Postharvest Treatment of Ascorbic Acid in Reducing Browning Development of Lotus Stolon: Insight into Ascorbic Acid-Quinones Redox Cycling

Postharvest browning in lotus stolon (Nelumbo nucifera) leads to significant reductions in quality and marketability. The objective of this study was to explore the potential of ascorbic acid (ASA) treatment in mitigating browning in lotus stolon, focusing on enzymatic browning and ASA-quinones redox cycling. Lotus stolons were immersed in ASA at concentrations of 0.2%, 0.5%, 1%, and 2% for 5 min, compared to distilled water, and stored at 29 ± 2 °C and 65 ± 5% relative humidity for 48 h. The results indicated that lotus stolon exhibited rapid browning within 12 h postharvest, with the severity increasing thereafter. Application of 0.2%, 0.5%, 1%, and 2% ASA can reduce browning index by 12%, 21%, 29%, and 31%, respectively, compared to the control throughout storage. The 1% and 2% ASA treatments increased endogenous ASA level, maintained total phenolics content, reduced quinones and H₂O₂ accumulations, inhibited polyphenol oxidase and peroxidase activities, and enhanced ascorbate peroxidase activity. Additionally, the 0.5% ASA treatment enhanced ASA/dehydroascorbate redox state with increased activities of monodehydroascorbate reductase and dehydroascorbate reductase, while the 0.2% ASA treatment had only a minimal impact on physiological processes. These findings suggest that ASA treatments reduce browning in lotus stolon through concentration-dependent mechanisms.