Changes in lipids and medium- and long-chain fatty acids during the spontaneous fermentation of ripened pu-erh tea.

During the fermentation of ripened pu-erh tea (RPT), the composition of lipids and other compounds changes significantly. In this study, we conducted industrial fermentation of RPT and observed that the levels of water extract, tea polyphenols, free amino acids, catechins, caffeine, rutin, theophylline, luteolin, and myricetin decreased, while the level of soluble sugar increased. Additionally, the levels of gallic acid, quercetin, ellagic acid, and kaempferol first increased and then decreased during fermentation. We identified a total of 731 lipids, which were classified into seven categories using a lipomics method. Among these lipids, 85 with relatively high contents decreased, while 201 lipids with low contents increased after fermentation. This led to an overall decrease in the sum contents of lipids and dominant lipids, including glycerophospholipids and saccharolipids. We also detected 33 medium- and long-chain fatty acids, with α-linolenic acid (881.202 ± 12.13-1322.263 ± 19.78 µg/g), palmitic acid (797.275 ± 19.56-955.180 ± 30.49 µg/g), and linoleic acid (539.634 ± 15.551-706.869 ± 12.14 µg/g) being the predominant ones. Coenzymes Q9 (62.76-63.57 µg/g) and Q10 (50.82-59.33 µg/g) were also identified in the fermentation process. Our findings shed light on the changes in lipids during the fermentation of RPT and highlight the potential bio-active compounds, such as α-linolenic acid, linoleic acid, Coenzymes Q9, and Q10, in ripened pu-erh tea. This contributes to a better understanding of the fermentation mechanism for RPT.

Changes in sensory characteristics, chemical composition and microbial succession during fermentation of ancient plants Pu-erh tea.

"Ancient tea plants" are defined as tea trees > 100 years old, or with a trunk diameter > 25 cm; their leaves are manufactured to high - quality, valuable ancient plants pu-erh tea (APPT). In this study, a fermentation of APPT were developed, and outstanding sweetness of APPT infusion was observed. During fermentation, the content of soluble sugars, theabrownins (p < 0.05), as well as 41 metabolites were increased [Variable importance in projection (VIP) > 1.0; p < 0.05 and Fold-change (FC) FC > 2]; While relative levels of 72 metabolites were decreased (VIP > 1.0, p < 0.05 and FC < 0.5. Staphylococcus, Achromobacter, Sphingomonas, Thermomyces, Rasamsonia, Blastobotrys, Aspergillus and Cladosporium were identified as dominant genera, and their relative levels were correlated with contents of characteristic components (p < 0.05). Together, changes in sensory characteristics, chemical composition and microbial succession during APPT fermentation were investigated, and advanced the formation mechanism of its unique quality.

The dynamics of microbial community and flavor metabolites during the acetic acid fermentation of Hongqu aromatic vinegar.

In this study, we investigated the dynamics of microbial community and flavor metabolites during the traditional fermentation of Hongqu aromatic vinegar (HAV) and subsequently explored the potential relationship between microbiota and flavor metabolites. The microbiome analysis based on high-throughput sequencing (HTS) of amplicons demonstrated that Lactobacillus, Acetobacter and Clostridium were the dominant bacterial genera, while Alternaria, Candida, Aspergillus and Issatchenkia were the dominant fungal genera during the acetic acid fermentation (AAF) of HAV. A total of 101 volatile flavor compounds were identified through gas chromatography-mass spectrometry (GC-MS) during HAV fermentation, including esters (35), alcohols (17), aldehydes (11), acids (11), ketones (7), phenols (10), and others (10). Redundancy analysis (RDA) was used to reveal the correlation between microbiota and volatile flavor compounds. Lactobacillus and Acetobacter were the two bacterial genera that have the great influence on the production of volatile flavor components in HAV. Among them, Lactobacillus was positively correlated with a variety of ethyl esters, while Acetobacter positively contributed to the formation of several organic acids. Furthermore, the non-volatile metabolites were detected by ultra-high-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS). A total of 41 dipeptides were identified during HAV fermentation, and most of them may have sensory characteristics and biological activities. RDA showed that Aspergillus, Epicoccum, Issatchenkia, Candida and Malassezia were the most influential fungal genera on non-volatile metabolites. In particular, Epicoccum was first reported in Hongqu vinegar and showed a positive correlation with the production of various organic acids. In conclusion, this study provides a scientific basis for understanding the flavor generation mechanism of HAV, and may be valuable for developing effective techniques to select suitable strains to improve the flavor quality of HAV.

[Pollution Characteristics and Risk Assessment of Antibiotics in Lianhua Reservoir].

Thirteen typical antibiotics in surface water of the Lianhua Reservoir were analyzed using HPLC/MS/MS to assess the pollution characteristics and risk levels. Ten antibiotics except for erythromycin, sulfadiazine, and sulfamethoxazole were detected in surface water and the total concentration of antibiotics varied between non-detectable (n.d.) and 925.26 ng ·L-1. Azithromycin had the highest concentration (n.d.-232.61 ng ·L-1) with the detection frequency of 75%, followed by enrofloxacin (n.d.-187.69 ng ·L-1), tetracycline (n.d.-155.05 ng ·L-1), and ciprofloxacin (n.d.-83.66 ng ·L-1) with the detection frequencies over 60%. The spatial distribution of antibiotics was as follows: total concentration of upstream (sampling point 1) > Aoxi River stream tributary (sampling point 2) > reservoir downstream (sampling point 3) > reservoir entrance (sampling point 4) > reservoir area (sampling point 5). The seasonal variations in the concentrations of antibiotics were evident; total concentrations in the dry season were significantly higher than those in the wet and normal seasons. The results of the environmental risk assessment indicated that ofloxacin, enrofloxacin, and ciprofloxacin pose significant risks to the environment. In the Lianhua Reservoir, ciprofloxacin showed high potential risk to the ecological environment, while the environmental risks of other antibiotics in the reservoir were below the medium level. The combined risk value of the antibiotics in the dry season was higher than that in the wet and normal seasons.