ Temp = dec. water binding

• Extreme ^ Temp = dec. hydrogen bondingbetween protein and water

• Ex) cooked meat– ^ Aggregation (denaturation) = dec. surface area

– Aggregation & precipitation

– Gelation properties

– Denatured molecules aggregate through variousbonds to form a 3D protein network

– Hydrogen bonding, disulfide bonds, hydrophobicinteractions, ionic bonds

– Large amounts of water (98%) can beentrapped in protein matrix

• Tofu

• Bread dough (gluten,disulfide bridges)

• Gelatin gels

• Yogurt

• Surimi gels

• Heat induced gelation

• Acid coagulation

• Enzyme action

• Mixture of fishprotein, water, andsalt

• Mixture is heated,then cooled indifferent moldshapes, or spuninto protein fibersand shaped

Thermally reversible

Thermally irreversible

– “Thermoset”

– Myosin gels (surimi), ovalbumin gels (cookedegg whites, custard)

– More disulfide bridges

– Turbid, opaque, and transparent gels

– “Thermoplastic”

– Gelatin (collagen)

– Hydrogen bonding forms junction zones

– Can melt and reform gel

• Proteins act at surfaces between phases

• Includes the following:

– Emulsification properties

• oil and aqueous phases

– Foaming properties

• gas emulsions

• Formation and stabilization of emulsions

• Proteins migrate to and adsorb at interfacebetween oil and aqueous phase

• Proteins act as surfactants

• Amphiphilic structure

• Solubility (migrate to interface)

• Partial unfolding (flexibility)

• Loops andtail in aqueousphase

• More trains = dec. interfacialtension

pH of solution or food matrix

protein solubility

• Effects solubility and aggregation

• Effects shape of protein (denaturation)

• ^ Protein solubility = ^ emulsion stability(Proteins dissolve and migrate to surfaces)

• Any factor that influences solubility will influenceemulsification properties

• Emulsion stability

– how long does emulsion last?

– use graduated cylinder, and follow phaseseparation

• Emulsion capacity

– amount of oil that can be emulsified

– continue adding oil and homogenizinguntil viscosity decreases

• Salami, a meatemulsion

• Emulsion ofprotein and fat

• Salt is added tosolubilizemyofibrillarprotein

gas emulsions

Dispersions of gas bubbles in continuous liquidor semisolid phase

typically air or CO2

– Formed by whipping or beating aqueous proteinsolution in presence of bulk gas phase

– Or, by sparging: bubble gas into aqueoussolution of low protein concentration

– A gas emulsion forms, and the true foamseparates

– Thin liquid (or semi-solid film) layers separate gasbubbles

– Proteins act as soluble surfactant to decreasesurface tension of continuous phase

– If proteins completely denatured, then ineffective

• high rate of diffusion

• ability to unfold at interface

• ability to form a stable film around gas bubble

– Increase viscosity of liquid phase

• Sucrose, gums, polyols

• Addition of insoluble solids such as flour,starch

– Acids increase denaturation

• Cream of tartar

• Lemon juice

• Vinegar

• Texturization

– Texturized proteins(soy flour, wheatgluten)

– Films, fiberformation (meatsubstitutes)

• Coloring:

– Myoglobin: meatcolor

– Maillard browning

– To improve functional properties of proteins forspecific applications

• Chemical, enzymatic, and physical methods

– Crosslinking (chemical or enzymatic)

• inter- or intramolecular crosslinking

– Hydrolysis

– Adding new groups (fatty acids, succinic acid,phosphate, carbohydrates)

– Deamidation (eg. Glutamine glutamic acid)

• Major energy source for world population

• >70% world caloric intake

• Abundant, widely available, inexpensive

• Primarily provided by plants

• Common component of food: natural andas added ingredients

• Many forms: sugars, starches, fibers, gums, …

– Bulk

– Structure

– Viscosity

– Stability (emulsions & foams)

– Water holding capacity

– Browning

– Flavors & aromas

•“simple sugars”

• cannot be hydrolyzed

• occur naturally in small amounts

• Polyhydroxylated aldehydes or ketones

• Hydrophilic OH groups = soluble in water

• Decompose easily from heating (losewater)

Hexoses

– Glucose: small amounts (aka dextrose)

– Fructose: “Fruit sugar”

– Galactose: not present in “free” form

– Mannose (another glucose isomer)

• disaccharides, trisaccharides ….

