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1.
Bacterial resistance after pulsed electric fields depending on the treatment medium pH 总被引:3,自引:0,他引:3
D. García N. Gmez J. Raso R. Pagn 《Innovative Food Science and Emerging Technologies》2005,6(4):388-395
The objective was to evaluate and compare the pulsed electric field (PEF) resistance of four Gram-positive (Bacillus subtilis, Listeria monocytogenes, Lactobacillus plantarum, Staphylococcus aureus) and four Gram-negative (Escherichia coli, E. coli O157:H7, Salmonella serotype Senftenberg 775W, Yersinia enterocolitica) bacterial strains under the same treatment conditions. Microbial characteristics such as cell size, shape or type of the cell envelopes did not exert the expected influence on microbial PEF resistance. The most PEF resistant bacteria depended on the treatment medium pH. For instance, L. monocytogenes, which showed the highest PEF resistance at pH 7.0, was one of the most sensitive at pH 4.0. The most PEF resistant strains at pH 4.0 were the Gram-negatives E. coli O157:H7 and S. Senftenberg. A subsequent holding of PEF-treated cells in pH 4.0 for 2 h increased the degree of inactivation up to 4 extra Log10 cycles depending on the bacterial strain investigated. Under these treatment conditions, the most PEF resistant bacterial strains were still the pathogens S. Senftenberg and E. coli O157:H7.
Industrial relevance
The design of appropriate food preservation processes by PEF requires the selection of an adequate target bacterial strain, which should correspond to the most PEF resistant microorganism contaminating food. This study indicates that the pH of the treatment medium plays an important role in determining this target bacterial strain. On the other hand, the combination of PEF and subsequent holding under acidic conditions has been proven to be an effective method in order to achieve a higher level of microbial inactivation. 相似文献2.
Mass transfer in potato slices and strips after Pulsed Electric Fields (PEF) treatment was examined to evaluate potential application of PEF in potato processing. PEF treatment on cell material leads to pore formation in cell membrane and thus modifies diffusion of intra- and extracellular media. Results showed enhanced release of intracellular molecules from permeabilized tissue as well as improved uptake of low molecular substances into the sample. Sugar, one substrate for the Maillard reaction, was decreased in PEF treated potatoes, while conductivity increased after electroporation and soaking in sodium chloride solution, indicating the improved diffusion of salt caused by PEF. Higher release of cell liquid during drying of PEF treated potatoes was noticed in comparison to untreated potato slices. This effect increased with the treatment intensity. Furthermore, it was revealed that PEF application leads to a distinct reduction of fat content after deep fat frying and thus provides a potential for the production of low-fat French fries. It can be presumed that PEF is a capable assistance to thermal treatments in the processing of potato chips or French fries for the achievement of structural modifications and improved process conditions. 相似文献
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Electroporated and dried apples were characterised in terms of physical properties, such as sorption profile and mechanical test, in order to understand the treatment effects. Thermodynamic relationship between water activity and equilibrium moisture content at constant temperature and pressure has been mathematically expressed by sorption isotherm. High coefficient of determination of BET equation fitting was obtained, ranging from 0.974 to 0.990 (RMSE 0.07–0.08). The highest electric field strength (1.5 kV/cm) reveals a change in sorption isotherm shape. The III type of isotherm observed indicates a major presence of crystalline molecules increasing a water surface interaction.Compression test were applied to the samples at different hydration level and PEF intensity applied. The plasticizing effect was observed as a function of hydration level raise and involved a reduction of the maximum force from about 14.85 (±2.44) N to 8.45 (±0.59) N. The opposite anti-plasticizing effect was a consequence of electric filed strength increase. Particularly, at low hydration level, where plasticizing effect did not produce softening of structures, PEF treatment induced a toughness and stiffness increase, revealing the anti-plasticizing effect. Fermi equation showed high coefficient of determination (0.902–0.959) and Y0 value change from 17 to 35, as a function of PEF treatment intensity increase, confirming the structural differences in the analysed samples.Thus, main results revealed the modification of water holding capacity induced by PEF and drying. Sorption profile and mechanical properties well described plasticizing and anti-plasticizing induced effect, underling the enhanced mobility of the system promoted by treatments. 相似文献
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Comparative study on shelf life of orange juice processed by high intensity pulsed electric fields or heat treatment 总被引:1,自引:0,他引:1
