Effect of Frequency and Waveform on Inactivation of Escherichia coli O157:H7 and Salmonella enterica Serovar Typhimurium in Salsa by Ohmic Heating

Abstract

The effect of frequency of alternating current during ohmic heating on electrode corrosion, heating rate, inactivation of foodborne pathogens, and quality of salsa was investigated. The impact of waveform on heating rate was also investigated. Salsa was treated with various frequencies (60 Hz to 20 kHz) and waveforms (sine, square, and sawtooth) at a constant electric field strength of 12.5 V/cm. Electrode corrosion did not occur when the frequency exceeded 1 kHz. The heating rate of the sample was dependent on frequency up to 500 Hz, but there was no significant difference (P > 0.05) in the heating rate when the frequency was increased above 1 kHz. The electrical conductivity of the sample increased with a rise in the frequency. At a frequency of 60 Hz, the square wave produced a lower heating rate than that of sine and sawtooth waves. The heating rate between waveforms was not significantly (P > 0.05) different when the frequency was >500 Hz. As the frequency increased, the treatment time required to reduce Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium to below the detection limit (1 log CFU/g) decreased without affecting product quality. These results suggest that ohmic heating can be effectively used to pasteurize salsa and that the effect of inactivation is dependent on frequency and electrical conductivity rather than waveform.O hmic heating is a highly attractive technology by which internal heating as a result of electrical resistance is rapidly induced when passing an alternating current through a food product (1). This technology can provide a uniform temperature distribution with the absence of a cold spot in the product, because both liquid and solid phases can be heated simultaneously (2). Therefore, it is ideally suited to thermal processing of solid-liquid food mixtures with little structural, nutritional, or organoleptic changes and as well as those that are microbiologically safe and can be successfully treated using a short processing times (3). Commercial ohmic sterilization has been developed for particulate and multiphase foods based on applied research of ohmic heating (4-6), and it has been widely used in blanching, evaporation, dehydration, fermentation, extraction, and pasteurization (7).Although viewed as a promising food processing technology, ohmic heating has some technical limitations. Most ohmic heating systems have been used at an alternating current frequency of 50 to 60 Hz. One constraint of low alternating current frequency in ohmic heating is that electrolytic reactions can take place at the electrode surface, leading to product burning and corrosion of electrodes (8, 9). To prevent undesirable electrochemical reactions between electrodes and solid or viscous liquid products, increasing the frequency or changing the waveform of alternating current has been suggested (10). There have been some efforts to clarify the impact of frequency and waveform of alternating current on ohmic heating rates of solid or semisolid foods (11-15). However, there has been n...

Effect of pH for inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in orange juice by ohmic heating

“…This result is similar to those of other research studies (Lee et al, , 2013Leizerson & Shimoni, 2005). In conclusion, we confirmed that ohmic heating technology achieved more effective inactivation of food-borne pathogens in orange juice when combined with higher acidity without damaging quality.…”

“…Because these two organisms are most difficult to control, by inactivating them, other pathogenic organisms will also likely be controlled (US FDA, 1998). We used a voltage frequency of 20 kHz because no electrochemical reactions e which can cause electrode corrosion during ohmic heating occur at that frequency (Lee, Ryu, and Kang, 2013;Park & Kang, 2013). When using ohmic heating, heating rates differed for each pH level because added salts necessary for adjusting pH caused samples to have different electric conductivity.…”

Comparative Effects of Ohmic and Conventional Heating for Inactivation of Escherichia coli O157:H7, Salmonella enterica Serovar Typhimurium, and Listeria monocytogenes in Skim Milk and Cream

“…Note the advantag es of using ohmic heating to pasteurize skim milk and cream: (i) ohmic heating can increase temperature much more rapidly than conventional heating and (ii) quality parameters were degraded less by ohmic heating than by conventional heating. Because electrode corrosion is a factor that limits widespread application of ohmic heating (9), further study will be needed to investigate electrode coiTosion during ohmic heating used for dairy product pasteurization processing.…”

“…Ohmic heating treatments were carried out in a previously described apparatus (9). The ohmic heating system ( Fig.…”

Effect of Electropermeabilization by Ohmic Heating for Inactivation of Escherichia coli O157:H7, Salmonella enterica Serovar Typhimurium, and Listeria monocytogenes in Buffered Peptone Water and Apple Juice

“…In the present study, the sample pH was fixed at 7.2 using BPW to evaluate the effect of moderate electric fields to reduce food-borne pathogens without altering other conditions. Moreover, since electrochemical reactions, which produce chemicals affecting inactivation of food-borne pathogens, can occur at the standard line voltage frequency (60 Hz) during ohmic heating, 20 kHz, a high frequency that does not cause electrochemical reactions, was used in this study (28,29). Reductions of 2.42, 3.21, and 0.70 logs with treatment at 58°C for 30 s and reductions of 3.59, 3.48, and 3.40 logs with treatment at 60°C for 30 s in E. coli O157: H7, S. Typhimurium, and L. monocytogenes, respectively, were induced by ohmic heat electric fields.…”