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1.
The influence of electrical pulse protocol parameters on cell rupture of onion tissues was investigated in order to improve fundamental understanding and to enhance the processing of plant tissues with pulsed electric fields (PEFs). The impact of PEF parameters on cell integrity of 20 mm dia, 4-mm thick disks of Don Victor onions (Allium cepa L.) was determined by ion leakage measurements. Electric field strength, pulse width, total pulse duration, and frequency effects were determined in relation to their effects on cell damage as a function of pulse protocol. Electric field strengths up to 500 V/cm increased the damage efficiency but there was no significant difference in efficiency beyond this field strength. Larger pulse widths increased the degree of tissue disintegration at a constant pulse number. Higher PEF efficiency was achieved with shorter pulse widths and a larger number of pulses at a constant total treatment time. Lower frequencies caused a greater degree of disintegration at constant number of pulses. 1H-NMR experiments were performed to determine the proton relaxation components of the PEF-treated onion samples and to obtain cell damage information nondestructively. Paramagnetic ion uptake by the onion sample was used to identify different proton relaxation components. Five different proton relaxation components were observed and changes in the 2 components representing different proton environments showed high correlations with ion leakage results (R2= 0.99), indicating that T(2) distributions can be used to obtain information about cell membrane integrity in PEF-treated samples. 1H-NMR proved to be an effective method for nondestructive quantification of cell membrane rupture in onions.  相似文献   

2.
The influence of electrical field strength and number of pulses on cell rupture of onion tissues was investigated by two different methods to understand the changes in cell viability of plant tissues after pulsed electric field (PEF) treatment. The impact of pulsed electric field parameters on cell integrity of 20 mm diameter, 4 mm thick disks of Sabroso onions (Allium cepa L.) was determined by ion leakage measurements and microscopic method. The effect of treatments on cellular integrity was visualized by neutral red staining of the onion cells. Cell rupture is essential for optimal process design before extraction of desirable compounds and/or drying of plant tissues. Experimental results were obtained for onion disks treated with electrical pulses at field strengths of E  167 V/cm and 333 V/cm, pulse width of ti = 100 μs, frequency of f = 1 Hz and the number of pulses, n = 1 to 100. At 167 V/cm electric field strength treatment cell rupture was not observed however ion leakage increased and air spaces around cell walls disappeared, most likely due to changes in cell membrane permeability. Irreversible cell rupture occurred at 333 V/cm. Ion leakage values and ruptured cells count were increased with increasing pulse number. 92.2 ± 5.9 % of the onion cells were ruptured after 333 V/cm and 100 pulse treatment. Small plant cells that are located near vascular bundles and upper epidermis showed higher resistance to pulsed electric field treatments.Industrial RelevanceThe aim of this study was to determine the response of plant tissues with different cell type to the pulse electric field treatment. Two different methods, neutral red staining and ion leakage, were used to visualize and determine the cell rupture on onion tissues. Industry may choose one of these methods to evaluate treatment efficiency on the basis of cell rupture; especially ion leakage measurements which require lower investment cost and easy to apply or microscopic method for visualize the cells layer by layer. The paper stresses the importance of cell type, size and distribution of cells were found to the ability to resist cell rupture during pulsed electric field treatment. It is critical to explain overall changes caused by PEF on the structure of plant tissue at a cellular level in order to optimize the quality of PEF processed foods.  相似文献   

3.
In this study, we performed the pulsed electric field (PEF)-assisted aqueous extraction of betalains from fresh red beetroot, simultaneously evaluating a disintegration degree of red beetroot tissue. The extraction results showed that the application of 3 pulses (1 Hz) with 100 μs duration and 2.0 kV/cm pulse strength (delivering total specific energy of 2.53 kJ/kg) resulted in extraction up to ~70% (extracted for 1 h at 22 °C) of total betalains. It was observed that at low specific energy inputs (0.8 and 2 kJ/kg – 0.5, 1.0, 1.5 and 2.0 kV/cm), the PEF treatment duration has a significant effect on the extraction yield of betalains. We show that comparing the efficiency of PEF treatments with different PEF strengths and durations, but the same specific energy inputs (0.8, 2.0, and 4.0 kJ/kg), higher permeabilization index (Zp) does not refer to a higher extraction yield of betalains.Industrial relevancePEF-assisted aqueous extraction of betalains from the fresh red beetroot is effective, energy favourable and environmentally friendly method and could serve as an alternative to the conventional extraction techniques. Our study shows that the extraction yield of betalains is better reflected by measurements of supernatant conductivity rather than Zp.  相似文献   

