Pulsed electric field processing of functional foods.

摘要

Pulsed electric field (PEF) is a nonthermal alternative to traditional food processing. PEF is effective in microbial inactivation without significant impair on food quality, including flavor, nutrition, and physical properties such as color, viscosity and electric conductivity. Dielectric breakdown of cellular membrane in microorganisms has been widely accepted as the mechanism corresponding to microbial inactivation by PEF. To execute its microbial inactivation effect, PEF needs to acquire electric field strength higher than the critical value that can induce higher than 1 volt of transmembrane potential to most of the vegetative cells. Inactivation of food enzymes has been extensively studied since 1960s. Inactivation effect of PEF depends on both the dosage and the structures of the target enzymes.;PEF is effective in inactivating natural flora and can significantly extend microbial stability of the bovine milk concentrate enriched soymilk. PEF treatment at higher electric field strength shows higher natural flora inactivation and results in higher microbial stability during a 30-day storage test at 4°C. PEF treatment at 41.1kV/cm for 54mus inactivates 5.3 logs of natural flora population (p 0.01). With continuous thermal processing, 78°C for 120s is needed to achieve same microbial inactivation. Temperature increase per pair of PEF treatment chambers (dT), with inlet temperature (T 1) ranging from 13°C to 27°C and electric field strength ranging from 0 to 38kV/cm, is primarily a function of electric field strength and energy input. Sample inlet temperature does not show significant influences on dT. However, T1 determines the maximum temperature induced in PEF treatment chambers. PEF significantly inactivates E. coli 8739 cells (p 0.05). The inactivation effect increases with the increase of electric field strength and the number of pulses delivered to samples. When electric field strength is higher than 30kV/cm, increase in treatment time and sample inlet temperature cause an increase in PEF inactivation of E. coli 8739. Nevertheless, when electric field strength is lower than 25kV/cm, the microbial inactivation effect of treatment time and T 1 is negligible. Experimental data illustrate that the microbial inactivation effect of PEF is due to the high intensity of electric field strength. Thermal effect contributes minimal to the total inactivation of natural flora and E. coli 8739. (Abstract shortened by UMI.)