Comparison of metabolites between brown rice and germinated brown rice in a Korean weedy rice germplasm

Weedy rice is a semi-wild species that has survived for a very long time in rice fields, so its seeds could contain more functional substances than cultivated rice. Additionally, during the process of seed germination, some physiologically active substances that were not present in the seed are newly synthesized, so the functional compounds of germinated seeds could be improved over those of untreated raw seeds. From this perspective, we evaluated metabolite compounds of the brown rice (BR) and germinated brown rice (GBR) of WD3 compared with a cultivated rice, Sindongjin (SDJ). WD3 is a weedy rice selected for antioxidant activity from 199 accessions of Korea-native weedy rice germplasm (Cho et al., J Crop Sci 63:219-228, 2018). Metabolites were measured by using UPLC coupled with tandem mass spectrometry. Pareto scaling method prior to statistical and chemometric analysis were used for data acquisition and processing for metabolize compounds. OPLS-DA was conducted to develop discriminatory models. To support the potential biomarkers identification and further understanding of this study, the information on compounds was queried on the Chemspider web page. The obvious separation of metabolites between WD3 and SDJ in both BR and GBR were observed, in which a total of 103 compounds were detected. Among them, 52 compounds were known and 51 compounds were unknown. In the known compounds, long aliphatic chains were commonly found and the others were steroids, alkaloids, polyols, peptide and aromatic acid. Some metabolites such as 3 alkaloid compounds, 2 steroids, 1 aromatic acid and 15 long aliphatic chains were significantly increased after germination in WD3 seeds. Among them, the content of C45H84NO7P was increased by more than 1,000,000 times after germination. These compounds found in the GBR of WD3 might also be correlated to the nutritionally qualities claimed to be responsible for the advantageous properties of GBR.