Download Enzymes

Enzymes
Overview
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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
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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:
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Break down starch
Tenderize meat
Clarify wines
Coagulate milk
B-3.03 -- Enzymes
Naturally-Occurring Enzymes
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Trigger enzymatic browning
Found in large amounts in:
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pineapple
papaya
figs
Meat tenderizers made from
compounds in fruit
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Bromelain -- Pineapple
Papain -- Papaya
Ficin -- Fig
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Enzymatic Reaction
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Factors that Affect Enzyme
Activity
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Two factors will affect
enzyme activity:
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water availability
amount of substrate
Enzymatic reactions
generally occur in the
presence of water.
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Water Availability
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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
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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
Factors that Denature Enzymes
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Enzymes are proteins.
Denaturation:
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changes the structure of the
protein
stops enzyme activity
Enzymes denatured by:
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heat
pH
salts
enzyme inhibitors
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Heat
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Enzymatic reaction rates
increase as temperature
increases.
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Denaturation occurs at 104°F
or hotter.
Too much heat slows and stops
enzyme activity.
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Heating can destroy enzymes
that alter food quality.
Example -- blanching
vegetables to prevent spoilage
during frozen storage.
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pH
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pH and rate of enzymatic reaction
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pH and denaturation of enzymes
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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
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Lemon juice to apples
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Salts
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Salt is commonly used
in food production
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Binds to enzymes in
food that cause spoilage
Changes the water
activity
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Enzyme Inhibitors
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Substance that will prevent the enzymesubstrate complex
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Naturally occurring
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Enzymatic reactions slowed or stopped.
Egg whites
Pesticides that are naturally part of a plant
structure
Synthetic compounds
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Enzyme Activity
Effects on Food
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Positive effects:
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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:
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Enzymatic browning
Spoilage
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Make Food Easier to Eat
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Meat tenderizers, enzymes that can be
added:
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during aging
prior to cooking
Enzymes break down tough protein
fibers for a more tender product.
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Preserve Food
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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
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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
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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
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Prevent oxygen from combining with
the enzyme phenolase
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Cold storage slows enzyme activity.
Add preservatives, such as:
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sulfites,
ascorbic acid,
citric acid, and/or
acetic acid
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Spoilage
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Prolonged enzyme activity can cause
food to spoil.
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Overripening of fruit
Food processors control enzymatic
activity by:
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replacing oxygen to slow action of oxidases
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Phytochemicals
Definition and Benefits
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Phytochemicals -- group of compounds
naturally produced by plants
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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
Seven Families
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6.
7.
Allyl sulfides
Carotenoids – carotenes, xanthophylls
Flavonoids – isoflavones
Indoles – isothiocyanates
Phenolic acids (or phenols) – polyphenols
Saponins
Terpenes
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Characteristics
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Scientists are examining their:
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structure,
stability in food, and
sources.
Function
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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
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Contain sulfur
Increase enzyme
reactions
Sources -- onions, garlic,
leeks, chives
Benefits in raw and
cooked forms
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2 -- Carotenoids
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Over 600 known
carotenoids
Precursors to vitamin
A
Subgroups
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Carotenes
Xanthophylls
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Carotenes
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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
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Yellow and orange in
color
Stability related to food
source
Lutein and zeaxanthin
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3 -- Flavonoids
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Most red and white in color
Responsible for flavor
Potential benefits
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Anti-flammatory/anti-carcinogen
Sources
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Apples
Broccoli
Cranberries
Onions
Red grape juice, and
Tea
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Isoflavones
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Subgroup of flavonoids
Also called phytoestrogens or
plant hormones
Genistein and daidzein are
best known.
Sources:
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Soy
Chickpeas
Licorice
Oriental vegetables -- Chinese
cabbage and bok choy
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4 -- Indoles
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Found in cruciferous vegetables
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Stimulate enzymatic reactions
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Broccoli, cabbage, kale, and
cauliflower
Heating and thorough chewing
speed these chemical reactions
Isothiocyanates
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subgroup that forms aroma in
Brussells sprouts, cabbage, turnips,
mustard greens, watercress, and
radishes
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5 -- Phenolic Acids
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Weak acids
Sources:
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Carrots
Citrus
Nuts
Raspberries
Strawberries
Tomatoes
Whole grains
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Polyphenols
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Sources
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Green and black teas
(green are higher)
Red and purple
grape products
Rosemary
Sunflower seeds,
barley, and apples
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6 -- Saponins
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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
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Flavor compound in
citrus, cherries and
many seasonings and
herbs
Taxol
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Best known
Found in Pacific Yew
tree
Can be very toxic
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Best Sources of Phytochemicals
Fruits
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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
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