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1.
Pulsed electric field (PEF) processing is a novel mild treatment for pumpable foods preservation at low or moderate temperatures. The electric field strength and the temperature distribution in the treatment chamber have been identified as the key processing parameters affecting the treatment efficacy and possibly the sensorial and nutritional quality of the food. A full 3D computational fluid dynamics (CFD) model of a pilot-scale PEF system with co-linear configuration of the electrodes was developed. The model couples the fluid dynamics and the electrical field and can be used to predict the liquid’s flow pattern, electric field distribution, temperature increase, and residence time in the treatment chamber. A total of 48 process conditions with different settings of applied voltage V, pulse length τ, pulse repetition rate (frequency) f and flow rate in combination with four different inlet temperatures were simulated for a model liquid food (NaCl solutions with two different electrical conductivities) and whole milk. The simulated PEF energy dissipated into the liquids was between 4 and 66 kJ/kg and process temperatures ranged from approximately 25 to 80 °C. The predicted temperature data agree well (R2 > 0.99) with experimental measurements in five locations of the treatment chamber using fibre optic probes.  相似文献   

2.
This work discusses the temperature effects (T = 30-80 °C) on degradation of colorants and kinetics of their extraction from the red beet both untreated and treated by pulsed electric field (PEF). PEF treatment was done using the trains of monopolar rectangular 100 μs pulses with electric field strength E = 375-1500 V cm−1, and total treatment time tPEF = 0-0.2 s. The degradation of colorants and their extraction were characterized by means of absorbance and electrical conductivity measurements. PEF treatment was found effective for acceleration of the extraction of betalains and reducing the time of extraction. Electroporation was shown to be responsible for intensification of the release of colorants through aqueous extraction.  相似文献   

3.
The effects of pulsed electric field (PEF) treatments at field intensities of 25–37 kV cm 1 and final PEF treatment temperatures of 15 °C and 60 °C on the inactivation of alkaline phosphatase (ALP), Total Plate Count (TPC), Pseudomonas and Enterobacteriaceae counts were determined in raw skim milk. At 15 °C, PEF treatments of 28 to 37 kV cm 1 resulted in 24–42% inactivation in ALP activity and < 1 log reduction in TPC and Pseudomonas count, while the Enterobacteriaceae count was reduced by at least 2.1 log units to below the detection limit of 1 CFU mL 1. PEF treatments of 25 to 35 kV cm 1 at 60 °C resulted in 29–67% inactivation in ALP activity and up to 2.4 log reduction in TPC, while the Pseudomonas and Enterobacteriaceae counts were reduced by at least 5.9 and 2.1 logs, respectively, to below the detection limit of 1 CFU mL 1. Kinetic studies suggested that the effect of field intensity on ALP inactivation at the final PEF treatment temperature of 60 °C was more than twice that at 15 °C. A combined effect was observed between the field intensity and temperature in the inactivation of both ALP enzyme and the natural microbial flora in raw skim milk.Industrial relevanceMilk has been pasteurised to ensure its safety and extend its shelf life. However, the need for retaining heat-sensitive nutrient and sensory properties of milk has resulted in interest in the application of alternative technologies. The results of the current study suggest that PEF as a non-thermal process can be employed for the treatment of raw milk in mild temperature to achieve adequate safety and shelf life while preserving the heat-sensitive enzymes, nutrients and bioactive compounds.  相似文献   

4.
The application of intense pulsed electric fields (PEF) in foods is intended to be a non-thermal method to inactivate microorganisms. However, it is well known that an increase in temperature is present in this process due to ohmic heating, where the pulsed electric field energy input is transformed into heat. The aim of this study was to investigate the computer modeled temperature increase in the outflow for different flow-through PEF treatment chamber designs. Given equal experimental conditions, the temperature increase is indicative of the PEF dose, and a more uniform temperature profile is thus indicative of a more homogeneous PEF treatment. The radial distribution of the temperature increase was simulated in computer models of four different chambers. The temperature increase was found to be more homogeneous in the treatment chambers making use of a decrease in the insulator diameter, i.e. a design letting the insulators and electrodes intersect at angles close to 90°. The maximum temperature increase was found close to the wall, where the flow velocity is low. Cooling of the electrodes and electric insulators is recommended to avoid too high a temperature increase. The minimum temperature increase found was 29% of the calculated average in the worst case studied here. The minimum PEF dose to which the food was subjected would thus is less than the intended dose, since the food clearly was not subjected to the intended electric field strength during the intended exposure time. This is an important result in terms of food safety in the sense that a minimum PEF treatment should be guaranteed. The microbiological inactivation was experimentally evaluated using two of the treatment chamber designs. The result is consistent with the simulations and shows a small increase in inactivation and less needed energy input giving less average temperature increase for the chamber implementing a contraction of the diameter of the insulating spacer.  相似文献   

