Molecular Hydrogen Improves Storage Quality of Bok Choy by Reducing Water Loss and Maintaining Cell Wall Integrity

Bok choy (Brassica rapa var. chinensis) experiences rapid postharvest quality decline, primarily due to water loss. This study aims to evaluate the effect of H₂-modified atmosphere packaging (MAP; containing 0.01%, 0.1%, and 1% H₂) on extending the shelf life of bok choy. First, we observed that the storage of bok choy for 9 d (4 °C and 85% relative humidity) was accompanied by a decreasing tendency of molecular hydrogen (H₂) production. Subsequently, the effects of hydrogen (H₂) administered via modified atmosphere packaging on the preservation of bok choy were investigated. The results showed that among the treatments, 0.1% H₂ MAP could effectively improve the storage quality of bok choy under identical storage conditions. Compared to the control groups at 9 d, the contents of chlorophyll a/b, carotenoids, total phenols and flavonoids, and total soluble solids were increased by 43.75%, 40%, 27.78%, 28.89%, 102.38%, and 7.29%, and weight loss rate and electrolyte leakage were reduced by 31.77% and 50.19% (p < 0.05). Meanwhile, the combined water fraction was increased and respiration rate was decreased. Biochemical evidence further showed that xyloglucan endotransglycosylase 2/3 (XET2/3) transcripts and xyloglucan endotransglycosylase (XET) activity, responsible for cell wall degradation, were decreased. By contrast, peroxidase 31/37 (POD31/37) genes and peroxidase (POD) activity, key to the synthesis of lignin, were increased. Importantly, these changes were positively matched with the maintenance of cell wall integrity by H₂ MAP. Together, the results clearly suggested that H₂ MAP could maintain the postharvest quality of bok choy via alleviating water loss and maintaining cell wall integrity. These findings thus provide a useful technology for improving the storage quality of vegetables prone to water loss.