Effects of Postharvest Methyl Jasmonate (MeJA) and γ -Aminobutyric Acid (GABA) on the Quality and Storability of Granny Smith Apple Fruit

This study investigated the effects of postharvest methyl jasmonate (MeJA) and γ-aminobutyric acid (GABA) treatments on the quality and storability of Granny Smith apples harvested from a private orchard in Duhok Governorate, Kurdistan Region, Iraq. The reported treatment concentrations were 0, 0.75, 1.5, and 2.5 mM MeJA, applied by dipping for five minutes, and 0, 5, 10, and 15 mM GABA, applied by dipping for fifteen minutes. Fruit were stored for 30, 60, and 120 days at a reported temperature of 1 ± 1 ∘C and 85–90% relative humidity. The tabulated results showed that 2.5 mM MeJA maintained greater firmness and ascorbic acid content and reduced weight loss compared with the untreated MeJA level. GABA treatments also maintained firmness, while their effects on weight loss, acidity, and ascorbic acid depended on concentration. Main effects of either treatment on total soluble solids and total phenolic content were not statistically significant according to the reported Duncan groupings. Titratable acidity was numerically higher at the two highest MeJA concentrations, but the MeJA main-effect means shared the same significance letter. Superoxide dismutase and catalase activities were evaluated after 120 days and were generally greater in treated fruit, although the strongest response depended on the enzyme and treatment combination. Across storage periods, firmness and titratable acidity decreased, whereas weight loss and total soluble solids increased. Ascorbic acid and total phenolic content reached their highest storage-period means at 60 days. Overall, the results support the potential of MeJA and GABA dipping treatments to preserve selected quality attributes, while demonstrating that benefits were specific to the response variable and storage interval rather than uniform across all measured characteristics.