Zinc Sulfate Stress Enhances Flavonoid Content and Antioxidant Capacity from Finger Millet Sprouts for High-Quality Production

Abstract

The enhancement of flavonoid content and antioxidant capacity in plants remains a significant area of focus in the investigation of plant-derived functional foods. This study systematically investigated the impact of exogenous zinc sulfate (5 mM ZnSO4) stress on flavonoid content and antioxidant capacity in finger millet (Eleusine coracana L.) sprouts, along with its underlying molecular mechanisms. The results demonstrated that treatment with 5 mM ZnSO4 significantly increased the flavonoid content in sprouts, reaching a maximum value of 5.59 μg/sprout on the 6th day of germination. ZnSO4 stress significantly enhanced the activities of PAL, 4CL, and C4H, while also considerably upregulating the expression levels of flavonoid-biosynthesis-related genes. Physiological indicators revealed that ZnSO4 stress increased the contents of malondialdehyde, hydrogen peroxide, and superoxide anion in the sprouts, while inhibiting sprout growth. As a stress response, ZnSO4 stress enhances the antioxidant system by increasing antioxidant capacity (ABTS, DPPH, and FRAP), antioxidant enzyme activity (POD and SOD), and related gene expression (POD, CAT, and APX) in sprouts. This study provides experimental evidence for ZnSO4 stress to improve flavonoid accumulation and antioxidant capacity in finger millet sprouts and provides important theoretical and practical guidance for the development of high-quality functional foods.