Browning reactions in foods

Some foods are naturally brown

Some foods are expected to be brown

Some are expected not to be brown

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Browning can be

Desirable:Cooking meat, bread crust,

coffee, chocolate

Undesirable:Fruits, vegetables, sauces

Much of the undesirable browning occurs during storage

Lowers quality FSTC 605 MURANO

How do you formulate a food to limit browning?

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3 major types of browning in foods

1.) Caramelization

2.) Enzymatic browning

3.) Non-enzymatic browning (Maillard reaction)

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Caramelization-Formation of melanoidins by

heating sugar to high temperatures in low water conditions

-No protein or nitrogenouscompounds are involved

-Dehydration reaction resulting in polymerization

-Used to produce caramel colors and flavorsFSTC 605 MURANO

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Generic progression of reaction

1.) Sucrose is dispersed in a small amount of water

-Start with disaccharide

C12H22O11 -Subjected to heat

-Crystals melt at 160C

2) Heat to 200C for 25 minutes - Loose 4.5% of original weight - Weight loss is water from the

polymerization reaction- Very light brown color

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3) Heat to 200C for 55 more minutes- Loose 9% of original weight (water)

Form pigment called Caramelan C24H36O18

Light brown colorSome bitter flavors developing

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4) Heat at 200C for an additional 55 min

- Loose about 14% of original weightForm pigment named caramelen

C36H50O25

- More bitter flavors, darker color

5) Heat at 200C for an additional 55 minFormation of very dark and

very bitter insoluble compoundsForm pigment named caramelin

C125H188O80

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Enzymatic browning

Polymerization of phenolic compounds by PPO enzymes

PPO describes all enzymes with the capacity to oxidize phenolic compounds

Figure- PPO action

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Important in plant tissues especially wounded tissues

Detrimental in produce color and bitterness

Potato, apple, banana, avocado- loss of quality

Beneficial in coffee and tea production

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How to limit enzymatic browning

1)Minimize damage to tissues

2) Exclude or remove molecular oxygen

3) High pressure processing

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4) Water soluble antioxidants (ascorbic acid)

5) Blanching- heat treatment to deactivate PPO

6) Metal complexing agents can block active site

7) Sulfites can prevent reactions with enzymes

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Non-enzymatic browningi.e. Maillard reaction

Desirable in cooking and baking

Undesirable browning during storage

Cannot stop it, but can limit / control reaction rate

Reactants are in food

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1) Amino group

-proteins-peptides

-amino acids

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2) Carbonyl group

-aldehydes and keytones

-mostly from reducing sugars

-some can come from oxidized lipids

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3) Time-Control reaction velocity by

manipulating product

-moisture, temperature, pH, concentration of reactants

- Temperature is critical2-3X faster for each 10C

rise in storage temperatureFSTC 605 MURANO

Involves a complex series of reactions

Figure – reaction sequence

3 major steps

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1) Condensation of carbonyl group with free amino group

Carbonyl + Free Glycosamine + water Group amino

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2) Rearrangement of glycosamine to produce flavor and odor compounds

3) Polymerization into larger melanoidin compounds- color development

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Limiting Maillard reaction in foods

1)Keep product cool

2) Limit reducing sugars

3) Optimize pH and moisture

4) Add inhibitors- sulfur dioxide- reacts with intermediate

- products to prevent polymerizationFSTC 605 MURANO