Combined effect of shear stress and moderate electric field on the inactivation of Escherichia coli K12 in apple juice

Induced electric field as alternative pasteurization to improve microbiological safety and quality of bayberry juice

Recently, unconventional techniques like induced electric field (IEF) for continuous pasteurization of liquid food have received great attention. In this study, the effect of IEF on temperature rise, microbiological and quality characteristics of bayberry juice was investigated. Voltage, current, and flow rate affected the terminal temperature. Both IEF (600 V, 4 L/h; 700 V, 6 L/h) and thermal pasteurization (95 °C, 2 min) completely inactivated total plate count, coliforms, yeast and mold in bayberry juice. The pH, total soluble solid and titratable acidity did not vary significantly post-IEF, but conductivity changed slightly. IEF-treated samples exhibited the lowest ΔE values without exceeding 3. Thermal pasteurization (95 °C, 2 min) scored the lowest in color, flavor, odor, and acceptance. GC-MS results demonstrated a significant increase in the content of total volatile compounds following IEF treatments, with the maximum increment reaching 10.65 %. Generally, IEF is a potential technology for processing liquid beverages.

Non-Thermal Technologies Combined with Antimicrobial Peptides as Methods for Microbial Inactivation: A Review

Non-thermal technologies allow for the nutritional and sensory properties of foods to be preserved, something that consumers demand. Combining their use with antimicrobial peptides (AMPs) provides potential methods for food preservation that could have advantages over the use of chemical preservatives and thermal technologies. The aim of this review was to discuss the advances in the application of non-thermal technologies in combination with AMPs as a method for microbial inactivation. Published papers reporting studies on the combined use of power ultrasound (US), pulsed electrical fields (PEF), and high hydrostatic pressure (HHP) with AMPs were reviewed. All three technologies show a possibility of being combined with AMPs, generally demonstrating higher efficiency than the application of US, PEF, HHP, and AMPs separately. The most studied AMP used in combination with the three technologies was nisin, probably due to the fact that it is already officially regulated. However, the combination of these non-thermal technologies with other AMPs also shows promising results for microbial inactivation, as does the combination of AMPs with other novel non-thermal technologies. The effectiveness of the combined treatment depends on several factors; in particular, the characteristics of the food matrix, the conditions of the non-thermal treatment, and the conditions of AMP application.

Inactivation of Escherichia coli O157:H7 in apple juice via induced electric field (IEF) and its bactericidal mechanism

Non-conventional heating technology based on electric fields can be utilized to process liquid foods. In this study, the induced electric field (IEF) was investigated to clarify its inactivation mechanism on E.coli. Staining results show that inactivation of E.coli by IEF can be attributed to the reversible destruction of the cell membrane, followed by the denaturation of intracellular enzymes, and finally the irreversible rupture of the cell membrane. The increased levels of extracellular proteins and nucleic acids were also observed. IEF treatment at 400 Hz and 800 V (or 53 V/cm) results in a reduction of 4.5 log CFU·mL^-1 in the number of E.coli. Storage life analysis shows that IEF treatment can improve the stability of apple juice and the content of bioactive components. Thus, IEF is a potential technique for liquid food processing.

Effect of pasteurization on Aspergillus fumigatus in apple juice: Analysis of the thermal and electric effects

Fungal spoilage in fruit juices is a currently relevant issue considering that recent reports have found unacceptable fungal levels even after traditional pasteurization processes. Ohmic heating demonstrated to be a good alternative process to conventional pasteurization, as it can promote higher heating rates and additional cell damage in some scenarios (nonthermal effects). However, the application of ohmic processing for fungi inactivation has not been properly investigated. The objective of this study was to analyze the inactivation of Aspergillus fumigatus, a highly distributed fungi species, in apple juice by ohmic and conventional heating at 75, 80, 85, 90 and 94 °C. Predictive primary and secondary models were fitted and the Weibull-Mafart models were the most accurate to describe the experimental behavior considering the statistical indices applied. Statistical differences between both thermal processes were found in the three lower analyzed temperatures (75, 80 and 85 °C), which is possibly related to nonthermal effects. When ohmic heating was applied, processing time was up to 23% shorter. The resulted model was successfully validated in two distinct temperatures (83 and 92 °C) and could be applied to obtain adequate processing times for apple juice pasteurization. This study contributes to deepen the knowledge concerning the use of ohmic heating for fungi inactivation.

Effects of induced electric field (IEF) on the reduction of Saccharomyces cerevisiae and quality of fresh apple juice

The non-conventional technologies about continuous sterilization of liquid food were focused on recently, which is benefits for industrialization. In this study, the machine with an induced electric field was used to sterilize S. cerevisiae in apple juice and the juice quality also was researched. The optimal condition is 800 V, 400 Hz, 5 rpm and 2 mm. Furthermore, the sterilization of the IEF was attributed to non-thermal and thermal effects. The IEF treatment group has a reduction of about 4.6 logs (CFU/mL) in S. cerevisiae at 400 Hz, 800 V, and 2 mm, while the non-thermal group is nearly 2 logs (CFU/mL). The improvement of conductivity and the reduction of pH value imply that IEF might destroy the cell structure. Meanwhile, polyphenol compounds and amino acids in the IEF group were protected well than other groups. Generally, IEF is a potential technology for industrial sterilization of liquid beverages.