Pedro Elez-Martínez Robert C. Soliva-Fortuny Olga Martín-Belloso 《European Food Research and Technology》2006,222(3-4):321-329
The effects of high intensity pulsed electric fields (HIPEF) processing (35 kV/cm for 1,000 μs; bipolar 4-μs pulses at 200 Hz)
on the microbial shelf life and quality-related parameters of orange juice were investigated during storage at 4 and 22 °C
and compared to traditional heat pasteurization (90 °C for 1 min) and an unprocessed juice. HIPEF treatment ensured the microbiological
stability of orange juice stored for 56 days under refrigeration but spoilage by naturally occurring microorganisms was detected
within 30 days of storage at 22 °C. Pectin methyl esterase (PME) of HIPEF-treated orange juice was inactivated by 81.6% whereas
heat pasteurization achieved a 100% inactivation. Peroxidase (POD) was destroyed more efficiently with HIPEF processing (100%)
than with the thermal treatment (96%). HIPEF-treated orange juice retained better color than heat-pasteurized juice throughout
storage but no differences (p<0.05) were found between treatments in pH, acidity and °Brix. Vitamin C retention was outstandingly higher in orange juice
processed by HIPEF fitting recommended daily intake standards throughout 56 days storage at 4 °C, whereas heat-processed juice
exhibited a poor vitamin C retention beyond 14 days storage (25.2–42.8%). The antioxidant capacity of both treated and untreated
orange juice decreased slightly during storage. Heat treatments resulted in lower free-radical scavenging values but no differences
(p<0.05) were found between HIPEF-processed and unprocessed orange juice. 相似文献
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高压脉冲电场杀菌对牛乳理化性质影响的研究 总被引:1,自引:0,他引:1
高压脉冲电场技术是目前较受关注的非热加工技术之一。本文研究了高压脉冲电场技术对牛乳几种理化性质的影响。结果表明,不同电场条件下,牛乳的pH值、电导率、乳糖含量、蛋白质质量分数差异均不显著。 相似文献
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Effect of high intensity pulsed electric fields and heat treatments on vitamins of milk 总被引:1,自引:0,他引:1
The effects of high intensity pulsed electric field (HIPEF) treatments at room or moderate temperature on water-soluble (thiamine, riboflavin, ascorbic acid) and fat-soluble vitamins (cholecalciferol and tocopherol) were evaluated and compared with conventional thermal treatments. Vitamin retention was determined in two different substrates, milk and simulated skim milk ultrafiltrate (SMUF). Samples were subjected to HIPEF treatments of up to 400 micros at field strengths from 18.3 to 27.1 kV/cm and to heat treatments of up to 60 min at temperatures from 50 to 90 degrees C. No changes in vitamin content were observed after HIPEF or thermal treatments except for ascorbic acid. Milk retained more ascorbic acid after a 400 microstreatment at 22.6 kV/cm (93.4%) than after low (63 degrees C-30 min; 49.7% retained) or high (75 degrees C-15s; 86.7% retained) heat pasteurisation treatments. Retention of ascorbic acid fitted a first-order kinetic model for both HIPEF and thermal processes. First-order constant values varied from 1.8 x 10.4 to 1.27 x 10(-3) micros(-1) for the HIPEF treatments (18.3-27.1 kV/cm) and, for thermal processing ranged from 5 x 10(-3) to 8 x 10(-2) min(-1) (50-90 degrees C). No significant differences were found between the results obtained after applying HIPEF treatments at room or moderate temperature. However, results depended on the treatment media. A beneficial effect of natural skim milk components, mainly proteins, was observed on the preservation of ascorbic acid, since skim milk retained more ascorbic acid than SMUF after HIPEF treatments. 相似文献
8.
Wen-bo Luo Zhong Han Xin-an Zeng Shu-juan Yu John F Kennedy 《Innovative Food Science and Emerging Technologies》2010,11(4):587-591
Chitosan solution was processed by applying pulsed electric fields (PEF) with different strengths up to 25 kV cm− 1. Changes of the physicochemical properties of chitosan, such as molecular weight and crystallinity degree, were measured by analyses of scanning electron microscopy (SEM), viscosity molecular weight (Mv), X-ray diffractometry (XRD), FTIR and UV spectra. The results showed that after being treated at 25 kV cm− 1, the chitosan granules were significantly deformed with many pits and cracks appeared on the surface. Mv was decreased with the increasing electric field strength, for example, the Mv was decreased from 2.81 × 105 Da (initial chitosan) to 1.54 × 105 Da after the PEF treatment at 25 kV cm− 1. Meanwhile, the crystalline region of the treated sample was significantly damaged from XRD patterns. All results showed that the PEF technique is a possible method to obtain low molecular-weight chitosan.
Industrial Relevance
Chitosan solution was treated by using pulsed electric fields (PEF) with different strengths up to 25 kV·cm-1. Changes of the physicochemical properties of chitosan were measured by analyses of scanning electron microscopy (SEM), viscosity molecular weight (Mv), X-ray diffractometry (XRD), FTIR and UV spectra. The results showed that the PEF technique is a promising method for scale-up industrial manufacture of low-molecular-weight chitosan. 相似文献9.