5.
以鸡肉和牛肉粉体香精及其经大肠杆菌人工污染的样品为研究对象,使用自制的脉冲电场杀菌装置对其进行杀菌试验,测定处理前后的菌落总数和理化指标.试验结果表明:高压脉冲电场对粉体香精具有显著的灭菌效果,当处理时间为6 s,电场强度为40 KV/cm时,细菌总数和大肠菌群数降低约1.6个对数值和2.7个对数值.高压脉冲电场对粉体物料中的一些主要物质如蛋白质、脂肪等不会产生降解或分解,或对其影响可以忽略不计;不会对肉味粉体香精的感官品质产生变化,能很好地保持着产品的原有色、香、味.  相似文献   

6.
The moderate thermal (MT), ultrasound (US), and pulsed electric field (PEF) pretreatments are studied to enhance the phenolics extraction from Cabernet Franc (CF) grapes. The next pretreatment conditions are investigated: MT (50 °C, 15 min, 125 kJ/kg), US1 (24 kHz, 5 min, 121 kJ/kg), US2 (24 kHz, 10 min, 242 kJ/kg), US3 (24 kHz, 15 min, 363 kJ/kg), PEF1 (0.8 kV/cm, 100 ms, 42 kJ/kg), and PEF2 (5 kV/cm, 1 ms, 53 kJ/kg). The qualitative parameters of extracts (pH, °Brix, and color intensity), their total polyphenols content, anthocyanins, tannins, and free radical scavenging activity were determined during the whole period of alcoholic fermentation. The results show that all studied pretreatments improve phenolics extraction (anthocyanins and tannins content), color intensity, and scavenging activity of the samples during red fermentation. However, the moderate (0.8 kV/cm) and high (5 kV/cm) PEF were the most effective pretreatments and increased the phenolics extraction yield, respectively, on 51 and 62 %, while the MT and US3 pretreatments increased the phenolics extraction yield, respectively, on 20 and 7 %. The anthocyanin and tannins were also better extracted, and the color intensity was highest after the PEF pretreatments in comparison with the MT and US pretreatments.  相似文献   

7.
The effect of culture temperature on the conformation of membrane lipid of Salmonella Typhimurium as well as their pulsed electric field (PEF) resistance was investigated. Results revealed that S. Typhimurium cells cultured at relatively lower temperature (10 and 25 °C) were more easily inactivated by PEF treatment than those cultured at relatively higher temperature (37 and 45 °C). Using a Weibull model, it was determined that the PEF treatment time to inactivate 90% S. Typhimurium cells cultured at 45 °C was almost fourfold compared to those cultured at 10 °C. Results of micro‐Raman spectroscopy indicated that as the culture temperature increased, the order degree of C–C and lateral packing order of membrane lipid chain also increased, resulting in a drop in the membrane fluidity. These results are important in considering the use of heat and PEF to inactivate microbe contaminants in food.  相似文献   

8.
高压脉冲电场非热处理技术因处理时间短、温升小、能耗低和杀菌效果明显等成为目前杀菌工艺中研究最为活跃的技术之一,而且在功能物质提取与保持物质活性等方面也展现了较好的应用前景。着重就高压脉冲电场对食品中的一些生物大分子如酶类、蛋白质等的影响进行综述。  相似文献   

9.
利用扫描电镜、激光粒度仪、X射线衍射仪、差示扫描量热仪对脉冲电场前处理玉米醋酸酯淀粉的物化性质进行研究,同时与未经脉冲电场前处理的玉米醋酸酯淀粉性质进行比较。结果表明:玉米淀粉经过脉冲电场处理后更容易引入乙酰基;激光粒度分析发现,脉冲电场前处理的醋酸酯淀粉颗粒较未经脉冲电场前处理的醋酸酯淀粉颗粒的体积平均粒径和表面积平均粒径都大;X射线衍射图谱表明,脉冲电场前处理玉米醋酸酯淀粉的相对结晶度较小;热特性分析发现,脉冲电场前处理醋酸酯淀粉较未经脉冲电场前处理的To,Tp和ΔH均下降。  相似文献   

