Numerical analysis of polyphenol oxidase inactivation in non-Newtonian characteristic liquid food with high viscosity during radio frequency treatment

Abstract

Enzymatic browning is one of the main problems in the food industry, especially in juice and jam processing. An efficient approach to reduce enzymatic browning is to inactivate key polyphenol oxidases (PPO) that cause color reactions. Radio frequency (RF) treatment has advantages of volumetric heating and no chemical residue, making it one of the most potential treatments to replace traditional heating for pasteurization. In this study, a finite element model was established using the commercial software, COMSOL, to investigate the feasibility and effectiveness of PPO inactivation in non-Newtonian characteristic liquid food with high viscosity during pilot-scale RF treatments. The PPO was represented by the tyrosinase, and four concentrations of carboxymethylcellulose (CMC) solutions were considered to have high viscosity and non-Newtonian characteristics for liquid food. The results showed that the relative residual enzyme activity rapidly decreased to 1.2% when the target temperature increased to 70 °C during a batch RF enzyme inactivation. Meanwhile, the simulated and experimental trends were consistent with an acceptable RMSE value. The low-concentration CMC solutions (0.5% and 1.0%) with shorter heating times may be more suitable for developing the batch RF enzyme inactivation technology. During continuous-flow RF enzyme inactivation, the F-value increased with an increase in the solution concentration but sharply decreased with an increase in the volumetric flow rate. The exponential function could be used to describe the relationship between the relative residual enzyme activity and the volumetric flow rate of the CMC solution after RF treatment. The optimal volumetric flow rates for reducing the activity of PPO in 0.5%, 1.0%, 1.5%, and 2.0% CMC solutions to 20% were 426.13, 467.87, 552.05, and 566.07 mL/min, respectively. This study can provide valuable information for inactivating enzymes in non-Newtonian characteristic liquid food with high viscosity.