Food Science - Principles of Dietetics - PDF

## DOMAIN I: PRINCIPLES OF DIETETICS ### TOPIC A: FOOD, NUTRITION AND SUPPORTING SCIENCES #### Food Science 1. Fruits and vegetables * Nutritive value and structure 1. 75-93% water, carbohydrates (digestible and indigestible) 2. some minerals (calcium in oranges, greens), vitamin...

## DOMAIN I: PRINCIPLES OF DIETETICS ### TOPIC A: FOOD, NUTRITION AND SUPPORTING SCIENCES #### Food Science 1. Fruits and vegetables * Nutritive value and structure 1. 75-93% water, carbohydrates (digestible and indigestible) 2. some minerals (calcium in oranges, greens), vitamins C, A, some B 3. crispness (state of turgor) is due to the osmotic pressure of water-filled vacuoles * Ripening and storage 1. chemical changes due to enzymes; starch changed to sugar * protopectin converted to pectin (ripe fruit) then converted to pectic acid (overripe fruit) 2. ethylene gas accelerates ripening of fruits during storage 3. most produce can be stored in the refrigerator * store frozen fruit at or near 0°F * store dried fruit at room temperature * avocados, bananas, pears and tomatoes ripen best at room temperature * aging is delayed in apples stored in controlled atmosphere (reduced oxygen) * Climacteric fruits ripen post-harvest (peach, pear, banana, apple, tomato) * Non-climacteric fruits: best when ripened before harvest (grapes, melon, citrus) * Pigments 1. green - chlorophyll * insoluble in water * olive green in acid - pheophytin * bright green in alkaline – chlorophyllin (mushy: hemicellulose broken down) 2. yellow, orange – carotenoids (least affected by changes in pH) * insoluble in water * little effect in acid or alkaline solution * lycopenes - antioxidant, phytochemical 3. flavonoids * red, blue, purple – anthocyanins (greatly affected by changes in pH) * soluble in water * bright red in acid * bluish in alkaline * colorless or white to yellow - anthoxanthins or flavones * soluble in water * colorless in acid (bleaching effect) * yellow in alkaline or when cooked in an aluminum pan (flavones chelate aluminum) * Principles of preparation and processing of Fruits and vegetables 1. raw - wash to remove dust and spray residues * berries and mushrooms should be washed just before serving * fruits low in vitamin C darken rapidly when cut due to enzymatic actions as an antioxidant * to prevent: dip in citrus juice, add sugar before freezing, heat to boiling * one dozen oranges will yield one quart of juice 2. cooked * softens cellulose, increases keeping quality, cooks starch * when sweetener is added to liquid of packing juice, the density of the syrup is expressed as a % by weight of sucrose * measured in degrees Brix by a Brix hydrometer * expressed on label as extra light, light, heavy, extra heavy syrup * coulis is a thin puree of fruit or vegetable, sugar and water used as a sauce * compote is a fruit cooked (stewed) in syrup * potatoes have phenolic compounds which cause color changes in raw, peeled or bruised potatoes - enzymatic browning * green color under skin - due to chlorophyll that develops when potato is exposed to light during storage. May be accompanied by solanine, a natural toxicant. * starch changes to sugar during storage (changes in taste, color and texture). Old potatoes taste sweeter, cook to a darker brown (Maillard reaction), and are softer in texture. 3. cooking methods * boil - small amount of salted water for a short time, covered pan unless otherwise indicated * acidic vegetables that need more time to cook: use more water, no lid * steam - perforated container, covered, over boiling water * pressure cooking - retains color, flavor; cut small * stir-fry - use tender vegetables, high in moisture; don't drain * frozen - shorter cooking time than fresh because blanching and freezing have made them tender. Blanching is immersion in boiling water for a short time. * preparation suggestions: * Cook cauliflower for a short time, covered. * Broccoli in microwave: less time, same flavor, slightly better retention of color, better retention of vitamin C, no large difference in eating quality. * Cabbage: to minimize the development of a strong flavor: cook for a short time, keep lid off initially to let acids escape, cook in large amount of water. * canned * #10: 6 lbs. 9 oz./ 13 cups * 20-25 servings * #3: 46 ounces/ 5 1/2 cups * 12-15 servings * #2 1/2: 1 lb. 13 oz./ 3 1/2 cups * 6-8 servings * #2: 1 lb. 4 oz./ 2 1/2 cups * 4-6 servings * #300: 14-16 oz./ 1 1/2 cups * 3-4 servings * Flavor * vegetables * sugars in peas and corn * glutamic acid found in young