Course:FNH200/Lessons/Lesson 05/Page 05.4

5.4 Enzymes Endogenous to Foods

Enzymes can catalyze reactions leading to chemical changes in foods. Living organisms (animal and plant) have their own enzyme balance. This enzyme balance is disrupted once the animal is killed or the plant is harvested, but the enzymes may continue to catalyze chemical reactions within foods even after slaughter or harvest.

Some examples of enzymatic deterioration in foods are described below:

• The softening of fruit tissue and the changes in flavour and colour during storage after picking are examples of deterioration of food quality by enzymes. It is enzymatic action that causes the softening of apple tissue during storage, with texture changing from that of a crisp apple to a somewhat soft and mealy apple with a concomitant loss of sweetness. Enzymes in the apple tissue degrade pectins that cement the cells together, leading to the textural change.
• You also no doubt have experienced the browning of apples, potatoes and peaches after they have been sliced and exposed to oxygen in the atmosphere. This browning phenomenon is known as enzymatic browning and is catalyzed by an enzyme known as polyphenol oxidase which catalyzes the oxidation of colorless phenols in the tissues to brown colored compounds, as shown in the following equation:

Enzymes can catalyze reactions leading to chemical changes in foods. Living organisms (animal and plant) have their own enzyme balance. This enzyme balance is disrupted once the animal is killed or the plant is harvested, but the enzymes may continue to catalyze chemical reactions within foods even after slaughter or harvest.

Enzymes can be inactivated by means of heat, chemicals (e.g. antioxidants), and by controlling the gaseous environment.