Polyphenols, brown

There are two important sources of brown polyphenols, cocoa and tea, used as colorants for foods. Both are very old and date back to antiquity. 

The cacao plant, Theobroma cacao, is the source of chocolate which is well known and highly prized in international commerce. The cacao pods contain beans which are fermented and pressed to provide a brown liquid which is the raw material for chocolate. The press cake is ground and sold as cocoa and it also provides a brown colorant. The pods, beans, shells, husks and stems have also been suggested as colorants. They contain a very complex mixture of acyl acids, leucoanthocyanins, flavonoid polymers, tannins, and catechin-type polymers.33 

The tea plant, Thea sinensis, has provided a desirable beverage for centuries but it is also used as a colorant. Extracts of tea contain a very complex mixture of glycosides of myricetin, quercitin and kaempferol, epicatechin, epigallocatechins, acyl acids and many other polyphenol compounds.33 In black tea, the above compounds may act as precursors to the poorly defined compounds thearubin and theaflavin. 

Both cocoa and tea are used in a variety of food products, including beverages, bakery products, confections, toppings, dry mixes, etc. 

Tarka40 wrote an extensive review of the toxicology of cocoa and the methylxanthenes, theobromine, caffeine and theophyllin. The review involved 

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Francis, F.J., Caramel, brown polyphenols and iridoids, in Colorants, Eagan Press, St. Paul, MN, 83,1999. 

FRANCIS, F. J. Caramel, Brown Polyphenols, and Iridoids. Chap. 10 in Colorants, Eagen Press, St. Paul, MN, 1999, pp. 83-8. 

It is interesting to underline that there is another (plant) enzyme which possesses a coordinatively similar dicopper environment catechol oxidase.11 As already mentioned in Chapter 6, Section 3, such an ubiquitous enzyme catalyses the two-electron oxidation by molecular dioxygen of catechols to the corresponding quinones (the so-generated quinones in turn polymerize to form brown polyphenolic catechol melanins, which protect damaged plants from pathogens or insects). 

A novel synthetic method for polyphenols was described by Inoue and co-workers [172] w-cresol, 3-methylcatechol, 4-methylcatechol and 4-ethylcatechol were polymerised using a redox reaction between phenol derivatives and gold ions. The oxidised phenol derivatives produced by the reduction of gold ions formed water-insoluble polymers with MW of approximately 1,000 g/mol. Alternatively, Wei and co-workers [173] described the electrochemical polymerisation of phenol on 304 stainless steel anodes and the subsequent coating structure analysis. Anodic oxidation was carried out using 304 stainless steel anodes in a neutral 0.1 mol/1 phenol solution with an electrolyte composed of 0.1 mol/1 sodium sulfate. This oxidation generated a yellow brown polyphenol coating on the steel surface of the anode. 

HA is a dark-brown, polyphenolic, amorphous substance soluble in alkali and insoluble in mineral acids. Elemental analysis shows HA to comprise predominantly carbon and oxygen but in addition it always contains hydrogen and nitrogen (Table 4). HA s also contain phosphorus... 

In the production of opalescent or natural-type apple juice, ascorbic acid is added to the fmit pulp before pressing, or to the juice as it comes from the press, to retain more of the apple flavor (4). Ascorbic acid addition and pasteurization of the juice as soon as possible after pressing prevent polyphenol oxidation, which causes browning and contributes to pulp flocculation. 

Ragan, M. A. and Glombitza, K.-W. 1986. Phlorotannins, brown algal polyphenols. Prog. Phycol. 

Biogeographical variation in brown algal polyphenolics and other secondary metabolites comparison between temperate Australasia and North America. Oecologia 78 373-382. Stevens, J. F., Ivancic, M., Hsu, V. L. and Deinzer, M. L. 1997. Prenylflavonoids from Humulus lupulus. Phytochemistry 44 1575-1585. 

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... 

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