Investigation on the Lipid Profile of Ripened Pu-erh Tea and Relationships Between Their Changes and Key Aromatic Volatiles.

Ripened Pu-erh tea is a special tea with unique flavor and obtained by solid fermentation of microorganisms. This work aimed to investigate the changes of lipid metabolites during fermentation and the association between lipids and the aroma of ripened Pu-erh tea based on ultra-high-performance liquid chromatography-high resolution mass spectrometry and GC-MS. A total of 217 lipids and lipid-soluble substances covering 19 subclasses were detected and characterized. Compared with green tea, black tea, and raw Pu-erh tea, ripened Pu-erh tea showed the highest levels of fatty acids. The contents of 36 lipids varied remarkably with fermentation time, and thus these compounds were screened as differential metabolites. These changes were mainly caused by the degradation of glycerophospholipids (folds change: 0.48-0.13) and the formation of fatty acids (folds change: 5.2-11.2). Results of Pearson correlation analysis showed that a few of the aromatic volatiles, including 2-octenal, 3,5-octadien-2-one, 2,4-heptadienal, and 2,6-nonadienal showed obvious negative correlations with phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol, but significant positive correlations with fatty acids 18:2 and 18:1. This study provided a further understanding of the lipid composition of ripened Pu-erh and their changes during tea production.