vegetables - used in form of salt (MSG) * sulfur - onion, cabbage * when cut, enzymes and sulfur are mixed * flavor of fruit due to acids, sugar, aromatic compounds * tannins cause astringent feeling in mouth (underripe banana) * Grades * USDA-Fruits and Vegetables * based on quality, firmness, color, maturity, freedom from defects, uniform size and shape * canned fruits and vegetables * Grade A - desserts, salads (Fancy) * Grade B – processed (Choice) * Grade C - puddings, pies (Standard) * fresh produce: Fancy, Extra #1, #1, Combination, #2 * Meat, poultry, fish, meat alternatives * Structure and composition * muscle composed of bundles of fibers - myofibrils * sheet of connective tissue holds fibers in bundles * collagen - structural part of tendon that surrounds muscle * in heat - hydrolyzed to gelatin; becomes tender * elastin - resistant to heat - little change in cooking * found in ligaments, cartilage; yellow color * fat - deposited around organs, muscles, in muscles (marbling) * finish - amount of fat cover on carcass * shape of bone identifies cut (round bone - leg; T-bone - back and ribs) * Nutritive value * 16-23% protein * carbohydrate - glycogen in liver, glucose in blood * vitamins, minerals - thiamin, niacin, riboflavin, iron, copper, trace minerals * pork - good source of thiamin * calcium content is high in fish canned with bones, oysters, shrimp * Pigments * main contributor to meat color - myoglobin * myoglobin + oxygen -> red -> brown -> green * green colors are due to further myoglobin breakdown * Post-mortem changes and aging * hold in cold storage to age and ripen - about 10 days * aging increases tenderness * change in muscle protein brought about by enzymes which increase the water-holding capacity of the muscle * acid (vinegar) and salt also increase tenderness by increasing water-holding capacity of muscle * physical activity of animal will NOT increase tenderness * vacuum-packing meat in an oxygen-impermeable film, stored unfrozen at 0°C is anaerobic (sous vide) - extends storage life of meat * MAP modified atmosphere packaging; prolongs shelf life * air (oxygen) is removed and replaced with gases (carbon dioxide, nitrogen) * prevents deterioration by slowing respiration * Inspection (mandatory) and grading: USDA, done at slaughter * Wholesome Meat Act of 1967 assures consumer that the animal was healthy at the time of slaughter and the meat is fit for human consumption (assures wholesomeness) * shown with round purple stamp "USDA Inspected and Passed" * grading indicates quality * grade appears on a shield * states federally graded by Agricultural Marketing Service of the USDA * grades: prime, choice, select, standard (determined at slaughter) * grading based on maturity of animal, marbling of fat, color and texture of lean * standard grades have the least marbling; prime the most * meat specifications - uses a numbering system for order wholesale cuts * IMPS - Institutional Meat Purchasing Specifications * NAMP - National Association of Meat Purveyors * Cookery principles * temperature - 325'F for roasting * high temperatures increase shrinkage, toughen * a slow-cooked roast yields less waste * insert meat thermometer BEFORE cooking * Safe minimum internal temperatures * 145' F pork, beef, veal, lamb, steaks, roast, fish * 160' F ground beef, ground veal, ground lamb * 165' F turkey, chicken, duck * physical and chemical changes * protein coagulates * collagen is hydrolyzed to gelatin and softens * tough cuts need to be cooked well done because they have more collagen which needs more time to be softened * surface browns due to breakdown of pigments * heat changes interior from red to pink to brown to gray * heat denatures globin; iron is oxidized * cured meats are pink from nitrites (inhibit botulism) * heat meat to 160 before dehydration (beef jerky); heat poultry to 165 * tempering meat allows it to cook more evenly * Methods of cooking determined by cut of meat * dry heat - no water involved, for tender cuts near backbone (loin, sirloin) * frying * desirable property of fat used in frying is a high smoke point >400'F * temperature to which fat can be heated before puffs of smoke occur * decreasing order: safflower 513; soybean, canola, corn, palm, peanut, sunflower, sesame, olive 375; lard 375, shortening 365-370, butter 350 * monoglycerides (shortening) have lower smoke points * do not fry tough cuts of meat (bottom round) * rancidity involves the uptake of oxygen in an unsaturated fatty acid * healthiest plant oils are all highly unsaturated (olive oil has more MUS; less