Carbohydrates, Lipids, and Proteins in Food: Functions, Types, and Properties, Study notes of Food science

Download Carbohydrates, Lipids, and Proteins in Food: Functions, Types, and Properties and more Study notes Food science in PDF only on Docsity! Lecture 6 – Main topics FOOD SAFETY (cont.) Intoxications - Bacterial intoxications. Examples Botulism is a rare, but deadly disease. Caused by toxin produced by Clostridium botulinum bacteria. It is a neurotoxin (if untreated, can cause paralysis and respiratory failure), which can be destroyed by high temperatures. SEAFOOD POISONING Paralytic shellfish poisoning: caused by of saxitoxins produced by dinoflagellates. These can grow to large numbers leading to "red tides." Shellfish that have caused this disease include mussels, clams, scallops among others. In cases of severe poisoning, muscle paralysis and respiratory failure occur, may result in death. Saxitoxins are heat stable. Pufferfish Poisoning (Fugu Poisoning): Toxicity is due to Tetrodotoxin; there is no antidote available. Treatment is supportive, to maintain respiration. OTHERS Mushroom Poisoning. The mushroom Death cap produces amatoxins, the most hazardous of the mushroom toxins. A single mushroom can kill an adult. Protection of Food Supply FDA : All foods, except meat and poultry USDA: Meat and Poultry products ____________________ Smell, Taste & Flavor Olfactory receptors in the nasal passages can detect volatiles. Basic Tastes: Sweetness, Saltiness, Bitterness, Sourness, Umami Astringency Pungency (see McGee p. 270-272) ____________________ Food as energy source Energy-yielding nutrients Carbohydrates: 4 Calories/g Lipids: 9 Calories /g Proteins: 4 Calories/g Lecture 7 – Main topics CARBOHYDRATES Simple Sugars Monosaccharides, ex.: Glucose, Fructose, Galactose Disaccharides, ex.: Sucrose, Lactose, Maltose Glucose (also called dextrose), Fructose (also called levulose) SUCROSE = glucose + fructose LACTOSE = glucose + galactose MALTOSE = glucose + glucose Glycosidic bond: Linkage between 2 monosaccharide units Sweetness - Simple sugars differ in sweetness (taste intensity) - Sucrose is used as the reference sugar - RELATIVE SWEETNESS is a measure of how sweet a specific substance is in relation to sucrose. Sucrose 100 Lactose 20; Glucose 70; Fructose 120 Common Sweeteners Natural Sweeteners - Sugar (table sugar) - Honey - Maple Syrup - Corn Syrup - High Fructose Corn Syrup Sugar (table sugar); refined sugar > 99.9% Sucrose Disaccharide: Glucose-Fructose Only taste is sweetness Commercial sources: - sugarcane - sugar beets Molasses from sugar cane: Contain substances other than simple sugars. Various grades & darkness of color, such as “blackstrap molasses”. Brown sugar: Most is produced by the addition of molasses to refined white sugar - Has a more complex flavor than white sugar - It is hygroscopic (holds moisture and makes things stay moist) Sucrose Hydrolysis by invertase: Sucrose →Glucose + Fructose Honey main sugars: glucose and fructose Maple syrup: 2/3 sugars and 1/3 water; main sugar is sucrose Alternative Sweeteners - Sugar alcohols: are reduced-calorie sweeteners. Nutritive Sweeteners - High Intensity Sweeteners, also called Nonnutritive, Artificial, or Synthetic Sweeteners Sugar alcohols, ex.: sorbitol, mannitol, xylitol, etc. Commercially prepared by hydrogenation of simple sugars. Xylitol is as sweet as sucrose; it is non-cariogenic. High Intensity Sweeteners: Taste sweet, but without the added calories. Approved by the FDA: saccharin, aspartame, acesulfame K, sucralose and neotame. Lecture 10 – Main topics Lipids (cont.) Oil Refining: removes undesired compounds. Refined oil has higher smoke point than the correspondent unrefined source. Trans Fat 0g on the label: food contains less than 0.5 g of trans fats per serving. Mayonnaise: an emulsion (a dispersion made with 2 immiscible liquids), (see McGee p.626). Emulsifiers stabilize emulsions, prevent droplets from aggregating. Lecithin is a common emulsifier; egg yolks contain lecithin (see McGee p.802). PROTEINS Polymers formed by different building blocks: amino acids. Each protein has its own sequence of amino acids. Proteins vary in size, shape. Proteins have many different biological functions. Some Protein Functions (in the body): Structural (bone, skin, hair, nails); Motor/Mechanical (muscles); Enzymes; Antibodies; Hormones (ex.: insulin); Transport (ex.: hemoglobin); Others; Energy. Amino Acids: protein building blocks. There are 20 amino acids commonly found in