• can be hydrolyzed

• 10 > monosaccharide units

• Large # of monosaccharide units

• Starch = 100-2,000 monosaccharide units

• Same formula, different structure

• C6H12O6

• Catalyzed by base or enzyme

• Ex) glucose isomerase convertsglucose to fructose to produce highfructose corn syrup

• Carbonyl group reacts with own alcoholgroups to form a hemiacetal or hemiketal:

– 5-membered furanose ring

– 6-membered pyranose ring (more stable)

• Hemiacetal/hemiketal:

– Carbon bonded to OH group and ORgroup

– Ring conformation open chain

– Structure: fructose and sucrose mostsoluble

– Purity: Mixed sugars have higher solubility

– Temperature: Higher temp increasessolubility– Mechanical energy: Increases solubility

• Sugar alcohols

• Glyconic acids

• Glycuronic acids

• No carbonyl group, each carbon ishydroxylated

• Occur naturally in some fruits– Pears (sorbitol), celery (mannitol),strawberries (xylitol)

• Produced by hydrogenation (reduced):– Glucose + H2 = sorbitol– Xylose + H2 = xylitol

• Poorly absorbed in intestine

• Nonfermentable

• Sugar free chewing gum, mints, etc.

• Glyconic acids: oxidizedsugars with a carboxyl groupat carbon #1

• Glucose → Gluconic acid

• Mannose → Mannonic acid

• Galactose → Galatonic acid– Gluconic acid

• fruit, honey, wine

• food additive : leavening agent,acidifier

• Oxidized sugars with acarboxyl group at highestnumbered carbon

• Glucose → Glucuronic acid

• Mannose → Mannuronic acid

• Galactose → Galacturonicacid

• Important constituent of manygums

• Any sugar with a free hemiacetal group

• H is given up from the *OH group, and thesugar becomes oxidized

• Reducing sugars can reduce metal ions– Cu2+ → Cu+ (color change from blue to redbrown:“sugar stick” tests)– Ag+ → Ag0

non-enzymatic browning

glucose, fructose, mannose,maltose, etc., but not sucrose

• Two monosaccharide units linked by aglycosidic bond

• Condensation reaction with loss of 1water molecule

– Anomeric carbon on the hemiacetalreacts with alcohol to form acetal

– Acetals have a carbon bonded to two -OR groups

• Carbohydrate acetals = glycosides

• Homogeneous or heterogeneous

• Stable in water

• Can be hydrolyzed:– Acid, heat, or enzymes

glucose hemiacetal +galactose

– Beta 1, 4 glycosidic bond

– Milk sugar

– Reducing sugar

glucose + glucose

– Alpha 1, 4 glycosidic bond

– Malt sugar, corn syrup

– Reducing sugar

glucose + fructose

– Alpha 1, 2 glycosidic bond

– Table sugar, beet sugar,cane sugar

– Non-reducing sugar

Caramelization

Invert sugar

– A type of non-enzymatic browning

– Sucrose or corn syrup typically used

– High temperatures required (thermolysis)

• > 160 C

– Complex set of reactions:

• Dehydration of sugar molecule

• Formation of double bonds

– Conjugated double bonds produce color

• Molecules polymerize

• Hundreds of products are formed

– Melanoidin pigments, bitterflavors, & aromatic compoundsare formed

– Products are used as colorantsin food industry• Soft drinks, beer, soy sauce,caramel candies, gravy, bakedgoods, dry seasoning powders

– Syrup or liquid

– Produced by sucrosehydrolysis

– Use enzyme (invertase) oracid (tartaric, citric, ..)

– Produces mixture of glucoseand fructose

– Partially or completelyhydrolyzed

– Sweeter taste

– Lower freezing point

– Acts as humectant

• Hygroscopic: keeps products moist

– Sweetener in beverages

– Used in confectionery industry:

• Prevents crystallization ofsugar in icings, fondants,jellies and jams

• Fructose: 150

• Sucrose: 100

• Xylitol: 95

• Glucose: 74

• Sorbitol: 54

• Galactose: 48

• Maltose: 46

• Lactose: 39

• Synthesized from sucrose

• Three OH groups selectivelysubstituted with chlorine

• 600x sweeter than sucrose

• Non-metabolizable, non caloric

• Heat and acid stable

• Produced in 1976, FDA approvalin 1998

• AKA Splenda: contains dextrose,maltodextrin, sucralose

• Raffinose– 3 units: glucose + fructose + 1 galactose

• Stachyose– 4 units: glucose + fructose + 2 galactose

• “Galactosides”

