Transcript Enzymes
Enzymes Overview Enzymes -- proteins that catalyze a specific chemical reaction. Each enzyme is specific to a specific chemical reaction. The substance on which an enzyme acts is known as a substrate. The structure of the enzyme does not change as a result of the reaction. B-3.03 -- Enzymes 2 Key Functions of Enzymes Ripen fruits and vegetables. Spoil fruits and vegetables after harvest. Change flavor, color, texture, and nutritive value of food. Decrease shelf-life if not inactivated. Extract and purify commercially to: Break down starch Tenderize meat Clarify wines Coagulate milk B-3.03 -- Enzymes Naturally-Occurring Enzymes Trigger enzymatic browning Found in large amounts in: pineapple papaya figs Meat tenderizers made from compounds in fruit Bromelain -- Pineapple Papain -- Papaya Ficin -- Fig B-3.03 -- Enzymes 4 Enzymatic Reaction B-3.03 -- Enzymes 5 Factors that Affect Enzyme Activity Two factors will affect enzyme activity: water availability amount of substrate Enzymatic reactions generally occur in the presence of water. B-3.03 -- Enzymes 6 Water Availability Water acts as a reactant and solvent in enzymatic reactions. Less water available the slower the enzymatic reaction. Reactions occur more slowly in dried foods (dried milk) than in moist foods (fluid milk). B-3.03 -- Enzymes 7 Amount of substrate Substrate is molecule upon which enzyme acts. Substrate binds with the enzyme's active site and enzyme-substrate complex formed. More substrate in a solution, the greater the rate of the reaction Enzymes have more product with which to react. B-3.03 -- Enzymes 8 Denaturation of Enzymes Factors that Denature Enzymes Enzymes are proteins. Denaturation: changes the structure of the protein stops enzyme activity Enzymes denatured by: heat pH salts enzyme inhibitors B-3.03 -- Denaturation of Enzymes 10 Heat Enzymatic reaction rates increase as temperature increases. Denaturation occurs at 104°F or hotter. Too much heat slows and stops enzyme activity. Heating can destroy enzymes that alter food quality. Example -- blanching vegetables to prevent spoilage during frozen storage. B-3.03 -- Denaturation of Enzymes 11 pH pH and rate of enzymatic reaction pH and denaturation of enzymes Specific to each enzyme Optimal pH range. Most enzymes will denature if pH is too high or too low. Changing the pH can speed up, slow, or stop enzymatic reactions Lemon juice to apples B-3.03 -- Denaturation of Enzymes 12 Salts Salt is commonly used in food production Binds to enzymes in food that cause spoilage Changes the water activity B-3.03 -- Denaturation of Enzymes 13 Enzyme Inhibitors Substance that will prevent the enzymesubstrate complex Naturally occurring Enzymatic reactions slowed or stopped. Egg whites Pesticides that are naturally part of a plant structure Synthetic compounds B-3.03 -- Denaturation of Enzymes 14 Enzyme Activity Effects on Food Positive effects: Make food easier to eat – meat tenderizer Preserve food – change milk into cheese Improve flavor, quality, or appearance – add lactase to produce lactose-free dairy products. Negative effects: Enzymatic browning Spoilage B-3.03 -- Enzyme Activity in Food 18 Make Food Easier to Eat Meat tenderizers, enzymes that can be added: during aging prior to cooking Enzymes break down tough protein fibers for a more tender product. B-3.03 -- Enzyme Activity in Food 19 Preserve Food Converting milk into cheese increases shelf-life of milk. Rennin (an enzyme) is added to coagulate milk proteins. Some enzymes are also released by bacterial cultures to create unique flavors, textures, and colors. B-3.03 -- Enzyme Activity in Food 20 Improve flavor, quality, or appearance Amylases – baked goods Invertase – artificial honey and candy Lactase – lactose- free milk Pectic enzymes – fruit juices Protease – baked goods, meat Rennin -- cheese B-3.03 -- Enzyme Activity in Food 21 Enzymatic Browning Reaction of oxygen and the enzyme (phenolase) Results in desirable and undesirable color and structure changes Desirable changes – browning of raisins, figs, dates