Effects of Pulsed Electric Fields on the Activities of Microorganisms and Pectin Methyl Esterase in Orange Juice

Orange juice was treated with pulsed electric fields (PEF) in a pilot‐plant system to optimize PEF‐processing conditions for maximum microbial inactivation and to investigate the effects of PEF on pectin methyl esterase (PME) activity. Electric‐field strengths of 20,25,30, and 35 kV/cm and total treatment times of 39, 49, and 59 μs were used. Higher electric‐field strengths and longer total treatment times were more effective to inactivate microorganisms and PME (p < 0.05). PEF treatment of orange juice at 35 kV/cm for 59 μs caused 7–log reductions in total aerobic plate count and yeast and mold counts. About 90% of PME activity was inactivated by PEF treatment at 35 kV/cm for 59 μs. PEF‐treated orange juice at 35 kV/cm for 59 ms did not allow growth of microorganisms and recovery of PME at 4, 22, and 37 °C for 112 d.     

Inactivation of Oxidative Enzymes by High-Intensity Pulsed Electric Field for Retention of Color in Carrot Juice

The effects of high-intensity pulsed electric fields (HIPEF) on oxidative enzymes and color of fresh carrot juice were studied. A response surface methodology (RSM) was used to evaluate the effect of pulse polarity (mono or bipolar mode), pulse width (from 1 to 7 μs), and pulse frequency (from 50 to 250 Hz) on color and peroxidase (POD) inactivation of carrot juice treated by HIPEF. The total treatment time and the electric field strength were set at 1,000 μs and 35 kV/cm, respectively, at a temperature below 35°C. The physicochemical characteristics of carrot juice were measured. There was a linear relationship between electrical conductivity and temperature of the carrot juice. The results showed that HIPEF-treated carrot juice at 35 kV/cm for 1,000 μs applying 6 μs pulse width at 200 Hz in bipolar mode led to 73.0% inactivation of POD. The color coordinates did not change significantly. Therefore, HIPEF was effective in POD inactivation and carrot juice color preservation.     

ENZYME INACTIVATION ON APPLE JUICE TREATED BY ULTRAPASTEURIZATION AND PULSED ELECTRIC FIELDS TECHNOLOGY

Apple juice was pasteurized by an ultra-high temperature treatment (UHT) at 115, 125 and 135C for 3 and 5 s, and compared with a high-voltage pulsed electric field treatment (PEF) at ranges between 33 and 42 kV/cm with frequencies of 150, 200, 250 and 300 pulses per second (pps). Enzyme inactivation and physicochemical properties of the treated juices were compared using a nontreated sample as control. The UHT treatment was more efficient in enzyme inactivation, reducing 95% the residual activity of polyphenoloxidase at the maximum temperature and time. However, a PEF treatment at 38.5 kV/cm and 300 pps combined with a temperature of 50C achieved a 70% reduction of residual PFO activity. In terms of quality characteristics as a function of physicochemical properties, color, pH, acidity and soluble solids were all less affected by PEF than by UHT when compared with the untreated juice.

PRACTICAL APPLICATIONS

Apple juice is a popular beverage worldwide and it is consumed nearly as much as orange juice. Consumers prefer fresh-squeezed fruit juices with high nutrient value and fresh-like sensory attributes. Enzymatic browning negatively impacts appearance, nutritive value and flavor of fruit juices. The use of ultra-high temperature processing is efficient in microbial control, as well as in enzyme inactivation. Any thermal processing may, however, decrease the overall quality of the treated juices. Pulsed electric field processing provides a potential alternative to thermal pasteurization of fruit juices.     

Effects of pulsed electric field on colloidal properties and storage stability of carrot juice

The effects of pulsed electric fields (PEF) and high‐temperature short time (HTST) on the colloidal properties of carrot juice initially after PEF processing and throughout storage period were studied. Compared with HTST treatments, PEF treatments have less effect on the colloidal properties, such as cloud stability, zeta potential, viscosity and particle size distribution (PSD). Pectin methyl esterase (PME) could influence the colloidal properties of carrot juice by de‐esterification of the pectin. In the present work, PME activity was reduced significantly as electric‐field strength (from 15 to 30 kV cm^?1) and treatment time (from 100 to 800 μs) increased. The results also showed that the emergency of a new peak in PSD of samples occurred when the electric intensity exceeded 30 kV cm^?1. Images of transmission electron microscopy showed that particles slightly gathered after PEF treatment. However, under HTST treated, these smaller particles aggregated into net‐like structures that further gathered larger particles. At the micro level, both PEF treated (30 kV cm^?1, 800μs) and HTST treated kept good stability for more than 1 month.     

