Tea plants have a long cultivation history in the world, but there are few studies on polysaccharides from fresh tea leaves. In this study, tea polysaccharides (TPSs) were isolated from fresh tea leaves. Then, we investigated the characteristics of TPSs during in vitro simulated digestion and fermentation; moreover, the effects of TPSs on gut microbiota were explored. The results revealed that saliva did not significantly affect TPSs’ molecular weight, monosaccharide composition, and reducing sugar content, indicating that TPSs cannot be digested in the oral cavity. However, TPSs were partially decomposed in the gastrointestinal tract after gastric and intestinal digestion, resulting in the release of a small amount of free glucose monosaccharides. Our in vitro fermentation experiments demonstrated that TPSs are degraded by gut microbiota, leading to short-chain fatty acid (SCFA) production and pH reduction. Moreover, TPSs increased the abundance of Bacteroides, Lactobacillus, and Bifidobacterium but reduced that of Escherichia, Shigella, and Enterococcus, demonstrating that TPSs can regulate the gut microbiome. In conclusion, TPSs are partially decomposed by gut microbiota, resulting in the production of SCFAs and the regulation of gut microbiota composition and function. Therefore, TPSs may be used to develop a prebiotic supplement to regulate the gut microbiome and improve host health.

Tea polysaccharides (TPSs) are receiving increasing attention because of their diverse pharmacological and biological activities. Here, we explored the immunoregulatory mechanisms of TPSs from fresh tea leaves in a mouse model of cyclophosphamide (CTX)-induced immunosuppression in terms of gut microbiota and metabolites. We observed that TPSs significantly increased the body weight and alleviated CTX-induced thymus atrophy in the immunosuppressed mice; they also increased the plasma levels of immunoglobulins A and M, interleukin (IL) 1β, IL-6, inducible nitric oxide synthase, and tumor necrosis factor α. Furthermore, we conducted 16S rDNA sequencing of cecal contents, resulting in the acquisition of 5008 high-quality bacterial 16S rDNA gene reads from the sequencing of mouse fecal samples. By analyzing the data, we found that TPSs regulated the gut microbiota structure and diversity and alleviated the CTX-induced dysregulation of gut microbiota. The colonic contents of mice were subjected to analysis using the UPLC-Q-TOF/MS/MS technique for the purpose of untargeted metabolomics. In the course of our metabolite identification analysis, we identified a total of 2685 metabolites in positive ion mode and 1655 metabolites in negative ion mode. The analysis of these metabolites indicated that TPSs improved CTX-induced metabolic disorders by regulating the levels of metabolites related to tryptophan, arginine, and proline metabolism. In conclusion, TPSs can alleviate CTX-induced immunosuppression by regulating the structural composition of gut microbiota, indicating the applicability of TPSs as novel innate immune modulators in health foods or medicines.

The flooding of tea plantation caused by natural rainfall is a common natural disaster, which has adverse effects on the soil quality of tea plantation, the growth of tea trees, and the yield and quality of tea. This article systematically studied the multidimensional effects of natural rainfall (flood conditions) on tea plantation soil for the first time. In this study, the physicochemical properties, heavy metals, and microbial communities of tea plantation soil samples were analyzed at six time points after natural rainfall (flood conditions) at 0, 15, 18, 21, 24, and 27 days. The results showed that natural rainfall (flood conditions) had a significant impact on soil nutrients and heavy metal concentrations in tea plantations. With the extension of flooding time, compared with the pre-flooding control (0 days), soil pH, organic matter, available potassium, available phosphorus, alkali-hydrolyzable nitrogen, and the concentrations of eight heavy metals first increased and then decreased with prolonged flooding, and the concentrations of all heavy metals were lower than the limits of soil environmental quality standards. After flooding, Proteobacteria was the dominant group of bacterial community, and Acidobacterita, Chloroflexi, and Actinobacteriota were also abundant. The fungal community is dominated by Ascomycota and Basidiomycota. Soil components were significantly correlated with microbial community, in which organic matter, available potassium, and pH value had the greatest impact on bacterial community, while fungal community was mainly affected by available potassium, organic matter, Cr, and As. In general, natural rainfall (flood conditions) will reduce the content of nutrients and heavy metals in tea plantation soil and change the soil microbial community structure, which provides a scientific basis for evaluating the impact of natural rainfall on tea plantation soil health.

The contents of biochemical components, such as theanine, tea polyphenols, water extract, and soluble sugar in Hakka stir-fried green tea (HSGT), serve as important indicators reflecting the intrinsic quality of tea leaves. In this study, 171 HSGT samples are collected, and their near-infrared spectroscopy (NIRS), together with the contents of the four indicators, are determined. The aim is to establish prediction models for these four indicators by extracting multiple features from the NIRS data. First, the NIRS data is preprocessed. Then, multiple features are extracted using competitive adaptive reweighted sampling (CARS), adaptive Fourier decomposition (AFD), fast Fourier transform (FFT), continuous wavelet transform (CWT), and band combination (BC). Finally, ridge regression (RR) and partial least squares regression (PLSR) models are constructed based on the NIRS features to predict the four indicators. Experimental results show that the model combining multiple features, namely CARS + AFD + BC, delivers the best overall performance. Specifically, the RR model based on multiple features provides the most accurate predictions for theanine, tea polyphenols, and soluble sugar, while the PLSR model performs better for water extract. This study provides a rapid and accurate method for detecting the substance content in HSGT.

Cicada black tea is made from Empoasca onukii-infested tea leaves. The biochemical differences between Cicada black tea and regular black tea, and the dynamic changes in volatile components during processing, remain unclear. This study focused on the withering and fermentation stages, which most significantly affect the quality of black tea, to systematically investigate cicada black tea aroma formation. Ninety volatile compounds were identified, among which 12 key volatiles significantly contributed to the aroma characteristics. During withering, floral and fruity aromas were enhanced. Fermentation primarily intensified honey-like and sweet notes, which were mainly regulated by carotenoid-derived volatiles with low odor thresholds, such as β-Damascenone. Withering to a moisture content of 55% (17 h) and fermenting for 5 h comprised the optimal processing parameters to achieve the best aroma attributes. These insights into the mechanism of Cicada black tea aroma formation will lead to improved processing techniques to enhance its unique flavor.