Inactivation Of Enzyme And Microorganism In Banana Juice By "Pulsed Electric Field-based"Technology

Pulsed electric field (PEF) technology is a novel non-thermal processing technology in food processing. It has been proved to be an effective treatment on enzyme inactivation and sterilization. A laboratory scale PEF system was used in this study. A combination of PEF and temperature were applied to polyphenol oxidase (PPO) and peroxidase (POD) in banana to evaluate the enzyme inactivation effect. PEF combine with Maillard reaction products (MRPs) were applied to Staphylococcus aureusand Escherichia coli in banana juice to study the sterilization effect. Combination of MRPs and PEF was adopted to develop banana juice's processing technology of low temperature characteristics which will retain the original odor and color. The conclusions were made as follows.(1) The residual activity of POD and PPO decreased with the increase in electric field strength and treatment time, and PPO was more susceptible than POD to PEF treatment.(2) The inactivation of PPO and POD by thermal treatment below70?was unsatisfactory. But higher level of decrease in the enzymatic activity for PPO and PODwere obtained by usinga combination of preheating PEF treatment. No activity of PPO or POD can be observed at the treatment condition50?,50kV/cm for1600?s in this study.(3) PEF showed good effect on Staphylococcus aureusand Escherichia coli inactivation in banana juice. The inactivation of both microorganisms increased with the increase in electric field strength and treatment time. Escherichia coli were more resistant than Staphylococcus aureusat same parameters of PEF treatment. After PEF at40kV/cm for1600?s treatment,6log cycle reductions of Escherichia coliandStaphylococcus aureus was achieved.(4) MRPs could inhibit the growth of Staphylococcus aureusand Escherichia coli in this study. The inhibition was more effective in solid medium than in liquid medium. As a kind of pre-treatment, PEF could strengthen the bacteriostatic effect of MRPs.(5) Before pulping, banana slices should be soaked in0.5%citric acid solution. The MRPs of0.0625mg/mL concentration could keep color of banana pulp from browning for30minutes after mashing. The best parameters for enzymolysis is as follows:the pectinase concentration is0.05%; temperature is45?for30min. Then, microorganisms in filtrate can be effectively inactivated after PEF treatment at50kV/cm for1200?s. The resultant banana juice could maintain the original color and flavor.