Polyphenoloxidase

Investigations have focused on the content of polyphenoHcs, tannins, and related compounds in various foods and the influence on nutrient availabiHty and protein digestibiHty. It has been estabHshed that naturally occurring concentrations of polyphenoloxidase and polyphenols in products such as mushrooms can result in reduced iron bio availabiHty (75). Likewise, several studies have focused on decreased protein digestibiHty caused by the tannins of common beans and rapeseed (canola) (76—78). 

DEVECE C, RODRIGUEZ LOPEZ J N, FENOLL L G, TUDELA J, CATALA J M, DE LOS REYES E and GARCIA CANOVAS F (1999) Enzyme inactivation analysis for industrial blanching applications comparison of microwave, conventional, and combination heat treatments on mushroom polyphenoloxidase activity , J g-nc Food Chem, 47 (11) 4506-11. 

Im, J.S., Parkin, K.L., and Von Elbe, J.H., Endogenous polyphenoloxidase activity associated with the black ring defect in canned beet (Beta vulgaris L.) root slices, J. Food ScL, 55, 1042, 1059, 1990. 

Two main groups can be discerned (1) endogenous factors such as plant enzymes like polyphenoloxidase, peroxidase, and P-glucosidase and (2) conditions prevailing in the extraction medium will decide the fates of betalain pigments among which temperature, oxygen, and pH are considered the most important conditions. 

Endogenous and exogenous enzymes — While the role of (3-glucosidase affecting betalains is quite clear, the roles of polyphenoloxidase and peroxidase are less obvious. Betacyanin glycosides may be cleaved into the corresponding aglycones, the... 

Amon, D.E., Copper enzymes in isolated chloroplast. Polyphenoloxidase in Beta vulgaris. Plant Physiol., 24, 1, 1949. 

French researchers provided an alternative to the tartrazine synthetic colorant (E 102), valorizing a phloridzine oxidation product (POP) generated as a by-product of the cider industry. Phloridzine is a polyphenol specific to apples and shows good antioxidant capacity. When apples are pressed to yield juice, phloridzine, oxygen, and polyphenoloxidase enzyme combine to form POP. This brilliant yellow natural colorant with nuances dependent on pH level can be incorporated easily into water-based foods such as beverages (juices, syrups) and confectionery creams because it is stable during production processes. Details about the specific formulations of these colorants are presented in Section 5.1. 

Model systems indicate that aldehydes may also be produced by the action of polyphenoloxidases on amino acids in the presence of catechin, all of which are present in coffee beans at some stage between green and roasted. For example, valine yields isobutanal, leucine yields isopentanal, and isoleucine yields 2-methyl-butanal.14 Some of these aldehydes probably undergo condensation reactions in the acidic medium of the roasted bean when moisture is present.15 Some dienals in green coffee beans have recently been identified as (E,E)-2,4- and (E,Z)-2,4-nonadienal and (E,E)-2,4- and (E,Z)-2,4-decadienal.18... 

Polyphenoloxidase, produced by Alternaria or CJadosporium, can be used to improve the brown coloration in a coffee extract.221... 

Oliveira, J. C., Silva, D. M., Amorim, H. V., Enzymatic activity of polyphenoloxidase and catalase in Coffea arabica L. seeds and seedlings, Cientifica, 4, 68, 1976. (CA85 139854e)... 

Motoda, T., Color improvement of cacao and coffee beans with polyphenoloxidase, Jpn. Kokai Tokkyo Koho 79,143,561, 1979. (CA92 109427v)... 

Arnon, D.I. (1949). Copper enzymes in isolated chloroplasts. Polyphenoloxidases in Betula vulgaris. Plant Physiology 24 1-15. 

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. 

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... 

Figure 4.2. Monophenolase and diphenolase activities of polyphenoloxidase and stabilization of the formed quinones. (A) Quinone reduction. (B) Descarboxylation. (C) Modification by an exomolecular nucleophile. (D) Modification by an endomolecular nucleophile.

Polyphenoloxidase in Fungi and Defense against Fungal Attack... 

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. 

Sanchez-Ferrer A, Bru R and Garcia-Carmona F. 1989. Novel procedure for extraction of a latent grape polyphenoloxidase using temperature-induced phase separation in Triton X-114. Plant Physiol... 

Goupy P, Amiot MJ, Richard-Forget F, Duprat F, Aubert S and Nicolas J. 1995. Enzymatic browning of model solutions and apple phenolic extracts by apple polyphenoloxidase. J Food Sci 60 497—501, 505. 

Flurkey WH. Polyphenoloxidase in higher plants immunological detection and analysis of in vitro translation products. Plant Physiol 1986 86 614-618. 

Moore BM, Flurkey WH. SDS activation of a plant polyphenoloxidase effect of SDS on enzymatic and physical characteristics of purified broad bean polyphenoloxidase. Biol Chem 1990 265 4982-4988. 

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