10.
Pulsed electric fields (PEF) processing of sour cherry juice with the measurement of pH, ºBrix, titratable acidity, conductivity, colour (L*, a* and b*), nonenzymatic browning index, metal ion concentration, total ascorbic acid and total antocyanin content as well as microbial inactivation were searched in the study. Applied PEF treatment parameters did not cause any significant difference on measured properties of sour cherry juice (P > 0.05). On the other hand, inactivation of Escherichia coli O157:H7, Staphylococcus aureus, Listeria monocytogenes, Erwinia carotowora, Pseudomonas syringae subs. syringae, Botrytis cinerea and Penicillum expansum significantly increased with increased electric field strength and treatment time (P ≤ 0.05). It was revealed that PEF is a viable option to process sour cherry juice with significant amount of microbial inactivation and without adversely affecting important physical and quality parameters.  相似文献   

11.
A model was developed that enables the quantification of thermal and electric field effects during the pulsed electric field (PEF) inactivation of alkaline phosphatase (ALP) and lactoperoxidase (LPO) in milk as well as Escherichia coli in apple juice.  相似文献   

12.
Whole milk was processed using selected combinations of pulsed electric fields (PEF) and thermal treatments to inactivate Listeria innocua. Electric field intensities of 30 and 40 kV/cm were applied at selected number of pulses (1–30) and temperatures (20–72 °C) for less than 10 s. A maximum microbial reduction of 4.3 log cycles was achieved using 10, 17.5, 20 and 25 pulses, when processing milk at 30 kV/cm and initial temperatures of 43, 33, 23 and 13 °C, respectively. Around 4.3 log cycles of L. innocua was observed when treating milk at 40 kV/cm using 3, 10, 12.5, 15, and 20 pulses and 53, 33, 23, 15, and 3 °C, respectively. Milk treated with 40 kV/cm of electric field intensity, few pulses, and initial temperature close to 55 °C showed the best balance between L. innocua inactivation and energy-consumption. An energy expenditure of around 244 J/mL was achieved, which can be further reduced to 44 J/mL using a thermal regeneration system.  相似文献   

13.
The compound 1,8-cineole is known to elicit the perception of eucalyptus flavour. There is debate over whether eucalyptus flavour is positive or should be considered a taint in red wine. The current experiment measured a consumer rejection threshold (CRT) in red wine, using samples spiked with increasing concentrations of cineole. Results estimated the CRT in red wine at 27.5 ppb. Analysis of a post-experiment questionnaire suggested that preference for cineole is not significantly influenced by gender, age, level of experience or prior experience, though these results were based on a small sample. Results suggest that a moderate intensity of eucalyptus character in red wine should not be considered a taint and that some consumers may consider moderate intensities preferable to no eucalyptus character. The CRT determined allows quantitative decisions to be made in response to measured levels of cineole in red wine. Winemakers and wine marketers considering promoting eucalyptus character as a taste dimension in wine now have a quantitative basis on which to be guided.  相似文献   

14.
15.
脉冲电场对牛奶酪蛋白功能性质的影响   总被引:1,自引:0,他引:1  
研究了脉冲电场对酪蛋白功能性质的影响.结果表明:随着脉冲强度和脉冲处理时间的延长,酪蛋白的溶解度下降,乳化性、起泡性及疏水性增加.当脉冲强度或处理时间大于25kV/cm或144(288)μs时,部分功能性质反而下降.  相似文献   

16.
The need for enhancing microbial food safety and quality, without compromising the nutritional, functional and sensory characteristics of foods, has created an increasing world-wide interest in low-temperature innovative processes for food preservation. In contrast, to the traditional thermal processes, these emerging technologies are predominantly reliant on physical processes, including high hydrostatic pressures, pulsed electric fields and low-temperature plasmas that inactivate microorganisms at ambient or moderately elevated temperatures and short treatment times. The current review presents the latest developments in the two most recent of these technologies, pulsed electric field and low-temperature plasma treatments for food preservation and disinfection of food contact surfaces.  相似文献   

