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Understanding nonvolatile metabolite alterations during processing and their impacts on potential function is crucial for technological innovations in tea manufacturing. In the present work, specific metabolite alterations during Zijuan black tea processing and their potential effects on nicotine-induced human oral epithelial cell (HOEC) injury were investigated. The results showed that leucine, isoleucine, and tyrosine were the main hydrolysis products during withering, and theaflavin-3-gallate (TF-3-G), theaflavin-3'-gallate (TF-3'-G) and theaflavin-3,3'-gallate (TFDG) were mainly formed during rolling. Moreover, oxidation of flavonoid glycosides, catechins and dimeric catechins took place during fermentation. During drying, amino acid conversion became dominant. Meanwhile, processing samples effectively attenuated nicotine-induced oxidative stress and inflammation in HOECs. TF-3'-G, TF-3-G, phenylalanine, and kaempferol-3-coumaroylglucoside exhibited strong associations with protective action, which indicates that modifying the processes in which black tea are produced to be rich in those specific components could be beneficial for the oral health of people who smoke.

Tea polysaccharide conjugates (TPS conjugates) are receiving worldwide attention in the recent decades, after they were recognized as critical components of coarse tea, and were responsible for their therapeutic effects in patients with diabetes. Existing evidences indicate that TPS conjugates not only benefit human health, but also can be used as carriers for drugs and as films for food packaging, and as emulsifiers. Despite their many practical applications, molecular structures of TPS conjugates are not well worked out yet, making their mechanisms of action difficult to understand. Their structural variations are attributed mainly to the differences in the processing of different tea. This comprehensive review summarises the compositions, structural characteristics, and bioactivities of TPS conjugates from different tea-leaf products, discusses the relationships between their compositions and structures, and the specific functions, and suggests the conjugation among polysaccharides, proteins and polyphenols occurring in tea leaves during processing which is mainly responsible for the alteration in composition and structure of TPS conjugates derived from different kinds of tea. [Display omitted] • The impacts of tea processing techniques on composition and structure of TPS conjugates are explored. • The relationships between structures and specific functions of TPS conjugates are discussed. • Regulation on intestinal flora of TPS conjugates plays a critical role in its health benefit effects. • Tea leaves could be used to produce specific function-targeting TPS conjugates. [ABSTRACT FROM AUTHOR]

Tea cultivar 'Zijuan', a mutant of Camellia sinensis var. assamica , has high content of anthocyanins in fresh leaves which makes it suitable for producing black tea with distinctive flavor and bioactivity. In the present work, the processing conditions were optimized based on sensory evaluation, the composition of volatile and non-volatile compounds and in vitro antioxidant activity and α-glucosidase inhibition of Zijuan black tea were also investigated, the relationships among them were analyzed further. 14.1 h, 34.6 °C and 2.3 h were the best condition for withering time, fermentation temperature, and fermentation time in the process of Zijuan by sensory evaluation, respectively. Benzeneacetaldehyde, followed by (E)-2-hexenal, benzaldehyde, linalool, methyl salicylate and geraniol were the main odor-contributing volatiles; glutamine (Gln) had significant relationship with taste, and those with DPPH scavenging ability and α-glucosidase inhibition were theaflavin (TFs) and theabrownine (TBs). Interestingly, weak and insignificant correlations were found between flavor and bioactivities of Zijuan black tea. • Zijuan is suitable for processing high quality black tea with distinctive flavor. • Benzenacetaldehyde and benzaldehyde mainly contribute to the aroma attributes of Zijuan black tea. • Glutamine has a significant relationship with the taste of Zijuan black tea. • Correlations between flavor and bioactivities of Zijuan black tea are weak and insignificant. [ABSTRACT FROM AUTHOR]

Plant hormones play an important role in the chemical metabolism of postharvest plants. However, alterations in plant hormones of postharvest tea and their potential modulation of quality-related metabolites are unknown. In this study, the dynamic alterations of abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), and critical metabolites, such as catechins, theanine, and caffeine, in tea leaves were analyzed during withering from 0 to 24 h. It was found that the ABA content increased from 0 to 9 h but decreased thereafter, JA continuously increased, and the SA content showed no significant change. With the exception of gallocatechin (GC) and epicatechin (EC), the amounts of other critical components were significantly reduced at 24 h. Transcriptome analysis showed that compared with 0 h, 2256, 3654, and 1275 differentially expressed genes (DEGs) were identified at 9, 15, and 24 h, respectively. For all comparisons, DEGs corresponding to the pathways of "phenylalanine, tyrosine, and tryptophan biosynthesis" and "phenylalanine metabolism", involved in the biosynthesis of catechins, were significantly enriched. Weighted correlation network analysis (WGCNA) of co-expression genes indicated that many of the modules were only correlated with a specific trait during the withering process; the dark olive-green module, however, was correlated with two traits, ABA and theanine. Our study indicates that withering induced dramatic alterations in gene transcription as well as levels of hormones (ABA, JA, and SA) and important components, and that ABA regulated theanine metabolism during this process. [ABSTRACT FROM AUTHOR]

[Display omitted] • The critical mechanisms underlying the microbiome assembly in the tea plants are revealed. • There is a trade-off between stochastic and deterministic processes in microbiome assembly in the tea plants. • Assembly processes were dominated by deterministic processes in bulk and rhizosphere soils. • The stochastic processes in roots and leaves was critically driven by amino acids for environmental selection. • The core taxa assembled in phyllosphere could attenuate the virulence of a prevalent foliar pathogen. Assembly and co-occurrence of the host co-evolved microbiota are essential ecological and evolutionary processes, which is not only crucial for managing individual plant fitness but also ecological function. However, understanding of the microbiome assembly and co-occurrence in higher plants is not well understood. The tea plant was shown to contribute the forest fitness due to the microbiome assembled in the phyllosphere; the landscape of microbiome assembly in the tea plants and its potential implication on phyllosphere homestasis still remains untangled. This study aimed to deciphering of the microbiome networks of the tea plants at a continental scale. It would provide fundamental insights into the factors driving the microbiome assembly, with an extended focus on the resilience towards the potential pathogen in the phyllosphere. We collected 225 samples from 45 locations spanning approximately 2000-km tea growing regions across China. By integration of high-throughput sequencing data, physicochemical properties profiling and bioinformatics analyses, we investigated continental scale microbiome assembly and co-occurrence in the tea plants. Synthetic assemblages, interaction assay and RT-qPCR were further implemented to analyze the microbial interaction indexed in phyllosphere. A trade-off between stochastic and deterministic processes in microbiomes community assembly was highlighted. Assembly processes were dominated by deterministic processes in bulk and rhizosphere soils, and followed by stochastic processes in roots and leaves with amino acids as critical drivers for environmental selection. Sphingobacteria and Proteobacteria ascended from soils to leaves to sustain a core leaf taxa. The core taxa formed a close association with a prevalent foliar pathogen in the co-occurrence network and significantly attenuated the expression of a set of essential virulence genes in pathogen. Our study unveils the mechanism underpinning microbiome assembly in the tea plants, and a potential implication of the microbiome-mediated resilience framework on the phyllosphere homeostasis. [ABSTRACT FROM AUTHOR]