FCH - BROWNING Flashcards
One of the most important reactions taking place during food processing and storage.
Browning
Two types of browning reaction in food:
- Enyzmatic
- Non-enzymatic
Ubiquitous in nature, seen not only plants but also in animal food products.
Browning reactions
Occur due to wounding, mechanical damage and cutting common to fruits and vegetables.
Browning reactions
Also occurs due to physiological changes such as senescence, which is a condition or process of deterioration with age. During senescence cell and tissue breakdown occurs allowing browning to occur rapidly
Browning reactions
Storage and food process conditions also play a major role in the onset of _________________.
Browning reactions
Elevated temperature such as frying and baking leads to favorable browning qualities of baked and fried products.
Browning reactions
Low temperature storage may also cause browning due to chill injury which affects frozen products negatively.
Browning reactions
Plant diseases also cause ___________________ as a result of cellular leak that favors browning reactions.
Browning reactions
Other horticultural crops such as apples are prone to C02 injury which also causes browning to this fruit.
Browning reactions
Enzymatic browning or also known as ______________________.
Phenolase browning
One of the most important color reactions that affect fruits, vegetables, and seafood.
Enzymatic browning
Enzymatic browning is catalyzed by the enzyme _________________.
Polyphenol oxidase
Polyphenol oxidase is also preferred to as:
- phenol oxidase
- phenolase
- monophenol oxidase
- diphenol oxidase (DPO)
- tyrosinase
The abundance of _________________ in plants may be the reason for naming this enzyme PPO.
Phenolics
_____________ can affect color, flavor, and nutritional value of foods, hence, can cause tremendous economic losses.
Enzymatic browning
By-product of ortho-quinone and is the brown pigmentation in enzymatic browning.
Melanins
_______________________ catalyze the oxidation of phenolic constituents to quinones, which finally polymerize to colored melanins.
Polyphenol oxidase enzymes (PPOs)
Products of enzymatic browning play key _____________ roles.
Physiological
________________ produced as a
consequence of PPO activity.
Melanins
Melanins may exhibit the following properties:
- Antibacterial
- Antifungal
- Anticancer
- Antioxidant
Affect fruits, vegetables, and seafood in either positive or negative ways.
Enzymatic browning
Positive effect of Enzymatic browning.
These reactions, for instance, may contribute to the overall acceptability of foods such as tea, coffee, cocoa, and dried fruits (raisins, prunes, dates, and figs).
The polyphenolic compound that contributes to browning and stringent and bitter flavor of tea
Tannin
Undesirable during processing of fruit slices and juices
Negative effect of Enzymatic browning
Negative effect of Enzymatic browning
Lettuce, other green leafy vegetables; potatoes and other starchy staples, such as sweet potato, breadfruit, and yam; mushrooms; apples; avocados; bananas; grapes; olives etc. Crustaceans are also extremely vulnerable to enzymatic browning
Is an oxidoreductase able to oxidize phenol
compounds, employing oxygen as a hydrogen acceptor.
PPO (EC 1.10.3.1; o-diphenol oxidoreductase)
Directly responsible for enzymatic browning reactions in damaged fruits during postharvest handling and processing.
Polyphenol oxidase (PPO)
PPO catalyzes two basic reactions:
- hydroxylation to the o-position adjacent to an existing hydroxyl group of the phenolic substrate (monophenol oxidase activity).
- oxidation of diphenol to o-benzoquinones (DPO activity).
Properties of PPO
- PPO, active between pH 5 and 7, does not have a very sharp pH optimum.
- At lower pH values of approximately 3, the enzyme is irreversibly inactivated.
- Reagents that complex or remove copper from the prosthetic group of the enzyme inactivate the enzyme.
Substrates of PPO
- Tyrosine
- Other phenolic compounds such as caffeic acid and chlorogenic acid also serve as substrate.
The major substrate for certain phenolases
Tyrosine
Common phenolic compounds present in foods:
- Quinic acid
- Dopamine
- Ferulic acid
- Catechol
- Chlorogenic acid
Three Control of Enzymatic Browning:
- Direct Inhibition
- Chemical Modification
- Non-enzymatic Reduction
Most preferred control of enzymatic browning.
Direct Inhibition
Factors why direct inhibition is preferable.
- Reducing agents
- Acidulants
- Chelating agents
- Complexing agents
- Enzyme inhibitors
- Enzyme treatments