The withering and fermentation degrees are the key parameters to measure the processing technology of black tea. The traditional methods to judge the degree of withering and fermentation are time-consuming and inefficient. Here, a monitoring model of the biochemical components of tea leaves based on hyperspectral imaging technology was established to quantitatively judge the withering and fermentation degrees of fresh tea leaves. Hyperspectral imaging technology was used to obtain the spectral data during the withering and fermentation of the raw materials. The successive projections algorithm (SPA), competitive adaptive reweighted sampling (CARS), and uninformative variable elimination (UVE) are used to select the characteristic bands. Combined with the support vector machine (SVM), random forest (RF), and partial least square (PLS) methods, the monitoring models of the tea polyphenols (TPs), free amino acids (FAA) and caffeine (CAF) contents were established. The results show that: (1) CARS performs the best among the three feature band selection methods, and PLS performs the best among the three machine learning models; (2) the optimal models for predicting the content of the TPs, FAA, and CAF are CARS-PLS, SPA-PLS, and CARS-PLS, respectively, and the coefficient of determination of the prediction set is 0.91, 0.88, and 0.81, respectively; and (3) the best models for quantitatively judging the withering and fermentation degrees are FAA-SPA-PLS and TPs-CARS-PLS, respectively. The model proposed in this study can improve the monitoring efficiency of the biochemical components of tea leaves and provide a basis for the intelligent judgment of the withering and fermentation degrees in the process of black tea processing.

Tea plants are highly susceptible to the adverse effects of a high-temperature climate, which can cause reduced yield and quality and even lead to plant death in severe cases. Therefore, reducing the damage caused by high-temperature stress and maintaining the photosynthetic capacity of tea plants is a critical technical challenge. In this study, we investigated the impact of small oligopeptides (small peptides) and surfactants on the high-temperature-stress tolerance of tea plants. Our findings demonstrated that the use of small peptides and surfactants enhances the antioxidant capacity of tea plants and protects their photosynthetic system. They also induce an increase in gibberellin (GA) content and a decrease in jasmonic acid (JA), strigolactone (SL), auxin (IAA), and cytokinin (CTK) content. At the same time, small peptides regulate the metabolic pathways of diterpenoid biosynthesis. Additionally, small peptides and surfactants induce an increase in L-Carnosine and N-Glycyl-L-Leucine content and a decrease in (5-L-Glutamyl)-L-Amino Acid content, and they also regulate the metabolic pathways of Beta-Alanine metabolism, Thiamine metabolism, and Glutathione metabolism. In summary, small peptides and surfactants enhance the ability of tea plants to resist high-temperature stress.

The physiological state of overwintering tea leaves is crucial for the growth and quality formation of spring tea shoots. Low temperatures in winter can easily cause damage to overwintering tea plants, leading to leaf chlorosis and abnormal physiological functions. Many pieces of research have shown that shading could promote chlorophyll (Chl) accumulation in tea leaves, but the impact on overwintering tea plants is not yet known. In this study, different shading rates (no-shading, S0%; 30% shading, S30%; 75% shading, S75%) were used to treat overwintering tea plants, which explored the effect of shading on the color and physiological functions of tea leaves. The results showed that Chl, carotenoid, and soluble sugar (SS) contents were S75% > S30% > S0%, and the net photosynthetic rate (Pn) was S75% > S30% > S0%. Transcriptome analysis showed that the genes involved in chlorophyll and carotenoid metabolism (such as protochlorophyllide reductase POR and zeaxanthin epoxidase ZEP) and photosynthesis (such as photosystem II P680 reaction center D2 protein PsbA and photosystem II CP47 chlorophyll apoprotein PsbB) were significantly up-regulated under shading. In addition, many differentially expressed genes (DEGs) were enriched in “starch and sucrose metabolism (ko00500)” and “anthocyanin biosynthesis (ko00942)” pathways. In summary, this study provided a theoretical basis and technical support for maintaining green leaves and normal physiological functions of overwintering tea plants.