Enzymatic oxidation

Browning is the process of food turning brown due to the chemical reactions that take place within. The process of food browning is one of the most important reactions that take place in food chemistry and represents an interesting research topic regarding health, nutrition, and food technology. Though there are many different ways food chemically changes over time, browning in particular falls into main 2 categories; enzymatic and non-enzymatic processes. The browning process of foods may yield desirable or undesirable results, depending on the type of food.

Browning has many important implications on the food industry relating to nutrition, technology, and economic cost. Researchers are especially interested in studying the control (inhibition) of browning and the different methods that can be employed to maximize this inhibition and ultimately prolong the shelf life of food.

Enzymatic browning is one of the most important reactions that takes place in most fruits and vegetables as well as in seafood. These processes affect the taste, color, and value of such foods. Generally, it is a chemical reaction involving polyphenol oxidase, catechol oxidase, and other enzymes that create melanins and benzoquinone from natural phenols. Enzymatic browning (also called oxidation of foods) requires exposure to oxygen. It begins with the oxidation of Phenols by Polyphenol oxidase into Quinones, whose strong electrophilic state causes high susceptibility to a nucleophilic attack from other proteins. These Quinones are then polymerized in a series of reactions, eventually resulting in the formation of brown pigments (melanosis) on the surface of the food. The rate of enzymatic browning is reflected by the amount of active polyphenol oxidases present in the food. Hence most research investigating methods to inhibit enzymatic browning has focused on hindering polyphenol oxidase activity. However, not all browning of food produces negative effects.

Examples of beneficial enzymatic browning:

Examples of non-beneficial enzymatic browning:

A variety of methods are used to prevent or slow down enzymatic browning of foods, each method aimed at targeting specific steps of the chemical reaction. The control of enzymatic browning has always been a challenge for the food industry. In addition, the use of chemicals to inhibit browning, such as sulfite (a powerful antibrowning chemical) have been reconsidered due to the potential hazards it causes along with its activity. Much research has been conducted regarding the exact types of control mechanisms that take place when confronted with these enzymatic process. The different types of enzymatic browning control can be classified different groups.

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