Bai-Lin Qin

Non-thermal food preservation: Pulsed electric fields

The use of electric discharges to inactivate microorganisms and enzymes in food products has evolved since the 1920s from the ‘ElectroPure process’ (ohmic heating process) to the use of high-intensity pulsed electric fields in the 1990s. The non-thermal inactivation of microorganisms and enzymes using electric fields was demonstrated in the 1960s with a variety of microorganisms suspended in simulated food systems. A variety of liquid foods and beverages, including orange, apple and peach juices, pea soup, beaten eggs and skim milk, has been successfully processed during the 1980s and 1990s by several research groups. Little by little, the food industry is demonstrating increasing interest in this promising emerging technology; furthermore, it is expected that it will soon be adopted to process several liquid food products.

Inactivating microorganisms using a pulsed electric field continuous treatment system

High-voltage pulsed electric fields (PEFs) can be used to inactivate microorganisms in liquids. Applying PEF technology to food pasteurization is a promising nonthermal method, which may radically change food preservation processes and provide consumers with microbiologically safe, minimally processed, fresh-like products. A continuous-flow system in a laboratory-size prototype was constructed for the nonthermal pasteurization of liquid foods with PEF technology. Major components in the prototype include a high-voltage repetitive pulse generator, a coaxial liquid food treatment chamber, a fiber-optic temperature sensing instrument and a data acquisition system. Microbial inactivation tests were conducted in the continuous PEF treatment system. Repetitive high-voltage pulses with an exponential decaying waveshape were applied to the liquid food which was pumped through the treatment chamber. Test microorganisms selected for inactivation were Escherichia coli, Staphylococcus aureus and Saccharomyces cerevisiae. Over 6-order-of-magnitude reductions in the viability of selected microorganisms were achieved while the food temperature was maintained below 40/spl deg/C.

Nonthermal inactivation of Saccharomyces cerevisiae in apple juice using pulsed electric fields

Abstract High intensity pulsed electric fields were utilized in a continuous system for inactivation of Saccharomyces cerevisiae in apple juice. The applied electric energy inactivated microorganisms in apple juice and, because the pulse duration was only 2.5μs, energy remaining to heat the apple juice was minimized. The microbial inactivation was defined in terms of applied field intensity and treatment time. Less than 10% of the electrical energy for HTST was needed for achieving 6 log reduction in inactivation of S. cerevisiae in apple juice. The PEF-treated apple juice, at both 4°C and 25°C storage, had a shelf-life of more than 3 weeks.