4.
Pulsed electric field (PEF) was applied to basil leaves prior air drying at 40 °C. The parameters of the electric treatment were designed in such a way that (i) electroporated the tissue reversibly, provoking a permanent opening of the stomatal guard cells and (ii) electroporated the tissue irreversibly, damaging the cells. Treated leaves lost some volatile compounds due to both PEF treatments, probably related with the direct effect of permeabilization on the secretory cells of glandular trichomes. Upon drying, the irreversible permeabilization treatment showed the highest influence on the profile of volatiles in the dried leaves showing better retention of some terpenoids than the control. The performed statistical analysis allowed to select six compounds that can be used as markers both for the effect of pre-treatments prior dehydration and for the effects of dehydration itself on the volatile compounds of basil leaves.  相似文献   

5.
The relationship between membrane permeabilization and loss of viability by pulsed electric fields (PEF) depending on the treatment intensity and the treatment media pH in two gram-positive (Lactobacillus plantarum, Listeria monocytogenes) and two gram-negative (Escherichia coli, Salmonella senftenberg 775W) bacterial species has been investigated. Loss of membrane integrity was measured as increased uptake of the fluorescent dye propidium iodide (PI). Non-permanent/reversible permeabilization was detected when cells stained with PI during PEF resulted in higher fluorescence than that measured in cells stained after PEF. Whereas loss of viability of the two gram-negative bacteria was correlated with the sum of non-permanent and permanent membrane permeabilization when treated at pH 7.0, in the case of the two gram-positives, loss of viability was correlated with a permanent loss of membrane integrity. At pH 7.0, the four bacteria exhibited reversible permeabilization. However, whereas the gram-positives capable of reversing permeabilization survived, the gram-negative cells died, despite their capacity to reverse permeabilization immediately after PEF. Thus, resealing is not necessarily related to the survival of PEF-treated cells. In contrast, when cells were PEF-treated at pH 4.0 a more complicated picture emerged. Whereas loss of viability was correlated with a permanent loss of membrane integrity in L. monocytogenes cells, in L. plantarum the degree of permeabilization was higher, and in the gram-negative strains, much lower than the percentage of inactivated cells. These results support the view that membrane permeabilization is involved in the mechanism of bacterial inactivation by PEF, but the nature of membrane damage and its relationship with cell death depends on the bacterial species and the treatment medium pH.  相似文献   

6.
A systematic study of the impact of pulsed electric fields (PEF) parameters (1–7 kV/cm, 5–40 pulses, specific energy of 0.006–0.19 kJ/kg per pulse, pulse frequency of 1–10 Hz, pulse width of 2–5 μs, square and exponential decay pulses) on the kinetics of the sucrose extraction from sugar beet at different temperatures (20–70 °C) has been carried out in this investigation. The efficiency of the solid-liquid extraction was independent of the frequency, as well as of the pulse width, and the pulse shape at 7 kV/cm, and it was influenced by the electric field strength applied and by the temperature of the extracting medium. Sucrose yield increased with both field strength, time of extraction, and temperature. The effect of the field strength was higher the lower the temperature. The application of 20 pulses at 7 kV/cm (3.9 kJ/kg) increased the maximum yield by 7 and 1.6 times, compared to non-PEF-treated samples, at 20 and 40 °C, respectively. A mathematical expression was generated, which enabled to evaluate the influence of the electric field strength (from 0 to 7 kV/cm) and temperature (from 20 to 70 °C) on the sucrose extraction efficiency and the extracting time in a solid-liquid PEF-assisted sucrose extraction process. Based on this equation, for 80%-sucrose extraction in 60 min, the temperature could be reduced from 70 °C to 40 °C, when 20 pulses of 7 kV/cm were applied.  相似文献   