Undesirable changes -- fruit becomes discolored, mushy, bruised B-3.03 -- Enzyme Activity in Food 22 Preventing Enzymatic Browning Prevent oxygen from combining with the enzyme phenolase Cold storage slows enzyme activity. Add preservatives, such as: sulfites, ascorbic acid, citric acid, and/or acetic acid B-3.03 -- Enzyme Activity in Food 23 Spoilage Prolonged enzyme activity can cause food to spoil. Overripening of fruit Food processors control enzymatic activity by: replacing oxygen to slow action of oxidases B-3.03 -- Enzyme Activity in Food 24 Phytochemicals Definition and Benefits Phytochemicals -- group of compounds naturally produced by plants Found in vegetables, fruits, grains, herbs, spices. Gives plant foods color and flavor. Helps plants resist pests and disease. Provides potential health benefits. B-3.03 -- Phytochemicals 26 Sources of Phytochemicals B-3.03 -- Phytochemicals 27 Seven Families of Phytochemicals Seven Families 1. 2. 3. 4. 5. 6. 7. Allyl sulfides Carotenoids – carotenes, xanthophylls Flavonoids – isoflavones Indoles – isothiocyanates Phenolic acids (or phenols) – polyphenols Saponins Terpenes B-3.03 -- Seven Families of Phytochemicals 30 Characteristics Scientists are examining their: structure, stability in food, and sources. Function Gives foods color and flavor. Helps plants resist pests and disease. Provides potential health benefits. B-3.03 -- Seven Families of Phytochemicals 1 -- Allyl Sulfides Contain sulfur Increase enzyme reactions Sources -- onions, garlic, leeks, chives Benefits in raw and cooked forms B-3.03 -- Seven Families of Phytochemicals 32 2 -- Carotenoids Over 600 known carotenoids Precursors to vitamin A Subgroups Carotenes Xanthophylls B-3.03 -- Seven Families of Phytochemicals 33 Carotenes Contain only carbon and hydrogen atom Not readily destroyed by heat Alpha-carotene – pumpkins and carrots Beta-carotene – dark green & yellow vegetables Lycopene – tomatoes, watermelon, guava, and red peppers B-3.03 -- Seven Families of Phytochemicals 34 Xanthophylls Yellow and orange in color Stability related to food source Lutein and zeaxanthin B-3.03 -- Seven Families of Phytochemicals 35 3 -- Flavonoids Most red and white in color Responsible for flavor Potential benefits Anti-flammatory/anti-carcinogen Sources Apples Broccoli Cranberries Onions Red grape juice, and Tea B-3.03 -- Seven Families of Phytochemicals 36 Isoflavones Subgroup of flavonoids Also called phytoestrogens or plant hormones Genistein and daidzein are best known. Sources: Soy Chickpeas Licorice Oriental vegetables -- Chinese cabbage and bok choy B-3.03 -- Seven Families of Phytochemicals 37 4 -- Indoles Found in cruciferous vegetables Stimulate enzymatic reactions Broccoli, cabbage, kale, and cauliflower Heating and thorough chewing speed these chemical reactions Isothiocyanates subgroup that forms aroma in Brussells sprouts, cabbage, turnips, mustard greens, watercress, and radishes B-3.03 -- Seven Families of Phytochemicals 38 5 -- Phenolic Acids Weak acids Sources: Carrots Citrus Nuts Raspberries Strawberries Tomatoes Whole grains B-3.03 -- Seven Families of Phytochemicals 39 Polyphenols Sources Green and black teas (green are higher) Red and purple grape products Rosemary Sunflower seeds, barley, and apples B-3.03 Seven Families of Phytochemicals 40 6 -- Saponins Product of a sugar and alcohol Sources: Spinach, potatoes, tomatoes, oats, beans, legumes, soybeans, sugar beets, peanuts, and asparagus B-3.03 -- Seven Families of Phytochemicals 41 7 -- Terpenes Flavor compound in citrus, cherries and many seasonings and herbs Taxol Best known Found in Pacific Yew tree Can be very toxic B-3.03 -- Seven Families of Phytochemicals 42 Best Sources of Phytochemicals Fruits Apples Berries -- blueberries, raspberries, blackberries, and strawberries Citrus peel Dark orange fruits -- mango, papaya, apricots, peaches, nectarines Red and purple grapes Vegetables Black and green tea Dark green and orange Herbs Legumes Nuts Onions and garlic Soy Tomatoes B-3.03 -- Seven Families of Phytochemicals 43