17.
Potato starch–water suspensions (8.0%, w/w) were subjected to pulsed electric fields (PEF) treatment at 30 kV·cm− 1, 40 kV·cm− 1 and 50 kV·cm− 1, respectively. The physicochemical properties of PEF-treated potato starch samples were investigated using scanning electron microscopy (SEM), laser scattering technique, X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and the Brabender rheological method, with native potato starch as reference. It has been concluded from SEM analysis that dissociation and damage of PEF-treated potato starch granules appeared. Some granules aggregated with each other and showed gel-like structures. It was revealed from particle size analysis that there was an obvious increase of the granule size after PEF treatment. This has been attributed to the aggregation among granules. It was also demonstrated from other analysis that relative crystallinity, gelatinization temperatures, gelatinization enthalpy, peak viscosity as well as breakdown viscosity of modified samples all decreased with increasing electric field strength.

Industrial relevance

In this study, the effect of PEF treatment (up to 50 kV·cm− 1) on physicochemical properties of potato starch has been investigated. The results from SEM images showed that dissociation, denaturation and damage of potato starch granules had been induced by the PEF treatments. Some of granule fragments showed gel-like structures, and congregated with each other or with other starch granules. Laser scattering measurements of particle size revealed that an obvious increase of granule size under electric field strength of 50 kV·cm− 1, which was attributed to the aggregation of the starch granules. The X-ray diffraction pattern showed an obvious loss of crystalline structure after the PEF treatment at 50 kV·cm− 1, which induced a trend of transformation from crystal to non-crystal in potato starch granules. DSC analysis showed a decrease in gelatinization temperatures (To and Tp) and gelatinization enthalpy (ΔHgel) with increasing electric field strength. Brabender rheological method has been used to show that the peak viscosity and breakdown viscosity decrease with increasing electric field strength of PEF treatment. All the results reveal that the PEF treatment can lead to an intragranular molecular rearrangement of potato starch granules, which induces changes of various physicochemical properties of the treated starch thus may endow it some new characteristics and functions. This phenomena may warrant further more detailed study.  相似文献   

18.
In this work, the susceptibility to pulsed light (PL) treatments of both a Gram-positive (L. innocua 11288) and a Gram-negative (E. coli DH5-??) bacteria inoculated in apple (pH = 3.49, absorption coefficient 13.9 cm− 1) and orange juices (pH = 3.78, absorption coefficient 52.4 cm− 1) was investigated in a range of energy dosages from 1.8 to 5.5 J/cm2. A laboratory scale continuous flow PL system was set up for the experiments, using a xenon flash-lamp emitting high intensity light in the range of 100-1100 nm. The flashes lasted 360 ??s at a constant frequency of 3 Hz.The results highlighted how the lethal effect of pulsed light depended on the energy dose supplied, the absorption properties of liquid food as well as the bacterial strain examined. The higher the quantity of the energy delivered to the juice stream, the greater the inactivation level. However, the absorbance of the inoculated juice strongly influenced the dose deliver and, therefore, the efficiency of the PL treatment. Among the bacteria tested, E. coli cells showed a greater susceptibility to the PL treatment than L. innocua cells in both apple and orange juices. Following treatment at 4 J/cm2, microbial reductions in apple and orange juices were, respectively, 4.00 and 2.90 Log-cycles for E. coli and 2.98 and 0.93 Log-cycles for L. innocua.Sublethally injured cells were also detected for both bacterial strains, thus confirming that membrane damage is an important event in bacterial inactivation by PL.  相似文献   

19.
胡芬  曾新安  韩忠  高文宏 《食品工业科技》2012,33(24):140-142,146
实验以玉米淀粉为研究对象,经过30、40、50kV·cm-1的脉冲电场处理后,利用偏光显微镜观察、差示扫描量热仪等方法,研究了脉冲电场对玉米淀粉酶解特性及消化特性的影响。结果表明,经过脉冲电场处理之后,淀粉颗粒被破坏、结晶区特征减弱,糊化的温度和焓值也减小,同时,玉米淀粉的酶解率和RDS值均有所增加,而SDS值有所降低。  相似文献   

20.
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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