Preharvest and Postharvest γ-Aminobutyric Acid Treatment Enhance Quality and Shelf Life in Strawberry (Fragaria × ananassa) Fruits

Strawberry fruits are among the popular berries due to their bright colour and desirable flavour. However, their rapid quality loss results in a short shelf life and low economic value. This study aimed to comprehensively examine the effects of preharvest spraying at small green (SG), large green (LG), white (W), and red-turning (RT) fruit stages, along with postharvest treatments using γ -aminobutyric acid (GABA) and its synthesis inhibitor, 3-mercaptopropionic acid (3-MP), on fruit quality and shelf life. Preharvest application of 10 mM GABA at RT stage significantly enhanced the fruit colour, weight, firmness, soluble solids content (SSC), and the contents of GABA, citric acid, Vc, and soluble sugars at harvest. Postharvest treatment with 10 mM GABA notably delayed the decreases in organic acids, soluble sugars, firmness, colour, and SSC. In addition, postharvest 10 mM GABA treatment reduced the decay incidence and weight loss, while 0.2 mM 3-MP had opposite effects in both preharvest and postharvest treatments. GABA partially induced or inhibited the expression of genes involved in citrate metabolism. Overall, GABA demonstrates effectiveness in improving fruit quality (e.g., increase in organic acids, soluble sugars, firmness, colour, and SSC after preharvest treatment or delaying the decrease of these indices) and extending shelf life by modulating the transcripts of genes related to citrate metabolism.