Enzyme-catalyzed oxidative browning of fruit

An excellent discussion of the many enzymes occurring in fruits is provided by Dilley (247). Of the numerous enzymes present in fruits, and as in the case of grapes, oxidizing enzymes have received considerable attention from researchers because their activity is usually accompanied by undesirable changes in raw product quality. A complete account of enzyme-catalyzed oxidative browning of fruits and their products is presented by Joslyn and Ponting (248). 

Joslyn, M. A., and Ponting, J. D. 1951. Enzyme-catalyzed oxidative browning of fruit products. Advances in Food Research 3, 1-44. 

Figure 4.91 presents the catalytic cycle of tyrosinase, an enzyme presently of commercial and industrial interest since it is involved in the browning of fruits in the presence of oxygen, due to the oxidation of the phenols catalyzed by this enzyme. The most important feature to note is that the enz5nne uses a binuclear Cu site able to bind a molecule of oxygen in a bridging mode. In contrast to the other monooxygenases, the two electrons required to split the molecule of... 

Acetic acid can be produced by the enzyme-catalyzed oxidation of ethyl alcohol. The brown acetic acid in vinegar is produced from fruit juices (apple or grape juice) and is known as natural acetic acid. 

These two processes are also referred as cresolase activity or monophenolase activity and diphenolase activity, respectively. Such reactions represent the initial steps of vertebrate pigmentation (melanin biosynthesis) and the browning of fruits and vegetables.Catechol oxidases (EC 1.10.3.1) are ubiquitous plant enzymes, which also catalyze the oxidation of a broad... 

Oxidation of Phenolic Compounds. Phenolic compounds are widespread throughout the plant kingdom and are prevalent in fruits where they are important contributors to color and flavor (46). Phenolic compounds, particularly flavonoids and derivatives of chlorogenic acid, play a crucial role in the development of a number of postharvest disorders through their oxidation to brown compounds that discolor many fruits and vegetables and substantially reduce their quality. A number of enzymes catalyze the biosynthesis or oxidation of phenolic compounds, among them phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL), cinnamic acid-4-hydroxylase (CA4H), polyphenol oxidase (PPO), and catechol oxidase (CAO). The chemistry... 

The melting point of a DNA molecule is the temperature at which the double-helical strand breaks apart. Suppose you are given two DNA samples. One sample contains 45 percent C-G base pairs while the other contains 64 percent C-G base pairs. The total number of bases is the same in each sample. Which of the two samples has a higher melting point Why When fruits such as apples and pears are cut, the exposed parts begin to turn brown. This is the result of an oxidation reaction catalyzed by enzymes present in the fruit. Often the browning action can be prevented or slowed by adding a few drops of lemon juice to the exposed areas. What is the chemical basis for this treatment ... 

When fruits such as apples and pears are cut, the exposed parts begin to turn brown. This is the result of an oxidation reaction catalyzed by enzymes present in the fruit. Often the browning action can be prevented or slowed by adding a few drops of lemon juice to the exposed areas. What is the chemical basis for this treatment ... 

When fruits such as apples and pears are cut, the exposed parts begin to turn brown. This is the result of an oxidation reaction catalyzed by enzymes... 

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