JOERG RIENER FRANCESCO NOCI DENIS A CRONIN DESMOND J MORGAN JAMES G LYNG 《International Journal of Dairy Technology》2009,62(1):1-6
Pulsed electric fields (PEF) were applied to fresh bovine raw milk using a laboratory-scale continuous PEF system to study the impact on selected native enzyme activities and on vitamin degradation. The activities of protease, lipase, alkaline phosphatase and lactoperoxidase following PEF treatment at electric field strengths ranging from 15 to 35 kV/cm for treatment times of 12.5 µs to 75 µs were examined. Reductions in enzyme activity, even under the most severe conditions employed, were quite modest, amounting to 14%, 37% and 29% for lipase, protease and alkaline phosphatase, respectively, while the activity of lactoperoxidase remained unchanged. The PEF treatment had no effect on the levels of thiamin, riboflavin, retinol and α-tocopherol in the milk . 相似文献
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《Innovative Food Science and Emerging Technologies》2001,2(2):105-112
The aim of this study was to examine the influence of pH, water activity (aw) and temperature on the killing effect of pulsed electric fields (PEF). Escherichia coli and Saccharomyces cerevisiae suspended in a model media were subjected to 20 pulses with 4 μs duration in a continuous PEF system, during which the effects of pH (4.0–7.0), aw (1.00–0.94) and inlet temperature (10°C and 30°C) could easily be studied. Electrical field strengths were set to 25 kV/cm for S. cerevisiae and 30 kV/cm for E. coli and the highest outlet temperature was monitored to 44°C. A synergy of low pH values, high temperatures and PEF processing was observed. A drop in pH value from 7.0 to 4.0 resulted in the reduction of E. coli by four additional log units, whereas for S. cerevisiae, the pH effect was less pronounced. Lowering aw seems to protect both E. coli and S. cerevisiae from PEF processing. 相似文献
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Isabel López-Alfaro Lucía González-Arenzana Noelia López Pilar Santamaría Rosa López Teresa Garde-Cerdán 《Food chemistry》2013
The purpose of this paper was to study the effect of pulsed electric fields (PEF) on the stilbene content of three grape varieties. For this purpose, four different PEF treatments were applied using a continuous system over three varieties, Graciano, Tempranillo and Grenache, destemmed and crushed. In addition, the influence of PEF on their physicochemical composition was studied. PEF treatments did not affect the pH or total acidity of Graciano, however, musts from Tempranillo and Grenache had higher pH values and lower total acidity. In the three varieties, all treatments resulted in an increase of potassium content, deeper colour intensity and total polyphenol index and lower tonality, more pronounced in the treatments with higher time and energy. The stilbene content of the must significantly increased with respect to the control. This increase depended on the variety and the treatment applied. Tempranillo increased up 200% the total stilbene concentration, Grenache 60% and Graciano 50%. For the three varieties, the treatment with the highest time and energy was the most effective on the total stilbene extraction. These results indicate that PEF could be a suitable technology for obtaining musts with deeper colour and higher phenolic content, including resveratrol and piceid. 相似文献
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《Journal of dairy science》2022,105(8):6589-6600
Whey proteins are being integrated as high-value food product ingredients due to their versatile and tunable techno-functionality. To meet high food quality and clean label expectations by consumers, electric field (EF) technologies have been proposed to open new frontiers in this field. Despite a variety of studies, it remains ambiguous which EF parameters are crucial to achieving targeted whey protein modifications. Reconstituted liquid whey protein concentrate (WPCL) and filtered, non-heat-treated liquid whey (WPL_filt) at low protein dry weight concentrations (0.4% wt/wt) were exposed to microsecond pulsed electric field (μsPEF) treatments at EF intensities between 1.25 and 12.5 kV/cm, pulse repetition frequencies between 0.38 and 85 Hz, and pulse lengths set to 10 or 100 μs. Protein aggregations were quantified spectroscopically. We report here that aggregates formed at lower temperatures for μsPEF compared with purely thermal treatments in identical treatment geometries at similar time-temperature profiles. We suggest that the observed increase in absorbance is linked to protein migration, the isoelectric point, local deprotonation phenomena of thiol groups, and cation precipitation. The μsPEF treatment time, which is dependent on the pulse repetition frequency, pulse length, and time of process, is the main driver of the increase in absorbance. High EF intensities balanced with shorter pulse repetition frequencies to ensure similar energy inputs resulted in no aggregate formation. For WPL_filt, 12.5 kV/cm, 10 μs, 0.38 Hz (620 ± 96 kJ/kg; ± standard deviation) did not result in an increase in absorbance, whereas 1.25 kV/cm, 10 μs, 50 Hz (634 ± 57 kJ/kg) with similar time-temperature profiles increased the absorbance at a wavelength of 380 nm by a factor of 8.2 ± 1.7 compared with untreated WPL_filt. In conclusion, the treatment time seems to dominate over high EF intensities at similar energy inputs for aggregate formation and increase in absorbance. 相似文献
