Effect of selenium on green tea preservation quality and amino acid composition of tea protein

To increase the selenium content of tea produced in areas of China poor in selenium, sodium selenite was added to tea garden soil or was sprayed onto tea leaves. Effects of selenium on green tea quality and the amino acid composition of tea protein were studied. Selenium-enriched green tea and poor selenium green tea were extracted with hot water (100 degreesC) at a 1:50 ratio (w/v). The tea leaf extracts were stored at 30 degreesC for 12 h, the colour changes of selenium-enriched green tea extract were more stable than with poor selenium green tea extract. The teas were packaged in polypropylene plastic bags and then stored at room temperature for 90 d. The reduced ratio of vitamin C in selenium-enriched green tea was 21% compared with poor selenium content green tea at 52%. These results demonstrated that selenium-enriched green tea produced a more desirable quality than poor selenium green tea. The total amino acid amounts, essential amino acid, methionine acid and cystine acid content of different selenium-enriched green tea protein were increased by 8.3%-14.8%, 8.8%-14.8%, 6.0%-8.7% and 39%-96%, respectively, compared with the low selenium green tea. Green tea quality was raised by selenium treatment.