http://en.wikipedia.org/wiki/Enzymatic_browning
Các hợp chất polyphenols (tanin thuộc nhóm này) dưới sự có mặt của oxygen và enzyme polyphenol oxidase sẽ chuyển hóa thành melanin, 1 chất có màu tối.
Enzymic browning
Enzymic (or enzymatic) browning is a chemical process, involving
polyphenol oxidase or other
enzymes that create
melanins, resulting in a brown color. Enzymic browning is an important color reaction in fruit, vegetables, and seafood. Enzymic browning of fruits and vegetables creates heavy economic losses for growers.
Enzymic browning is beneficial for:
Enzymic browning is detrimental to:
Enzymic browning is usually controlled with chemicals (such as
sodium bisulfite), or by destroying the responsible chemicals with heat.
Blanching to destroy the enzymes is commonly used to preserve color in vegetables.
Lemon juice and other acids are used to preserve color in fruit, particularly
apples, by lowering the
pH and removing the copper
cofactor necessary for the enzyme to function.