Determination and analysis of contents of different tea oligopeptides

【Objective】 To construct a quantitative method for tea oligopeptides suitable for general physical and chemical laboratory operations, and to provide methodological support for tea oligopeptide research.【Method】 With 30 samples of six major tea types taken as test materials, effects of solvent concentration, extraction temperature and extraction time on oligopeptide content in tea were investigated. After precipitating the large molecular weight proteins in the extract by trichloroacetic acid, the free amino acid content and the total amount of free amino acids and oligopeptides in the extract were determined by formaldehyde titration and Kjeldahl method, respectively, and the difference between the two was calculated as the oligopeptide content. At the same time, the established oligopeptide quantitative analysis method was used to analyze the difference of oligopeptide content of different teas.【Result】 Extraction solvent significantly influenced the content of tea oligopeptides(P<0.05), the effect of extraction temperature was small, but the extraction time did not have a significant effect(P>0.05). The optimized extraction conditions were as follows:50% ethanol, heating at 80℃ and reflux extraction for 30 min;this method showed a good stability(relative standard deviation of repeated test < 5.00%), and it could be used for the actual determination of oligopeptide content in 30 tea samples of six teas. The determination results showed that the order of mean oligopeptide content of the six major teas was as follows:yellow tea>white tea>dark tea>green tea>black tea>oolong tea, among which, oligopeptide content in yellow tea and white tea was 3.88%-6.00%, in dark tea and green tea was 2.45%-6.53%, in black tea was 1.90%-4.84%, and in oolong tea was 0.70%-3.93%.【Conclusion】 Through optimized extraction method combining Kjeldahl nitrogen determination method with formaldehyde titration method, the quantitative determination of tea oligopeptide can be well operated;at the same time, the processing technology and tenderness of tea raw materials may influence the content of oligopeptides in teas.