Electrical breakdown or disruption of a biological membrane by high-voltage pulsed electric field (PEF) is well understood to occur by electromechanical compression, which results in the formation of transmembrane pores. If the total area of the induced pores becomes unfavorably large, the membrane is no longer able to repair these perturbations (irreversible disruption), and that results in sterilization. A preliminary research work for PEF inactivation of microorganisms was reported about 40 years ago. Recently many reports are published on the biotechnological applications of PEF including sterilization of some kinds of microorganisms in liquid foods. We investigated effective sterilization by using fast rising high voltage pulse with changing design parameters of the reactor and operating conditions. The treatment temperature or growth temperature, and the shape of the reactor were found to have a great effect on PEF sterilization. To raise the energy efficiency for PEF sterilization to minimize consumed electrical energy, we proposed concentration of electric field by using spiral wire electrode reactor. We also proposed the textile electrode system for improvement of energy efficiency. The PEF-induced reversible disruption could be utilized for the selective release of intracellular proteins from yeast and certain gene-engineered Escherichia coli. The secretion of periplasmic protein from E. coli was achieved during cultivation. In the present paper, some biotechnological applications of high-voltage pulsed electric field are reviewed.
The optimum conditions for subcritical water treatment to produce an extract with a high phenolic content and radical scavenging activity from defatted rice bran were determined using response surface methodology. The effects of the weight ratio of bran to water from 0.05 to 0.2 and treatment time from 20 to 120 min on the total phenolic content and DPPH radical scavenging activity were evaluated using the Design-Expert program. Both the total phenolic content and DPPH radical scavenging activity increased with an increase in the bran/water ratio, but decreased with the treatment time. The optimum bran/water ratio and treatment time were 0.2 and 20 min, respectively, to attain a relatively highest total phenolic content and DPPH radical scavenging activity.