Postharvest Application of Γ-Aminobutyric Acid As a Natural Bioactive Compound Enhances Quality Retention in Hawthorns During Cold Storage Via Activation of Antioxidant Defense Mechanisms

The limited storability of hawthorn fruits is primarily due to rapid metabolic changes that compromise fruit quality. While cold storage is recommended to stall this process, it can induce chilling injury (CI) characterized by pitting. In this study, the impact of gamma-aminobutyric acid (GABA) (GABA-0, GABA-5 mM, and GABA-10 mM) on "Sultan" hawthorns stored at 2 degrees C and 90% RH for 120 days was evaluated. Both GABA treatments effectively reduced CI, maintaining fruit quality with greener peels, higher membrane stability index (MSI), and better retention of firmness and titratable acidity (TA), while reducing total soluble solids (TSS) compared to the control. GABA treatments reinforced the antioxidant defense system, increasing activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as concentrations of total phenol content (TPC), total flavonoid content (TFC), and vitamin C. Treatment with GABA reduced the activities of hydrolytic enzymes and polyphenol oxidase (PPO), as well as microbial counts and decay incidence. The findings indicate that GABA at 10 mM reduced CI by 6% compared with the control (20% after 120 days of cold storage), while also contributing to delayed senescence and improved maintenance of quality attributes in hawthorn fruit.