Polyphenols degradation

An excellent classification of this type of enzymes was that of Burton (2003). Because of their importance in polyphenol degradation, we have studied four enzymes closely related with the oxidation of phenolic compounds polyphenoloxidase, peroxidase, laccase, and lipoxygenase. 

Laccase is one of the main oxidizing enzymes responsible for polyphenol degradation. It is a copper-containing polyphenoloxidase (p-diphenoloxidase, EC 1.10.3.2) that catalyzes the oxidation of several compounds such as polyphenols, methoxy-substituted phenols, diamines, and other compounds, but that does not oxidize tyrosine (Thurston, 1994). In a classical laccase reaction, a phenol undergoes a one-electron oxidation to form a free radical. In this typical reaction the active oxygen species can be transformed in a second oxidation step into a quinone that, as the free radical product, can undergo polymerization. 

Coir. Coir is a valuable and versatile fiber derived from the coconut husk. The best quality coir is produced from green coconut, which is more difficult to harvest and has a lower copra yield than more mature coconut. The amount of copra and the quantity of coir produced are inversely related (61). Husks must be retted to manufacture coir. This process involves holding the husks under water, away from air, with mud and leaves for a period of a few months to a year. Fermentation is accomplished by short rod bacteria such as Pseudomonas, Rerobacter, and Bacillus. The microbial process is a polyphenolic degradation in which the pectic substances are decomposed. Slow moving and slightly saline water in a natural source speeds the process and produces a better quality fiber (66). 

In recent years, numerous papers have been published about one of the most important groups of phytochemicals, the polyphenols (Manach and others 2004). These compounds, which possess an array of healthy properties, but also some disadvantages that will be discussed in this chapter, are present in a variety of plants used in both human and animal diets. However, the structure of this type of compound means that they can be oxidized by several pro-oxidant agents. The objective of this chapter is to describe the main enzymatic agents responsible for the degradation of polyphenols. In order to understand the mechanisms of degradation that will be described in the following sections, a brief summary of the main properties of the polyphenols is required. 

Because of the easily oxidizable structure of the polyphenols previously described, many studies have been published about the enzymatic degradation of these antioxidant compounds. This chapter exhaustively reviews the main publications concerning the degradation of this type of antioxidant compound by several enzymes. 

Many papers have been published about the enzymatic degradation of polyphenols through the action of oxidizing enzymes. Thus, various classifications have been provided for these types of biocatalytic molecules, according to their coenzyme requirements or according to the nature of the oxidizing substrate (the electron acceptor) and the reaction products (Fig. 4.1). 

As previously indicated, four enzymes related to the enzymatic degradation of polyphenols, polyphenoloxidase, peroxidase, laccase, and lipoxygenase, are extensively reviewed in this chapter. The first enzyme described is polyphenoloxidase. 

Polyphenoloxidase (PPO, EC 1.14.18.1) is one of the most studied oxidative enzymes because it is involved in the biosynthesis of melanins in animals and in the browning of plants. The enzyme seems to be almost universally distributed in animals, plants, fungi, and bacteria (Sanchez-Ferrer and others 1995) and catalyzes two different reactions in which molecular oxygen is involved the o-hydroxylation of monophenols to o-diphenols (monophenolase activity) and the subsequent oxidation of 0-diphenols to o-quinones (diphenolase activity). Several studies have reported that this enzyme is involved in the degradation of natural phenols with complex structures, such as anthocyanins in strawberries and flavanols present in tea leaves. Several polyphenols... 

Plants including fruits and vegetables are a vast reservoir of different phytochemicals. As stated previously, flavonoids are a diverse group of polyphenolic compounds, some of which are relatively stable, whereas others such as anthocyanins are labile under ambient conditions. Sample preparation is of paramount importance in studying flavonoids because a good method prevents compounds of interest from being degraded... 

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