Effects of ultrasound, microwave, and their combined treatments on the shelf life and quality characteristics of fresh litchi juice

This study investigated the effects of ultrasound and microwave and their combinations on preserving the quality of litchi juice during 21 days of storage. The physiochemical analysis exhibited that, the pH and Vitamin C content decreased gradually, whereas TSS, TA, and color values increased over the storage period. It was observed that the synergistic approach of sonication and microwave had positively impacted the bioactive components of fresh litchi juice. The results indicate that the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant properties of fresh litchi juice were changed significantly (p≤0.05) and reduced with increases in the treatment time. For instance, combined treatment (T6) exhibited the TPC (81.84±0.72 to 55.74±0.47 mg GAE/100 mL of juice) and TFC (3.31±0.136 to 3.12±0.126 mg QE/100 mL of juice) for 0 to 21 days of storage. On the other hand, the DPPH radical scavenging activity of litchi juices was increased notably (p≤0.05) and subsequently decreased after treatments, where the values ranged between 106.35±0.66 to 123.42±1.09 mg AAE/100 mL of juice at initial storage. The highest microbial growth inhibition was found in T6, and the values were (4.05-5.01 log10 cfu/mL) for total plate count and (3.63-4.78 log10 cfu/mL) for total yeast and mold during initial storage. Therefore, the combined treatment of sonication and microwave could be employed without chemical preservatives to treat fresh litchi juice with better retention of physicochemical attributes and bioactive phytochemicals.