• Soybean and other legumes

• Not hydrolyzed, non-digestible

• Antinutritional factor: flatulence

– Processing methods can decrease levels

• Cyclic, non-reducing oligomer

• Glucose subunits: (6), (7) and γ (8)

• Alpha 1,4 linkages

• Donut shape with central hydrophobiccore

• Good binding properties incentral hydrophobic portion

– Masks bitter or unwanted flavors

– Can remove caffeine andcholesterol

• Good flavor carrier and stabilizer

• Protects vitamins, PUFAs, andcolors

• Produced from hydrolyzedstarch using cyclodextringlucotransferase

Non-enzymatic browning

Thermal processing and storage

Foods containing protein and reducingcarbohydrates (or other carbonylcompounds)

Results in flavor, aroma, and colordevelopment

Browning of bread crust

Chocolate flavor: roasting of cocoa beans

“Meaty” flavor and color production inroasted meats

Coffee flavor: roasting of coffee beans

Brown discoloration in french fries and potato chips in frying

Discoloration of dried milk

Discoloration and unwanted flavors indried egg

Decrease in protein quality

Glycosylamine formation

Formation of amadori product

Complex of intermediate rxns

Formation of melanoidins or volatilecompounds

- condensation reaction between a nonionizedamino group and carbonyl ofopen chain reducing sugar

- the free amino group on a free aminoacid, an amino acid R-group, or theterminal alpha-NH2 of a protein

- reversible step

- non-stable intermediary product

- rearrangement of glycosylamine

- stable products formed: ketosamine andaldosamine

- non-reversible

- Aldosamine and ketosamine -> -> carbonyl derivatives and othercompounds

- a series of degradation andcondensation reactions

- melanoidin pigments formed:

- brown nitrogenous compounds

- contain pyrazine and imidazole rings

- contain HMF (5-hydroxymethyl furfural)

Temp.

metal ions

Conc. of reactants

Water activity

pH

Type of sugar

Amino Acid

– ^ Temperature = ^ browning

– cooking, evaporation, drying,pasteurization, condensation

– Iron and copper catalyze reaction

– ^ concentration = ^ browning

– From 0.2 to 0.8:

• ^ water activity = ^ browning

– Over 0.8:

• excess moisture inhibits (negative feedback)

– decreased pH = decreased browning– due to ^ protonation of amine

– reducing sugar (open chain)

– monosaccharides > disaccharides

– Lysine very reactive (due to extra epsilon amine group)

• significant loss of essential amino acid lysine

– proline, arginine, asparagine

• Decrease water activity

• Reduce processing and storagetemperatures

• Acidify product

• Modify sugar composition

– Change formulations

– Add glucose oxidase to dried eggs

• Addition of sulfur dioxide / bisulfites

– prevents condensation into melanoidins

• Does not prevent lysine loss

– also reacts w/thiamine

• Fried, roasted or bakedfoods

• Maillard browning

• Reaction betweenasparagine and reducingsugars or other reactivecarbonyls

• Temperatures > 120C

• Levels increase with intensity and duration ofthermal processing.

• Cancer in rats when administered orally inhigh dose experiments.

– added to bread or potato mixtures

– reduces acrylamide formation during thermalprocessing.

• Plant seeds: guar, locust bean

• Plant exudates: gum arabic, ghatti,tragacanth

• Seaweeds: agar, carrageenan, alginate

• Microorganisms: xanthan, gellan gum

TIC Gums

FMC Biopolymer

Cargill

• Viscosity

• Gelling

• Suspension

• Emulsion & foam stabilization

• Encapsulation

• Film forming

• Water binding & management

• Fat replacement

• Dietary fiber

• Hydrophilic polysaccharides

• Provide viscosity at low concentrations ( < 1%)

• Linear or branched molecules

• Polymers can be up to 10,000 units

• ^ MW = ^ viscosity

• ^ Branching = decreased viscosity– more compact

• decreased radius of gyration

– decreased interactions w/other gums

– ^ hydrogen bonding w/water

• Salts of alginic acid (Ca, Mg, Na)

• Linear heteropolymer

• Mannuronic acid and guluronic acid

• Absorbs water and swells

• Gels formed by acid precipitation or byaddition of calcium salts – no heat needed!

• Cross-linking with polyvalent cations

• Gels stable to heat and pH changes

– Thickeners and emulsifiers:

• Chocolate milk

• Ice cream

• Sauces

• Pie fillings

– Gelling agent:

• Jellies, jams

• Sulfated polysaccharides

• Extracted from red seaweed (Irish moss)

• D-galactose and 2,3,6, anhydrogalactose

• Several polymers: kappa and lambda important infoods

• # and position of sulfate groups effectproperties

gelling

nongelling

• Interact synergistically w/othergums:

– ^ Viscosity, gel strength

• Gel formers, thickeners,emulsifying agents, stabilizers

• Chocolate milk: carrageenananion interacts w/protein.Prevents chocolateprecipitation.

