Combined aqueous ozone and ultrasound application inhibits microbial spoilage, reduces pesticide residues and maintains storage quality of strawberry fruits

Inappropriate use of pesticides and unhygienic supply chains contaminate fresh fruit and vegetables with health-hazardous micro-organisms and chemical residues. Here, combined efficacy of aqueous ozone and ultrasound to disinfect and decontaminate strawberry fruits from food-borne microbial pathogen and pesticide residues was evaluated. Strawberry fruits were exposed to either ozone (flow rate ≥ 3.3 mg min⁻¹ for 125 g strawberry L⁻¹ water) or ultrasound (40 kHz at 100 W) for 3, 6 and 9 min. Treatment of strawberry fruits with either ozone or ultrasound for 3 min effectively reduced bacterial survival by 44-fold and 17-fold, respectively, compared to control. Then, strawberry fruits were simultaneously treated with both ozone and ultrasound for 1, 2 or 3 min and stored at 2 ± 0.5 °C and 95% relative humidity for 12 days. Ozone and ultrasound treatment for 3 min was most effective in reducing bacterial survival (98%) and residues of various pesticides (98–99%) compared to control. Strawberry fruits treated with ozone and ultrasound for 3 min exhibited delay in fungal decay by 4 days and 4% reduction in weight loss during cold storage for 12 days. Also, gradual decline in total soluble solids, titratable acidity, pH, ascorbic acid and anthocyanins in cold-stored strawberry fruits was also hindered. Ozone and ultrasound treatment for 3 min also restrained 62% higher catalase, 52% higher peroxidase, and 70% higher superoxide dismutase in strawberry tissues compared to control after 12 days in cold storage. Thus, combined treatment of ozone and ultrasound for 3 min increased marketable life of strawberry fruits for 6 more days under cold storage conditions. Overall, results revealed a positive effect of ozone and ultrasound on disinfecting and decontaminating strawberry fruits along with extending their marketable life under cold storage conditions.