Classification of raw Pu-erh teas with different storage time based on characteristic compounds and effect of storage environment

Contents of catechins, flavonoids, purine alkaloids and amino acids in raw Pu-erh teas (RPTs) of a storage time scale below 10 years and old RPTs stored in Yunnan and Guangdong Province, were determined by HPLC. Tea quality improved highly significantly (p < 0.01) after 8 years of storage through sensory evaluation. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) could classify RPTs into 3 categories (new, chen and old tea group, respectively) completely based on detected compounds. Gallic acid (GA), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG), (-)-gallocatechin gallate (GCG), (-)-epigallocatechin, (-)-gallocatechin, L-tyrosine, L-theanine, L-glutamic acid, L-asparagine and L-valine with highly significant (p < 0.01) variations could discriminate the storage time. The highly significant (p < 0.01) increase of GA might be attributed to the hydrolyzation of ECG, EGCG and GCG by existed microbes in the storage. Kaempferol and myricetin contents were increased highly significant (p < 0.01) during the storage. Hot-humid storage environment accelerated the degradation of ester catechins, L-theanine, L-asparagine, L-alanine and L-valine, and the accumulation of GA, kaempferol and quercetin. This study helps to reveal quality and chemical change rules of RPTs during the storage.