7.
The impact of pulsed electric fields (PEF) on cellular integrity and texture of Ranchero and Sabroso onions (Allium cepa L.) was investigated. Electrical properties, ion leakage rate, texture, and amount of enzymatically formed pyruvate were measured before and after PEF treatment for a range of applied field strengths and number of pulses. Critical electric field strengths or thresholds (E(c)) necessary to initiate membrane rupture were different because dissimilar properties were measured. Measurement of electrical characteristics was the most sensitive method and was used to detect the early stage of plasma membrane breakdown, while pyruvate formation by the enzyme alliinase was used to identify tonoplast membrane breakdown. Our results for 100-μs pulses indicate that breakdown of the plasma membrane occurs above E(c)= 67 V/cm for 10 pulses, but breakdown of the tonoplast membrane is above either E(c)= 200 V/cm for 10 pulses or 133 V/cm for 100 pulses. This disparity in field strength suggests there may be 2 critical electrical field strengths: a lower field strength for plasma membrane breakdown and a higher field strength for tonoplast membrane breakdown. Both critical electric field strengths depended on the number of pulses applied. Application of a single pulse at an electric field up to 333 V/cm had no observable effect on any measured properties, while significant differences were observed for n≥10. The minimum electric field strength required to cause a measurable property change decreased with the number of pulses. The results also suggest that PEF treatment may be more efficient if a higher electric field strength is applied for a fewer pulses.  相似文献   

8.
目的研究高压脉冲电场(high-voltage pulsed electric field,PEF)技术辅助提取玉米皮多糖。方法以玉米皮粉(纤维素含量21.25%)为原料,以多糖提取率为衡量指标,以电场强度、电场频率和液固比为3个重要因素,根据单因素及响应面试验设计构建PEF技术提高玉米皮粉酶解效果的回归模型,优化出最佳工艺参数;同时对提取的多糖进行中红外(mid-infrared spectroscopy,MIR)测定,与PEF辅助水提法比较分析提取多糖的结构差异。结果 PEF辅助水提法的最佳工艺参数为:电场强度25 k V/cm,电场频率2080 Hz,液固比42:1 mL/g,此条件下PEF辅助酶法对玉米皮多糖的提取率最高可达(15.36±0.25)%,与PEF辅助水提法相比提高了6.4%。中红外谱图结果表明,PEF辅助水提法和PEF辅助酶提法多糖在O-H振动及C=O振动上有着明显差别。结论PEF技术可以提高玉米皮多糖的提取率且PEF辅助酶提法效果更佳。  相似文献   

9.
The olive oil extraction industry often uses unit-constructed processing lines lacking in the necessary efficiency and sustainability. The development of efficient processing lines is seen as crucial in obtaining higher product quality and extraction yields. In recent years, numerous researchers and companies have explored the possibilities of assistance from pulsed electric fields (PEF) technology as a mean of reducing processing time and increasing extraction yields from different food crops. The current article shows the application of PEF technology in olive oil extraction, and specifically it researches the results from application of PEF technology in a pilot plant of industrial-layout olive oil extraction process. The experimental methodology involves construction of a plant meeting specific functional and cost criteria, capable of delivering unipolar electric pulses with amplitude <10 kV, current <200 A and 3 kW maximum average power. The analyses then focalize on the assessment of the results from PEF assistance on oil extraction, particularly in terms of extractability from crop and enhancement of bioactive substances content. The proposed PEF unit was found to be easy to install within existing plants, flexible in control and capable of continuous operation. Operating at different pulse and power levels, the plant results in increased process efficiency and content of desirable substances.  相似文献   

