Liyong Luo

Due to inadequate fixation, early tea produced in the Chuanyu region exhibits high astringency. To mitigate the astringency of early tea, this study identified the astringent compounds present in the tea, subsequently optimized its fixation process based on the key astringent substances. Initially, 20 early tea samples were categorized into three groups (low, middle, and high astringency) according to the differences in astringency. Metabolomics revealed a total of 129 differential metabolites, of which 8 metabolites were positively correlated to the astringency of early tea. Finally, DoT (Dose-over-threshold: concentration-to-threshold ratio) values, taste recombination, omission, and addition experiments confirmed that (−) epigallocatechin (EGC), hyperin, and rutin were the key astringent compounds of early tea. Ultimately, the orthogonal test determined that the best fixation parameters of early tea were fixation temperature of 300 °C, fixation time of 65 s, and leaf amount of 150 kg/h, which significantly reduced the astringency of early tea.

Congou black tea has garnered significant interest among customers because of its distinctive floral-fruity aroma. To determine the differences in characteristic volatile compounds among various varieties, a total of 147 volatile compounds were identified across 25 samples via gas chromatography–mass spectrometry (GC-MS). Through hierarchical clustering analysis (HCA), 25 samples were classified into two clusters, in which the Fuding variety, Jinguanyin variety, Huangguanyin variety, and Meizhan variety were clustered into one category, whereas the Sichuan population variety was clustered into the other. These two categories were further analyzed via orthogonal partial least squares discriminant analysis (OPLS-DA), and 48 differential compounds were identified. The Sichuan population variety was found to contain a higher concentration of floral and fruity aroma compounds while exhibiting fewer green or grassy odor compounds. To explore the floral-fruity aroma components of Sichuan Congou black tea (SCBT), forty-nine aroma-active compounds were identified through multidimensional GC–MS/olfactometry (MDGC-MS/O). Among them, six components with odor activity values (OAVs) ≥1 were regarded as key floral-fruity aroma components. Recombination and omission tests ranked the contributions of these compounds as follows: geraniol, linalool, methyl salicylate, benzeneacetaldehyde, beta-myrcene and benzaldehyde. Addition experiments confirmed for the first time that linalool, beta-myrcene and methyl salicylate are the key citrus-like compounds, offering valuable insights for the exploration of germplasm resources and quality control of black tea with special aromas.

Circadian rhythm disruption (CRD) can induce a variety of metabolic disorders. Our previous laboratory studies have shown that Pu-erh tea could alleviate CRD-induced syndromes, including obesity, intestinal dysfunction, and tryptophan metabolism disorders. However, its potential protective mechanism against CRD-induced hyperuricaemia remains unclear. In this work, we found that polyphenols of Pu-erh tea were significantly released in the stage of intestinal digestion, which might promote their interaction with gut microbes. Through animal experiments, C57BL6/J mice were given water or different doses of Pu-erh tea for 60 days, followed by a 90-day CRD, the lifestyle of modern individuals who frequently stay up late. Our results indicated that CRD mice exhibited high serum uric acid levels and gut microbiota disorders. Pu-erh tea intake significantly reshaped the gut microbiome, especially increasing the abundance of Bifidobacterium, Akkermansia and Faecalibaculum, and increased the production of short-chain fatty acids (SCFAs), especially acetic acid, which restored the function of the intestinal barrier. This improvement further regulated oxidative stress pathways (NRF2/HO-1), reduced systemic inflammatory response (IL-6, IL-1β, and TNF-α), restored hepatic function (SOD, MOD, CAT, and GSH) and modulated the activity of enzymes related to UA metabolism in the liver (XOD and ADA). Finally, Pu-erh tea intake promoted the excretion of UA and reduced the levels of UA and xanthine in the serum. Moreover, the results of antibiotic experiments showed that the UA improvement effect of Pu-erh tea depended on the existence of the gut microbiota. Collectively, Pu-erh tea intake has the potential to prevent CRD-induced hyperuricaemia by reshaping the gut microbiota.

Correction for ‘Long-term Pu-erh tea consumption improves blue light-induced depression-like behaviors’ by Sibo Zhao et al., Food Funct., 2023, https://doi.org/10.1039/d2fo02780a.

Blue light emitted by smartphones and tablets at night increases the risk of depression. Pu-erh tea has been reported to reduce the risk of depression by regulating tryptophan metabolism, but its underlying protective mechanism on depression induced by blue light at night (BLAN) remains unclear. In this work, two groups of C57BL6/J mice were given water or 0.25% (w/v) Pu-erh tea for 120 days, followed by a 45-day BLAN treatment (400 lux blue light between 21:00 and 23:00) to simulate blue light emitted from electronic equipment. Our results indicated that BLAN induced depression-like behaviors and gut microbiota disorders in healthy mice. Pu-erh tea intake significantly reshaped the gut microbiome (especially Bifidobacterium) and regulated the metabolism of short-chain fatty acids (SCFAs) which protected the integrity of the intestinal barrier. This improvement further reduced blood–brain barrier (BBB) damage and alleviated neuroinflammation by inhibiting MyD88/NF-κB pathways which finally regulated neurotransmitters such as brain-derived neurotrophic factor (BDNF) and serotonin (5-hydroxytryptamine, 5-HT). Collectively, 0.25% (w/v) Pu-erh tea has the potential to prevent BLAN-induced depression-like behaviors by reshaping the gut microbiota and increasing the generation of SCFAs via the gut–brain axis.