Differences and correlations between chiral amino acid contents and microbiota in different processing stages of...

Keemun black tea (KBT) is one of the most famous black teas globally, and this study explored the differences of chiral amino acids in different types, grades, and processing stages, revealing the correlations with microbiota. The total and D-form amino acids ranged between 4.46 and 44.2 and 0.069-0.403 g/kg across grades, respectively, which decreased with the decrease of tea grade. Predominant D- and L-form amino acids were D-glutamic acid and L-aspartic acid/L-theanine, respectively. The chiral amino acids increased with processing stages, and L-glutamic acid showed the greatest increase (7.4-fold). The microbiota richness and diversity in fermentation stage increased significantly, but decreased significantly in drying stage. Bacteroidota and Proteobacteria were the primary microbiota, and their functions of Metabolism of cofactors and vitamins, Carbohydrate metabolism, and Amino acid metabolism were significant positive related to the increase of amino acid contents. These results provided data support for KBT amino acid formation.