Comparative study on antioxidant properties of carrot juice stabilised by high‐intensity pulsed electric fields or heat treatments

BACKGROUND: The effect of high‐intensity pulsed electric field (HIPEF) processing (35 kV cm^?1 for 1500 µs using 6‐µs bipolar pulses at 200 Hz) on the antioxidant features (vitamin C, β‐carotene, total phenolic compounds and antioxidant capacity) of carrot juice as well as on peroxidase activity was investigated and compared to the observed in heat pasteurised juices (90 °C for 60 s or 30 s) having the fresh juice as a reference. RESULTS: HIPEF and heat‐treated carrot juices had higher β‐carotene and lower vitamin C contents than the untreated juices immediately after processing. The antioxidant capacity of the juices was significantly modified neither by HIPEF nor by thermal treatments. POD activity decreased drastically (≥93.3%) after processing irrespective of the treatment applied. Vitamin C and β‐carotene content decreased throughout the storage following an exponential trend (R² = 0.801–0.984) with degradation rates between 1.7 × 10^?2 and 3.5 × 10^?2 day^?1. Vitamin C and β‐carotene contents were better maintained in HIPEF‐treated than in heat‐pasteurised juices throughout the storage. Total phenolic content and the antioxidant capacity of the HIPEF‐treated juice did not substantially differ from that of the thermally treated juice for 56 days. CONCLUSION: HIPEF processing may help to achieve fresh‐like carrot juices with increased amounts of health‐related phytochemicals. Copyright © 2009 Society of Chemical Industry     

高压脉冲电场对蓝莓汁杀菌效果及品质的影响

研究了高压脉冲电场(PEF)对蓝莓汁的杀菌效果及其对蓝莓汁理化性质的影响。结果显示:随电场强度、处理时间的增大,PEF对蓝莓汁中大肠杆菌的杀灭效果增强。当电场强度为35 kV/cm,处理时间为82μs时,蓝莓汁中大肠杆菌致死率为5.12个对数。电场强度一定时,电导率增大,PEF对大肠杆菌的钝化效果略微下降。PEF对蓝莓汁VC、花青素、总酚、可滴定酸、还原糖、可溶性固形物及色泽等理化性质没有影响。     

Inactivation Kinetics of Tomato Juice Lipoxygenase by Pulsed Electric Fields

ABSTRACT: Pulsed electric field (PEF) inactivation models for tomato juice lipoxygenase (LOX) were studied. Tomato juice was treated by PEF with the combinations of electric field strength (0, 10, 15, 20, 30, 35 kV/cm), PEF treatment time (20, 30, 50, 60, 70 μs), and PEF treatment temperature (10, 20, 30, 40, 50 °C). The first-order inactivation models, Hulsheger's model, Fermi's model, and the 2nd-order polynomial equation adequately described the LOX inactivation. Calculated D values were 161.0, 112.9, 101.0, and 74.8 μs at 15, 20, 30, and 35 kV/cm, respectively, at 30 °C. The activation energy for the inactivation of LOX by PEF was 35.7 kJ/mol. Applied electric field strength was the primary variable for the inactivation of LOX.     

Inactivation of Pectin Methyl Esterase in Orange Juice by Pulsed Electric Fields

ABSTRACT: Pulsed electric fields (PEF) treatments were applied to nonpasteurized orange juice using a bench top PEF system to study effects of PEF on the activity of pectin methyl esterase (PME). Effects of electric strength on PME activity at a constant water bath temperature were studied using electric field strengths up to 35 kV/cm at 30 °C. Increase of electric field strength caused a significant inactivation of PME with increase in orange juice temperature ( p < 0.05). A thermal inactivation study showed that heating of orange juice at the same temperature as orange juice during PEF treatment was not effective as PEF treatment in inactivating PME. Effects of electric field strength at different water bath temperatures were studied using electric field strengths up to 25 kV/cm and water bath temperatures of 10–50 °C. Higher electric field strengths at higher water bath temperature were the more effective to inactivate PME. A combination of PEF treatment at 25 kV/cm and a water bath temperature of 50 °C caused 90% inactivation of PME.     