susceptible to rancidity than soybean oil which has more PUS) * broiling - form of radiated heat * roasting * when meat is removed from oven, "carry-over cooking" occurs for about 10 minutes; internal meat temperature will rise 15-25' F * allow roast to stand 30 minutes before carving * grilling * moist heat – water involved, less tender cuts with more connective tissue (bottom round, chuck, brisket) * cook bottom round in water for several hours * braising - flour meat, brown, cover and simmer in liquid; in oven or range-top * simmer - heat in water to 170-185'F with appearance of bubbles * steam - heat over, not in, water * stewing - add water or other liquid during cooking * proteolytic enzyme (papain) tenderizes meat (blend of papaya and salt) * Meat alternatives: legumes, nuts, seeds * soybeans * methionine is the limiting amino acid * protein concentrates - ≥70% protein; protein isolates ≥ 90% protein * used in textured protein products (TVP) * mixed with ground meats - extends number of servings, lowering costs * soy protein adds juiciness because of water content * edamame (soybean pod), tofu (coagulated soy protein), miso (paste of soy and grains), tempeh (aged soybean and grain), natto (fermented soybeans) * Fish cookery * use dry or moist heat. more perishable than meat so store at lower temperatures * fresh fish with head attached should have bright red gills and bright, shiny skin. If gills are dull and gray... reject it. * surimi - purified and frozen minced fish with a preservative, used in analogs, may have egg white or starch added to create desired structure * histamine toxicity: linked to inadequate refrigeration of tuna, mackerel, mahimahi * Eggs * Structure and composition * porous shell - exchanges moisture and gases; covered with bloom that prevents excessive loss and protects contents * color of shell is unrelated to food value or quality * inner membrane contracts leaving air space in large end * air space becomes larger with age * indicator of good quality is a high proportion of thick white * yolk is surrounded by vitelline membrane, chalazae are yolk anchors * egg yolk is a naturally occurring oil in water emulsion * Nutritive value * 80 calories, 6 grams protein, 5 grams fat, vitamins A, D, riboflavin * yolk is more concentrated than white: has more protein (by weight), fat, minerals, vitamins * % composition of protein: egg white 11%, egg yolk 17.5% * fat is present in an emulsified form * color of yolk depends on amount and type of pigment in hen's diet * Quality * grades AA, А, В * candling - pass an egg in front of bright light to view contents * judge thickness of white, location and condition of yolk * grading does NOT include the color of the shell, nor the size of the egg * size: not a part of grading, classified on basis of weight per dozen * freshness * raw eggs can be stored in refrigerator at 40-45'F for 3-5 weeks * Grade A eggs can be maintained for 6 months in cold storage (29-32'F) * a fresh egg will sink to the bottom in a pan of cold water and has a dull, rough shell * Preparation and processing Eggs * coagulation * protein coagulates at 62-70'C (sets a custard) * used to bind, gives firmness, stability, coats food, browns, clarifies liquids * syneresis (weeping)- liquid released from a coagulated product * occurs when cooked at too high a temperature, or too low a temperature for too long a time; creates a tough, watery product * leavening - depends on amount of air beaten in and retained * when an egg foam is heated, air expands, egg white stretches and protein coagulates * an acid stiffens an egg white foam by tenderizing the protein and allowing it to extend more easily - Cream of tartar * egg white foams are compared by measuring specific gravity * measures the relative density of a substance in relation to that of water * weight of given volume divided by weight of same volume of water * egg whites at room temperature whip more quickly and yield a larger volume due to LOWER surface tension * sugar also stabilizes an egg white foam * emulsification * protein in egg forms a thin film around droplets of oil; stabilizes emulsion * egg yolk yields a stiffer, more stable emulsion than egg white because it has more protein (by weight) * yolk is naturally occurring oil in water emulsion * lecithin helps yolk act as an emulsifier * lipoproteins stabilize the emulsion by interacting at the surface of the oil droplets to form a layer * mayonnaise - food emulsion stabilized by egg yolk * methods of cooking * water preparation * when poaching or coddling, use a high