Impact of ultrasound-assisted mild heat treatment on safety, quality, and shelf life of fresh watermelon juice

• Ultrasound with mild heat was used to enhance the safety and shelf life of watermelon juice. • Quality parameters and bioactive compounds did not change considerably after treatment. • Ultrasound with mild heat treatment significantly reduced microbial loads of the juice. Ultrasound is an emerging non-thermal food processing method gaining popularity among health-conscious consumers. However, its limited microbial reduction necessitates combination with mild heat to increase disinfection efficiency. This study investigated the effect of ultrasound- assisted mild heat treatment (45 °C) applied for (0, 15, 30, 45, and 60 min) on the decontamination efficacy, quality and shelf life of fresh watermelon juice (FWJ). Microbial loads, physicochemical, bioactive and antioxidant properties were monitored during storage at 3 °C for 21 days. Untreated juice exceeded the acceptable limit (6.0 log CFU/mL) and developed off-odors by day 7. In contrast, for 60 min treated sample maintained significantly lower microbial loads, remaining within safe limits up to 14 days. A slight increase in color difference (∆E*) was observed following treatment. No significant changes ( p > 0.05) were found in pH and total soluble solids after treatment, whereas titratable acidity and vitamin C content showed significant changes. Quality parameters gradually declined during storage. Total phenolic, flavonoid and tannin contents remained unchanged after 15, 30, and 45 min treatments. Notably, 30 min treatment showed the highest antioxidant activity (21.24 mg/100 mL), which decreased during storage. Findings indicate that ultrasound-assisted mild heat treatment improves microbial safety and prolongs the shelf life of watermelon juice.