Synergistic impact of sonication and high hydrostatic pressure on microbial and enzymatic inactivation of apple juice

- Combined sonication and high hydrostatic pressure inactivated enzymes of apple juice.
- Complete destruction of total plate counts, yeast and molds in apple juice was achieved.
- Improvement of ascorbic acid, total phenols, flavonoids and flavonols was observed.
- Antioxidant capacity and DPPH free radical scavenging activity were increased.
- No significant differences were observed in soluble solids, pH and titratable acidity.

The combination of innovative, non-thermal technologies for the production of safe and quality fruit juices is a recent trend in food processing. The purpose of this study was to evaluate the effects of combined treatment of ultrasound (US) and high hydrostatic pressure (HHP) on enzymes (polyphenolase, peroxidase and pectinmethylesterase), microorganisms (total plate counts, yeasts and molds) and phenolic compounds (total phenols, flavonoids and flavonols) of apple juice. Moreover, its effects on ascorbic acid, antioxidant capacity and DPPH free radical scavenging activity, color values, pH, soluble solids and titratable acidity were investigated. Fresh apple juice was treated with US (25 kHz and 70% amplitude) at 20 °C for 60 min with subsequent HHP treatment at 250, 350 and 450 MPa for 10 min at room temperature. The results revealed that the combined US-HHP450 treatment caused highest inactivation of enzymes with complete inactivation of total plate counts, yeasts and molds. It also significantly improved the phenolic compounds, ascorbic acid, antioxidant capacity, DPPH free radical scavenging activity and color values. The present results suggest that the combination of US and HHP can act as a potential hurdle to produce safe and high quality apple juice with reduced enzymes and microbial activity and improved nutrition.