Pulsed Electric Field Treatment Conditions Research Articles

Effect of Pulsewidth on Medium Temperature Rise and Microbial Inactivation Under Pulsed Electric Field Food Treatment

In the context of developing pulsed electric field (PEF) food treatment as a potential nonthermal method in producing high-quality food products, knowledge of pulse parameters on temperature rise is important. In this research, a newly developed high-voltage square pulse generator is implemented to study the effect of pulsewidth and pulse frequency on temperature rise, keeping both the applied electric field and energy constant. Real-time temperature changes in the treatment zone during PEF treatment are measured using an infrared camera. In addition, bacterial inactivation tests are carried out to validate the functionality of the pulse generator, under the same PEF treatment conditions.

The effects of pulsed electric fields applied to red and white wines during bottle ageing on organic acid contents

The evolution of the principal individual organic acids throughout 210 days of bottle ageing of red wine from Merlot grapes and white wine from Chardonnay grapes was investigated, and their organic acids contents have been compared with those in two kinds of wine treated by pulsed electric fields (PEF), respectively.. The PEF strength with 12 kV/cm and pulse numbers 300 resulted in the similar trends of L-malic acid, citric acid L-lactic acid, pyravic acid, tartaric acid, or succinic acid concentrations with red wine of bottle ageing. In white wine untreated by PEF, the change trends of tartaric acid, oxalic acid, citric acid, or succinic acid is similar to those of white wine treated by PEF of 6 kV/cm and pulse numbers 100. And the results obtained in this paper showed the strength of PEF applied to white wine would be required lower than red wine. These results indicated that PEF could be a suitable technology for obtaining the same evolution of the principal individual organic acids with bottle ageing wine, or reducing bottle ageing time, if favorable PEF treatment conditions are chosen.

Impact of pulsed electric field on cell disintegration and mass transfer in sugar beet

This study investigated the effects of pulsed electric field (PEF) treatments on sugar beet tissues. A PEF system was used to vary field strength, pulse number and capacitance in respective range of 0.5–6kVcm−1; 1–100 pulses; 0.5–32μF. It was observed that tissue damage in sugar beet was most influenced by total energy input and electric field strength. Furthermore, the energy consumption for cell disintegration by PEF treatment was significantly lower compared to thermal treatment indicating average values of about 8kJkg−1 and 156kJkg−1 respectively. The transfer of solids at room temperature from PEF pretreated sugar beet (1 or 2kVcm−1, 8μF, and 20 pulses) was higher than the untreated and thermal treated samples at 75°C. The overall results showed that the optimization of PEF treatment conditions is very important to achieve high cell disintegration and sugar beet yield.

Effectiveness of combined Pulsed Electric Field (PEF) and Manothermosonication (MTS) for the control of Listeria innocua in a smoothie type beverage

The combination of novel, non-thermal technologies for preservation purposes is a recent trend in food processing research. The objectives of the current study were (i) to optimise PEF or MTS treatment conditions which would achieve a maximum reduction of up to 3 log cycles of Listeria innocua in a milk based smoothie, when these technologies were applied individually, and (ii) to investigate possible additive or synergistic effects of the combined technologies. Microbiological analysis was performed by inoculating the smoothie with L. innocua and enumerating populations pre- and post-processing. All technologies applied within combinations significantly reduced L. innocua in the smoothie, when compared to untreated controls (p ≤ 0.0001). The sequence in which the MTS and PEF were applied was found to have a significant impact on the level of microbial reduction achieved (p ≤ 0.05). The sequence of MTS followed by PEF was the most effective in inactivating L. innocua achieving a mean reduction of 5.6 log cfu/ml, thereby exceeding the 5 log cycles minimum requirement specified by the United States Food and Drug Administration (US FDA). Significantly (p ≤ 0.05) lower reductions of 4.2 log cfu/ml were achieved when the PEF + MTS sequence combination was applied. The combination of MTS + PEF achieved inactivation comparable to thermally treated samples (p > 0.05). This study has shown the combination MTS + PEF is a promising hurdle preservation approach to control undesirable microorganisms in milk based smoothie beverages.

