Starch

1. Starch Chapter 13

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.

3. 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)

4. Milling Wet milling Process used to separate starch from grains and tubers.

5. 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.

6. 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

7. Terminology Gel Colloidal dispersion that holds shape Colloidal Intermediate between small particles in solution and large particles in suspension

8. 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

9. Kinds – Native Starches Cornstarch Tapioca Wheat Potato Rice Arrowroot Sago

10. Kinds – Improved Native Starches Developed through plant breeding or genetic engineering No physical or chemical modification of the starch

11. 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

12. 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

13. 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

14. 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

15. 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

16. Effect of Heat and Cooling Moist heat Starch granules insoluble in cold water Colloidal dispersion produced with heating Starch paste

17. 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

18. Factors Affecting Starch Pastes Temperature and time of heating Agitation and stirring Acidity Addition of other ingredients

19. 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

20. 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

21. 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

22. Starch Cookery Combining starch with hot liquids Roux Slurry

23. Mother Sauces Thickened with starch Béchamel Velouté Espagnole May be thickened with starch Tomato Thickened with an emulsion Hollandaise

24. Cream Soups Often use mirepoixfor 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

25. 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 Tempereggs

26. Microwave Cooking of Starch Best for small batches Stop microwave and stir in approximately once every 1 minute