proteins. Some are called essential amino acids; these must be obtained from foods. They cannot be made by the body, or are made in insufficient amount to meet our needs. One of the nonessential amino acids is glutamic acid. Its sodium salt is monosodium glutamate, or MSG. (see McGee p.806). Peptide bonds: join amino acids. Dipeptide (2 amino acids); Tripeptide (3 amino acids); Oligopeptide (a few amino acids); Polypeptide (many amino acids). Polypeptide chains are linear. (see McGee p.806). Protein Structure: 4 levels of organization: primary, secondary, tertiary and quaternary structures. Primary structure is the linear sequence of amino acids that forms the polypeptide chain. It determines the folding of the protein, and its final shape. Even a single amino acid makes a difference (ex.: sickle cell disease is an example of an inherited variation in the amino acid sequence). Two major classes of proteins: Globular: are soluble in water; most enzymes are globular proteins. Fibrous: insoluble in water; they have structural roles (ex.: collagen). Collagen: consists of 3 polypeptide chains that form a strong structure (see McGee p.598). Foods and Protein Cooking. Effect of heat and protein denaturation: loss of 3-dimensional structure of a protein (see McGee p.808). Lecture 11 – Main topics Egg white and foams (see McGee p.101-2, including figure). Enzymes are catalysts (compounds that make reactions occur faster). Enzymes are specific for various substrates. They convert a substrate to a product, example invertase splits sucrose in fructose + glucose. Protein Hydrolysis (in the body). Food proteins are denatured (during cooking and by acids in the stomach), then hydrolyzed in the stomach and small intestine. Enzymes that hydrolyze proteins are called proteases or proteolytic enzymes. The released amino acids are then absorbed, and pass to the bloodstream. Absorbed amino acids can be incorporated in the proteins needed by the body. Proteases are not involved only in digestion of foods, they have also application in foods (ex.: in meat tenderizers). Protein Quality. It depends on protein digestibility and amino acid composition. Not all proteins are well digested and used by the body. Proteins differ greatly in proportions of essential and nonessential amino acids. Animal Proteins are high quality proteins, or complete proteins. They provide enough of all essential amino acids. Exception: gelatin. Plant Proteins have lower quality (Incomplete) than animal proteins. Exception: soybeans. In general, plant proteins lack one or more essential amino acids. Legumes are low in methionine; cereal grains are low in lysine; nuts and seeds are low in lysine. Limiting amino acid is the essential amino acid that is present in the lowest amount, and limits the body’s ability to make proteins. Complementary Proteins: proteins from 2 or more sources that can complement each other. Example: rice (grain) and beans (legume); corn (grain) and beans (legume). COLLAGEN and gelatin. (see McGee p.598, including figure). Tenderness/Toughness of meats depend on: - age of the animal; - type of muscle (exercise/work it does, and amount of connective tissue); - muscle fat/“marbling” (see McGee p.129-130). Tough cuts of meat become tender when slowly cooked, such as in a “pot roast”, “stew meat” (see McGee p.150: “Falling- apart….”). Maillard reactions – Browning. Maillard reactions: require - amino groups (amino acids or proteins), -sugar; - high temperatures. (see McGee p.778). In contrast, caramelization involves only sugar. Wheat and leavened breads. Wheat proteins Glutenins and Gliadins are fundamental in breadmaking. They form gluten, which gives elasticity and softness to the dough. Gluten is a very elastic mass; it also traps and holds air bubbles during mixing/kneading. Baker’s yeast: Saccharomyces cereviseae ferments sugar. Glucose → alcohol + carbon dioxide (CO2). CO2 is trapped in the dough. (see McGee p.531). Adverse reactions to Food: allergies and intolerances. Food Allergy: Abnormal immune response to a food; generally, an immediate reaction. It occurs each time the food is eaten (even in small amounts). Food Intolerance: nonimmune reaction to a food. Example: Lactose Intolerance. There 8 common allergenic foods: 1-milk, 2-eggs, 3-fish, 4-shellfish. 5- tree nuts, 6-peanuts, 7-wheat, 8- soybeans. These common allergens should be listed on food labels (Food Allergen Labeling -2004) by their common name or the food source may be listed, ex.: lecithin (soy); flour (wheat).