food chem exam 2 polysaccharides

Define and Classify polysaccharides

• Polysaccharides - 10 -20 monosaccharides bonded by glycosidic bond

• starch, cellulose, gums

polysaccharide uses in food industry

• modify viscosity

• form gels

• stabilize emulsions

• control water

• texture

• thickening

• anti-staling

• film formation

• foam application

• binding

basic structure of starch

• is a polysaccaride composed of repeating glucose monomers and has organized units called granules

  • α 1-4 for linear amylose

  • α 1-6 for branched chain amylopectin

• predominant food reserve in plants and one of our main carb sources

amylose decreased ___

viscosity

amylose has ___ glycosidic bonds

a-1-4

amylose structure

____ but forms helical structure with weak hydrogen bond

linear

amylose is smaller____

than amylopectin

amylose good for ____ because retrogradation and high packing ability

gelling

amylose

____ in cold water but slightly at high temps

insoluble

amylopectin

good for ____ but not gelling because branched chains take too long to reasscociate

• thickening and forming paste

amylopectin ____ chains and ___ molecule size

branched, large

amylopectin ____ glycosidic bonds

α 1-6

amylopectin is____ than amylose

bigger

amylopectin glucose phospate derivatives carry ____

negative charges which repell each other and increase starch viscosity

homo-polymer

• two examples are ___ and ___

• composed of ___ monosaccharide unit with one or more type of glycosidic linkages (repeating glucose units)

• can have ___ and un-___

• starch (amylose) and cellulose

  • starch is repeating glucose monomeric units

• single

• branched

hetero-polysaccarides

• composed of ___ monosaccharides

• the four types are ___, ___, ___,____

• examples include:

• more than one type of

• copolymers (a-b-a-b)

  • carrageenan gum

• blocked polymers (a-a-a-b-b-b)

  • alginate gum

• branched polymers

  • guar gum

• random polymers (random and branched)

  • locust bean gum, dietary fiber, pectins

Type A: ___ grains

cereal

• corn, wheat, rice

• low weight amylose and short chain amylopectin

• high degree of packing/crystallinity because short chains

• low swelling power

• opaque gels upon cooling

Type B: ____ and ____ starches

root and tuber

• potato and cassava

• high molecular weight amylose and long branched chain amylopectin also more disorganized

• low degree of packing/crystallinity

• lower gelatinization/pasting temp

• high swelling power

• highly viscous/paste

• weak gel bc fewer amylose molecules can escape into environment

waxy starches

• GMO to contain almost all amylopectin

• less order and packing in a granule

• high swelling power

• no or very poor gelatinization bc no amylose to leak out and gel

• heavy body and stringy paste

• INSTANT PUDDING

iodine stain

• amylose - dark blue (iodine gets into the amylose)

• amylopectin - red

waxy starch

• 0-8% amylose basically all amylopectin

• paste rather than gel

normal starch

• 20-30% amylose

• some gelling ability

• aka native starches and cereal grains

high amylose starch

• 40-70% amylose (remember 100% amylose is not possible)

• very high gelling ability (high temp required tho)

maltese cross

• demonstrates crystalline property and the tight packing and extensive H bonding of amylose/lopectin

• maltese cross disappears when starch gelatinization occurs

• type A starch granules are small, type B are large

why would starch require higher gelatinization temps

• more H bonds

• higher degree of packing in a granule

• longer chains

• higher phosphate groups?

gelatinization

when starch is heated sufficiently enough that hydrophobic and H bonds are broken and in the presence of water, the starch granule swells and amylose leaks out

amylose reassociates outside of granule upon cooling and forms gel

pasting

second stage of swelling where starch is heated above gelatinization temp and reaches maximum viscosity, leaches all amylose out into environment and eventually the starch granule completely disrupts

barbender graph

starch retrogradation

if you do not force gel quickly at cooling, amylose is insoluble at cold temp and precipitates out as a solid bc it reforms as an organized structure

more amylose faster retro bc smaller

heating reverses

anti staling agents: lipids and emulsifiers (CMM is example)

stale bread

freezing slows down staling, fridge speeds up

happens when amylopectin branches slowly reassociate upon cooling (bread hardens and gets crumby)

amylose also leeches out and retrogrades almost fully upon cooling which gives fresh bread its elastic and tender crumb

Ingredient interactions with starch

• sugar competes w starch which raises gelatinization temp, retards gelatinization, and sucrose has higher effect than fructose bc sucrose is more soluble

  • proteins and gums also compete for water

• lactose increases gel temp but less than sucrose bc poor solubility

• acids break glycosidic linkages

  • limits swelling and lowers viscosity

  • acid breaks glucose off of starch and glucose is more soluble

  • ph below 4 acid hydrolysis is complete unless cross linked starch

• lipids

  • coat surface of starch and create waterproof granule

• water

  • if too low, no gelatinization

  • dextrinization instead

uses of low amylose starch

salad dressing emulsifier

uses of high amylose starch

donut film to prevent oil absorption!!! (cellulose)

quick candy hardening

coating battered products

why do we modify starches

withstand high heat, acids, storage and transport, improve characteristics, freeze/thaw stability, fat replacer, binder

physical modifications of starch

• pre gelatinized

• instant pudding

chemical modifications of starch: cross link

cross link

• acid hydrolysis

  • acids hydrolize starch into smaller units (oligosacc and D-glucose)

