Metabolomics and electronic tongue reveal the effects of different storage years on metabolites and taste quality of Oolong Tea

Oolong tea have better richness, sweetness and throat after a certain time of storage. These variations in taste and quality are closely related to changes in the composition of oolong tea during storage, however, the metabolic profiles of oolong tea during storage have not been reported so far. Therefore, we evaluated the differences in taste quality of oolong tea in four storage years (1991, 2001, 2011 and 2021) by using electronic tongue technology, and the results showed that the bitterness, astringency and richness of oolong tea are significantly reduced during storage, but the acidity have the opposite trend, while the sweetness did not trend, with the least sweetness in 2011 and no difference in sweetness in the rest of the years. We further explored the metabolites contributing to the differences in taste quality of Dancong tea in four storage years (1991, 2001, 2011 and 2021) using metabolomics technique and the results showed that a total of 1245 metabolites were detected, of which nine were taste characteristic components of Aged Dancong tea. Dancong tea mainly increased azelaic acid, suberic acid, 2-hydroxyphenylacetic acid and other sour characteristic components in aged tea by regulating phenylalanine metabolism, metabolic pathways, and pyrimidine metabolism and mainly decreased benzamide, propyl 4-hydroxybenzoate, pyrrole-2-carboxylic acid and other bitterness and astringency characteristic components by regulating arginine and proline metabolism, flavonoid biosynthesis, biosynthesis of secondary metabolites, which enhanced the sour and umami of aged tea and reduced its bitterness and astringency. This study provides theoretical support for the quality of aged oolong tea, with a view to providing guidance for the storage of oolong tea.