Effects of high pressure CO2 treatments on microflora, enzymes and some quality attributes of apple juice

The inactivation of microorganisms and enzymes of cloudy apple juice, and some physico-chemical properties of the juice were investigated after continuous high pressure carbon dioxide (HPCD) at 25 MPa and 43 °C, for 2 min and at 22 MPa and 60 °C for 3, 5 and 10 min, respectively. The coliform bacteria were completely inactivated in all the cases. Total aerobic bacteria was reduced by 3.72 log cycles, pectin methylesterase was reduced by 54.3% and polyphenol oxidase was completely inactivated after 10 min treatment at 22 MPa and 60 °C. The yeasts and molds were completely inactivated and the turbidity increased at 22 MPa and 60 °C regardless of time, while the L and a value reduced, but browning degree did not change. The particle size distributions of the juice changed after HPCD but were regained as treatment time was prolonged. The pH was reduced at 22 MPa and 60 °C for 3 or 5 min.