To understand differences in the quality of different conventional japonica rice varieties and variations in metabolites related to rice quality, the quality of three conventional japonica varieties was determined, and the metabolites of the milled rice were investigated using nontargeted metabolomics technology. The results showed that the taste value (TV) of Yangda 4Hao (YD4) was significantly higher than that of Yangda 3Hao (YD3) and Huaidao 5Hao (HD5). The protein content (PC) of HD5 was significantly higher than that of YD3 and YD4. PC was significantly negatively correlated with TV. Ninety-one differential metabolites (59 increased and 32 decreased) were identified between YD3 and HD5. A total of 144 differential metabolites (96 upregulated and 48 downregulated) were identified between YD4 and HD5. A total of 114 differential metabolites (40 increased and 74 decreased) were identified between YD3 and YD4. The metabolites with a high correlation to rice quality were mostly involved in the amino acid metabolism pathway. Amino acid metabolites play an important role in the formation of rice quality. The key metabolites in the synthesis and regulation of metabolic pathways are sucrose, levan, and amylose, which are carbohydrates, and L-glutamine, L-aspartic acid, and L-asparagine, which are amino acid metabolites. It can be seen from this study that the metabolites of sucrose, levan, amylose, L-glutamine, L-aspartic acid, and L-asparagine may be the key metabolites in the quality formation of high-quality rice varieties.
Keywords: amino acid; carbohydrates; conventional japonica rice; metabolic pathway; metabolomics; rice quality.