Comparative Metabolomic Analysis Reveals the Varied Accumulations of Functional Nutrients in Differentially Pigmented Mung Bean Seeds

Coat color is closely associated with the nutritional and functional properties of mung bean (Vigna radiata L.) seeds. However, the relationship between the coat color and efficiency in nutrients of mung bean seeds has not been clearly clarified. In this study, comparative metabolomic analysis, bioactive compounds’ content measurement, and antioxidant capacities’ (ABTS+, DPPH, FRAP) determinations were conducted on four distinct varieties with different seed coat colors (black: BL, yellow: YE, yellow-green: YG, green: GR). A total of 1544 metabolites were identified in these mung bean seeds, with amino acids and derivatives, flavonoids, phenolic acids, lipids, and terpenoids, as the top five classes with high relative signal abundance. BL was abundant in flavonoids (20.12%), flavonols, anthocyanins (with six anthocyanins accounting for 22.32–565.21-fold of that in other varieties), free fatty acids, and phenolic acid. YE accumulated more amino acids and derivatives (31.85%), isoflavones (with daidzein accounting for 1.97–9.34-fold of other varieties), flavones, and lignans/coumarins. Antioxidant capacity determination results showed that BL exhibited the strongest FRAP (p < 0.05), YG had the highest DPPH scavenging activity (p < 0.05), while YE showed numerically the highest ABTS+ scavenging capacity (p > 0.05). Notably, anthocyanin accumulation was positively correlated with FRAP, while isoflavone and amino acid accumulations were positively correlated with ABTS+ scavenging capacity. These findings suggested that the overall antioxidant activity of mung bean seeds was jointly regulated by multiple metabolite classes. This study elucidates seed metabolomic variations among mung bean varieties, providing insights for functional breeding and precision food development.