Pectin methyl esterase and natural microflora of fresh mixed orange and carrot juice treated with pulsed electric fields

The effects of pulsed electric fields (PEFs) on pectin methyl esterase (PME), molds and yeast, and total flora in fresh (nonpasteurized) mixed orange and carrot juice were studied. The PEF effect was more extensive when juices with high levels of initial PME activity were subjected to treatment and when PEF treatment (at 25 kV/cm for 340 micros) was combined with a moderate temperature (63 degrees C), with the maximum level of PME inactivation being 81.4%. These conditions produced 3.7 decimal reductions in molds and yeast and 2.4 decimal reductions in total flora. Experimental inactivation data for PME, molds and yeast, and total flora were fitted to Bigelow, Hülsheger, and Weibull inactivation models by nonlinear regression. The best fit (lowest mean square error) was obtained with the Weibull model.     

Comparative study on color,viscosity and related enzymes of tomato juice treated by high-intensity pulsed electric fields or heat

The effects of high intensity pulsed electric fields (HIPEF) processing (35 kV/cm for 1,500 μs using bipolar 4-μs pulses at 100 Hz) on color parameters and viscosity, as well as peroxidase (POD), pectin methylesterase (PME) and polygalacturonase (PG), were evaluated during 77 days of storage at 4 °C and compared to thermal treatments at 90 °C for 1 min or 30 s for unprocessed tomato juice. HIPEF-treated tomato juice showed higher values of lightness than the thermally processed and the untreated juice throughout storage time (P < 0.05). Viscosity of HIPEF-treated tomato juice was also greater than both thermally treated and untreated for the first 35 days of storage. POD of HIPEF-treated tomato juice was inactivated by 97% whereas in the case of the thermally treated, 90 and 79% inactivation was achieved after 1 min and 30 s, respectively. The highest PME inactivation in tomato juice was obtained by PEF (82%) and heat treatment at 90 °C for 1 min (96%). PG of PEF-treated tomato juice was inactivated by 12% whereas thermal treatments at 90 °C for 1 min or 30 s achieved 44 and 22%, respectively. Despite the low rates of PG inactivation obtained, the pattern followed in the residual activity along the storage time was similar in the tomato juice treated by HIPEF than the thermally processed.     

Commercial-Scale Pulsed Electric Field Processing of Orange Juice

Effects of commercial‐scale pulsed electric field (PEF) processing on the microbial stability, ascorbic acid, flavor compounds, color, Brix, pH, and sensory properties of orange juice were studied and compared with those of thermal processing. Freshly squeezed orange juice was thermally processed at 90 °C for 90 s or processed by PEF at 40 kV/cm for 97 ms. Both thermally processed and PEF‐processed juices showed microbial shelf life at 4 °C for 196 d. PEF‐processed juice retained more ascorbic acid, flavor, and color than thermally processed juice (P<0.05). Sensory evaluation of texture, flavor, and overall acceptability were ranked highest for control juice, followed by PEF‐processed juice and then by thermally processed juice (P<0.01).     

Identification of equivalent processing conditions for pasteurization of strawberry juice by high pressure,ultrasound, and pulsed electric fields processing

