Abstract: An ultra-high performance liquid chromatography quadrupole/orbitrap high resolution mass spectrometry (UPLC-Q-Orbitrap HRMS)-based lipidomics approach was developed for evaluating lipids in milk fermented by Streptococcus thermophilus. HRMS scan information dependent acquisition-product ion scan was performed using an electrospray ionization (ESI) source in the positive and negative ion modes to acquire mass spectra. The lipid composition of the fermented milk was analyzed in detail at the molecular level. A total of 1 716 lipids were detected in the sample, including 861 glycerides, 540 phospholipids, 282 sphingolipids and 33 glycolipids. Under the positive mode, the contents of glycerolipids, phospholipids and sphingolipids were determined to be 95.84%, 3.08% and 1.08%, respectively, and triacylglycerols (TG) 16:0/6:0/14:0, 4:0/14:0/16:1, and 10:0/10:0/12:0 were the dominant lipid components (> 5%). Under the negative mode, the contents of phospholipids, sphingolipids and glycolipids were determined to be 35.34%, 28.15% and 36.51%, respectively, and monogalactosylmonoacylglycerol (MGMG, 2:0) was the main lipid component ( > 5%). Good detection performance was observed on glycerides in the positive ion mode, and on phospholipids, sphingolipids and glycolipids in the negative ion mode. MS analysis in the positive and negative ion modes could provide a full understanding the composition of lipid components in milk fermented by S. thermophilus. The proposed method for lipid analysis had the characteristics of high throughput, high sensitivity and high accuracy. It provides a reliable method for analysis of lipids in fermented milk and lays the foundation for enriching research on the biological functions of dairy lipids.

Key words: fermented milk; lipidomics; Streptococcus thermophilus; lipid