Abstract:
In order to explore the dynamic changes and correlations of the physicochemical components and quality characteristics of Zhenghe white tea during the storage process, eight samples of Zhenghe baimudan white tea from the same origin but different years (2015~2022), with identical tea tree variety, picking standards, processing technology, and storage conditions were selected for sensory evaluation and determination of main physicochemical components. Multivariate statistical analysis was employed for further investigation. The results showed that over a period of 1~8 years in storage, there was a progressive deepening in color intensity observed in dry tea, tea infusion and infused leaves. Furthermore, the taste profile of Zhenghe baimudan white tea exhibited improvements in sweetness and mellowness while freshness and bitterness gradually diminished year by year. The levels of water extract, flavonoids, tea polyphenols, free amino acids, catechins, theophylline, and the obromine experienced significant decreases throughout the storage duration. However, the concentrations caffeine and gallic acid remained relatively stable. In terms of amino acid constituents, cysteine, tyrosine and phenylalanine content increased whereas arginine, methionine, lysine, serine, leucine, isoleucine, glycine, alanine, threonine, aspartate, glutamate and valine content decreased. The contents of theanine, histidine and proline displayed an increase-decrease-increase pattern. The critical period for quality transformation of Zhenghe baimudan white tea is from the 5th to 6th year of storage, during which it transitions from new tea to aged tea: teas stored for 1~5 years are considered new, while those stored for more than 5 years are classified as aged. Throughout the storage process, there are nine key differential taste compounds that undergo changes: EGCG, ECG, caffeine, theanine, GCG, histidine, serine, gallic acid and arginine. Notably, the reduction of bitterness as well as the enhancement of the mildness and sweetness of the tea infusion were significantly influenced by the decrease in the content of EGCG, ECG, and GCG. This study could provide a theoretical basis for exploring changes in taste substances as well as understanding quality differences in Zhenghe baimudan white tea during storage. It also offers valuable insights for quality identification and improvement of white tea in different years.