FOOD SCIENCE AND PROCESSING 3 (2+1)

Lesson 28 : Processing and Preservation of Fruits- II

Enzymatic browning

The rapid darkening of the cut surface of apple, (brinjal and potato) and banana are examples of enzymatic browning. Normally the natural enzymatic compounds present in intact tissues and do not come into contact with the phenol oxidases present in some tissues. When the tissues are cut, or injured and the cut surface is exposed to air, phenol oxidase enzyme released at the surface, act on the polyphenols present, oxidising them to orthoquinones. The orthoquinones rapidly polymerise to form brown pigments. Tyrosine, chlorogenic acid, the various catechins and several mono and dihydroxyphenols are among the many compounds that can serve as substrates for oxidation by poly phenoloxidase to cause browning or other discolouration in these foods. Phenolase is also known by other names as polyphenol oxidase, tyrosinase or catecholase, each is specific for certain substrate. The optimum pH for the activity of the enzyme polyphenolase is between 5 and 7.

• Can bananas be stored in refrigerator?
• Prevention of enzymatic browning