Enzymatic and non-enzymatic BrowningIntroductionThe process of changing into brown and in particular foodstuff is called browning. In some instances, browning of food may be desirable in such cases like caramelization or undesirable in situation when an apple turns brown after cutting it or undesirable discoloration that takes place on fresh vegetables and fruits as illustrated by Alan (2005). Various foods such as beverages and fruits can change into brown. They are two types of browning that include enzymatic and non-enzymatic browning. They are similarities and differences in enzymatic and non-enzymatic browning of foods in terms of chemical reactions involved.
The major difference in the two types of browning is that enzymatic browning requires an enzyme while non-enzymatic browning does not require an enzyme. It is also significant to appreciate different reaction processes that the reaction undergoes. The reactions vary as illustrated within the essay. Enzyme browning reaction has differing reaction to that of non-enzyme browning reaction. However, it is worth to note that they are two major reactions in non-enzyme browning as will be clearly illustrated in the essay.
Enzymatic browning is a chemical process that takes place in vegetables and fruits by enzyme polyphenoloxidase resulting in brown pigments. They are two major components used in enzymatic browning that include polyphenols and polyphenoloxidase. Enzymatic browning is usually observed in vegetables (potatoes, lettuce, mushrooms), seafood (crabs, spiny lobsters, and shrimps), and fruits (grapes, pears, bananas, and apricots). Enzymatic browning is harmful to quality and in particular post-harvest storage of juices, vegetables, fresh fruit, and shellfish. In some instances, enzymatic browning is important for the taste and color of chocolate, tea, and coffee.
Enzymatic browning as a chemical process involves catechol oxidase, polyphenol oxidase, among other enzymes that create benzoquinone and melanin leading to brown color. Polyphenoloxidase, catechol oxidase catalyze phenols oxidation in fruits leading to formation of quinines compounds that polymerize to form melanin responsible of brown pigments. Polyphenols are usually unstable and they usually undergo oxidation when exposed to air due to a series of biochemical reactions that converts it from one substrate to another as described above. Exposure to oxygen is a major factor contributing to enzymatic browning.
Polyphenoloxidase catalyze two basic reactions including oxidation and hydroxylation that make use of molecular oxygen as a co-substrate according to Alan (2005). The reaction depends on the air presence, ph or acidity. It is important to note that reaction does not occur when pH is less than 5 or alkaline is greater than pH 8 conditions. A chemical process that results to color brown in foods with no involvement of enzymes activities is referred to as Non-enzymatic browning. The two major non-enzymatic browning include Maillard and caramelization reactions. However, both vary in rate of reaction as a function of water.
The Maillard reactions are a chemical reaction between (the carbonyl group) a reducing sugar and free amino acid of a protein or an amino acid. Heat usually accelerates the rate of maillard reaction although it can proceed at lower temperatures but a rate that is slower. Caramelization is the water removal process from a sugar including glucose or sucrose followed by steps like isomerization and polymerization. It is a chain of complicated chemical reactions. Non-enzymatic browning is responsible for several desirable and pleasant flavors and aromas.
However, they are still some undesirable effects of non-enzymatic browning (Yiu & Jozsef, 2006).