PULSED ELECTRIC FIELD INDUCED STRUCTURAL MODIFICATION OF SOY PROTEIN ISOLATE AS STUDIED BY FLUORESCENCE SPECTROSCOPY

ABSTRACT The effects of electric field intensities of 22 and 25 kV/cm and pulse numbers of 30, 60, 90 and 120 on the intrinsic fluorescence intensity, the extrinsic fluorescence intensity and the surface hydrophobicity of the soy protein isolate (SPI) were measured. The pulsed electric field (PEF) treatment increased the intrinsic tryptophan fluorescence intensity of the SPI causing a 2–6 nm red shift in the emission wavelengths. The extrinsic fluorescence intensity of the SPI also increased resulting in a 2–6 nm blue shift. These results indicated that the microenvironment of the soy protein's tryptophan residues changed from a less polar to a more polar environment. Also the changes in the extrinsic fluorescence intensity indicated that the soy protein fractions were partly denatured under the PEF treatment conditions that subsequently led to increase in the surface hydrophobicity. These observations confirmed that PEF treatments modified the protein structure of the SPI and increased its surface hydrophobicity. PRACTICAL APPLICATIONS Soy protein isolate (SPI) is usually the main ingredient in most soy food products and is used to manufacture textured vegetable proteins. Pulsed electric field (PEF) treatments increased the intrinsic and extrinsic fluorescence as well as the surface hydrophobicity of the SPI. These changes and modification of the SPI are valuable and useful during the production of specific food products. For example, in the processing of liquid foods containing SPI, controlled PEF treatments could be used to modify the structure and functional properties in order to achieve the desired or specific food products. The PEF treatments could also be used either as an alternative or in combination with other processing methods to induce the required structural modifications.

Influence of mild pulsed electric field conditions on the growth and protease activity of Streptococcus thermophilus

Pulsed electric field (PEF) processing involves the application of pulses of voltage for less than one second to fluid products placed between two electrodes. Streptococcus thermophilus is an important bacterium used for the production of fermented dairy products. Objective of this study was to determine the influence of a mild PEF condition on the growth and protease activity of Streptococcus thermophilus. A range of mild pulsed electric field conditions were earlier screened by the author to arrive at an optimum overall mild pulsed electric field condition for various probiotic characteristics. Freshly thawed Streptococcus thermophilus was suspended in 0.1% w/v sterile peptone water and treated in a pilot plant PEF system. The treatment was a mild PEF condition of positive square unipolar pulse of 3 µs, pulse period of 0.5 sec. and voltage of 1 kV/cm. Control was run through PEF system but without receiving any pulsed electric field condition. Control and treated samples flow rates were kept constant at 60 ml/min. Samples were individually inoculated in lactobacillus MRS broth. Samples were plated in duplicate. Pour plates were incubated aerobically at 37°C for 3 days. Growth was determined hourly for 20 hours. The extracellular protease activity of Streptococcus thermophilus was determined by the o-phthaldialdehyde (OPA) spectrophotometric assay. Experiments were replicated three times.The control and mild PEF treated samples had the same counts of 10.97 (+/- 0.25) log cfu/ml at 0 hour. The mild PEF treated samples reached the log phase an hour earlier than control. Although at most time points, counts were within the same log cfu/ml for the control and treated samples, the mild PEF treated samples had significantly (p<0.05) higher counts compared to control for most of the time points over the 20 hours of growth. The mild PEF condition enhanced growth of Streptococcus thermophilus. Mild PEF treatment conditions had a significant influence on the protease activity of Streptococcus.thermophilus where a significant enhancement in its proteolytic activity compared to the control has been detected.

Review: Application of Pulsed Electric Fields in Egg and Egg Derivatives

This work overviews works published on the application of pulsed electric fields (PEF) in egg and egg derivatives, grouped by subject, and arranged chronologically in terms of the factor studied (microorganisms, quality aspects, shelf life and structural changes in gel formation properties). The inactivation of microorganisms by PEF in egg is very considerable, 3.5 decimal reductions in egg white were achieved by PEF in Salmonella enteritidis, 5.5 log reductions of Listeria innocua by means of a synergistic effect of PEF and nisin in liquid whole egg, and 5.6 log reductions of Escherichia coli in beaten fresh liquid egg by PEF treatment applied continuously or discontinuously in five steps. The shelf life of PEF-treated fresh liquid egg was extended to 4 weeks in refrigeration, and quality (colour, viscosity and sensory attributes) was not affected by PEF treatment. PEF treatment did not cause notable changes in proteins in a solution of ovalbumin and dialysed fresh egg white. However, some structural changes and functional modifications were observed in fresh egg white as a result of PEF treatment. The texture and microstructure of gels were affected by the application of PEF, and therefore PEF treatment conditions in egg white must be optimised to minimise possible modifications.

Control of Lactobacillus plantarum and Escherichia coli by pulsed electric fields in MRS Broth, Nutrient Broth and orange–carrot juice

Pulsed electric fields (PEF) are an emerging non-thermal treatment valid for liquid foods. This novel technology offers a relevant alternative to traditional thermal methods avoiding thermal damage to the product (loss of flavour and nutritional value). The aim of this work was to evaluate the influence of PEF treatment conditions, inoculum size (initial cell concentration) and substrate conditions after PEF treatment on the inactivation and potential growth of Lactobacillus plantarum and Escherichia coli in orange–carrot juice. Although a maximum inactivation of 1.3 and 2.6log reductions were achieved for L. plantarum and E. coli, respectively, after PEF treatment, it was effective inducing sub-lethal injury. An increase in the lag-phase duration was evidenced under refrigeration conditions. When sub-lethal damage could be repaired, the subsequent growth rate was not affected. An increased inhibitory effect of PEF, low temperature and low inoculum size on the delay in lag phase was observed.