The objective of this study was to evaluate the effectiveness of high pressure processing (HPP), ultrasound (US) and pulsed electric fields (PEF) for the pasteurization of strawberry juice (SJ). Acid-adapted Escherichia coli was used to inoculate SJ prior to treatment with HPP, US, and PEF. HPP was applied at several pressures (200–400 MPa) up to 2 min while US (120 μm, 24 kHz) was conducted at 25, 40, and 55 °C up to 10 min in continuous pulsing mode. In order to avoid excessive use of SJ, PEF was performed using a model solution (MS) basically composed of citric acid (8 g/L), fructose (35 g/L), glucose (35 g/L), Na₂HPO₄ (0.2 M) and NaCl (5%) to simulate the SJ electrical conductivity, pH, and total soluble solid (TSS). A face-centered composite design was conducted for PEF processing at different electric field intensities (EFI) (25–35 kV/cm) and treatment times (5–27 μs). Processing conditions were selected that resulted in 5-log CFU/mL inactivation of E. coli. HPP at 300 MPa for 1 min, and US at 55 °C (thermosonication) for 3 min reduced E. coli in SJ by 5.75 ± 0.52 and 5.69 ± 0.61 log CFU/mL, respectively. PEF treatment at 35 kV/cm, 27 μs treatment time, 350 mL/min flow rate, and 2 μs pulse width in monopolar mode resulted in 5.53 ± 0.00 log reduction of E. coli in MS. Likewise, E. coli population in SJ was also reduced by 5.16 ± 0.15 log after applying the same PEF conditions to SJ. No E. coli was detected in SJ subjected to conventional thermal pasteurization at 72 °C for 15 s. All technologies reduced the natural microbiota below 2 log CFU/mL in terms of the total aerobic bacteria and yeast-mold counts. Thus, this study identified the equivalent conditions for the SJ pasteurization by three nonthermal processing technologies.Industrial relevanceConsumers have an increasing interest towards fresh-like food products with desirable nutritional and sensorial attributes. High pressure, ultrasound and pulsed electric field are three relevant novel nonthermal technologies as alternatives to conventional thermal treatments. This study identified the processing conditions of these three nonthermal technologies for the pasteurization of strawberry juice based on equivalent inactivation of acid-adapted E. coli. From an industrial point of view, the established processing conditions are useful references for the development of novel berry juices. In addition to microbiological safety, this study on equivalent processing allows direct efficacy and quality comparisons of a given juice pasteurized by the three nonthermal technologies under consideration.     

Pulsed Electric Field Processing of Orange Juice: A Review on Microbial,Enzymatic, Nutritional,and Sensory Quality and Stability

During the last decades pulsed electric field (PEF) processing received considerable attention due to its potential to enhance food products or create alternatives to conventional methods in food processing. It is generally acknowledged that PEF processing can deliver safe and chill‐stable fruit juices with fresh‐like sensory and nutritional properties. Relatively low‐processing temperature and short residence times can achieve highly effective inactivation of microorganisms while retaining product quality. A first commercial application of PEF for preservation of fruit juices was launched in 2006 in the United States. Since then, industrial‐scale processing equipment for liquid and solid products were developed and, in Europe in 2009, an industrial juice preservation line was installed using 20 kV/cm pulses at 40 to 50 °C to extend the chill‐stability of fruit juices, including citrus juices and smoothies, from 6 to 21 d. The related PEF processing costs are in the range of US $0.02 to 0.03 per liter and are justified due to access to new markets and reduced return of spoiled product. However, despite its commercial success there are still many unknown factors associated with PEF processing of fruit and citrus juices and many conflicting reports in the literature. This literature review, therefore, aims to provide a comprehensive overview of the current scientific knowledge of PEF effects on microbial, enzymatic, nutritional, and sensory quality and stability of orange juices.     

Effect of refrigerated storage on ascorbic acid content of orange juice treated by pulsed electric fields and thermal pasteurization

Application of pulsed electric fields (PEF) can lead to longer shelf life of fruit juices with minimal product quality loss and good retention of fresh-like flavour. The aim of this study was to evaluate the effect of PEF and conventional pasteurization (90 °C, 20 s) on ascorbic acid content of orange juice, and to assess modifications in ascorbic acid concentration of orange juice stored in refrigeration at 2 and 10 °C for 7 weeks. The ascorbic acid degradation rate was −0.0003, −0.0006, −0.0009 and −0.0010 μs⁻¹ for fields of 25, 30, 35 and 40 kV/cm, respectively. With selected PEF treatment (30 kV/cm and 100 μs) the shelf life based on 50% ascorbic acid losses was 277 days for the PEF-treated orange juice stored at 2 °C, while for the pasteurized juice was 90 days.     

Inactivation of orange juice peroxidase by high‐intensity pulsed electric fields as influenced by process parameters

The inactivation of orange juice peroxidase (POD) under high‐intensity pulsed electric fields (HIPEF) was studied. The effects of HIPEF parameters (electric field strength, treatment time, pulse polarity, frequency and pulse width) were evaluated and compared with conventional heat pasteurization. Samples were exposed to electric field strengths from 5 to 35 kV cm^?1 for up to 1500 µs using square wave pulses in mono‐ and bipolar mode. Effect of pulse frequency (50–450 Hz), pulse width (1–10 µs) and electric energy on POD inactivation by HIPEF were also studied. Temperature was always below 40 °C. POD was totally inactivated by HIPEF and the treatment was more effective than thermal processing in inactivating orange juice POD. The extent of POD inactivation depended on HIPEF processing parameters. Orange juice POD inhibition was greater when the electric field strength, the treatment time, the pulse frequency and the pulse width increased. Monopolar pulses were more effective than bipolar pulses. Orange juice POD activity decreased with electric energy density input. The Weibull distribution function adequately described orange juice POD inactivation as a function of the majority of HIPEF parameters. Moreover, reduction of POD activity related to the electric field strength could be well described by the Fermi model. Copyright © 2005 Society of Chemical Industry     