  • changes from shortened chains include increased sweetness, increased reactivity as reducing sugars, decreased viscositt, increased gelling, increased solubility, increased fermentability, less swelling bc smller units cannot swell as much

  • amorphous amylopectin regions more hydrolyzed than amylose

  • simple and cheap but off pigments and caramelization

  • increased DE (dextrose equiv)

• oxidation

chemical mods: enzyme hydrolysis

• dextrinization (enzyme hydrolysis)

  • alpha amylase

    • endo-enzyme

    • cleaves at non crystalline 1-4 linkage within starch

    • more specific than acid

    • products are dextrins (smaller starch units) mainly maltose and matotriose

  • beta amylase can cleave at:

    • exo-enzyme (hydrolyzes starch at non reducing end)

    • product is maltose and limit b- dextrins

  • glucoamylase (amyloglucosidase)

    • exo-enzyme at non reducing end of a-1-4 and 1-6 links

    • removes b-D-glucose and a-limit dextrins

    • enzymed used to produce light beers

  • isoamylase and pullulanase

    • hydrolyze at a-1-6 bonds (remove branched chains)

chemical modifications of starch: degradation and subs

degradation

• esters and ethers

substitutions

• esters

products of enzymatic hydrolysis

• dextrins

  • used in splenda! (small amt of sugar molecules but negligible)

• maltodextrin

  • added to splenda to make 1:1 sugar sub

  • bland no flavor or sweetness but addes bult and good humectant also has fat llike properties

• corn syrups

  • corn starch plus acid and heat or

  • a-amylase, glucoamylase, fructase

cross linked starch

• chemically link starch molecules together with cross bridges

• less water is able to enter molecule so minimized swelling

• strong due to extensive H bonding

• phorylchloride or sodium trimetaphosphate

• used in canned soup, spaghetti sauce, pie fillings

phosphorylated starches

• negative charge = molecule repulsion = decreased gelling

• lower gel but increased viscosity

• can drop viscosity with salt to mask phosphate neg charge

• good thickening agent for frozen or thawed foods

oxidized starch

bleach flour, less retrodegradation, adheres well to proteins through charge interactions and cross linking

breakfast corn dogs bc neg charged batter binds to meat protein

Hydroxypropylated Starches

Treat starch with propylene oxide

Substitution occurs on the –OH at C2

alkaline ph to avoid dextrinization

Improves starch swelling and solubility

Great cold-storage and freeze-thaw stability = clear paste with no retrogradation

Used in frozen foods and desserts as thickening agent

Also, smooth texture and often used to improve viscosity under acidic conditions

resistant starch

• Is a starch and its degradation products that resist digestion in the small intestine

• Ferments in large intestine creating butyrate

• Feeds gut bacteria • Naturally in foods • Brown rice • Beans • Whole grain bread and pasta • Lentils

types of resistant starch

• Type 1 – physically inaccessible starch

• Surrounded and entrapped by a cell wall or protein matrix (e.g. legume seeds, coarsely ground grains)

• Type 2 – Ungelatinized

  • Indigestible because of their chemical configuration (e.g. uncooked potato, green banana flour, high-amylose cornstarch or grains)

• Type 3 – Retrograded amylose

  • The heating and cooling of starches during processing render them inaccessible to enzymatic hydrolysis (e.g. cooked and cooled potato, bread, cornflakes)

• Type 4 – Chemically modified starch

  • Derivatives interfere with the binding of the starch to hydrolytic enzymes (e.g. commercial starch products used in processed foods (salad dressing cheese sauces, gravies, soups, etc.))

• Type 5 – Amylose-lipid starch

  • Rigid helical conformation interferes with the binding of the starch to hydrolytic enzymes

homopolymer examples

starch and cellulose

heteropolymers examples

pectin and most gums

gums

a viscous secretion of some trees and shrubs (or from microorganisms) that hardens on drying but is soluble in water (at STP) from which adhesives and other products are made.

cellulose

• like starch, insoluble in cold water

• cotton, wood

• BETA 1-4 glycosidic bonds

• linear and rigid (straight chain crystalline regions = hella H bonds)

• humans cant digest so passes right through G.I. and no cals

• can be added as fiber to breads, no cal bulk for fat free foods

• can slightly improve upon heated bc H bonds break and slight swelling but not a ton

modified cellulose

• microcrystalline cellulose MCC

• Methylcellulose (MC)

• Carboxymethyl cellulose (CMC)