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Leguérinel I Spegagne I Couvert O Coroller L Mafart P 《International journal of food microbiology》2007,116(1):88-95
The influence of heating treatment temperature, pH of heating and recovery medium on the survival kinetics of Salmonella typhimurium ATCC 13311 is studied and quantified. From each non-log linear survival curve, Weibull model parameters were estimated. An average shape parameter value of 1.67 was found, which is characteristic of downward concavity curves and is in agreement with values estimated from other S. typhimurium strains. Bigelow type models quantifying the heating temperature, heating and recovery medium pH influences are fitted on scale parameter delta data (time of first decimal reduction), which reflects the bacterial heat resistance. The estimate of z(T) (4.64 degrees C) is in the range of values given in the literature for this species. The influence of pH of the heating medium on the scale parameter (z(pH): 8.25) is lower than that of the recovery pH medium influence (z(')(pH): 3.65). 相似文献
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High-intensity electric fields have been successfully applied to the destruction of Salmonella Enteritidis in diaultrafiltered egg white. The effects of electric field strength (from 20 to 35 kV x cm(-1)), pulse frequency (from 100 to 900 Hz), pulse number (from 2 to 8), temperature (from 4 to 30 degrees C), pH (from 7 to 9), and inoculum size (from 10(3) to 10(7) CFU x ml(-1)) were tested through a multifactorial experimental design. Experimental results indicate that, for Salmonella inactivation, the electric field intensity is the dominant factor with a strongly positive effect, strengthened by its positive interaction with pulse number. Pulse number, temperature, and pH have also significant positive effects but to a lesser extent. In the most efficient conditions, the pulsed electric field (PEF) treatment is capable of 3.5 log10 reduction in viable salmonellae. Simultaneously, the measure of surface hydrophobicity does not indicate any increase after PEF treatment. These results suggest that no protein denaturation occurs, unlike what is observed after comparable heat treatment in terms of Salmonella inactivation (55 degrees C for 15 min). 相似文献
18.
Influence of treatment temperature on the inactivation of Listeria innocua by pulsed electric fields
《LWT》2005,38(2):167-172
The effect of treatment temperature on the bactericidal effectiveness of pulsed electric fields (PEF) applied on Listeria innocua suspended in McIllvaine buffer was investigated. Electric field intensity and number of applied pulses were applied in the ranges of 31–40 kV/cm and 5–35 pulses, respectively. Studied treatment temperatures were sustained for 10 s, and ranged between 19°C and 59°C depending on the amount of energy delivered by the PEF treatment. The application of PEF at higher temperatures proved to be more effective than either PEF at low temperatures or the applied thermal treatments by themselves. A maximum bacterial inactivation of 6-log cycles was obtained by applying either: 20 pulses of 40 kV/cm at 65°C, 25 pulses of 36 kV/cm at 61°C, or 31 pulses of 31 kV/cm at 56°C. On the other hand, a thermal treatment of 66°C sustained for 30 s reduced the bacterial population on its own by only 5-log cycles, and the application of 60 pulses of 31 kV/cm at 30°C caused only 3-log cycles of bacterial inactivation. The findings in this study suggest that PEF technology may be effectively used as an enhanced mild thermal preservation method. 相似文献
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Effects of pH,temperature, and pre-pulsed electric field treatment on pulsed electric field and heat inactivation of Escherichia coli O157:H7 总被引:1,自引:0,他引:1
This investigation was undertaken to study the inactivation of Escherichia coli O157:H7 by pulsed electric field (PEF) treatment and heat treatment after exposure to different stresses. E. coli O157:H7 cells exposed to different pHs (3.6, 5.2, and 7.0 for 6 h). different temperatures (4, 35, and 40 degrees C for 6 h), and different pre-PEF treatments (10, 15, and 20 kV/cm) were treated with PEFs (20, 25, and 30 kV/cm) or heat (60 degrees C for 3 min). The results of these experiments demonstrated that a pH of 3.6 and temperatures of 4 and 40 degrees C caused significant decreases in the inactivation of E. coli O157:H7 by PEF treatment and heat treatment (P < 0.05). Pre-PEF treatments, pHs of 5.2 and 7.0, and a temperature of 35 degrees C, on the other hand, did not result in any resistance of E. coli O157:H7 cells to inactivation by PEF treatment and heat treatment (P > 0.05). 相似文献