10.
This study was aimed at relating diffusion rates during osmotic dehydration of red bell peppers in two different osmotic solutions (sucrose/sodium chloride, 21.86 and 2.02 g/100 g respectively, and sucrose, 50°Brix at 30 °C) to the extent of membrane permeabilisation induced by pulsed electric field (PEF) using varying field strength of 1, 1.5 and 2 kV/cm with a constant pulse number of 20 at a pulse duration of 400±50 μs. The development of pores with time within the membrane after PEF was monitored, changes in sample weight and composition in the product liquid phase were analysed. The initiation of pore formation and pore growth within the cell membrane after PEF was found to be time dependent and not an instantaneous process. A fractional ruptured membrane area, Fp=0.003% was detected after about 20 s of application of 2 pulses at 2 kV/cm (320 J/kg energy input per pulse and approx. 0.2 °C temperature change) and this increased to 0.0166% within 300 min. Osmotic dehydration of bell peppers was highest at the beginning of the process. The application of PEF resulted in enhanced rate of transfers as indicated by an increase of 11–25% in water loss and 2–5% in solids gain as compared to the untreated samples in the two osmotic solutions. Conditions of PEF that induced an average fractional ruptured area of 0.008%, 5 min after PEF treatment were found adequate to markedly improve diffusion kinetics during the osmotic dehydration under atmospheric pressure conditions.  相似文献   

11.
Reversible electropermeabilization of plant tissues with heterogeneous structure represents a technological challenge as the response of the different structures within the same specimen to the application of electric field may differ due to different cell sizes, extracellular space configurations, and electrical properties. The influence of five different pulsed electric field protocols with different pulse polarity, number of pulses (25, 50, 75, 100, 250, and 500), and intervals between pulses (no intervals and 1- and 2-ms intervals) on the reversible permeabilization of rucola (Eruca sativa) leaves was investigated. The electric field intensity was 600 V/cm. Electrical resistance of the bulk tissue was measured before and after electroporation, and propidium iodide was used to analyze the electroporation at the surface of the leaf. Leaf viability was assessed from survival in storage, and cell viability was investigated with fluorescein diacetate. Results indicate that the viability of the leaves could not be predicted by measurements of electrical resistance or permeabilization levels of the leaf surface. Higher survival rate was demonstrated when applying bipolar pulses compared with monopolar pulses, but the latter proved to be more effective than bipolar pulses for permeabilizing the surface of the leaves. Longer intervals between bipolar pulses resulted in increased viability preservation, while the number of electroporated cells on the leaf surface was comparable for all tested protocols.  相似文献   

12.
A cell viability assessment method based computer vision analysis of the uptake of neutral red dye was used to quantify cell membrane integrity in raw and processed parenchyma cells of onion tissues. The presence of stained vacuoles was used as an indicator of tonoplast membrane integrity and photomicrographs were acquired for microscopic image analysis and cell integrity quantification. Two different image analysis methods, involving the analysis of the saturation and green components of RGB (red, green, blue) images, were compared to the conventional cell count method. Use of the saturation component of RGB images allowed for the visualization and quantification of viable and inviable cells as well as extracellular air spaces. The combination of neutral red uptake, as visualization by light field microscopy, and saturation image analysis, allowed for quantitative determination of the effects of high pressure processing on onion cell integrity. PRACTICAL APPLICATION: Preservation of vegetable tissues may involve heating or other methods that result in the loss of tissue integrity and potentially quality deterioration. In this study, we stained unprocessed and processed onion tissues with neutral red dye and then used a microscope and a computer imaging program to quantify how many cells were intact or ruptured.  相似文献   

13.
Consumption of unpasteurized melon and watermelon juices has caused several disease outbreaks by pathogenic microorganisms worldwide. Pulsed electric field (PEF) has been recognized as a technology that may inactivate those bacteria present in fluid food products at low temperatures. Hence, PEF treatment at 35 kV/cm, 4 mus pulse duration in bipolar mode and square shape were applied on Salmonella Enteritidis, E. coli and L. monocytogenes populations inoculated in melon and watermelon juices without exceeding 40 degrees C outlet temperatures. Different levels of treatment time and pulse frequency were applied to evaluate their effects on these microorganisms. Treatment time was more influential than pulse frequency (P相似文献   

