Metabolomics Reveals Antioxidant Metabolites in Colored Rice Grains

Abstract

Colored rice is richer in nutrients and contains more nutrients and bioactive substances than ordinary white rice. Moderate consumption of black (purple) rice has a variety of physiological effects, such as antioxidant effects, blood lipid regulation, and blood sugar control. Therefore, we utilized nontargeted metabolomics, quantitative assays for flavonoid and phenolic compounds, and physiological and biochemical data to explore the correlations between metabolites and the development of antioxidant characteristics in pigmented rice seeds. The findings indicated that, among Yangjinnuo 818 (YJN818), Hongnuo (HN), Yangchannuo 1 hao (YCN1H), and Yangzi 6 hao (YZ6H), YZ6H exhibited the highest PAL activity, which was 2.13, 3.08, and 3.25 times greater than those of YJN818, HN, and YCN1H, respectively. YZ6H likewise exhibited the highest flavonoid content, which was 3.8, 7.06, and 35.54 times greater than those of YJN818, HN, and YCN1H, respectively. YZ6H also had the highest total antioxidant capacity, which was 2.42, 3.76, and 3.77 times greater than those of YJN818, HN, and YCN1H, respectively. Thus, purple rice grains have stronger antioxidant properties than other colored rice grains. Receiver operating characteristic (ROC) curve analysis revealed that trans-3,3',4',5,5',7-hexahydroxyflavanone, phorizin, and trilobatin in the YZ6H, HN, and YCN1H comparison groups all had area under the curve (AUC) values of 1. Phlorizin, trans-3,3',4',5,5',7-hexahydroxyflavanone, and trilobatin were recognized as indices of antioxidant capability in colored rice in this research. This research adds to the understanding of antioxidant compounds in pigmented rice, which can increase the nutritional value of rice and promote the overall well-being of individuals. This type of information is of immense importance in maintaining a balanced and healthy diet.

Keywords: antioxidant activity; colored rice; flavonoids; metabolomics.

Figure 1

Analysis of differences in physiological and biochemical indices of colored rice grains: (A) CAT activity; (B) POD activity; (C) SOD activity; (D) PPO activity; (E) PAL activity; (F) TP content; (G) flavonoid content; (H) OPC content; (I) ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) value; (J) DPPH (2,2-diphenyl-1-picrylhydrazyl) value; (K) FRAP (ferric ion reducing antioxidant power) value. Different lowercase letters indicate significance at the p = 0.05 level.

Figure 2

Overview of grain metabolite information: (A) YZ6H grain sample, (B) HN grain sample, (C) YJN818 grain sample, (D) YCN1H grain sample, (E) PCA score, (F) PLS-DA permutation test, (G) Overview of the PLS-DA model, (H) PLS-DA permutation test, (I) Comparison of differentially abundant metabolites between groups, and (J) Venn diagram of the groups.

Figure 3

Schematic diagram of the phenylpropanoid, flavonoid, and anthocyanin synthesis pathways. Orange boxes represent key differentially abundant metabolites; red squares represent higher-abundance metabolites; green squares represent lower-abundance metabolites; blue represents the coexistence of both; and arrows represent synthesis paths.

Figure 4

ROC analysis: (A) ROC analysis of trans-3,3′,4′,5,5′,7-hexahydroxyflavanone, phlorizin, and trilobatin between YZ6H and YJN818; (B) ROC analysis of trans-3,3′,4′,5,5′,7-hexahydroxyflavanone, phlorizin, and trilobatin between YZ6H and HN; (C) ROC analysis of trans-3,3′,4′,5,5′,7-hexahydroxyflavanone, phlorizin, and trilobatin between YZ6H and YCN1H; (D) ROC analysis of trans-3,3′,4′,5,5′,7-hexahydroxyflavanone, phlorizin, and trilobatin between YJN818 and HN; (E) ROC analysis of trans-3,3′,4′,5,7′,7-hexahydroxyflavanone, phlorizin, and trilobatin between YJN818 and YCN1H; (F) ROC analysis of trans-3,3′,4′,5′,7-hexahydroxyflavanone, phlorizin, and trilobatin in HN and YCN1H.