Catechins are key functional components in tea and have many health benefits, including relieving diabetes. Glucose is necessary for maintaining life. However, when the glucose in the serum exceeds the threshold, it will lead to hyperglycemia. Hyperglycemia is mainly caused by insufficient insulin secretion or insulin resistance. Persistent hyperglycemia can cause various disorders, including retinopathy, nephropathy, neurodegenerative diseases, cardiovascular disease, and diabetes. In this paper, we summarize the research on the underlying mechanisms of catechins in regulating diabetes and elaborate on the mechanisms of catechins in alleviating hyperglycemia by improving insulin resistance, alleviating oxidative stress, regulating mitochondrial function, alleviating endoplasmic reticulum stress, producing anti-inflammatory effects, reducing blood sugar source, and regulating intestinal function. This review will provide scientific direction for future research on catechin alleviating diabetes.

The recent availability of a number of tea plant genomes has sparked substantial interest in using reverse genetics to explore gene function in tea (Camellia sinensis). However, a hurdle to this is the absence of an efficient transformation system, and virus-induced gene silencing (VIGS), a transient transformation system, could be an optimal choice for validating gene function in the tea plant. In this study, phytoene desaturase (PDS), a carotenoid biosynthesis gene, was used as a reporter to evaluate the VIGS system. The injection sites of the leaves (leaf back, petiole, and stem) for infiltration were tested, and the results showed that petiole injection had the most effective injection, without leading to necrotic lesions that cause the leaves to drop. Tea leaves were inoculated with Agrobacterium harboring a tobacco rattle virus plasmid (pTRV2) containing a CsPDS silencing fragment. The tea leaves exhibited chlorosis symptoms 7–14 days after inoculation, depending on the cultivar. In the chlorosis plants, the coat protein (CP) of tobacco rattle virus (TRV) was detected and coincided with the lower transcription of CsPDS and reduced chlorophyll content compared with the empty vector control, with 81.82% and 54.55% silencing efficiency of ‘LTDC’ and ‘YSX’, respectively. These results indicate that the VIGS system with petiole injection could quickly and effectively silence a gene in tea plants.

Different origins and qualities can lead to differences in the taste and aroma of tea; however, the impacts of origin and quality on the taste and aroma characteristics of Wuyi rock tea and Huizhou rock tea have rarely been studied. In this study, high-performance liquid chromatography (HPLC), gas chromatography–mass spectrometry (GC–MS), and sensory evaluation methods were used to compare the quality components of Wuyi rock tea and Huizhou rock tea. The sensory evaluation showed that they each have their own characteristics, but the overall acceptability of Wuyi rock tea is ahead of Huizhou rock tea (p < 0.01). Biochemical experiments showed that HT was the highest in water leachables, about 43.12%; WT was the highest in tea polyphenols, about 14.91%; WR was the highest in free amino acids, about 3.38%; and the six rock teas had different health benefits. High-performance liquid chromatography showed that the theanine contents of WS and WR were 0.183% and 0.103%, respectively, which were much higher than those of other varieties. The OPLS-DA model predicted the factors that caused their different tastes, in order of contribution: CG > ECG > caffeine > EGCG > theanine. Ten volatile substances with OAV ≥ 1 and VIP > 1 were also found, indicating that they contributed greatly to the aroma characteristics, especially hexanoic acid, hexyl ester, and benzyl nitrile. The results of the correlation analysis showed that theanine was significantly correlated with taste (p < 0.05), and hexanoic acid, hexyl ester, and benzyl nitrile were significantly correlated with smell (p < 0.05). Substances such as theanine, hexanoic acid, hexyl ester, and benzyl nitrile give them their unique characteristics. Analysis of the differences in the quality components of the six rock teas can provide reference value for the cultivation and processing of rock teas.

The sensory quality of black tea is intrinsically linked to cultivar genetics, yet comprehensive characterization of flavor compounds in emerging northern Guangdong black tea (NGBT) remains limited. This study employed high-performance liquid chromatography-ultraviolet (HPLC-UV) and headspace solid-phase microextraction coupled with GC-MS (HS-SPME-GC-MS) to analyze non-volatile and volatile compounds in five NGBT cultivars—Jinshahong (JSH), Danxia No.1 (DXY), Danxia No.2 (DXE), Yingde Black Tea (QTZ), and Yinghong No.9 (YHJ)—alongside sensory evaluation. Orthogonal partial least squares-discriminant analysis (OPLS-DA) identified key non-volatile discriminants (VIP > 1) ranked by contribution: total catechins > simple catechins > CG > EGCG > ester catechins > EGC. HS-SPME-GC-MS detected 97 volatiles, with eight aroma-active compounds exhibiting OAV > 1 and VIP > 1: Geraniol > Methyl salicylate > Linalool > β-Myrcene > Benzyl alcohol > (Z)-Linalool Oxide > Phenethyl alcohol > (Z)-Jasmone. These compounds drive cultivar-specific aromas in NGBTs. Findings establish a theoretical framework for evaluating cultivar-driven flavor quality and provide novel insights for targeted breeding and processing optimization of NGBTs.

Sooty mould (SM) disease affects the growth, development and metabolism of plants and reduces the commodity and economic value of crops. SM disease is one of the important leaf diseases in tea plants. Nonetheless, studies on the effect of SM disease in tea plants are rare. Herein, we found that SM disease disrupted the cell morphology and structure and reduced the contents of caffeine, theanine, and catechins in the mature leaves of tea plants. Transcriptome analysis revealed that SM disease inhibited the biosynthesis of lignin, chlorophyll, catechin, caffeine, and theanine and affected the plant-pathogen interactions in the mature leaves of tea plants by downregulating gene expression. In addition, two fungal isolates, MTzyqA and MTzyqB, were obtained from the mature leaves of diseased tea plants. These strains were identified as Cladosporium pseudocladosporioides by mulitgene phylogenetic analysis, and they grew epiphytically on the leaves of tea plants. The biocontrol bacteria JT68, ZGT5, and BX1 had obvious inhibitory effect on MTzyqA and MTzyqB. These results provide a basis for understanding the effect of SM disease in tea plants.