Inactivation of polyphenol oxidase and peroxidase enzymes during pulsed, static and cyclic pressurization of litchi (Litchi chinensis) juice

Abstract

Effects of three pressurization modes, namely pulsed pressurization (PP), static pressurization (SP) and cyclic pressurization (CP), were studied on enzymes polyphenol oxidase (PPO) and peroxidase (POD) in litchi juice. Process parameters considered were pressure (300–600MPa), number of pressure pulses or cycles (1–3) and isobaric pressure-hold time (1s to 45min). PP resulted in increased activity of both the enzymes, and its effect was more pronounced on POD than PPO. Effect of SP on enzymes was assumed as a two-stage inactivation: initial impact of pressurization–depressurization step calculated as pulse effect (PE), and effect of isobaric stage described using various kinetic models, among which the biphasic first-order reaction model fitted best. Further, an empirical model was proposed to explain the combined effect of pressurization–depressurization and isobaric phases on the enzymes inactivation as a function of pressure and hold-time during SP of litchi juice. During CP, the effect of number of cycles was found to be dissimilar on both the enzymes in litchi juice, and it was relatively more effective than SP for their inactivation. Within the studied domain of process parameters, the baroresistance of POD was found to be more than PPO in litchi juice, irrespective of the pressurization mode.