[Show abstract][Hide abstract] ABSTRACT: High-intensity pulsed electric fields (HIPEF) is a non-thermal preservation method which is believed to be able to inactivate spoilage micro-organisms such as Lactobacillus brevis. The effects of HIPEF parameters (electric field strength, treatment time, pulse polarity, frequency and pulse width) and heat pasteurization (90 °C/1 min) were evaluated on samples of orange juice inoculated with L. brevis (108 cfu/ml). HIPEF as well as heat treatments were carried out in continuous flow equipments. Electron microscopy was performed in order to observe L. brevis cell damage induced by HIPEF treatment. HIPEF processing of orange juice was more effective in inactivating L. brevis than thermal processing. The extent of microbial inactivation depended on the processing parameters (p<0.01). L. brevis destruction was greater when the electric field strength and the treatment time increased, and also when the pulse frequency and the pulse width decreased. L. brevis was inactivated to a maximum of 5.8 log reductions when inoculated orange juice was processed at 35 kV/cm for 1000 μs using 4 μs pulse width in bipolar mode and 200 Hz at less than 32 °C. Mechanical breakdown of cell walls was observed in L. brevis when orange juice was processed by HIPEF.
No preview · Article · Aug 2005 · Food Microbiology
[Show abstract][Hide abstract] ABSTRACT: Saccharomyces cerevisiae is often associated with the spoilage of fruit juices. The purpose of this study was to evaluate the effect of high-intensity pulsed electric field (HIPEF) treatment on the survival of S. cerevisiae suspended in orange juice. Commercial heat-sterilized orange juice was inoculated with S. cerevisiae (CECT 1319) (10(8) CFU/ml) and then treated by HIPEFs. The effects of HIPEF parameters (electric field strength, treatment time, pulse polarity, frequency, and pulse width) were evaluated and compared to those of heat pasteurization (90 degrees C/min). In all of the HIPEF experiments, the temperature was kept below 39 degrees C. S. cerevisiae cell damage induced by HIPEF treatment was observed by electron microscopy. HIPEF treatment was effective for the inactivation of S. cerevisiae in orange juice at pasteurization levels. A maximum inactivation of a 5.1-log (CFU per milliliter) reduction was achieved after exposure of S. cerevisiae to HIPEFs for 1,000 micros (4-micros pulse width) at 35 kV/cm and 200 Hz in bipolar mode. Inactivation increased as both the field strength and treatment time increased. For the same electric field strength and treatment time, inactivation decreased when the frequency and pulse width were increased. Electric pulses applied in the bipolar mode were more effective than those in the monopolar mode for destroying S. cerevisiae. HIPEF processing inactivated S. cerevisiae in orange juice, and the extent of inactivation was similar to that obtained during thermal pasteurization. HIPEF treatments caused membrane damage and had a profound effect on the intracellular organization of S. cerevisiae.
No preview · Article · Dec 2004 · Journal of food protection