Optimisation of the process parameters of combined high hydrostatic pressure and dense phase carbon dioxide on enzyme inactivation in feijoa (Acca sellowiana) puree using response surface methodology

• CO2 addition significantly aided enzyme inactivation in HHP process for PME, but had less effect on POD and PPO.
• The CO2 effect on enzyme is more due to its molecular interaction in the sample than its pH reduction.
• The response surface model can predict enzyme activities depending on process time, pressure, pH and CO2 levels.

The effects of pressure (200–600 MPa), process time (1–13 min), pH (3.0–3.6), and CO2 levels (no CO2, CO2 saturation, and saturation with addition of 8.5 mL CO2/g sample) in a combined high hydrostatic pressure (HHP) and dense-phase carbon-dioxide process on 3 enzymes: peroxidase (POD), polyphenoloxidase (PPO) and pectinmethylesterase (PME), of feijoa (Acca sellowiana) puree were studied using response surface methodology (27 treatments). Increasing treatment time reduced all enzyme activities, while increasing CO2 levels decreased PME activity, and pressure influenced PPO activity. The lower pH values tended to increase enzyme inactivation. The optimal process conditions of 13 min, 600 MPa, pH = 3, CO2 saturation, resulted in 74.3 ± 3.3%, 70.9 ± 2.6% and 53.9 ± 0.9% residual activity for POD, PPO and PME respectively. Combination of CO2 with HHP induced synergistic enzyme inactivation, and reduction of pH did not prove to be the main factor.Industrial relevanceHigh hydrostatic pressure (HHP) achieves the safety of beverages as a non-thermal method, but it may activate undesirable enzymes. Therefore, the product may have a short shelf life due to e.g. settling and colour change. Addition of carbon dioxide to HHP was shown to increase enzyme inactivation. Our study determined the optimal conditions to reduce enzyme activity in feijoa puree by this method. When industrial means become available to combine these processes, then in addition to safety and nutrient preservation, the shelf life of products will also increase.