quality egg - appearance is important * vinegar and salt improve shape by hastening coagulation * surfaces of yolks turn green when overcooked or allowed to cool slowly * due to combination of iron from the yolk and sulfur from the whole egg which creates ferrous sulfide * dried heat * overcooking toughens * undercooking results in excessive shrinkage when removed from oven * custards * the larger the % sag, the more tender the gel (objective measure of quality) * custards made from dehydrated eggs, may be grayer and less yellow, have an eggy flavor, and be watery * processing * frozen * remove from shell first; can be frozen whole or in parts * 10% salt or sugar (by weight of the yolks) are added as stabilizers * dried * can be vacuum-packed in nitrogen gas * dried fortified: 70% white, 30% yolk * baker's special eggs: sucrose added to improve foaming ability * egg substitutes * lower in fat, calories, cholesterol; often higher in sodium than fresh eggs * when cooking with egg substitutes, there will be color (added carotenoid) and flavor differences * storage * when eggs are held in refrigerator too long * deterioration affects appearance and use * loss of carbon dioxide makes eggs more alkaline * whites become watery, yolks flatten * odors are absorbed * Milk and milk products * Composition and nutritive value * 87% water, 3.7% fat, 4.9% carbohydrate (lactose) * 3.5% protein (complete, HBV) * 80% casein (precipitated at a pH of 4.6, forms soft curd) * whey is liquid that drains from curd of clotted milk * lactose, lactalbumin, lactoglobulin, water soluble vitamins, minerals * good source of calcium, phosphorus, riboflavin, vitamins A, D; low in iron and vitamin C * Processing * pasteurization - destroys pathogenic bacteria * 145'F for 30 minutes or 160'F for 15 seconds * UHT (ultra-high temperature) aseptically packaged milk can be stored without refrigeration if unopened * Types * homogenized * high pressure breaks fat globules to 1/5 regular size; film of protein surrounds each globule. More susceptible to action of lipase, but pasteurization process destroys lipase * vitamin D milk * 400 USP units added per quart of milk by feeding the cow vitamin D, irradiating the milk, or adding the vitamin. Must be labeled "vitamin D milk" * 2% milk has 1.5 - 2.25% fat * low fat milk has.5-2% fat * skim milk has < .5% fat * concentrated milks * evaporated milk - 60% water removed * must contain not less than 7.9% milk-fat * brown color due to caramelization of lactose in canning * sweetened condensed milk * concentrate (evaporate) whole milk * add 15-18% sucrose or glucose * dried whole milk: 26% fat; does not keep well * dried skim milk: not more than 1.5% fat; keeps well * condense skim milk; dry by spraying into a heated vacuum chamber * fermented milks * cultured buttermilk * add lactic acid bacteria to skimmed or partly skimmed milk * recipe: 1T vinegar or lemon juice, or 1 3/4 tsp cream of tartar; add enough milk to make 1 cup * when using buttermilk in place of regular milk in a recipe, increase the baking soda * sweet acidophilus milk * skim milk plus Lactobacillus acidophilus bacteria which reduces lactose * kefir - fermented by Lactobacillus kefir which reduces lactose * low lactose milk - Lactaid * treated with lactase in processing or add the enzyme to regular milk and hold in the refrigerator * yogurt * coagulated product; fermentation of milk sugars by lactic acid bacteria * filled milk * skim milk, vegetable fat (coconut oil), water; illegal in some states * imitation milk * resembles milk but contains neither milk fat nor other important dairy ingredients * made from casein derivatives or soybean protein and vegetable oils * Use of milk in food preparation * when milk is heated, whey protein precipitates out on bottom of pan or on surface of milk * to prevent a film from forming, cover or beat the milk to produce a foam * to prevent milk from coating on sides of pan, heat over water * to prevent curdling, add an acid slowly and agitate * an acid precipitates casein * Butter, cream * butter - 80% milk fat; margarine - 80% vegetable oil or animal fat * at room temperature, hydrolytic rancidity (uptake of water) leads to flavor changes in butter (saturated fat) * unsaturated oils are more subject to oxidative rancidity (soybean oil) (uptake of oxygen at a double bond in an unsaturated fat) * cream * heavy or thick: > 36% fat * medium: 30-36% fat * whipped cream: 35% fat * light or thin: 18-30% fat * sour cream: > 18% fat * half and half: no less than 10.5% fat * Cheese * production: warm milk, add