C3. Starch
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3 common polysacs? + 4 types of gums
starch + cellulose + pectins others: - seed gums: guar gum, locust bean gum - plant exudate gums: gum arabic, gum tragacanth - seaweed gums: agar, carrageenan - microbial gums: dextran, xantham gum
properties of polysacs are a function of (4)
• sugar/chemical makeup • presence of unique functional groups • molecular weight and degree of branching • combination thereof
are proteins or carbs more complex?
proteins! bc less variation in base units of carbs that make up the polymer
2 most abundant form of stored carb available on earth?
starch and cellulose - starch = energy store for seed germination
starch - main source of ________ ________ (4 ex) - large quantities isolated from ______ sources and used as functional ingredient in food industry due to 2 properties
• dietary carbohydrates (potatoes, rice, corn, wheat) • plant sources • thickening/texture-modifying agent + source of sugars and dextrins
starch - made up exclusively of __-__________ - made up of 2 fractions + describe (shape + linkage)
• D-glucose 1. amylose: long chain linear polymer composed of D-glucose linked by a-1,4 glycosidic bonds 2. amylopectin: branched polymer composed of D-glucose linked by a-1,4 glucosidic bonds in its linear portion and a-1,6 bonds at its branch points
starch is found in most plant sources as ______ water- soluble/insoluble granules
hard water-insoluble granules
each starch source contains ________ and _________ in genetically predetermined ________ ie: corn starch? vs waxy maize
• amylose and amylopectin in genetically predetermined ratios • corn starch: 28% amylose + 62% amylopectin • waxy maize: 100% amylopectin
starch is readily isolated from plant source by ____ _______, then ________ out of solution and _______ - produces _____ _______ powder composed of ________ starch granules - each granule is made up of _________ amylose and amylopectin tightly bound and held together by __________ between the polymers
• wet milling + centrifuged out + dried • dry white powder • anhydrous amylose and amylopectin • H-bonds
what leads to starch gelatinization? - process of gelatinization (5 steps)
heating in presence of moisture breaks the H-bonds = gelatinization 1. gradual swelling of the granule due to absorption of water facilitated by heat 2. increasing kinetic energy breaks H-bonds 3. granule slowly hydrates as water molecules access OH groups on the polymer 4. as kinetic energy is reduced, random H-bonds reform –> extensively H-bonded starch molecules trap water within matrix formed, producing a gel
at what temp does loss of granular integrity general occurs? - gelatinization temperature is a function of the starch ________
• 60-70°C • stach source
gelatinization: - when granules have swollen extensively, viscosity of solution increases/decreases drastically, causing ________ - if solution is stirred, granules break up and ________ to form a ________ solution
• increases causing pasting • disperse • colloidal solution
gelatinization: - if concentration of starch is high –> forms what? upon cooling - if concentration of starch is low –> forms what upon cooling?
• high starch = gel upon cooling • low starch = obtain a viscous solution that does not form a gel
gelatinization of starch occurs as function of 5 variables
• concentration of starch • amylose:amylopctin ratio of starch • average molecular weight (chain length) of starch • rate of cooling • presence of other components in solution (salt, sugar, fat)
amylose: - linear polymer with what structure? - solubility? why? - functionally useful?
• long thin helical filament-like structure • very low solubility bc readily hydrogen bonds to neighboring polymers to form large aggregates that precipitate out of solution • on its own, useless functionally in food systems bc insoluble
amylopectin: - structure? - soluble in water? - forms a _________ solution –> branching produces what in solution - in presence of amylose which acts as a _____-_________ agent, a _____ can form, _________ water
• highly branched water dispersible macromolecule • yes! • forms a viscous solution • branching produces a tangled net-like web in solution • amylose = cross-linking agent –> 3D gel can form, entrapping water
what is retrogradation? - happens when?
• when starch gels become firmer with time –> generally undesirable • due to continued hydrogen bond formation between starch molecules
what 2 problems arise with retrogradation?
• texture of gel changes over time, which is generally undesirable • syneresis (exudation of water) may occur, where gel tightens up so much that it starts to exude water
• retrogradation causes color change? • retrogradation is one of key processes responsible for (2)
• causes starch gels to become more opaque with time • staling of bread + stiffening of pie filling (when you expose starch to air
normal corn starch vs waxy maize starch vs potato and tapioca starch - which will form a gel? - why?
• normal corn starch (28% amylose) –> set to a rigid opaque gel • waxy maize starch (100% amylopectin) –> NOT form a gel • potato and tapioca starch (23-28% amylose) form reasonable stable gels that tend to maintain their clarity and do not stiffen appreciably with time attributed to their high average molecular weight = less mobile –> H-bonds continue to develop btw them over time but at a much slower rate
sugars tend to accelerate/retard gel formation and retrogradation why?
retard! - they compete for available water and interfere with starch to starch hydrogen bonding
surface-active agents (surfactants and emulsifiers) tend to activate/inhibit retrogradation and gelation –> forming what?
inhibit - form complexes with starch, most noticeable with high-amylose starch systems
pH of most foods lies in range of __-___ - affects behaviour of starches? why? - vs highly acidic food + heat –> possibility of what?
4-7 - nope because natural starches are uncharged - of reduction of viscosity due to hydrolysis of starch
does ionic strength have effect on most starches?
only minor effects bc most starches have no ionizable groups –> change in ionic strength has little influence relative to its effects on a macromolecules such as protein which may be extensively charged