Acidic Electrolyzed Water Activates Disease Resistance and Sustains Postharvest Quality of Yellow Passion Fruit

Passion fruit deteriorates rapidly after harvest owing to fungal decay and quality loss. This study examined whether acidic electrolyzed water (AEW, pH 2.5) could strengthen host defense responses and thereby prolong the marketable storage period of passion fruit. Freshly harvested yellow passion fruits (without any prior storage) were immersed for 20 min in AEW containing 0 (control), 30, 60 or 90 mg/L available chlorine concentration (ACC) and then packaged in polyethylene film bags and stored at 25 °C for 15 days to simulate typical ambient handling/marketing conditions, where polyethylene packaging is commonly used to maintain a high-humidity microenvironment and reduce moisture loss; physicochemical attributes, decay parameters and disease-resistance-related enzyme activities were then monitored. AEW—particularly at 60 mg/L ACC—significantly lowered decay incidence, disease index and cell membrane permeability while preserving pericarp color (hue angle h, L*) and pulp titratable acidity, vitamin C, total soluble solids, and total soluble sugars. The same treatment elevated the concentrations of disease-resistant metabolites (total polyphenolics, flavonoids and lignin) and up-regulated the activities of peroxidase, cinnamate-4-hydroxylase, 4-coumarate CoA ligase, phenylalanine ammonia-lyase, cinnamyl alcohol dehydrogenase, chitinase, and β-1,3-glucanase. These findings demonstrate that AEW mitigates postharvest deterioration of passion fruit by activating the metabolism of disease-resistant substances, highlighting its potential as an eco-friendly technology for maintaining quality during ambient handling/marketing conditions.