Insights on the microbial resistance mechanisms of Listeria monocytogenes to Pulsed Electric Fields (PEF) treatments.

Modelling of polyphenoloxidase inactivation by pulsed electric fields considering coupled effects of temperature and electric field

Effects of pulsed electric fields (PEF) treatment on physicochemical properties of potato starch

전기장의 세기 20 kV/cm, 펄스 폭 25 <TEX>${\mu}s$</TEX>에서 펄스 빈도 35 Hz(40 kJ/L), 55 Hz(70 kJ/L), 72 Hz(100 kJ/L) 및 85 Hz(130 kJ/L)로 달리하여 투입 에너지를 기준으로 사과 착즙액의 PEF 연속처리 살균 효과를 분석한 결과 일반세균수은 초기 5.3 log CFU/mL에서 130 kJ/L의 에너지로 처리하였을 때 3.0 log CFU/mL로 감소하였고 효모 및 곰팡이는 초기 4.6 log CFU/mL에서 130 kJ/L의 에너지로 처리로 < <TEX>$10^1$</TEX> CFU/mL 이하로 감소하였다. 그리고 대장균군수도 초기 4.7 log CFU/mL에서 130 kJ/L의 에너지 처리로 < <TEX>$10^1$</TEX> CFU/mL 이하로 감소하였다. PEF 처리에 따른 가용성 고형분, 유리당 등에는 처리 조건에 따른 유의적 차이가 없었으며(p<0.05), 총 페놀함량, DDPH 및 FRAP 값은 처리조건에 따라 부분적으로 유의적인 감소를 보였지만 <TEX>$65^{\circ}C$</TEX>에서의 가열처리보다는 감소량이 작았다. 전기장 세기 20.0 kV/cm, 펄스 빈도 85 Hz, 펄스 폭 25 <TEX>${\mu}s$</TEX>에서의 반복처리는 미생물 살균 효과가 제한적이었고 처리회수에 따라 총 페놀함량, DPPH 및 FRAP 값을 유의적(p<0.05)으로 감소시켰다. Apple juices were sterilized by continuous pulsed electric field (PEF) treatments of pulse width of 25 <TEX>${\mu}s$</TEX> at electric field intensity of 20.0 kV/cm, and with the varied pulse frequencies of 35 Hz (40 kJ/L), 55 Hz (70 kJ/L), 72 Hz (100 kJ/L) and 85 Hz (130 kJ/L). The PEF treatments of apple juice reduced the microbial counts from 5.3 log CFU/mL of initial state to 3.0 log CFU/mL after PEF treatment at energy density of 130 kJ/L. Also yeast and fungi after PEF treatments were reduced from 5.3 log CFU/mL to 3.0 log CFU/mL and Escherichia coli were from 5.3 log CFU/mL of initial state to 4.7 log CFU/mL to < <TEX>$10^1$</TEX> CFU/mL. The soluble solids and free sugars did not significantly differ (p<0.05) depending on conditions of PEF treatment. The total phenolic contents and antioxidant activity such as the DPPH and ferric reducing antioxidant power (FRAP) by PEF treatments were significantly partly reduced, but the PEF-reduced value came in smaller quantities than the heat treatment at <TEX>$65^{\circ}C$</TEX>. The iterative PEF treatments with pulse width of 25 <TEX>${\mu}s$</TEX> and pulse frequency of 85 Hz at electric field intensity of 20.0 kV/cm showed limited in microbial reduction. Also, total phenolic contents and antioxidant activity such as DPPH and FRAP, significantly decreased depending on treatment numbers of PEF (p<0.05).

The effect of pulsed electric field (PEF) treatments of different intensities on the electroporation of the cytoplasmatic membrane of Chlorella vulgaris, and on the extraction of carotenoids and chlorophylls were investigated. Staining the cells with propidium iodide before and after the PEF treatment revealed the existence of reversible and irreversible electroporation. Application of PEF treatments in the range of 20-25 kV cm(-1) caused most of the population of C. vulgaris to be irreversibly electroporated even at short treatment times (5 pulses of 3 µs). However, at lower electric field strengths (10 kV cm(-1)), cells that were reversibly electroporated were observed even after 50 pulses of 3 µs. The electroporation of C. vulgaris cells by PEF higher than 15 kV cm(-1) and duration is higher than 15 µs increased significantly the extraction yield of intracellular components of C. vulgaris. The application of a 20 kV cm(-1) for 75 μs increased the extraction yield just after the PEF treatment of the carotenoids, and chlorophylls a and b 0.5, 0.7, and 0.8 times, respectively. However, further increments in electric field strength and treatment time did not cause significant increments in the extraction yield. The extraction of carotenoids from PEF-treated C. vulgaris cells after 1 h of the application of the treatment significantly increased the extraction yield in comparison to the yield obtained from the cells extracted just after the PEF treatment. After PEF treatment at 20 kV cm(-1) for 75 µs, extraction yield for carotenoids, and chlorophylls a and b increased 1.2, 1.6, and 2.1 times, respectively. A high correlation was observed between irreversible electroporation and percentage of yield increase when the extraction was conducted after 1 h of the application of PEF treatment (R: 0.93), but not when the extraction was conducted just after PEF treatment (R: 0.67).

