Highlights-A combined treatment of HHP and DPCD was used to inactivate feijoa puree enzymes.-The residual activity of enzymes decreased with increasing pressure in all treatments.-The addition of CO 2 in the package enhanced the HHP inactivation of POD and PPO.-Using HHP and DPCD, lower HHP pressures may be used for a given inactivation level.1 samples were treated at 300, 450 and 600 MPa, for 5 min. Combined High Hydrostatic Pressure and Carbon Dioxide Inactivation of Pectin 40The residual POD and PPO activity decreased in the order HHP > HHPcarb > 41HHPcarb+CO2 at all pressures used. Treatments with HHP at 300 MPa increased POD 42 activity to 140 %. The residual PME activity of HHPcarb and HHPcarb+CO2 samples at 43 600 MPa (45-50 %) was significantly (p<0.05) lower than for HHP treatment (65 %). 44The simultaneous application of HHP and DPCD seems to synergistically enhance the 45 inactivation of the enzymes studied, the CO2 concentration being a key process factor.

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A higher microbial inactivation of Escherichia coli, Bacillus subtilis and Saccharomyces cerevisiae by combining dense phase carbon dioxide and high hydrostatic pressure was observed. For sweetened products there were no significant differences in sensory attributes and preferences between samples treated by the combined method and the fresh samples. In conclusion, addition of CO2 in HHP treatment of juices could reduce process severity and improve product quality.

High hydrostatic pressure (HHP) may activate undesirable enzymes such as polyphenoloxidase (PPO). Carbon dioxide (CO 2 ) addition to HHP could increase enzyme inactivation. We investigated the inactivation of combined HHP and dense phase carbon dioxide process on activity, secondary conformation and size of pure PPO from mushroom. Solutions (2.35μM, in phosphate buffer pH 6.8) were treated with HHP alone (HHP), or 3.6% w/w of CO 2 was injected into the package (HHP+CO 2 ). Treatment conditions were 600 MPa, 20°C, for 1, 3, 5, 7, and 9 min. HHP+CO 2 treatment significantly decreased residual enzyme activity (REA) to 30% to 12% after 1 to 9 min, respectively, whereas only HHP had no significant effect. Both HHP and HHP+CO 2 treatments caused changes in secondary conformations, however HHP+CO 2 changes were more extensive. Alpha-helix fractions were reduced by 32% and 41%, while β sheet, turn and unordered increased by 63% and 213%, 100% and 71%, and 118% and 82% for HHP and HHP+CO 2 , respectively after 9 min. The protein size in HHP+CO 2 samples was 5-to 6-fold larger than that of Control and HHP treatment, and this increase was inversely correlated with REA. The best inactivation kinetics of HHP+CO 2 model was the 2-fractional model with 2 simultaneous 1st-order steps, contributing 70% and 30% to original enzyme activity, with k labile = 12.15 min −1 and k stable = 0.07 min −1 , respectively. No recovery in activity, secondary conformation and size in all samples were observed after 1-mo storage. Addition of CO 2 in HHP treatment can improve enzyme inactivation, and therefore product shelf-life and quality.Practical Application: High hydrostatic pressure (HHP) achieves the safety of foods as a nonthermal method, but it may activate undesirable enzymes resulting in short shelf life due to, for example flavor and color changes. Our study determined that addition of CO 2 to HHP has significant effects on enzyme inactivation, secondary conformational and molecular size changes of mushroom PPO. No recovery in activity, secondary conformation and size in all samples were observed after 1 mo storage at 4°C. This combined process increases product shelf life, in addition to safety and nutrient preservation.