Ultrasound-assisted UV-C light treatment for Escherichia coli O157:H7 inactivation in apple juice and its effect on some physicochemical and antioxidant properties of juices

In this study, ultrasound-assisted ultraviolet (US + UV-C) light treatment was used as an alternative to conventional heat treatment for the inactivation of Escherichia coli O157:H7 in apple juice. The effect of this treatment on some quality properties of apple juice (pH, antioxidant activity (AA), total phenolic (TPC) and flavonoid contents (TFC) and color properties) was determined. Two different operating modes of US treatments (C: continuous and P: pulse) were used together at 5-min intervals in the US applications. Continuous US treatment was used in combination with pulses (US(C + P)). In commercial apple juice, E.coli O157:H7 was reduced by 5.05 log CFU/g following a 40-min combined US(C + P) + UV-C light treatment at 140 W US power, corresponding to 224 kJ of applied US energy, and the microbial reduction was 4.31 log CFU/g for a 35-min combined treatment. While this treatment combination used for either 35–40 min decreased the AA, TPC, and TFC of apple juice samples, changes in the the L* values of juice samples was insignificant (p > 0.05). On the other hand, slight but significant changes were found in the b* color values of juice samples (p < 0.05). Results showed that the novel 40-min combined treatment achieved a ~ 5-log reduction of E. coli O157:H7 in commercial apple juice while preserving key quality attributes, indicating its potential for microbial inactivation with minimal quality deterioration.