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

Effect of magnetic induction electric field treatment of soybean protein isolate on their structural and interfacial properties

Induction electric field (IEF) technology is a new green treatment technology based on electric field, and its application has not been widely reported, especially in the direction of soybean protein isolate (SPI) modification. Therefore, IEF and several commonly used physical modification methods were used to investigate the effect on the structure and interfacial properties of SPI. The IEF treatment was found to be superior to the other groups in terms of emulsification performance, solubility and flexibility, which were enhanced by 44.61 %, 16.33 % and 30.55 %, as compared to untreated SPI. DSC shows more prominent thermal stabilisation of proteins after treatment. Secondary structure measurements revealed a decrease in α-helix content and an increase in random coil content, as well as an increase in surface hydrophobicity and free sulfhydryl groups, demonstrating a shift towards a loosely packed and disordered protein structure. At the same time, the IEF treatment particle size reaches a minimum and is uniformly distributed under the microscope, showing specific advantages in stabilising emulsions. In short, IEF provides a new way of thinking about protein modification, which is conducive to expanding the range of applications in the food industry.

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.

Influence of induced electric field on cold brew coffee: Temperature rise, physicochemical properties, and shelf life

Cold brew coffee has gained significant popularity in the global market. This study examined the differences in chemical properties and flavor of cold brew coffee during storage, which was subjected to low-temperature pasteurization using induced electric field (IEF) at temperatures of 52 °C and 58 °C for 92 s, corresponding to 18.52 V/cm and 25.92 V/cm. Then, a high-temperature short-time (HTST) pasteurization was performed at 93 °C for 2 min as the control. Microbial analysis demonstrated that IEF treatment at 58 °C achieved a bactericidal effect. Both the IEF and HTST groups exhibited consistent trends in total sugar and total phenol content, showing approximately 28 μg GAE/mL after 28 days for IEF-2 group, compared to 25 μg/mL for HTST. Flavor analysis indicated that IEF group preserved the aroma characteristics during storage period. Further, IEF treatment effectively retained the key aroma compounds in cold brew coffee through GC-MS analysis, particularly pyrazine compounds with a relative content increased by 0.96 % in IEF-2 group after 28 days. Moreover, the bioactive compounds initially increased and subsequently decreased over the storage.

Encapsulation of Cinnamaldehyde and Vanillin as a Strategy to Increase Their Antimicrobial Activity

Many studies have suggested that the encapsulation of natural antimicrobials increases their antimicrobial activity. In this sense, the objective was to study the inactivation of microorganisms with encapsulated cinnamaldehyde and vanillin (E-CIN and E-VN), in comparison with the unencapsulated antimicrobials (CIN and VN) in protein beverages. Additionally, the microbial response was quantified through mathematical modeling. Cinnamaldehyde and vanillin were encapsulated using whey protein concentrate (WPC) as the encapsulating agent. The effectiveness at inactivating Escherichia coli, Listeria innocua, and Saccharomyces cerevisiae was evaluated in a protein-apple juice beverage during storage (4 °C). Encapsulation increased the effectiveness of cinnamaldehyde, reaching reductions of 1.8, 3.3, and 5.3 log CFU/mL in E. coli, L. innocua, and S. cerevisiae, respectively, while vanillin encapsulation had little effect on antimicrobial activity, reducing by 0.5, 1.4, and 1.1 log cycles, respectively. The combined treatments (E-CIN + E-VN) had an additive effect in reducing E. coli and a synergistic effect against S. cerevisiae. The Gompertz model was more versatile and better described the biphasic curves, whereas the Weibull model complemented the information regarding the spectrum of resistances within the microbial population. In conclusion, the encapsulation of cinnamaldehyde with WPC enhanced its activity. However, further studies are necessary to improve the antimicrobial activity of vanillin.

