Enzymes

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Enzymes
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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.

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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

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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

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Enzymatic Reaction
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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.

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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).

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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.

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Denaturation of Enzymes
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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

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Heat

• Enzymatic reaction rates increase as temperature
  increases.
• Denaturation occurs at 104F 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.

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pH

• pH and rate of enzymatic reaction
• Specific to each enzyme
• pH and denaturation of enzymes
• 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

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Salts

• Salt is commonly used in food production
• Binds to enzymes in food that cause spoilage
• Changes the water activity

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Enzyme Inhibitors

• Substance that will prevent the enzyme-substrate
  complex
• Enzymatic reactions slowed or stopped.
• Naturally occurring
• Egg whites
• Pesticides that are naturally part of a plant
  structure
• Synthetic compounds

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Enzyme Activity
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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

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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.

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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.

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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

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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

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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

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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

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Phytochemicals
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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.

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Sources of Phytochemicals
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Seven Families of Phytochemicals
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Seven Families

• Allyl sulfides
• Carotenoids carotenes, xanthophylls
• Flavonoids isoflavones
• Indoles isothiocyanates
• Phenolic acids (or phenols) polyphenols
• Saponins
• Terpenes

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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.

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1 -- Allyl Sulfides

• Contain sulfur
• Increase enzyme reactions
• Sources -- onions, garlic, leeks, chives
• Benefits in raw and cooked forms

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2 -- Carotenoids

• Over 600 known carotenoids
• Precursors to vitamin A
• Subgroups
• Carotenes
• Xanthophylls

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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

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Xanthophylls

• Yellow and orange in color
• Stability related to food source
• Lutein and zeaxanthin

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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

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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

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4 -- Indoles

• Found in cruciferous vegetables
• Broccoli, cabbage, kale, and cauliflower
• Stimulate enzymatic reactions
• Heating and thorough chewing speed these chemical
  reactions
• Isothiocyanates
• subgroup that forms aroma in Brussells sprouts,
  cabbage, turnips, mustard greens, watercress, and
  radishes

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5 -- Phenolic Acids

• Weak acids
• Sources
• Carrots
• Citrus
• Nuts
• Raspberries
• Strawberries
• Tomatoes
• Whole grains

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Polyphenols

• Sources
• Green and black teas (green are higher)
• Red and purple grape products
• Rosemary
• Sunflower seeds, barley, and apples

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6 -- Saponins

• Product of a sugar and alcohol
• Sources
• Spinach, potatoes, tomatoes, oats, beans,
  legumes, soybeans, sugar beets, peanuts, and
  asparagus

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7 -- Terpenes

• Flavor compound in citrus, cherries and many
  seasonings and herbs
• Taxol
• Best known
• Found in Pacific Yew tree
• Can be very toxic

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Best Sources of Phytochemicals

• Vegetables
• Black and green tea
• Dark green and orange
• Herbs
• Legumes
• Nuts
• Onions and garlic
• Soy
• Tomatoes

• Fruits
• Apples
• Berries -- blueberries, raspberries,
  blackberries, and strawberries
• Citrus peel
• Dark orange fruits -- mango, papaya, apricots,
  peaches, nectarines
• Red and purple grapes

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