Browning is the process of becoming brown, especially referring to food. Browning foods may be desirable, as in caramelization, or undesirable, as in an apple turning brown after being cut. Foods, including beverages, can turn brown through either enzymatic or non-enzymatic processes.
Enzymatic browning is a chemical process, involving polyphenol oxidase, catechol oxidase and other enzymes that create melanins and benzoquinone, resulting in a brown color. Enzymatic browning generally requires exposure to oxygen, thus the browning that occurs when an apple, for example, is cut.
Enzymatic browning can be beneficial for:
Enzymatic browning is often detrimental to:
A variety of techniques exist for preventing enzymatic browning, each exploiting a different aspect of the biochemical process.
Nonenzymatic, or oxidative, browning is a chemical process that produces a brown color in foods without the activity of enzymes. The two main forms of nonenzymatic browning are caramelization and the Maillard reaction. Both vary in reaction rate as a function of water activity.
Carmelization is the pyrolysis of sugar. It is used extensively in cooking for the resulting nutty flavor and brown color. As the process occurs, volatile chemicals are released, producing the characteristic caramel flavor.
The Maillard reaction is a chemical reaction between an amino acid and a reducing sugar, usually requiring the addition of heat. The sugar interacts with the amino acid, producing a variety of odors and flavors. The Maillard reaction is the basis of the flavoring industry, since the type of amino acid involved determines the resulting flavor; it also produces toast.