Variations in Chemical Quality among Spring and Summer Tea Made from Six Cultivars Grown in Motuo County, Tibet

Abstract

The water extract contents, polyphenol compositions, total free amino acid contents, caffeine (CAF) contents, amino acid compositions and catechin compositions of spring and summer tea made from six varieties planted in Motuo, namely Tezao 213, Zhuyeqi, Zhongcha 302, Tieguanyin, Yinghong 9 and Fenghuang Dancong were determined and compared. The results indicated significant differences between spring and summer tea in all quality components except tea polyphenols. The average phenol/ammonia ratio of spring and summer tea was 4.60 and 7.99, respectively, indicating summer tea to be suitable for processing into green and black tea. Altogether 18 amino acids were detected in the six cultivars, and the contents of different groups of amino acid were in the decreasing order of umami amino acids > sweet amino acids > bitter amino acids > aromatic amino acids. The contents of umami and sweet amino acids in spring tea were significantly higher than those in summer tea. Correlation analysis revealed that the synthesis of various metabolites were highly correlated. Principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) showed that season had a more significant effect on tea metabolites than variety. A total of 16 compounds were identified as differential metabolites between spring and summer tea, including 7 amino acids, 8 catechins and CAF, which could be used as potential markers to distinguish spring and summer tea. This study provides a valuable reference for tea processing.

Keywords

• tibet; motuo county; tea; season; quality components