lactic-acid bacteria, add enzyme rennet to coagulate casein forming the curd, separate curd from whey (liquid) * types * uncured - refrigerate immediately (cottage cheese, crearn cheese) * cured - additional whey removed, salt added, ripened * % moisture content high to low: cottage (79), cream, mozzarella (45-55), camembert, bleu, Swiss, cheddar, gorgonzola, parmesan (31) * processed - blend of several natural cheeses (American cheese) * emulsifier added (disodium phosphate): processed cheese better for cooking (fat will not separate out), high moisture content 41-50% * to prevent stringy, curdled-looking cheese products, cook for a short time at moderate temperatures * Flour, grains and cereals * Structure and nutritional value * starchy endosperm rich in protein, outer layer of hull and bran * scutellum - in germ; has most of the thiamin * 75% starch; partially complete protein; 2% fat - found in germ * vitamin E (in germ), thiamin, riboflavin, phosphorus * Preparation and processing * milling - air classification is a separation method that improves baking qualities by separating large flour particles from fine particles * processing of hot, ready to cook cereals * farina - inner portion of wheat kernel * quick-cooking cereals have disodium phosphate added * makes cereal alkaline so particles swell faster * avoid on low sodium diets * enzyme treated for quicker cooking means the proteins have been split to lessen cooking time * Wheat flours * graham, whole wheat - entire grain, use freshly ground, spoils quickly due to fat in germ * bread (hard wheat) - strong gluten; 11.8% protein * all-purpose (blend of hard and soft wheat) - less gluten; 10.5% protein * pastry (soft wheat) - weaker gluten; 7.9% protein * cake (soft wheat) - least and weakest gluten, more starch; 7.5% protein * enriched with thiamin, riboflavin, niacin, iron, folic acid * instant blending, agglomerated, instantized - no pre-sifting needed * self-rising: baking powder, flour, salt * Alimentary pastes * durum wheat - high in gluten * after bran and germ are removed, starch is ground to make semolina flour * products are flexible after cooking * noodles - contain egg yolk or egg solids * Rice cookery * vitamins are lost when cooked in excess water or when water is drained off * cook in an amount of water that will be absorbed during cooking * for 1 cup rice - use 2 cups water * Baked flour mixtures * functional properties of ingredients * flour * gluten - gives elastic properties, forms framework, holds in leavening agent; made from gliadin and glutenin through process of hydration and mixing * color due to carotenoids * natural agents cause oxidation during storage and turn flour from creamy yellow to white * if an oxidizing agent is added - labeled "Bleached" * strength of flour refers to capacity to retain leavening * depends on quality of gluten * bread flour is strong, cake flour is weak * adding bran decreases volume of end product * increase flour and liquid to compensate * liquids * hydrates gluten and starts its development * starts action of chemical leavening agent * dissolve salt, sugar; gelatinizes starch * leavening agent * steam expands the hollow shell formed by flour and egg * hot oven is required to raise liquid to boiling quickly * popovers, creampuffs * air expands when heated before proteins coagulate and retain it * to incorporate air: beat, sift, fold, cream * angel cake, sponge cake * carbon dioxide * from action of yeast on sugar, yielding carbon dioxide and alcohol * from action of acid on baking soda (sodium bicarbonate) * acids used: sour milk, cream of tartar, molasses * baking powder: provides both the acid and the alkali needed for reaction * mixture of baking soda (NaHCO3 provides carbon dioxide), a dry acid (sodium aluminum sulfate reacts with soda to release carbon dioxide), and cornstarch (keeps contents dry); types: tartrate, SAS-phosphate * use 1 1/2 tsp baking powder per cup flour * old baking powder is more alkaline causing loss of thiamin in baked goods * deeper brown crust: alkaline solution (baking soda) and solid sugar * salt - adds flavor, keeps yeast from sticking * egg - provides stability, retains leavening agent, distributes shortening by emulsification, introduces air, adds color and flavor * fat - adds tenderness by coating gluten particles * sugar * hygroscopic - modifies texture by tenderizing * softens gluten and prevents gluten development by absorbing some of the water that gluten needs * too much sugar results in coarse cells, thick walls, a shiny crust and a crumbly product * most