Effect of pH on Enzyme Inactivation Kinetics in High-Pressure Processed Pineapple (Ananas comosus L.) Puree Using Response Surface Methodology

Effect of pH and high-pressure process treatments viz. pressure, temperature, and dwell time on inactivation of polyphenoloxidase (PPO), peroxidase (POD), bromelain (BRM), and pectinmethylesterase (PME) in pineapple puree was studied. Experiments were conducted according to rotatable central composite design (RCCD) within the range (-alpha to + alpha) of 100-600 MPa, 20-70 A degrees C, and 0-30 min at three different pH levels (3.0, 3.5, and 4.0) followed by analysis through response surface methodology (RSM). Enzyme inactivation was significantly (p < 0.05) affected by all the process parameters, and temperature had the highest contribution among those. Enzyme inactivation kinetics was demonstrated with dynamic pressure-buildup period (pressure pulse effect) followed by static pressure-hold period (isobaric-isothermal first-order inactivation). Increased pulse effect (PE in log scale) values were obtained at lower pH and higher values of both pressure and temperature. Maximum PE values, obtained at 500 MPa/60 A degrees C/pH 3, were 0.332, 0.319, 0.392, and 0.278 for PPO, POD, PME, and BRM, respectively. The inactivation rate (k in min(-1)) revealed that PPO was the most resistive (k ranged between 0.0020 and 0.0379 min(-1)) when compared with other three enzymes within the experimental domain. Increased k at lower pH with constant pressure and temperature depicted that pH had negative effect on the inactivation process. The optimized conditions targeting maximum inactivation of PPO, POD and PME with simultaneous retention of BRM in pineapple puree, were 600 MPa/60 A degrees C/9 min, 600 MPa/60 A degrees C/10 min and 600 MPa/60 A degrees C/10 min for the samples of pH 3.0, 3.5, and 4.0, respectively.