Lipidomics reveals quality deterioration and fungal succession of rice under different humidity and brown rice rates

Stored rice susceptible to environmental influences may induce quality deterioration. To clarify the optimal storage condition for rice, the quality indicators including microbial counts and fatty acid values (FAVs) under different relative humidity (RH) and brown rice (BR) rates were monitored, and lipid composition and fungal community of three freshness rice were explored by liquid chromatography mass spectrometry (LC-MS) and internal transcribed spacer (ITS) sequencing. The results showed the fastest increase of microbial counts and FAVs at 80% RH and 8% BR, indicating the better rice quality stored at 60% RH and with a BR rate of less than 2%. During storage, Aspergillus significantly increased by 99.0%, while Alternaria decreased by 99.5%. Moreover, 927 lipid species belonging to 6 classes and 50 subclasses were identified, including glycerolipids (GLs, 40.45%), sphingolipids (SPs, 22.22%), and glycerophospholipids (GPs, 14.46%). The major differentially abundant metabolites (DAM), including SHexCer, PE-Cer, PMEOH, and SMGDG, can be identified as key markers in rice deterioration. Notably, glycerophospholipid metabolism and glycerolipid metabolism were the main pathways for poor-quality rice in contrast with sphingolipid metabolism for mild-quality rice. Additionally, the degradation of GLs, SPs, and GPs significantly correlated with the changes of Aspergillus, Wallemia, Fusarium during rice deterioration.