Abstract:To investigate the influence of different grades of sun-dried green tea on the quality of the roasted Pu-erh tea prepared from them, the raw materials of machine-harvested sun-dried green tea were sieved and divided into three grades. Three different grades of roasted Pu-erh tea, namely A, B and C, were processed and examined through sensory evaluation of tea leaves and metabolomic analysis. Grade B had the best sensory evaluation results, and grade A was notably different from the other specimens in principal component analysis. Of 238 differentially accumulated metabolites, 12 were screened. Of these, D-maltose was negatively correlated with grade, whereas the other 11 metabolites were positively correlated with grade. The relative total content for four key substances were in the order of A (0.053 mg/g) > B ( 0.007 mg/g) > C (0.006 mg/g) for amino acids and their derivatives, A (0.072 mg/g) > B (0.042 mg/g) > C (0.028 mg/g) for alkaloids, A (0.516 mg/g) > C (0.221 mg/g) > B (0.245 mg/g) for flavanones and flavonoids, and A (1.808 mg/g) > B (0.668 mg/g) > C (0.482 mg/g) for catechins and their derivatives. Phenylalanine metabolism was the most involved pathway among all differentially accumulated metabolites. The variation patterns of these differentially accumulated metabolites can provide a theoretical basis and scientific guidance for improvement of the quality of machine-harvested sun-dried green tea and its subsequent processing into roasted Pu-erh tea.
