Semi-quantitative lipidomics reveals the characteristics of lipid metabolism in sheep milk fermentation

In this study, a semi-quantitative lipidomics approach was utilized to comprehensively delineate the alterations in the lipid profiles of sheep milk before and after fermentation. A total of 887 lipids were identified in both raw sheep milk (RM) and fermented sheep milk (FM), which could be systematically classified into 30 subclasses, with triglycerides, phosphatidylethanolamines, and phosphatidylcholines emerging as the predominant lipid types in both sample groups. In total, 91 significantly different lipids (SDLs) were selected between RM and FM. Compared to RM, 33 SDLs were up-regulated in FM, while 58 SDLs were down-regulated. Furthermore, based on fold change (FC) values, phosphatidylserines (PS (18:1_20:2) and PS (16:0_20:0)) and lysophosphatidylethanolamines (LPE (18:1/0:0) and LPE (0:0/16:0)) were selected as potential biomarkers for distinguishing between RM and FM. Further analysis revealed that 91 SDLs were involved in 39 metabolic pathways, with glycerophospholipid metabolism identified as the most crucial among them. These results provided comprehensive lipidomics data on sheep milk and its fermented milk, which are invaluable for investigations into the nutritional health benefits and flavor characteristics of fermented milk.