Abstract: In order to analyze the differential metabolites between brown rice and white rice and related metabolic pathways, high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS)-based non-targeted metabolomics was used to analyze the metabolites of brown rice and white rice, and multivariate statistical analyses including principal component analysis (PCA), partial least square discriminant analysis (PLS-DA) and cluster analysis were conducted. Based on the significant changes with multiple difference ≥ 1.2 or ≤ 0.833 3, P < 0.05 and variable importance in the projection (VIP) ≥ 1, 460 differential metabolites including 300 up-regulated metabolites and 160 down-regulated metabolites were detected between brown rice and white rice in the positive ion mode, and 579 differential metabolites including 383 up-regulated metabolites and 196 down-regulated metabolites in the negative ion mode. In the positive mode, two metabolic pathways (phenylalanine, tyrosine and tryptophan biosynthesis, and histidine metabolism) with the involvement of four metabolites were determined. In the negative mode, five metabolic pathways (betalain biosynthesis, C5-branched dibasic acid metabolism, purine metabolism, zeatin biosynthesis and carbon metabolism) with the involvement of 10 metabolites were determined. These results showed that the differential metabolites were mainly up-regulated in brown rice compared with polished rice, and they regulated the contents of amino acids, polyphenols, and fatty acids in rice bran and embryos by affecting metabolic pathways such as amino acid metabolism, carbon metabolism, purine metabolism, zeatin metabolism, and betaine biosynthesis, thereby improving the nutritional quality of rice. This study provides a theoretical basis for the nutritional evaluation of brown rice, and the development of brown rice processing technologies and products.

Key words: brown rice; white rice; non-targeted metabolomics; differential metabolites; metabolic pathways