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.