14.
Efficiency of pulsed electric field (PEF) induced permeabilization at 293 K in selected fruit and vegetable plant tissues (apple, potato, carrot, courgette, orange, and banana) at electric field strength (E) of 400 V·cm(-1), 1000 V·cm(-1) and pulse duration (t(p)) of 1000 μs was studied experimentally. The mean cell radius (〈r〉) was within 30 to 60 μm, and the ratio of electrical conductivities of the intact and damaged tissues (σ(i)/σ(d)) was within 0.07 to 0.79 for the studied tissues. Electroporation theory predicts higher damage for tissue with larger cells; however, the direct correlation between PEF damage efficiency and size of cell was not always observed. To explain this anomaly, a theoretical Monte Carlo model was developed and checked for parameters typical for potato tissue. The model showed a strong dependence of PEF damage efficiency and power consumption (W) on σ(i)/σ(d) ratio. The optimum value of electric field strength (E(opt)) was an increasing function of σ(i)/σ(d), and plant tissues with high σ(i)/σ(d) ratio (σ(i)/σ(d) ≈ 1) required application of a rather strong field (for example, E(opt) ≈ 3000 V·cm(-1) for σ(i)/σ(d) ≈ 0.8). However, the PEF treatment at a lower field (E ≈ 400 V·cm(-1)) allowed regulation of the selectivity of damage of cells in dependence of their size. A good qualitative correspondence between experimental data and simulation results were observed.  相似文献   

15.
The effect of pulsed electric field (PEF) treatment, applied in a continuous system, on Saccharomyces cerevisiae and Bacillus cereus cells and spores was investigated. S. cerevisiae inoculated into sterilised apple juice and B. cereus cells and spores inoculated into sterilised 0.15% NaCl were treated with electric field strengths of 10–28 kV/cm using an 8.3 pulse number and with pulse numbers of 4.2–10.4 at 20 kV/cm, respectively. The inactivation of S. cerevisiae depended on the electric field intensity and number of pulses. The yeast inactivation increased when the applied electric field intensity and pulse number were increased. Approximately four log cycles reduction was achieved in apple juice using 10.4 pulses at 20 kV/cm. B. cereus cells were less sensitive to PEF treatment. The reduction in microbial count of B. cereus cells was hardly more than one log cycle using 10.4 pulses at 20 kV/cm. The applied PEF treatment was ineffective on Bacillus cereus spores.  相似文献   

16.
Consumer demand for fresh-like products with little or no degradation of nutritional and organoleptic properties has led to the study of new technologies in food preservation. Pulsed electric fields (PEF) is a nonthermal preservation method used to inactivate microorganisms mainly in liquid foods. Microorganisms in the presence of PEF suffer cell membrane damage. Nisin is a natural antimicrobial known to disrupt cell membrane integrity. Thus the combination of PEF and nisin represents a hurdle for the survival of Listeria innocua in liquid whole egg (LWE). L. innocua suspended in LWE was subjected to two different treatments: PEF and PEF followed by exposure to nisin. The selected frequency and pulse duration for PEF was 3.5 Hz and 2 micros, respectively. Electric field intensities of 30, 40 and 50 kV/cm were used. The number of pulses applied to the LWE was 10.6, 21.3 and 32. The highest extent of microbial inactivation with PEF was 3.5 log cycles (U) for an electric field intensity of 50 kV/cm and 32 pulses. Treatment of LWE by PEF was conducted at low temperatures, 36 degrees C being the highest. Exposure of L. innocua to nisin following the PEF treatment exhibited an additive effect on the inactivation of the microorganism. Moreover, a synergistic effect was observed as the electric field intensity, number of pulses and nisin concentration increased. L. innocua exposed to 10 IU nisin/ml after PEF exhibited a decrease in population of 4.1 U for an electric field intensity of 50 kV/cm and 32 pulses. Exposure of L. innocua to 100 IU nisin/ml following PEF resulted in 5.5 U for an electric field intensity of 50 kV/cm and 32 pulses. The model developed for the inactivation of L. innocua by PEF and followed by exposure to nisin proved to be accurate (p = 0.05) when used to model the inactivation of the microorganism by PEF in LWE with 1.2 or 37 IU nisin/ml. The presence of 37 IU nisin/ml in LWE during the PEF treatment for an electric field intensity of 50 kV/cm and 32 pulses resulted in a decrease in the population of L. innocua of 4.4 U.  相似文献   

