Discovering new lipid metabolites in food using untargeted liquid chromatography/mass spectrometry

Essential dietary nutrients, such as lipids, are the most important components of food. Despite significant advancements in analytical sciences, the analysis of lipid composition in food remains limited. This research aims to explore novel lipid metabolites in unexplored foods such as herbal tea, sorghum (Sorghum bicolor (L.) Moench) and rice (Oryza sativa subsp. Japonica). To achieve this, we extracted the total lipids through liquid-liquid extraction and performed the untargeted lipid analysis using UFLC/LTQ-Orbitrap XL along with lipid annotation by MS DIAL software.

Our analysis revealed over 300 lipid molecular species in herbal tea, including novel lipids such as short-chain fatty acid esters of hydroxy fatty acids, with 4-hydroxy phenyl nonanoic acid as the structural core. Additionally, we identified the abundance of α-linolenic acid (FA 18:3), an ω-3 fatty acid, in the herb Sasa vieitichi, while arachidonic acid (FA 20:4) ), an ω-6 fatty acid, in Equisetum arvense. We also explored the lipid composition of six sorghum cultivars grown in a single field trial in Australia. We identified and characterized over 194 lipid molecular species, including novel bioactive lipids known as FAHFAs (fatty acid esters of hydroxy fatty acids) in sorghum grains. Notably, the Buster cultivar exhibited the highest balance of unsaturated to saturated fatty acid ratios. Furthermore, we examined fifty-six japonica rice cultivars for their lipid profiles and discovered a unique class of FAHFA lipids that had not been previously identified. Interestingly, these FAHFAs appear to be more abundant in green pigmented rice compared to brown, and black varieties.

Our established untargeted analysis technique has led to the discovery of several unknown lipids and detailed lipid compositions in common dietary foods. This research is important for society because understanding the bioactive lipid composition in functional foods can help identify potential sources and be valuable for developing novel nutraceuticals.