Effects of Seven Sterilization Methods on the Functional Characteristics and Color of Yan 73 (Vitis vinifera) Grape Juice

Yan 73 (Vitis vinifera) is a dyed grape variety cultivated in China. Currently, most studies have focused on the mechanism of anthocyanins or the impact of anthocyanins as auxiliary color varieties on wine color. There is little research on its direct use or direct processing of products such as juice. In order to investigate the effects of different processing methods on the juice of Yan 73 grapes, the physicochemical and functional properties, as well as the sensory indexes of the juice, were analyzed by using thermal pasteurization (TP), thermosonication (TS), TS combined with nisin (TSN), TS combined with ε-Polylysine (TSε), irradiation (IR), and high hydrostatic pressure (HHP). The physicochemical indexes, functional properties, and sensory indexes of Smoke 73 grape juice were determined and analyzed. The results of the study showed that among the seven sterilization methods, total polyphenol content (TPC) in juice was significantly increased in all treatments except HHP. TPC was the highest in TP (3773.33 mg GAE/L). Total anthocyanin content (TAC) was increased except IR5, and TSN (1202.67 mg/L) had the highest TAC. In terms of color, TP (a* = 36.57, b* = 19.70, L* = 14.81, C* = 41.55, h° = 28.30, ΔE = 5.9) promotes the dissolution of anthocyanins because of high temperatures, which basically improves all the color indicators of grape juice and makes the color of grape juice more vivid. After HHP treatment, the color (ΔE = 1.72) and aroma indicators are closer to the grape juice itself. The Entropy weight-TOPSIS, CRITIC-Topsis, and PCA integrated quality evaluation models showed that all selected TP as the best integrated quality.

Putative inactivation mechanism and germicidal efficacy of induced electric field against Staphylococcus aureus

Induced electric field (IEF), as an alternative non-conventional processing technique, is utilized to sterilize liquid foods. In this study, the survival and sublethal injury of S. aureus under IEF were investigated in 0.85% normal saline, and the inactivation mechanism of IEF was expounded. The plate count results showed that the sublethal injury rates remained above 90% after IEF treatment for more than 8.4 s, and 7.1 log CFU/mL of S. aureus was completely inactivated after 14 s IEF treatment. Scanning electron microscopy and transmission electron microscope images showed that IEF caused the destruction of cell membrane and internal substructure, and the damage to intracellular substructure was more severe. Altered membrane integrity or permeability was demonstrated through flow cytometry and confocal laser scanning microscope analysis, and the different damage to cells was quantified by propidium iodide & 5-carboxy fluorescein diacetate single and double staining. In addition, IEF treatment also decreased the membrane potential and esterase activity of S. aureus cells. Putative inactivation mechanism of IEF against S. aureus is a complex process, and its apoptosis is the result of the combination of several factors, which provide a basis for understanding the inactivation mechanism of IEF.

Advances in pulsed electric stimuli as a physical method for treating liquid foods

There is a need for alternative technologies that can deliver safe and nutritious foods at lower costs as compared to conventional processes. Pulsed electric field (PEF) technology has been utilised for a plethora of different applications in the life and physical sciences, such as gene/drug delivery in medicine and extraction of bioactive compounds in food science and technology. PEF technology for treating liquid foods involves engineering principles to develop the equipment, and quantitative biochemistry and microbiology techniques to validate the process. There are numerous challenges to address for its application in liquid foods such as the 5-log pathogen reduction target in food safety, maintaining the food quality, and scale up of this physical approach for industrial integration. Here, we present the engineering principles associated with pulsed electric fields, related inactivation models of microorganisms, electroporation and electropermeabilization theory, to increase the quality and safety of liquid foods; including water, milk, beer, wine, fruit juices, cider, and liquid eggs. Ultimately, we discuss the outlook of the field and emphasise research gaps.

Non-Conventional Induction Heat Treatment: Effect of Design and Electrical Parameters on Apple Juice Safety and Quality

The proposed non-conventional induction heating, which combines an MSCP and VDC structure, was proved to have excellent thermal effect. Different from other electric field sterilization, this electrotechnology operates with no electrodes, and it is a continuous-flow process with short-duration (about 20 s). In current study, the parameters related to temperature rise were investigated, including applied voltage, frequency, the diameter of the secondary coil and heating tube, as well as their length, etc. It was demonstrated that a smaller diameter of the heating tube, parallel connection sample coils, and higher frequency were beneficial for the inactivation of microorganisms. At 500 Hz, the optimal condition is 800 V, d1 = 2 mm, and L1 = 10 cm. Notably, the system could inactivate all microorganisms and maintained the physicochemical properties of apple juice at 40 kHz. It suggests that this structural design has the potential for industrial applications and the proposed induction heating can realize the rapid sterilization of liquid food without applying electrodes.

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.