17.
Pulsed electric fields (PEF) accounts for one of the novel non-thermal processing and preservation technologies and is regarded as an emerging application with the advantage of minimising the loss of valued bioactive compounds in food processing. In this study, various PEF pulses were applied to jujube pulp before fermentation. The fermentation kinetics, compositions, volatile and sensory characteristics were investigated and compared. Results showed that the PEF pretreatment with ten exponential wave pulses at 1.5 kV cm−1, 1 Hz improved phenolic compounds extraction, especially for caffeic acid, morin and p-hydroxybenzoic acid. Besides, fifty pulses pretreatment enhanced 10% of the wine dry extract. In addition, PEF pretreatment significantly enriched the floral and fruity volatile notes to jujube wine with a decrease in fusel oil. Consequently, PEF preprocessing is a promising method that can be adopted in winemaking industry to promote wine quality and sensory profile.  相似文献   

18.
The effects of pulsed electric fields (PEF) treatment on the solubility, surface tension and fluorescence spectra of L‐tryptophan were systematically investigated using a range of PEF intensities (0–50 kV cm?1) and a number of pulses (0–216). PEF frequency and pulse width used in this experiment were 1000 Hz and 40 μs, respectively. Under these conditions, the solubility, pH value and maximum relative fluorescence value (RFV) of L‐tryptophan were generally increased and then decreased with both increasing the PEF intensity and pulse number. Conductivity of the solution was insensitive to changes but still increased slightly with increasing the PEF intensity. In addition, surface tension was decreased at higher PEF intensity and pulse number. Results from the mass spectrum analysis confirmed that after the PEF treatment, the basic structure of L‐tryptophan remained unchanged. These results suggested that PEF treatment induced some function alteration to the isolated L‐tryptophan without changing the basic structure.  相似文献   

19.
This research aims to evaluate the effect of pulsed electric field (PEF) pre-treatment for osmotic dehydration (OD) on physiological changes in organic strawberries and kiwifruits, in terms of metabolic heat production, measured by isothermal calorimeter, and of tissue damage, evaluated by fluorescence microscopy, texture analysis, and electrolytes leakage. Fruits were pre-treated at two electric field strengths (100 and 200 V/cm) using 100 near-rectangular shaped pulses (pulse width: 10 μs, repetition time: 10 ms) and then subjected to OD in hypertonic solutions (40% w/w) of sucrose or trehalose, both added with calcium lactate 1%. Results showed that OD alone allowed to retain the functionality of the membranes causing only a decrease in the endogenous heat production. The application of low electric field strength (100 V/cm) generally preserved the cell viability, which was drastically reduced after OD treatment. On the contrary, the application of 200 V/cm caused tissue damage and loss of cell vitality, probably due to irreversible electroporation.Industrial applicationPEF could be an interesting pre-treatment for reducing the intensity of osmotic dehydration of fruits. However, it is important to understand the implication of the treatment on the tissue metabolism and structure to control the effect on the quality of the final product. This study provides some useful information that could be exploited for the industrial production of intermediate moisture fruit products.  相似文献   

20.
Abstract: This study was conducted to evaluate the effect of pulsed electric field (PEF) treatment on anthocyanin extraction from red cabbage using water as a solvent. Mashed cabbage was placed in a batch treatment chamber and subjected to PEF (2.5 kV/cm electric field strength; 15 μs pulse width and 50 pulses, specific energy 15.63 J/g). Extracted anthocyanin concentrations (16 to 889 μg/mL) were determined using HPLC. Heat and light stabilities of the control and PEF-treated samples, having approximately the same initial concentrations, were studied. PEF treatments enhanced total anthocyanin extraction in water from red cabbage by 2.15 times with a higher proportion of nonacylated forms than the control (P < 0.05). The heat and light stabilities of the PEF-treated samples and control samples were not significantly different (P > 0.05). Practical Application: An innovative pretreatment technology, pulsed electric field processing, enhanced total anthocyanin extraction in water from red cabbage by 2.15 times. Manufacturers of natural colors can use this technology to extract anthocyanins from red cabbage efficiently.  相似文献   

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