Cold Shock-Induced Nanocomposite Polymer Packaging Maintains Postharvest Quality of Vegetable Soybeans

Vegetable soybean is a major crop in China with significant economic value. However, it is prone to yellowing and browning during postharvest storage, which reduces quality, marketability, and competitiveness. 'Tongdou No. 6' was used to evaluate postharvest quality preservation through combined cold shock treatment and nanocomposite polymer packaging. The results demonstrate that the combined treatment effectively slows the green-to-yellow color change by significantly reducing chroma a* value, weight loss, and chlorophyll degradation. Additionally, it markedly reduces the accumulation of malondialdehyde (MDA) and reactive oxygen species (H₂O₂ and O₂·^-), while decreasing the activities of polyphenol oxidase (PPO) and peroxidase (POD). The treatment also significantly enhanced the levels of antioxidant compounds, including ascorbic acid (AsA), total phenolics, and total flavonoids, and boosted the activities of key antioxidant enzymes-ascorbate peroxidase (APX), superoxide dismutase (SOD), phenylalanine ammonia-lyase (PAL), and catalase (CAT). Moreover, the combined application of cold shock and nanocomposite polymer packaging significantly enhanced the scavenging capacity against DPPH and hydroxyl (OH^-) radicals. Overall, combining these two techniques effectively delayed senescence-related discoloration by activating the antioxidant system, regulating ROS metabolism, and reducing oxidative damage. This approach is highly effective in maintaining postharvest quality and offers a promising solution to the storage-induced deterioration of vegetable soybeans.