Effects of methionine treatment on storage quality and antioxidant activity of postharvest jujube fruit

Jujube fruits usually suffer from physiological disorders or infectious diseases during storage, leading to quality deterioration, softening, or rotting. Therefore, this study aims to investigate the effect of methionine soaking treatment on the postharvest jujube fruit decay rate and storage quality. Methionine treatment significantly reduced the decay rate of postharvest jujube fruit and effectively maintained fruit color and titratable acid. Methionine treatment effectively delayed the decrease of firmness, soluble solids, ascorbic acid, and lignin contents in jujube fruit. Methionine treatment reduced the content of alanine and phenylalanine, and increased the content of glycine in jujube fruit, but displayed no significant effect on total amino acid content. In addition, jujube fruits in the methionine treatment group had a higher total phenolic and flavonoid content and antioxidant capacity, both in free and bound forms. Compared with the control, methionine treatment also significantly increased the content of individual phenolic acid fractions (gallic acid, vanillic acid, and syringic acid) and flavonoid fractions (catechin, epicatechin, rutin) in free form as well as individual phenolic acid fractions in bound form (gallic acid and ferulic acid) in jujube fruits. Overall, this study suggested that the methionine treatment could be used as a prospective preservative to reduce the postharvest decay of jujube fruit and alleviate its nutritional quality deterioration during cold storage at 4°C.