The consumption of green tea in colorless and transparent pet bottles has increased recently. However, there is a problem of the discoloration of thegreen pigment (chlorophyll) in green tea by light. This study was carried out to investigate the effect of (-) -epigallocatechin gallate (EGCG) on the discoloration of chlorophyll-a (Chl-a) by light irradiation. EGCG inhibited the discoloration of Chl-a when its concentration was 10 times greater the Chl-a concentration. Moreover, the simultaneous addition of EGCG and ascorbic acid resulted in a synergistic inhibitory effect on discoloration of Chl-a by light irradiation. All Chl-a in the green tea ethanol solution was decomposed by light irradiation for 4 hours. In spite of the addition of EGCG (1mM) to the green tea solution, the inhibition of the discoloration of Chl-a was not as strong as that predicted in this study. The concentration of catechins in the green tea solution decreased slightly during light irradiation. Therefore, although the inhibitory effect of EGCG on the discoloration of Chl-a was noted, it was not clearly observed in the green tea solution.

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Water extracts from 25 species of wild grasses were examined for their antimicrobial activities against four food spoilage bacteria, Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Proteus mirabilis. The water extracts were preliminarily screened for their antimicrobial activities at 1 % (w/v). The water extracts from Reynoutria japonica (leaves), Euphorbia maculata (leaves or aerial parts), Artemisia capillaries, Potentilla fragarioides, and Oenothera biennis inhibited the growth of all the bacteria tested. The minimum inhibitory concentration was determined by the two-fold dilution method. The water extracts from E. maculata (leaves) and O.biennis showed particularly low MICs, almost equal to that of green tea.

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The spectral profiles of edible burdock extract during browning reaction suggested that the oxidation of chlorogenic acid and its analogues mainly causes enzymatic browning in edible burdock. Polyphenol oxidase (PPO) was purified-16. 6-fold with a recovery rate of 21% using chlorogenic acid as substrate. The purified enzyme appeared as a single band on PAGE and SDS-PAGE. The molecular weight of the enzyme was estimated to be about 41, 000 and 40, 000 by gel filtration and SDS-PAGE, respectively. The purified enzyme quickly oxidized chlorogenic acid and (-) -epicatechin. The Km values of the enzyme were 0.4 mM for chlorogenic acid (pH 5. 0, 20°C) and 2.7 mM for (-) -epicatechin (pH 8.0, 20°C). The optimum pHs were 5.0 for chlorogenic acid oxidase (ChO) and 8.0 for (-) -epicatechin oxidase (EpO). In the pH range from 5 to 8, both ChO and EpO activities were quite stable at 4°C for 22 h. The optimum temperature of both activities was 20°C. Both activities were 50% inactivated after a heat treatment at 45°C for 30 min. Both activities were strongly inhibited by L-ascorbic acid and L-cysteine at 5 mM.

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