Glycine Betaine Treatment Enhanced Eggplant Chilling Tolerance by Modulating Peel and Flesh Metabolic Responses

Eggplant is highly susceptible to chilling injury (CI) when stored at temperatures below 10 °C. This study evaluated the efficacy of glycine betaine (GB) as a pre-storage treatment to enhance chilling tolerance in eggplant, focusing on tissue-specific responses in the peel and flesh. GB concentrations of 0, 5, and 10 mM were tested, with 10 mM identified as the most effective in mitigating CI symptoms and weight loss. Subsequently, eggplants treated with 10 mM GB were stored for 21 days at 4 °C, followed by 2 days at 20 °C, to assess their physiological and biochemical properties. At the end of the storage period, GB treatment significantly reduced all CI-related indicators, including the CI index, weight loss, respiration rate, softening, flesh browning, electrolyte leakage, and malondialdehyde content, thereby extending shelf life by five days compared with untreated fruit. Principal component analysis revealed that severe CI in control fruit was associated with elevated levels of proline, endogenous GB, and unsaturated fatty acids (UFAs) in the peel, indicating that this outer tissue is the primary site of cold-stress responses in eggplant. Conversely, GB-treated fruit exhibited enhanced chilling tolerance characterized by reduced softening, greater antioxidant retention in both tissues, and maintenance of UFA levels in the flesh, while peel proline, GB, and fatty acid contents remained stable. Overall, our findings provide the first evidence that GB confers cold protection by modulating tissue-specific metabolic responses in eggplant peel and flesh, offering a simple and cost-effective strategy to extend shelf life.