starch

Starch

Chapter 13

Introductory Foods, 13th ed.Bennion and Scheule

© 2010 Pearson Higher Education,Upper Saddle River, NJ 07458. • All Rights Reserved.2

Nutrition Starch – in breads, cereals, grains, potatoes,

and other foods – provides 70-80% of the world’s calories

Breads and cereals offer, in addition to starch, vitamins and minerals.



Sources Parts of plants

Seeds Roots Tubers

Foods Cereal grains (i.e. corn, wheat, rice, oats) Legumes (i.e. dried beans) Roots and tubers (i.e. potato, tapioca, arrowroot)



Milling Wet milling

Process used to separate starch from grains and tubers.



Starch Molecule

Starch is a polysaccharide.

Polysaccharide is made up of hundreds or thousands of glucose molecules.

Terminology Polysaccharide – a complex carbohydrate. Glucose – a monosaccharide or simple sugar.



Composition and Structure Starch molecule composed of many linked glucose

molecules

Two types or fractions Amylose

Long, chainlike molecule Gelling characteristics

Amylopectin Branched, bushy structure Thickening / cohesion properties



Terminology Gel

Colloidal dispersion that holds shape

Colloidal Intermediate between small particles in solution

and large particles in suspension



Composition and Structure Starch granule

Starch is deposited in plants in organized units called granules.

Starch molecules structured to form crystalline-like patterns in the granule With polarized light, a Maltese cross pattern can be

observed under microscope Called birefringence Pattern disappears when starch is heated



Kinds – Native Starches Cornstarch Tapioca Wheat Potato Rice Arrowroot Sago



Kinds – Improved Native Starches Developed through plant breeding or genetic

engineering

No physical or chemical modification of the starch



Kinds – Modified Starches

Chemical or physical modifications may be used to change function in food preparation.

Hydrolysis or acid-converted Cross-linked or cross-bonded Substitution or stabilization Physically modified

Instant or pregelatinized Cold-water swelling Heat treated



Modified Starch

Hydrolysis or acid-converted starch “Thin-boiling starch” Low viscosity paste Produces stiff gel Useful in confectionary industry

Cross-linked or cross-bonded Lower viscosity and increase temperature for hydration Resistant to shear or stirring Greater tolerance of heat Useful for canned soup, spaghetti sauces, and pie

fillings



Modified Starch Substitution or stabilization

Prevents retrogradation Improves clarity Reduces syneresis Useful for frozen or refrigerated starch-thickened foods

i.e. “clear gel” starch

Physically modified – Instant starch Will absorb cold water Useful in “instant” pudding



Kinds - Resistant Resistant starch is not digested by human body

Four main types RS1 RS2 RS3 RS4

May be used in food to increase fiber content



Effect of Heat and Cooling Dry heat

Starch becomes more soluble Reduced thickening ability Dextrinization Brown, nutty, toasted flavor develops

Examples Brown roux and Espagnole sauce A higher proportion of starch to liquid is needed



Effect of Heat and Cooling

Moist heat Starch granules insoluble in cold water Colloidal dispersion produced with heating Starch paste



Changes with Moist Heat and Cooling Gelatinization

With heat, starch granules absorb water and swell Increased viscosity and increased translucency

Pasting Gel formation or gelation

Occurs with cooling

Retrogradation Occurs with standing after gel formation Amylose molecules associate more closely Gel network shrinks

Syneresis



Factors Affecting Starch Pastes Temperature and time of heating

Agitation and stirring

Acidity

Addition of other ingredients



Factors Affecting Starch Pastes Temperature and time of heating

Thicker if cooked quickly If undercooked

Raw starch flavor Less smooth and silky

Agitation or Stirring Stirring desirable to disperse starch If excessive – starch granules may rupture

Slick and pasty mouthfeel



Factors Affecting Starch Pastes Acidity (pH)

May cause fragmentation and hydrolysis Decrease of thickening power Add acid late in cooking process

i.e. lemon pie



Factors Affecting Starch Pastes Addition of other ingredients

Sugar Raises temperature of gelatinization May decrease viscosity

Fats and proteins Delay hydration of starch Lowers rate of viscosity development



Starch Cookery Combining starch with hot liquids

Roux Slurry



Mother Sauces Thickened with starch

Béchamel Velouté Espagnole

May be thickened with starch Tomato

Thickened with an emulsion Hollandaise



Cream Soups

Often use mirepoix for flavoring Thickened with

Starch (roux or slurry) Cream Pureed starchy vegetables (i.e. potatoes)

Curdling Acid (i.e. tomatoes) Freshness of milk/cream Higher fat milk/cream is more stable than low or nonfat

milk



Starch-Thickened Desserts

Typical starch choices Corn starch

Clear and glossy Flour Tapioca

Separate starch by mixing with sugar then cold liquid

Cook starch mixture before adding eggs Temper eggs



Microwave Cooking of Starch Best for small batches

Stop microwave and stir in approximately once every 1 minute

starch

Documents

pearson higher education

upper saddle river

starchintroductory foods

arrowrootintroductory

suspensionintroductory

heatedintroductory foods

starch moleculestarch

linked glucose molecules