enzymes. b-3.03 -- enzymes2 overview enzymes -- proteins that catalyze a specific chemical reaction....

Enzymes

B-3.03 -- Enzymes 2

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.

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

B-3.03 -- Enzymes 4

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 5

Enzymatic Reaction

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

B-3.03 -- Enzymes 7

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).

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.



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

Salts

Salt is commonly used in food production Binds to enzymes in

food that cause spoilage

Changes the water activity



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

Enzyme Activity

B-3.03 -- Enzyme Activity in Food 18

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


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.

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.



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


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


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


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

Phytochemicals

B-3.03 -- Phytochemicals 26

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 27

Sources of Phytochemicals

Seven Families of Phytochemicals

B-3.03 -- Seven Families of Phytochemicals 30

Seven Families

1. Allyl sulfides2. Carotenoids – carotenes, xanthophylls3. Flavonoids – isoflavones4. Indoles – isothiocyanates5. Phenolic acids (or phenols) –

polyphenols6. Saponins 7. Terpenes

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


2 -- Carotenoids

Over 600 known carotenoids

Precursors to vitamin A

Subgroups Carotenes Xanthophylls

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


Xanthophylls

Yellow and orange in color

Stability related to food source

Lutein and zeaxanthin



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

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


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


5 -- Phenolic Acids Weak acids Sources:

Carrots Citrus Nuts Raspberries Strawberries Tomatoes Whole grains


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

7 -- Terpenes Flavor compound in

citrus, cherries and many seasonings and herbs

Taxol Best known Found in Pacific Yew

tree Can be very toxic



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

enzymes. b-3.03 -- enzymes2 overview enzymes -- proteins that catalyze a specific chemical reaction....

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