Polyphenols oxidation processes

There has been some evidence of a higher antioxidant effect when both flavonoids and a-tocopherol are present in systems like LDL, low-density lipoproteins (Jia et al., 1998 Zhu et al, 1999). LDL will incorporate a-tocopherol, while flavonoids will be present on the outside in the aqueous surroundings. A similar distribution is to be expected for oil-in-water emulsion type foods. In the aqueous environment, the rate of the inhibition reaction for the flavonoid is low due to hydrogen bonding and the flavonoid will not behave as a chain-breaking antioxidant. Likewise, in beer, none of the polyphenols present in barley showed any protective effect on radical processes involved in beer staling, which is an oxidative process (Andersen et al, 2000). The polyphenols have, however, been found to act synergistically... 

The current understanding of wine oxidation processes centers around pol)q5henols as the main initial substrate of wine oxidation, with crucial roles for catalytic metals in facilitating the reactions (Danilewicz, 2003). The amoimt of oxygen that can be taken up by a particular wine has been found to be proportional to the polyphenol content, an uptake that proceeds more rapidly at a higher pH where the phenolate anion forms of the polyphenols are more abundant (Singleton, 1987). 

FIGURE 4.2 Wine oxidation processes adapted from Danilewicz (2003) R = further organic groups such as the three-ring structure in the flavonoids, and further groups in nonflavonoid polyphenols. 

The lag time effect probably results from the inhibition of copper-containing oxidases and other copper-catalyzed oxidative processes in apple by Sporix. These oxidative reactions normally would bring about the rapid loss of AA and permit browning to occur once the added AA was depleted (18). Sporix also would inhibit PPO directly by chelation of its copper (3), thereby decreasing the rate of polyphenol oxidation and subsequent browning. The ability of Sporix to exert its effect on enzymatic browning by these two independent mechanisms probably accounts for the apparent synergism obtained with Sporix-AA combinations. 

Green tea and black tea are produced using different processing methods for tea leaves of Camellia sinensis. Green tea is produced by drying the leaves of Camellia sinensis at elevated temperatures to prevent polyphenol oxidation. The major... 

The NCI testing effort used tea extracts, tea polyphenol-enriched fractions, isolated catechin fractions, and a theaflavin-rich fraction. The black and green tea extracts were tested in both caffeinated and decaffeinated forms. The percentage of polyphenols in both green and black teas were approximately the same. However, levels of EGCG and caffeine in green tea are four- to five-fold that of black tea. Theaflavins are unique to black tea due to the oxidation process. 

So what causes this unique effect of red wine Part of the story is the high trace element content in comparison with beer or spirits, but this is not all. White wine and red wine are very similar as far as the main components are concerned. Red wine, however, contains about 20 times more of polyphenol derivatives than white wine. Alcohohc beverages are pro-oxidants, which means that they increase the intensity of oxidation processes. Alcohol itself is responsible for this effect. Red wine, however, is an antioxidant (—>3.31) thanks to its polyphenol content. Antioxidants were very intensely researched in the 1980s and 1990s, which also contributed to the increasing interest in red wine. The presence of polyphenols is required for this effect, but this is still not the whole story. 

Prevention of oxidation and stabilization of the wine color Chitosan has a good affinity to phenolic compounds, which are the main components involved in the wine oxidation processes and are responsible for browning. Chitosan reduced the polyphenol content and stabilized white wines to the same extent as did potassium caseinate, an adjnvant normally used in oenology. Moreover, chitosan could be reused after a simple regeneration process. 

FIa.VOnoIOxida.tlon, The fermentation process is initiated by the oxidation of catechins (1) to reactive catechin quinones (13), a process catalyzed by the enzyme polyphenol oxidase (PPO) (56). Whereas the gaHocatechins, epigaHocatechin, and epigaHocatechin gaHate, are preferred, polyphenol oxidase can use any catechin (Table 2) as a substrate. This reaction is energy-dependent and is the basis of the series of reactions between flavanoids that form the complex polyphenoHc constituents found in black and oolong teas. 

Enrichment of processed food with plant material or plant extracts rich in polyphenols has two aspects in relation to human nutrition and human health. Food protected against oxidation has better keeping quality and will stay healthy longer since formation of toxic oxidation products, like cholesterol oxides, is being prevented (Britt et al., 1998). The other aspect is the beneficial effects of the intake of polyphenols on human health. Both of these aspects are, however, related to the availability of the phenolic substances. 

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. 

In addition to all of the expected enzyme systems present in leaf tissue, fresh tea leaves contain a high level of polyphenol oxidase that catalyzes the oxidation of the catechins by atmospheric oxygen. Tea polyphenol oxidase exists as series of copper-containing (0.32%) isoenzymes. The major component has a molecular weight of about 144,000.54 The enzyme is concentrated in the leaf epidermis.55 Soil copper deficiency is sometimes responsible for inadequate oxidation during processing.56... 

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