Combination of TiO₂-UV Photocatalysis and High Hydrostatic Pressure to Inactivate Bacterial Pathogens and Yeast in Commercial Apple Juice

The purpose of this study was to investigate the effect of combined treatments using TiO₂-UV photocatalysis (TUVP) and high hydrostatic pressure (HHP) on inactivation of microorganisms in commercial apple juice as model liquid food. A synergistic effect was observed for combined treatments to inactivate microorganisms. Gram-positive bacteria, Listeria monocytogenes and Staphylococcus aureus, were completely inactivated from initial loads of 7.1 and 6.7 log CFU/mL, respectively, when treated with a combination of TUVP (8.45 J/cm²) and HHP (500 MPa). In contrast, reductions of only 4.8 log CFU/mL (L. monocytogenes) and 2.4 log CFU/mL (S. aureus) were achieved with 500 MPa HHP alone. Gram-negative bacteria, Escherichia coli O157:H7 and Salmonella Typhimurium, were reduced by 7.1 and 7.2 log CFU/mL, respectively, after a combined treatment using 8.45 J/cm² TUVP and 600 MPa (E. coli) or 400 MPa (S. Typhimurium) HHP which were significantly higher than the effects of HHP alone. A 6.2 log CFU/mL reduction in Saccharomyces cerevisiae count was monitored after treatment with a combination of 8.45 J/cm² TUVP and 500 MPa HHP whereas even 600 MPa alone could not achieve complete S. cerevisiae inactivation. Combined treatments (TUVP + HHP) were more effective for microbial inactivation than alone treatments. Scanning electron microscopic images of microorganisms showed highly deformed morphologies after TUVP + HHP treatment. In conclusion, pretreatment of commercial apple juice using TUVP before HHP processing results in better disinfection and may assure complete disinfection.