Inactivation of polyphenol oxidase in muscadine grape juice by dense phase-CO2 processing

The effect of dense phase-CO2 processing (DP-CO2) on polyphenol oxidase (PPO) activity, polyphenolic and antioxidant changes in muscadine grape juice under different processing pressures (27.6, 38.3, and 48.3 MPa) and CO2 concentrations (0, 7.5, and 15%) were measured. Subsequently two DP-CO2 conditions (48.3 MPa at 0 or 15% CO2) were evaluated for polyphenolic and antioxidant changes during storage (4 °C, four weeks). Pressure alone was responsible for a 40% decrease in PPO activity that resulted in 16–40% polyphenolic and antioxidant losses. Increasing CO2 from 0 to 7.5% was responsible for an additional 35% decrease in enzyme activity and a two-fold greater polyphenolic retention. However, insignificant changes in PPO activity or polyphenolic retention were observed when CO2 was increased to 15%. During storage, juices with residual PPO activity following processing resulted in greater polyphenolic (8- to 10-fold) and antioxidant capacity (four-fold) degradation compared to control juices with no PPO activity. This study demonstrated that partial PPO inactivation can be obtained by DP-CO2 and that CO2 level was the primary variable influencing PPO activity and polyphenolics and antioxidant capacity retention in muscadine grape juice.