Apples are a rich source of polyphenols including catchins of the flavonoid group and chlorogenic acid. It is thought that the polyphenols in apples are responsible for some of the health benefits of apples. The browning of apples during the ripening process is enzymatically controlled by the enzyme polyphenol oxidase. As the apple ripens, polyphenol oxidase converts polyphenols such as catechins within the flesh of the apple to quinones which can polymerise to form brown pigments that are seen as the brown colour of the fruit. However, the degree of browning depends on the variety of apples and the growing conditions and harvest time. One method to prevent the browning of apples and other fruits is to destroy the enzyme polyphenol oxidase. This can be achieved through the application of heat, which denatures the protein and prevents the browning reaction taking place. Another method is to keep the fruit cold, as the low temperatures reduce the activity of polyphenol oxidase and this slows the enzymatic browning.
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