The kinetics of inactivation of Clostridium sporogenes spores as a surrogate for the sterilization marker Clostridium botulinum using Pulsed Electric Field (PEF) treatment has not been previously investigated. Hence, this study aimed to evaluate and determine the kinetics of C. sporogenes spore inactivation by PEF. The spore suspensions of C. sporogenes were treated using PEF at an electric field intensity of 36 kV/cm with a residence time of 1.302 s. The spore inactivation kinetics were analyzed using several mathematical models, including log-linear, log-linear shoulder, and Weibull models. The electroporation effects were evaluated by measuring the concentration of Ca 2+ released into the suspension following PEF treatment. PEF treatment resulted in a reduction of C. sporogenes spores by up to 3.6 log cycles. The inactivation curve of C. sporogenes spores demonstrated a concave downward shape, with a shoulder pattern at the initial time and an exponential decrease as the process time increased. The spore electroporation was evidenced by an increase in Ca 2+ concentration in the suspension from 1.58 to 2.03 ppm after PEF treatment. The death rate of C. sporogenes spores ( kmax ) increased and the shoulder length ( S i ) decreased with higher electric field strengths. A concave downward curve of the inactivation curve is shown by a curve shape value ( p )&amp;gt; 1. The log-linear shoulder was the best model to describe C. sporogenes spore inactivation. The D PEF and Z PEF values of C. sporogenes spores in the log-linear, log-linear shoulder and Weibull models were in the ranges 2.46–4.222 s and 25–32 kV/cm. These findings demonstrate that PEF can effectively inactivate C. sporogenes spores and that kinetic modeling provides valuable parameters for predicting spore inactivation during PEF processing.

Effects of water activity (a w ) on the inactivation of Enterobacter cloacae inoculated in chocolate liquor and in a model system of 0.1 % (w/v) peptone water and glycerol by pulsed electric field (PEF) treatment were investigated. An electric field strength of 24.5 kV/cm, a total treatment time of 320 μs, a pulse duration time of 4 μs, a pulse delay time of 15 μs, and a pulse cycle time of 15 s were selected for PEF treatment. The inactivation of E. cloacae by PEF increased significantly as a w increased (P < 0. 05). As a w of chocolate liquor increased from 0.48 to 0.89, the log reduction ofE. cloacae increased from 0.1 to 1.3. The measured temperature change inside the PEF treatment chamber was 0.4C when the log reduction was 1.3. Similarly, as a w increased from 0.51 to 0.91 in the model system, the log reduction increased from 0.4 to 1.3. E. cloacae surviving a low a w environment had high resistance to PEF. PEF inactivated E. cloacae in the chocolate liquor with a w of 0.85 by 1 log at 0 h incubation. However, the log reduction was only 0.1 when PEF treatment was applied to E. cloacae which was incubated for 2 h in the chocolate liquor with a w of 0.85 before PEF treatment. E. cloacae surviving the low a w environment might have resistance not only to the low a w but also to PEF. The resistance to low a w environment may need to be considered when the inactivation of microorganisms by PEF is evaluated.

Impact of PEF treatment inhomogeneity such as electric field distribution, flow characteristics and temperature effects on the inactivation of E. coli and milk alkaline phosphatase

Summary form only given. Wastewater from hospitals carries large number of pathogenic and increasingly antibiotic resistant bacteria, which could spread in the environment. The pulsed electric field (PEF) treatment of wastewater as a non-chemical disinfection method is a suitable alternative method for reducing this bacterial freight. In the literature it was figured out, that continuous flow PEF treatment reduces more effectively bacterial contamination than batch reactor treatment. One explanation is that the heat generated during the PEF treatment in a continuous flow reactor is positively affecting the bacterial reduction. Depending on the PEF treatment energy, outlet temperatures of more than 70degC were achieved. Consequently, bacterial reduction depends on the initial wastewater temperature and on the electrical dissipated treatment energy. In our study we analysed the bacterial reduction depending on temperature. Filtered wastewater samples (from a wastewater purification plant) were inoculated with the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Enterococcus</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">faecium</i> (BRE; Strain 211, Mainz) and exposed to different PEF treatments at 40, 50 and 60degC. The lethal treatment temperature of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Enterococcus</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">faecium</i> by heat treatment over 3-4 min is around 56degC. Treatment with 60degC for the same duration provokes a bacterial reduction of 4 log. Simultaneous treatments of inoculated wastewater samples with PEF and heating (40, 50 and 60degC) reduced the bacterial contamination over the expected effect, calculated as a sum of effects induced from both treatments. This is an indication for a synergistic effect induced through the simultaneous treatment with PEF and heat. In all experiments the specific energy was kept constant by adjusting the number of pulses. At 2degC, the bacterial reduction saturates already for PEF treatments with specific energies higher than 120 J/ml. At higher temperatures (over 40degC), the bacterial reduction increased until the complete reduction (over 8 log) was achieved at 60degC. To separate the thermal effect from the PEF effect, samples were treated first with PEF in a batch chamber and afterwards, about 30 s later, by heating over 4 min. No significant variation of the efficiency of bacterial reduction compared to the simultaneous treatment was found. These results show that the duration of cell membrane damage, is far longer as the assumed healing time (mus-range). This finding can be used for further optimization of the PEF treatment in continuous flow.

