Some chemical changes in food products cause quality losses. Some of these changes occur by enzymatic pathways and some by non-enzymatic pathways. Enzymes that are effective in foods may naturally be in the structure of foods themselves or synthesized by microorganisms in the environment. Although microorganisms are killed during cooking, residual activities of enzymes that are heat-resistant and are not sufficiently inactivated may persist.

Oxidative changes may also occur in food products. The enzymes that cause these changes include peroxidases. As a result of these chemical reactions, food products sometimes have undesirable color changes (called enzymatic browning), sometimes no color change.

Some color changes occur in fruits and vegetables in cutting, multiplying, slicing, peeling and similar processes. These color changes in different shades are called browning. For example, browning of the cut apple is the oxidation of some substances in apple juice by the effect of oxygen in the air. This oxidation is also caused by peroxidase enzymes.

Peroxidase is the most heat resistant enzyme in fruits and vegetables. Therefore, it is monitored by testing the enzyme peroxidase whether the enzymes are inactivated during processing of fruits and vegetables.

During the processing of vegetables, both inadequate scalding and over-scalding cause deterioration of taste and aroma. Therefore, the residual activity must be inactivated until the initial peroxidase activity decreases to about the level of 10. Only in this case can the peroxidase be avoided. However, this rate varies according to the type of fruit and vegetables. For example, this percentage is maximum 6 percent in peas and 3 percent in green beans.

Peroxidase enzyme determination studies are carried out in laboratories, fruits and vegetables. In addition, the standards prepared by organizations operating in our country and in foreign countries and the methods of analysis and test criteria accepted in the world are complied with.