• Salad dressings, puddings, icecream, …

• Bacterium Xanthomonas campestris

• Beta-1,4, linked glucose units

• Cellulose backbone

• Trisaccharide branches on C3 (mannose,glucuronic, mannose)

• Very high molecular weight

• Soluble in hot and cold water

• Stable over large pH range

• Heat stable

• Very viscous

• Stabilizer, thickener

• Salad dressings, ice cream, juice…

• Freeze-thaw stability and syneresis infrozen starch thickened foods

• Syrups: CMC or xanthan gum used to buildback viscosity lost due to lower dissolvedsolids level in reduced calorie syrups

• Guar seeds

• 1,4-mannose backbonewith 1,6-galactose branch

• Hydrates in cold water

• Very viscous in solution

• Viscosity synergism w/wheat starch

• Ice cream, dressings, sauces

• Produced by plants

• Primarily cell wall structural polysaccharides

• Poorly defined– “Group of substances exhibiting various degrees ofresistance to human digestion”

• Soluble and insoluble forms

• Branched or linear

• Homopolymers and heteropolymers

– Cellulose, lignin, hemicellulose, pectin, andgums

– Women, ~25 g/daily

– Men, ~35 g/daily

Artichoke, lima beans, green peas, raspberries, prunes, oatbran, whole wheat, broccoli, avocado, oats, sweet potato, pecans, peanuts, carrots, apples

• Long linear polymer

• Beta 1,4 linked glucose units

• Thousands of subunits

• Water insoluble

• Used in foods/beverages:

– Bulking agent in low-calorie foods

– Source of dietary fiber

– Thickener

– Anti-caking agent

– Stabilizes emulsions

• Aka cellulose gum

• Chemically modified cellulose

– Sodium hydroxide & chloroacetic acid

• Dissolves in cold water, clear insolution

– Thickener

– does not gel

– Water binder (syneresis control)

– Suspending agent

– Foam & emulsion stabilizer

– Sugar free products

– Beverages

– Baked goods

– Reduces fat uptake in fried foods

– Sauces, syrups, toppings

– Dry blends

– Ice cream stabilizer

• Heterogenous group of substances

• Variety of sugars in backbone and sidechain

• Backbone: xylose, mannose, galactose

• Side chains: arabinose, galactose, uronicacid

• Water insoluble

• 50-200 units

• Randomnoncarbohydratepolymer

• < 50 phenol units

• Often covalently linkedto hemicellulose (cellwall)

• Water insoluble

• Pectic substances

• Soluble in hot water

• Forms gels

• Backbone of linear alpha 1,4, galacturonicacid• ^ Hydrophilicity due to OH and COOH groups

• Forms gels with calcium and magnesium

Sugar beets, apples, citrus peel

– gelling agent

– ensures consistent setting

– improves thermal stability of gels

– kosher and vegetarian formulas

– yogurt, fruit snacks, jams, jellies,condiments, candies, pharmaceuticals,and supplements.

– Sucrose oligomers with 1, 2, or 3fructose units added

– Natural: beets, banana, tomato, onion

– Manufactured: fungal enzyme action onsucrose

– pre-biotic additive

– non-caloric; non-cariogenic; 1/3sweetness of sucrose

– linear fructosemolecules (2-60 units)

– Beta 1,2 linkages

– chicory root extract

– soluble inhot water

• non-digestibleprebioticoligosaccharide

• fat replacer and fibersource in cheese,ice cream, spreads,yogurt, chocolate, …

– Branched glucosepolymer

– Sources:

• Yeast cell wall

• Oat, wheat and barleyfiber

– Mixture of β 1,3-glucanand β 1,6-glucan.

– Oats and barley containa mixture of β 1,3-glucanand β 1,4-glucan.

– Long chain α 1,4 glucose polymer

– Acts like fiber physiologically

• resistant to digestion

• not absorbed in small intestine

– Fermented in large intestine

– Natural component of some foods

– Retorting, high temperature drying, and bakingcan increase RS levels in food

– Processing can also destroy some forms of RS infood

partially milled grains, seeds, andlegumes

in green bananas, rawpotatoes, uncooked starch

incooked-cooled potatoes, bread crusts, breakfastcereals

Modified resistant starch