Impact of the long-term storage on flavor quality of Liupao tea using sensory evaluation combined with metabolomics analysis

Abstract

This study comprehensively investigated the impact of different storage times on the quality and metabolomic profiles of Liupao tea (LPT). The sensory evaluations revealed that both Maosheng (MS) and Tianyu (TY) teas exhibited a browning of tea appearance and brightening of tea infusion during storage. The taste evolved from bitterness and astringency to purity and briskness, while the aroma shifted from stuffy to woody and aged aromas. Notably, MS teas exhibited superior sensory quality after 10 years, while TY teas reached optimal quality in the 8th year of storage. Correlation analysis of metabolites and sensory attributes has underscored the integral influence of metabolites throughout the storage process, which significantly directed the development of tea quality. The non-volatile metabolites exerted significant influence on tea flavor by modulating key biochemical pathways, including the oxidation of catechins, the formation of alkaloids as well as the glycosylation and/or methylation of flavonoids. However, TY teas experienced both glycosylation and methylation, which promoted the transformation of bitterness and astringency, achieving a mellow and brisk taste more quickly than MS teas. The transformation pathways of volatile metabolites potentially involved the hydrolysis of linalool glycosides and phenylethanol glycosides, the synthesis of sesquiterpenes, the methylation of gallic acid and the degradation of carotenoids. However, the divergent trends observed in ketones and aldehydes between the two types of tea could culminate in distinct aromatic profiles, which might be due to different metabolic pathways or differences in the rates of metabolite formation and degradation during storage. Additionally, the antioxidant analysis revealed that both MS and TY teas exhibited a parabolic trend in comprehensive antioxidant capacity during storage, which primarily influenced by the oxidative polymerization of phenolic compounds and the glycosylation of flavonoids. In summary, this study emphasized the multifaceted attributes of tea quality and the importance of metabolites in shaping sensory quality and health properties. It was found that the optimal storage time of 8 to 10 years for LPT was conducive to attaining a desirable balance of flavor and health benefits.