of sugar in honey is glucose and fructose * when substituting Sweet and Low for sugar in a recipe, use half as much * Methods of mixing * use bowl with sloping sides and 1/2 full * beat - over and over to smooth and incorporate air * cream - work one or more foods until soft and creamy (cream fat into sugar) * cut-in - distributes fat into dry ingredients * fold - use in foams; a down, across, up and across the top motion; rotate bowl * knead - used in dough; push, pull, turn * stir - circular or figure eight motion to blend * whip - beat rapidly to incorporate air to form a foam * Quick breads (leavened with steam, air, chemical leavening agents) * examples: muffins, biscuits, popovers * basic ingredients: egg and flour * muffin method of mixing * sift dry ingredients; make well in center (2) blend liquids and add all at once to dry ingredients (3) mix just enough to dampen * excess mixing * loss of carbon dioxide, overdeveloped gluten * tunnels from top to bottom, tough, heavy product * characteristics of a good muffin * round, pebbled top, symmetrical shape, no long, narrow tunnels * Cakes * method of mixing * cream fat with sugar, add egg, add sifted dry ingredients in portions, alternating with portions of milk * types * shortened cake (layer, pound cakes) * comparatively large amount of fat; uses chemical leavening * layer cake: baking powder & Source of CO₂ * pound cake: air and steam * rich cake: increased fat, sugar, egg; increases keeping quality * gold cake: egg yolks; white cake - egg whites; yellow cake - whole egg * foam cake - uses air as leavening * angel cake: egg white foam * sponge cake: yolk foam and white foam * chiffon cake: liquid yolks, egg white foam, baking powder, oil * crumb structure depends on: ingredients, procedure used, pan shape and size, baking temperature, time elapsed before baking * alterations in the amount of sugar * The more sugar, the more time is needed to reach the elevated coagulation temperature of the gluten. As sugar increases, the volume of cake increases up to the point where the volume is so great, and the gluten so weak, that the gluten strands snap and the cake falls in the center (gummy, crystalline appearance). * causes of variations in cakes * yellowing: alkaline batter (excess soda) * fallen center: excess sugar, excess fat, excess baking powder, * tough, dry crumb: too much flour or egg, too much mixing, too little fat or sugar, over-baking * coarse texture: too much baking powder or sugar, oven temp too low * poor volume: too little baking powder, improper level of sugar or fat * Cookies * modified shortened cake; higher in fat, lower in sugar and liquid * Pastry * flour, fat, liquid, salt * lard and oil are each 100% fat; butter and margarine only 80% fat (when substituting butter for lard, need to use more) * mixing method: cut fat into flour and salt, add liquid * avoid over-handling; bake at 425-450'F for 10-15 minutes * Tenderness in pie crust is enhanced by using oil, soft fats, or fat cut into very small pieces. * Flakiness is promoted by leaving fat in coarse particles. Fat in pieces melts and flows, leaving a hole where steam collects and pushes upward against the upper surface of the resulting cell. The cell is locked into that extended position, resulting in a flaky crust. * spread meringue of a lemon pie on warm to hot filling, bake at 425'F 4-5 min * Classification of batters and dough according to proportion of flour to liquid * parts * liquid: 1 * flour: 1 * example: * waffles * parts * liquid: 1 * flour: 2 * example: * muffins * parts * liquid: 1 * flour: 3 * example: * bread * parts * liquid: 1 * flour: 4 * example: * pie crust * A high fat, high sugar batter absorbs most fat when deep fried. * All-purpose and bread flours absorb less fat during frying than does cake flour. * Yeast dough – use high protein bread flour (low protein flour causes crumbly products with poor texture) * yeast ferments sugar and releases carbon dioxide * methods of preparing dough * straight dough method * all ingredients are added before dough is allowed to rise * sponge method * combine liquid with yeast and part of flour and allow this sponge To ferment for several hours; add other ingredients and knead * proofing time (final raising of the dough) is shortened: use strong flour, high in protein (bread flour) * continuous bread-making method: reduces processing time * not as affected by fermentation time and temperature * commercial process that substitutes intense mechanical energy to a large degree for traditional bulk fermentation * Baking at high