Food Spoilage

How do enzymes spoil food?

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2009-05-01 14:08:31

Enzymes are large protein molecules that act as biological

catalysts, accelerating chemical reactions without being consumed

to any appreciable extent themselves. The activity of enzymes is

specific for a certain set of chemical substrates, and it is

dependent on both pH and temperature. The living tissues of plants

and animals maintain a balance of enzymatic activity. This balance

is disrupted upon harvest or slaughter. In some cases, enzymes that

play a useful role in living tissues may catalyze spoilage

reactions following harvest or slaughter. For example, the enzyme

pepsin is found in the stomach of all animals and is involved in

the breakdown of proteins during the normal digestion process.

However, soon after the slaughter of an animal, pepsin begins to

break down the proteins of the organs, weakening the tissues and

making them more susceptible to microbial contamination. After the

harvesting of fruits, certain enzymes remain active within the

cells of the plant tissues. These enzymes continue to catalyze the

biochemical processes of ripening and may eventually lead to

rotting, as can be observed in bananas. In addition, oxidative

enzymes in fruits continue to carry out cellular respiration (the

process of using oxygen to metabolize glucose for energy). This

continued respiration decreases the shelf life of fresh fruits and

may lead to spoilage. Respiration may be controlled by refrigerated

storage or modified-atmosphere packaging. Table 1 lists a number of

enzymes involved in the degradation of food quality.

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