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Fig. 12.11 Polar compounds isolated from oregano.
(EGCG) (the predominant catechin in green tea) theaflavin (TF), theaflavin
monogallate A (TH-1A), theaflavin monogallate B (TH-1B) and theaflavin
digallate (TH-2). However, the thearubigens are not fully characterized and
studied (Ho et al., 1997) (Figs 12.12 and 12.13).
Tea extracts exhibit marked antioxidant activity with the main mode of its
action resulting from oxygen-centered free radical scavenging (Yen et al.,
1997). It is also suggested that metal chelation (Gramza and Korczak, 2005) and
lipoxygenase enzyme inhibition (Xie et al., 1993) may play a role. Benzie and
Szeto (1999) noted that the antioxidant power of tea is highly correlated to its
phenolic content. Within the scope of stabilizing food against lipid oxidation, tea
extracts have shown good potential, accompanied by an increase in commercial
interest. In a study by Tang et al. (2000) tea catechins were found to reduce the
thiobarbituric acid reactive substance (TBARS) values in various meats and
tissues (chicken meat, liver and heart) if the chickens were supplemented with
tea catechins (40% EGCG, 24% EGC, 12% ECG and 10% EC). Koketsu and
Satoh (2007) showed that a slightly different green tea catechin composition
(27.1% EGCG, 19.3% GC, 16.7% GCG, 16.1% EGC, 8.1% ECG 7.5% EC, and
5.2% (+)-catechin) was a more effective antioxidant than tocopherols in lard and
soybean oil, and better than tocopherols and BHA in fish oil. Noodles fried in
lard, in presence of the latter catechin mixture, showed oxidative stability
proportional to the concentration of polyphenols. Green tea extracts have been
reported to have prooxidant effects in seal blubber oil and menhaden oil
(Wanasundara and Shahidi, 1998) and in a deoxyribose oxidation system
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