Abstract: Riboflavin (vitamin B2), a safe and non-toxic food additive, plays an important physiological role in plant growth, development and stress resistance. In this study, we investigated the effects of exogenous riboflavin on the postharvest quality maintenance of pak choi (Brassica rapa subsp. chinensis). Pak choi was treated at postharvest with different concentrations of riboflavin (0, 200, 400, 600, and 800 μmol/L) and evaluated for color, chlorophyll content, chlorophyll metabolism-related gene expression and antioxidant enzyme activity. The results showed that 400 μmol/L riboflavin treatment effectively maintained the quality of postharvest pak choi, mainly by 1) reducing the expression of chlorophyll catabolism-related genes (BrNYC1, BrPPH, BrPAO, and BrSGR1/2) to delay chlorophyll degradation, 2) reducing the total bacterial count on the surface of pak choi leaves to reduce pathogenic spoilage, and 3) upregulating the expression of antioxidant enzyme genes (BrPOD, BrSOD and BrCAT) and enhancing the antioxidant enzyme activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) to increase antioxidant activity. In addition, riboflavin treatment maintained high levels of antioxidants (ascorbic acid and total phenolics), thereby increasing the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity and reducing the production of malondialdehyde (MDA). These findings are helpful to understand how riboflavin affects the postharvest quality of leafy vegetables, which is of reference significant for improving the postharvest commercial value and quality of leafy vegetables.

Key words: pak choi; riboflavin; yellowing; antioxidant