MCC

microcrystalline cellulose

• prepared via acid hydrolysis

• basically amporphous regions removed so just left with crystalline

• Emulsifier, Stabilizes emulsions & foams

• Fat substitute and extender, Add “body” to foods

• can serve as a suspension aid

• Absorbs oils & syrups

• Anti-caking agent: dry mixes

• Keeping them free-flowing (e.g., keep dried honey granules free flowing

MC

methylcellulose

• created with very alkaline solution causing fibers to swell

• methyl chloride used bc reacts with sodium hydroxide and hydroxyl groups subbed with methyl

• Solubility decrease as temperature increases

• DONUTS no oil soaked during frying bc gels at higher temperatures and return to solution at lower temperatures

• fried meats

CMC

Carboxymethyl cellulose

• Cellulose treated with alkali (usually NaOH) to swell fibers and then chloroacetic acid is introduced:

• Some of the hydroxyl groups (-OH) are substituted with carboxymethyl ether (CH2CO2H) group

• non-digestible fiber in dietetic foods

• Hot and cold water soluble

• Common stabilizer in ice cream

• Foam stabilizer meringues

• Tends to interact with proteins due to charge, increasing their viscosity, solubility, & stability

  • Used to stabilize milk proteins in milk against casein precipitation • Used to stabilize egg whites

• cellulose gum on labels

pectin

• Complex polysaccharide derived from soft tissue of plants

• jams and jelliesss

• Linear chain of 1-4 -D-galacturonpryansyl units

• high degree of esterification in young unripe fruits

• from immature fruit and no gel, to ripe fruit that gels, to overripe fruit and no gel: protopectin, pectin (pectinic acid), and pectic acid

  • DE decreases as aging process happens

• low PH

• high sugar

• low DE methoxyl pectin gels need divalent cation such as calcium to gel (good for diet jams bc u dont need sucrose)

• pectin esterase removes cloudiness but u have to heat product to stop enzyme

gums origins

• Seaweeds (agar, carrageenan)

• Seeds (guar and locust bean gums)

• Microbes (xanthan and gellan gums)

• Modified starch and cellulose

gum properties

• very hydrophilic

• good gel formers

• (a) – stiff extended chain with a large radius that interacts with many water molecules and chains thus producing a large increase in viscosity

• (b) – chain that folds into a compact shape – only has a small effect on viscosity

• (c) – branching increases stiffness but reduces the radius. Lesser effect on viscosity than (a)

gum interactions

• Non-ionized gums = little effect of pH and salts

• ionized Negatively charged gums

  • Low pH = deionization = aggregation = precipitation

    • Can modify by placing a strong acidic group on gum so it remains ionized at low pH (important in fruit juices)

  • High pH = highly ionized = soluble = viscous

  • Ions (e.g. Na+ , K+ , Ca2+) = salt bridges = gels

• Proteins •

  • CMC Carboxymethylcellulose inhibits in-solubilization of proteins in fruit flavored milk drinks

  • Flours with poor bread making properties can be increased (xanthan or carrageenan)

  • Sugars

  • Salt

chewing gum

Modern chewing gum is composed of:

• Gum base (25-35%),

• Sweeteners (40-50% if caloric sweetener,

  • 0.05-0.5% if artificial sweetener),

• plasticizer (1-2%),

• flavor (1.5-3%)

• color (optional)

• Coating (starch, sorbitol, mannitol)

• Plasticizer softens the gum and increases the flexibility (lecithin, hydrogenated vegetable oil, glycerol etc.)

ionic gums

alginate, carrageenan

non-ionic gums

guar gum, locust bean gum, gum arabic

alginate

• brown algae/kelp

• used in pudding for gel texture, ice cream, “caviar”, foam stabilizer, salad dressing stabilizer

• forms gels at room temp if introduced to di or trivalent cations

carrageenan

• red seaweed

• KIL kappa iota lambda polymers

• cold water soluble and does not gel

• stabilizes proteins

• MILK and DAIRY PRODUCTS

guar and locust bean gum

• No effect of pH and ions (salts) since they are uncharged

• soluble in hot and cold water

• salad dressings (thixotropic = thickens up at rest but thins out if agitated)

• guar gum 2:1 mannose to galactose

• locust bean gum 4:1 mannose to galactose but un-uniform distribution

• locust + carrageenan or xanthan = lunch meat binder

• carob tree is source of guar gum (carat name origin)

gum arabic

• One of the oldest known gums mummy wrappings

• Produced naturally as a teardrop shaped globule extruding from the bark of the tree when it has been injured

• Very large complex polymer

• Readily dissolves in water

• Pseudoplastic behavior

  • Notable b/c does not significantly increase viscosity until high concentration

• starburst jellybeans

• lozenge

• retards sugar crystallization

• beverage powders

xanthan gum

• branched ionic

• Produced by Xanthomonas species a microbe that lives on leaves of cabbage plants

• Soluble in hot and cold water

• Cellulose backbone with charged trisaccharide branches

• Branching prevents gelation

• Very viscous due to charged branches

• Expensive ingredient

• Very high viscosity at low concentrations

• remain stable when sitting, but flow when poured

• Chocolate sauces – constant viscosity over wide temperature ranges

  • Easily flowable at refrigeration temperature