SummaryGreen tea is an unfermented tea containing a higher quantity of bioactive components. In this paper, the effects of pulsed electric field (PEF) treatments on the bioactive components (polyphenols, catechins and free amino acids), colour and flavour of green tea infusions were studied. PEF as a promising non‐thermal sterilisation technology could efficiently retain polyphenols, catechins and original colour of green tea infusions with electric field strength from 20 to 40 kV cm−1 for 200 μs. PEF treatments caused a significant increase in the total free amino acids of green tea infusions. The total free amino acids increased by 7.5% after PEF treatment at 40 kV cm−1. The increase in total amino acids induced by PEF treatment, especially to theanine, is beneficial for the quality of commercial ready‐to‐drink green tea infusion products. There was no significant effect of PEF treatment at 20 or 30 kV cm−1 on flavour compounds of green tea infusions. However, PEF treatment caused losses of volatiles in green tea infusions to different extents when PEF dosage was higher than a critical level. The total concentration of volatiles lost was approximately 10% after PEF treatment at 40 kV cm−1 for 200 μs.

Longan juice was processed using a pulsed electric field (PEF) treatment and compared with a conventional thermal pasteurization method. The PEF treatment was carried out using a laboratory unit, set with a bipolar pulse (3 µs wide), an intensity of 32 kV/cm. PEF-treated longan juice showed no noticeable difference compared with the untreated sample, although well-visible differences were found between untreated and thermal-treated juice. An analysis of variance for pH, titratable acidity and total soluble solids determinations showed no statistically significant difference between the untreated and both thermally pasteurized and PEF-treated samples. The effect of PEF on nonenzymatic browning index and hydroxymethylfurfurol is not significantly different, although thermal treatment show significant difference in comparison with untreated juice. Contents of total phenol compounds presented significant variability for the two compared pasteurization methods. The PEF-treated longan juice retained greater amounts of vitamin C and top five flavor compounds than thermally treated longan juice. PRACTICAL APPLICATIONS As a new nonthermal sterilization method, pulsed electric field (PEF) treatment is a useful tool in fruit processing. It has been used in some other fruit juice processing, and no apparent changes in physicochemical properties and flavor were directly caused by PEF treatment. We tried it on longan juice and obtained some data for longan juice processing. PEF treatment is a new processing technology that improves longan juice quality and enhances its value.

Reduction in Levels of Escherichia coli O157:H7 in Apple Cider by Pulsed Electric Fields

In this study, the effects of pulse electric field (PEF) treatment on the tenderization of beef semitendinosus muscle were investigated. An adjustable PEF chamber was designed to make direct contact with the surface of the beef sample without water as the PEF-transmitting medium. PEF treatment was conducted with electric field strengths between 0.5 and 2.0 kV/cm. The pulse width and pulse number were fixed as 30 μs and 100 pulses, respectively. The impedance spectrum of PEF-treated beef indicated that PEF treatments induced structural changes in beef muscle, and the degree of the structural changes was dependent on the strength of the electric field. Cutting force, hardness, and chewiness were significantly decreased at 2.0 kV/cm (35, 37, and 34%, respectively) (p < 0.05). Troponin-T was more degraded by PEF treatment at 2.0 kV/cm intensity (being degraded by 90%). The fresh quality factors such as color and lipid oxidation were retained under a certain level of PEF intensity (1.0 kV/cm). These findings suggest that PEF treatment could tenderize beef texture while retaining its fresh quality.

Effects of pulsed electric field treatment on (+)-catechin–acetaldehyde condensation

Mechanism of needle electrode-derived pulsed electric fields on the structural and physicochemical properties of pork salting.

This study investigated the effects of pulsed electric field (PEF) treatment on the peeling efficiency and textural properties of whiteleg shrimp (Litopenaeus vannamei). Shrimp samples were treated at field strengths of 0, 1.0, 1.5, and 2.0 kV/cm to assess PEF impact on peeling force, incomplete peeling percentage, and texture profile. The results showed that PEF treatment significantly reduced the peeling force from 50.88 N in controls to 42.99 N at 2.0 kV/cm, while the percentage of incompletely peeled shrimp decreased from 27.5% to 15.9%. Texture profile analysis indicated that PEF treatment had no impact on the key properties of hardness and chewiness (no significant difference), with a reduction in springiness observed at higher field strengths. Improvements in peelability are attributed to electroporation, which disrupts collagen in the connective tissue between the shrimp shell and muscle. These findings indicate that PEF treatment is an efficient, non-thermal method for enhancing shrimp peeling processes while preserving textural integrity. PEF technology offers a promising alternative to traditional mechanical and thermal methods in the seafood processing industry.