Synergistic effects of abscisic acid and ethylene on the ripening of ‘Eva’ apples: enhancing skin red coloration, secondary metabolites, and antioxidant activity

This study aimed to evaluate the effects of isolated and combined applications of ethylene and abscisic acid (ABA) on the red color development, phenolic compounds, biogenic amines, and antioxidant activity in ‘Eva’ apples to enhance fruit quality. The experiment was conducted in a commercial orchard, where ethylene (0.35 and 0.70 mg L -1 ) and ABA (400 and 600 mg L -1 ) were applied individually and in combination, following a randomized block design with four replicates. After harvest, fruits were evaluated for physicochemical parameters (soluble solids, titratable acidity, pH, and firmness), skin color (lightness, chroma, and hue angle), total phenolic compounds, total flavonoids, monomeric anthocyanins, antioxidant activity (2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays), and biogenic amines in both the skin and pulp using ultra-high performance liquid chromatography (UHPLC). The results demonstrated that the combined application of ethylene and ABA (0.70 + 6.0 mL L -1 ) significantly improved skin red coloration, reducing lightness by up to 39% and increasing anthocyanin content by more than 1200%, compared to control. Additionally, ABA treatments increased total phenolic compounds by up to 65% and enhanced antioxidant activity (FRAP) by up to 56% in the skin. The biogenic amine profiling revealed increases of up to 22% in total amines under combined treatments, particularly affectiong tryptophan and 5-hydroxytryptophan levels. These findings highlight that the synergistic application of ethylene and ABA is a promising strategy for improving the commercial and nutritional quality of ‘Eva’ apples by enhancing pigmentation, bioactive compounds, and antioxidant potential. Graphical abstract of ‘Eva’ apples subjected to ethylene (Et) and abscisic acid (ABA) application.