altitudes * decreased pressure causes gas to expand faster, steam forms earlier * expansion may be excessive before heat of oven has coagulated the protein and gelatinized the starch enough to stabilize the structure * to correct: decrease amount of baking powder, increase amount of liquid * longer cooking time is required because the temperature of boiling water is lower at very high elevations (drops1 degree F for every 500 foot rise) * Starch * Characteristics and structure * composed of amylose and amylopectin molecules * amylose is responsible for gelation in cooled, cooked pastes * waxy starches (corn, rice, sorghum) have only amylopectin (branched fraction: 1,4 and 1,6 a glucosidic linkages) * non-gelling; stable to freezing and thawing, used in frozen foods * corn starch is used most often * thickening ability of starches – in order of effectiveness * potato, waxy corn, waxy rice, waxy sorghum, tapioca, wheat * wheat flour is even less effective than pure wheat starch because of the protein content * waxy starches are more effective thickening agents in starch pastes than their standard counterparts * pastry and cake flour have more starch and less gluten so thicken better * Processing and modification * gelatinization is the swelling that occurs when starch is heated in water close to the boiling point. Heat dissociates bonds, water moves in and swells granules. Friction is created causing paste to thicken. * role of sugar * competes with starch for the water needed for gelatinization * increases translucency, reduces viscosity and gel strength * if too much sugar is used, consistency is thin * water needed to dissolve excess sugar is not available for the gelatinization of starch * add an acid when cooking is complete because acid breaks down starch and will produce a runny product * example: if lemon juice is added to lemon meringue pie before cooking is complete, filling will be runny * retrogradation * occurs in starches with a high proportion of amylose * After a starch paste has been cooled or chilled, it may become less soluble and recrystallizes to form a solid or rigid gel. It reverts (retrogrades) back to the insoluble form on freezing or ageing. This recrystallization is retrogradation. The hydrogen bonds that hold the gel together break and reform in an orderly crystalline fashion (giving a gritty texture). * undesirable – reduces the quality of food * examples - staling of starch products, such as bakery goods; separation when a gravy thaws; old pudding; stale bread * gently heating the food will break the bonds holding the amylose together * greatly accelerated by freezing * when a starch gel is thawed, water is lost because it is unable to rebind to the fragile spongy mass * prepare frozen products with a starch or flour from a waxy cereal - waxy corn, sorghum, rice * modified starch * chemical modification by acids and enzymes to change viscosity, and ability to gel * physical modification: pre-gelatinized starch used in instant puddings * used to stabilize frozen gravies: waxy maize, modified cornstarch * Uses in food preparation * dry heat * When making gravy, starch is heated without water. Temperature rises rapidly degrading the starch. Starch molecules break into fragments called dextrins (dextrinization). * color change occurs (browning of toast). * moist heat * starch granules do not dissolve in cold water, but form a suspension * when heated, molecules swell, thicken, become translucent due to gelatinization * When starch is not mixed well enough with the cold liquid or is added directly to hot liquid, lumps form which decreases thickening. Granules on the outside swell as they take up water. Those on the inside remain dry, decreasing thickening. * to prevent lumps, mix starch with fat, cold liquid or sugar * heat, acid and agitation will affect the stability of swollen starch granules in a paste * white sauce * melt fat, add flour (roux - half fat, half flour) * remove from heat, add liquid at 170-180'F; add salt * add an acid when cooking is complete * to get a clear, shiny, translucent sauce, use cornstarch as thickener * if product is starchy tasting and grainy - due to uncooked flour * souffle is an example of a thick white sauce * Crystallization in food preparation * Preparation of crystalline candies * Heat sugar and liquid to dissolve. Heat further. Crystallize under conditions that produce small crystals which have a smooth, creamy feeling. * Control of crystal size * crystal inhibitors (keep crystals small and smooth) * acid - cream of tartar, vinegar * sugar and