Effects of hot water treatment on chilling injury and fruit quality in peach during postharvest storage

To investigate the effects and mechanisms of postharvest hot water treatment (HWT) on alleviating chilling injury (CI) and maintaining storage quality of peach fruits, this study utilized 'HuijingMilu' peaches as experimental material. The research examined the impacts of three different hot water treatment protocols: HWT1 (40 ℃ for 20 minutes), HWT2 (46 ℃ for 10 minutes), and HWT3 (52 ℃ for 3 minutes) on various quality parameters during cold storage at 4℃ for 28 days, followed by room temperature storage (25 ℃) for 1 and 3 days. The study specifically focused on fruit quality attributes, chilling injury development, and antioxidant defense responses throughout the storage period. The experimental results demonstrated significant differences between the treatment groups and the untreated control (CK) group. Notably, while both HWT1 and HWT2 showed some positive effects, HWT3 emerged as the most effective treatment in multiple aspects of fruit quality preservation. HWT3 treatment successfully mitigated the development of chilling injury symptoms, moderated the increase in respiratory rate, and regulated ethylene evolution patterns. Furthermore, this treatment effectively suppressed the accumulation of malondialdehyde (MDA), a key indicator of membrane lipid peroxidation, and prevented excessive increases in cell membrane permeability, which is closely associated with cellular membrane integrity. Quantitative analysis revealed particularly striking results at specific time points during the storage period. For instance, at day 14 of storage, peach fruits treated with HWT3 showed a remarkable 45.5% reduction in MDA content compared to the control group. The treatment's effectiveness was further demonstrated at day 29 of storage, where the relative electrical conductivity in the control group exceeded that of the HWT3-treated group by a factor of 1.3, with statistical significance (P＜0.05). One of the most notable achievements of the HWT3 treatment was its ability to preserve important antioxidant compounds within the fruit tissue. The treatment effectively delayed the degradation of several key antioxidant components, including vitamin C, flavonoids, total phenolic compounds, and glutathione. A particularly remarkable observation was made on day 28 of storage, where the vitamin C content in HWT3-treated fruits maintained levels 2.52 times higher than those in the control group (P＜0.05), highlighting the treatment's exceptional effectiveness in preserving this essential nutrient. During the middle phase of storage, HWT3-treated peach fruits exhibited enhanced oxidative stress resistance, as evidenced by reduced levels of reactive oxygen species, specifically hydrogen peroxide (H₂O₂) and superoxide anion (O₂^-). This improvement in oxidative stress management was accompanied by significant upregulation (P＜0.05) in the expression of key antioxidant defense genes, including those encoding superoxide dismutase (SODs), catalase (CATs), and glutathione S-transferase (GSTs). These molecular changes suggest that HWT3 treatment enhances the fruit's inherent antioxidant defense mechanisms at both the biochemical and genetic levels. In conclusion, the study provides comprehensive evidence that HWT3 treatment effectively maintains fruit quality through multiple mechanisms. It successfully preserves antioxidant compound levels during late storage periods while enhancing antioxidant gene expression during mid-storage phases. This dual action effectively inhibits reactive oxygen species-induced damage and subsequently reduces chilling injury in peach fruits. The findings suggest that HWT3 represents an optimal hot water treatment protocol for maintaining peach fruit quality during cold storage and subsequent shelf life. The research contributes valuable insights into the molecular and biochemical mechanisms underlying the protective effects of hot water treatment against chilling injury in peach fruits, providing a scientific basis for its practical application in postharvest fruit preservation.