Food Science Cooking 2016 Food & Nutrition Conference Karin Allen, PhD

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1 Food Science Cooking 2016 Food & Nutrition Conference Karin Allen, PhD What s Cooking? Cooking is the transfer of energy from a heat source to a food that alters its: Molecular structure Texture Flavor Aroma Appearance Each component of the food reacts differently 1

2 How Heat Affects Food Culinary Version Sugars caramelize Starches gelatinize Fibers swell and soften Proteins coagulate Fats melt Water evaporates But what does that actually mean? First Let s Cook! Compare your ingredients before (raw) and after cooking Taste the vegetables Feel the chicken (make sure to wash your hands!) How thick is the cornstarch mixture before and after boiling? 2

3 Chicken Stir Fry (half recipe) Ingredients ½ cup chicken broth or stock 1 tsp cornstarch 4 tsp peanut oil 1-2 tsp minced garlic 1-2 tsp minced ginger ½ medium onion, julienne 2 (about ½ lb) boneless, skinless chicken breasts cut into thin trips ½ red bell pepper, julienne ¼ cup water chestnuts 1 cup broccoli florets, trimmed 2 Tbsp soy sauce 1 tsp sesame oil Instructions Prep onion, chicken, bell pepper, and broccoli. Combine cornstarch and chicken broth, set aside. Heat peanut oil over high heat. Add garlic, ginger, onion, and chicken. Cook until chicken and onions are browned, 2-3 minutes. Add red peppers, cook 1 minute. Add water chestnuts and broccoli, cook 1 minute. Add soy sauce and sesame oil, cook 1 minute. Add chicken broth/cornstarch slurry, bring to a boil. Cook 2-3 minutes until thick. Season with salt and pepper to taste. Serve immediately, with rice if desired. Makes 2 full servings How Heat Affects Food Science Version Sugars caramelize Starches gelatinize Fibers swell and soften Proteins coagulate Fats melt Water evaporates 3

4 Carbohydrates Sugar, Starch, and Fiber Nutritional Classifications Chemical Classifications Degree of Polymerization (DP) Common Uses Simple Sugars Monosaccharides 1 Disaccharides 2 Sweeteners Complex Carbohydrates Oligosaccharides 2 20 Polysaccharides Up to 15,000 Thickeners Sugars: Monosaccharides and Disaccharides 4

5 Physical Properties of Sugars Sweetness Hygroscopicity ability to attract and hold water Solubility Hygroscopicity and solubility are related to sugars ability to hydrogen bond Chemical Reactions of Sugars Hydrolysis Acid, heat, or combination Enzymes Caramelization Brown colors formed from sugar only Hydrolysis, degradation, polymerization 5

6 Starch: Polysaccharides Amylose Straight chain MW ~ 10 6 Chains take on a helical structure Amylopectin Branched chain MW 10 7 to 10 8 Branches make this less soluble than amylose Gelatinization UNIQUE TO STARCHES!!! Absorbtion of water Swelling as even more water is imbibed Leaching of amylose Amylopectin can stay in granule Gives thicker product, can gel Amylopectin can leave granule Gives thinner paste, no gelling 6

7 Gelation Gelation Gelatinization! Gelation of starch requires amylose Forms junction zones Potato, tapioca, and rice starches do not form gels Arrowroot forms a soft gel Corn, wheat starches form strong gels Flours form weaker gels than starches Fiber: Plant Structure 7

8 Fiber Soluble Gums & pectic substances Very limited caloric value Insoluble Cellulose, hemicelluloses & lignin No caloric value, provides bulk Protein Proteins are large, nitrogen containing molecules, composed of 100+ amino acids 20 Standard amino acids Basic structure amine, carboxyl, and a unique Rgroup R group gives the amino acid unique properties Combination of different amino acids gives each protein unique properties 8

9 Levels of Protein Structure Primary Protein Structure Order of amino acids in the peptide chain Held together by peptide bonds 9

10 Secondary Protein Structure Distinct structured regions (α helix, β sheet) Held together by H bonds Tertiary Protein Structure 3 D folding of protein chain Held together by H bonds, salt bridges, disulfide bonds, and hydrophobic interactions 10

11 Quaternary Protein Structure Association of multiple folded peptide chains (subunits) with each other Is protein structure changed by cooking? Quaternary? Yes, sub units are easily broken loose from each other Tertiary? Yes, this is what we commonly call denaturation or coagulation Secondary? Not usually. It is very difficult to disrupt secondary structure with heat. Primary? Not usually. Primary structure is only disrupted when the protein is hydrolyzed. 11

12 Protein Denaturation Physical change in the shape of the protein from its native state UV light or radiation, heat, salt, ph, solvents Coagulation can occur after proteins are denatured To be good emulsifiers or foamers, proteins must usually be denatured! Protein Hydrolysis Polypeptide is broken down Enzymes (peptidases) Strong bases (think of Drano ) Sometimes strong acids These situations are uncommon in cooking Exception: meat tenderizers containing enzymes from pineapple, kiwi, or fig 12

13 How Heat Affects Food Science Version Sugars caramelize Starches gelatinize Fibers swell and soften Proteins coagulate Fats melt Water evaporates Questions? Thank you for your attention! 13