FOOD CHEM starch

46問 • 1年前

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Starch is a plant _____________ stored in roots, seeds, and the endosperm of grain kernels.

polysaccharides

Provides ____ calories per gram and is hydrolyzed into glucose, which is essential for brain and central nervous system function.

Cooking starch causes irreversible swelling and leaching, making it useful as a thickener. - The characteristics of a starch-based food product depend on: - Starch source - Concentration - Heating temperature - Other components (e.g., acids, sugars)

remember

short-chain starch breakdown products can act as fat replacers in foods like salad dressings and frozen desserts.

dextrins

Sources of Starch - Common sources include: cereal grains (wheat, corn, rice) roots, tubers (cassava, potato) legumes (soybeans, garbanzo beans) fruits (bananas)

remember!

Enables gel formation.

amylose

Thickens but does not form a gel.

amylopectin

Higher amylopectin content ~More viscosity Higher amylose content ~Stronger gel.

remember!

Uncooked starch is insoluble in water forming a temporary _______.

suspension

Starch granules exhibit ___________ (Maltese cross formation) under polarized light due to their ordered crystalline structure.

birefringence

Water absorption (_____) begins in less dense areas of the starch granule.

imhibition

As heating continues, granules swell irreversibly and amylose leaches out This process is called _____________ leading to food thickening.

gelatinization

The crystalline structure is lost, forming a ____ (a colloidal system).

sol

Granule swelling increases as temperature _______.

increases

Excessive stirring can rupture granules thinning the mixture.

remember!

- Proper stirring ensures uniform swelling and prevents lumps. - Excessive stirring after gelatinization ruptures granules, causing thinning

agitation

Acid hydrolysis breaks down starch into dextrins, resulting in a thinner mixture - Late acid addition is preferred(e.g., vinegar, citrus, tomatoes).

acid

Starch-breaking enzymes (α-amylase, β-amylase, β-glucoamylase)hydrolyze starch. - α-Amylase~ Breaks starch into glucose, maltose, dextrins (useful in breadmaking). - β-Amylase~ Produces maltose by hydrolyzing α-1,4 glycosidic bonds - β-Glucoamylase~ Produces glucose and slowly hydrolyzes α-1,6 bond

enzymes

Breaks starch into glucose, maltose, dextrins (useful in breadmaking)

a-amylase

Produces maltose by hydrolyzing α-1,4 glycosidic bonds

b-amylase

Produces glucose and slowly hydrolyzes α-1,6 bond

b-glucoamylase

Fat coats starch granules delaying hydration and reducing viscosity. - Proteins (e.g., meat drippings in gravy) interfere with gelatinization

fats proteins

- Competes with starch for water, delaying gelatinization. - Increases gelatinization temperature - Best practice: Add sugar in stages for optimal thickening.

sugar

- Raises gelatinization temperature

salt

- Gelatinization occurs between 190°-194°F (88°-90°C), completing at 203°F (95°C) - Different starches gelatinize at different temperature range

temperature

Overheating/stirring ruptures granules, thinning the mixture. - Long cooking in an uncovered double boiler leads to water evaporation, thickening the mixture.

heating time

- Moist heat is necessary for gelatinization. - Dry heat hydrolyzes starch into dextrin creating a toasted flavor and brown color

type of heat

- Faster heating produces thicker starch mixtures at a given endpoint temperatur

rate of heating

Forms a gel upon cooling due to hydrogen bonding between molecules, creating a three-dimensional, elastic structure

amylose

Does not form a gel but remains a thickened sol due to its highly branched structure.

amylopectin

occurs when starch molecules, especially amylose, revert to a more crystalline structure upon cooling. This leads to changes in texture, often making food gritty or firm over time.

retrogradation

A______ Retrogradation:Causes water loss from gels, making them brittle. Improper gel formation leads to fragile amylose structures that quickly degrade.

amylose

A_______Retrogradation:Happens more slowly and is the main cause of food staling (e.g., hardening of baked goods and leftover rice).

amylopectin

______ is the separation of water from a cooled, cooked starch gel due to retrogradation.

syneresis

- Controlling syneresis: Use modified starches or amylopectin-rich starches. - Cooling conditions affect gel strength: - Too fast = weak gel - Too slow = excess water loss

remember!

Separating agents - ___: Forms a film around starch granules (e.g., roux in sauces).

fat

Separating agents -____ ____:Creates a starch slurry that prevents clumping.

cold water

Separating agents - _______:Separates starch granules in sweetened mixtures.

sugar

Swells in cold water (e.g., instant pudding).

pregelatinized starch

Used in no-cook dressings

cold water swelling starch

Resists high temperatures, acidity, and shear (e.g., pizza sauce).

cross linked starch

Prevents syneresis in frozen foods.

stabilized starch

Forms a strong gel upon cooling.

acid modified starch

Used in glue (e.g., postage stamps, cardboard).

non food use

Waxy Starches vs. Ordinary Starches - Waxy starches (e.g., waxy cornstarch)contain only amylopectin → do not gel. - Ordinary cornstarch contains 27% amylose → forms a gel. - High-amylose cornstarch contains 55% amylose → strong gel formation.

remember!

Starch food applications -Functions as a thickener water binder gelling agent - Used as a fat replacer (e.g., maltodextrins mimic fat texture). - Starch granules can act as flavor carriers (e.g., time-release of flavors).

remember!

biochem

velante · 99問 · 1年前

biochem