Effect of refrigerated storage on vitamin C and antioxidant activity of orange juice processed by high-pressure or pulsed electric fields with regard to low pasteurization

A better knowledge of the effect of refrigerated storage on the nutritional and antioxidant characteristics of foods processed by emerging technologies with regard to thermal traditional technology is necessary. Thus, freshly squeezed orange juice was processed by high-pressure (HP) (400 MPa/40 °C/1 min), pulsed electric fields (PEF) (35 kV/cm/750 μs) and low pasteurization (LPT) (70 °C/30 s). The stability of vitamin C and antioxidant activity was studied just after treatment and during 40 days of refrigerated storage at 4 °C. The determination of total vitamin C (ascorbic acid plus dehydroascorbic acid) was achieved by HPLC whereas the antioxidant activity was assessed by the measurement of the DPPH• radical scavenging. Just after treatment, all treated orange juices showed a decrease lower than 8% in vitamin C content compared with the untreated one. At the end of refrigerated storage, HP and LPT juices showed similar vitamin C losses (14 and 18%, respectively) in relation to untreated juice, although HP juices maintained better the vitamin C content during more days than LPT juices. Regarding antioxidant activity, after 40 days at 4 °C, differences among treated juices were no significant in terms of antiradical efficiency (AE=1/EC₅₀T_EC50). HP and PEF may be technologies as effective as LPT to retain antioxidant characteristics of orange juice during refrigerated storage.     

Comparing the impact of high pressure,pulsed electric field and thermal pasteurization on quality attributes of cloudy apple juice using targeted and untargeted analyses

The impact of low-oxygen spiral-filter press technology combined with thermal pasteurization (TP), pulsed electric field (PEF) and high pressure processing (HPP) on cloudy apple juice quality was investigated immediately after the treatments and after 3 weeks of storage at 4 °C. Based on equivalent levels of microbial safety and desired shelf-life, low and high processing intensities were selected: TP (72 °C/15 s; 85 °C/30 s), PEF (12.5 kV/cm, 76.4 kJ/L; 12.3 kV/cm, 132.5 kJ/L), and HPP (400 MPa/3 min; 600 MPa/3 min). High intensity thermal treatment resulted in a bright, yellowish color which was maintained during storage. PPO and POD activities were largely reduced by high intensity PEF and TP yet showed high resistance to HPP. The highest vitamin C content was provided by fresh juice followed by PEF-treated juices. Due to oxidative degradation reactions, vitamin C of all treated samples significantly decreased during storage. Immediately after processing, high cloud stability values were obtained in all samples; however, cloud stability decreased during storage particularly for HPP juices with high residual PME. No significant changes were observed in pH, titratable acidity, organic acid and sugar content which also corresponded to sweet and sour taste. Results from untargeted volatile profiles showed that esters increased after PEF and were better retained after HPP. Contrary to TP treatment where ester degradation reactions occurred together with the formation of off-flavors. Most of the volatiles decreased during storage which could be linked to oxidation and ester hydrolysis reactions.Industrial relevanceBeing one of the most popular fruit juices consumed worldwide, cloudy apple juice can still undergo quality changes such as color degradation, cloud loss (fast sedimentation) and flavor changes during processing and storage. This study evaluates the potential of low-oxygen spiral-filter press in combination with different preservation technologies to obtain a maximal quality of cloudy apple juice. Results showed that high intensity thermal pasteurization can effectively inactivate quality-degrading enzymes, therefore it is useful to obtain an optimal cloudy apple juice product in terms of color and cloud stability. Although HPP has minimal impact on aroma of the juice, shelf-life of the juice may be limited due to incomplete enzyme inactivation. In the case of PEF treatment, thermal effects may contribute to maintain apple juice quality.     

Combined effect of temperature and pulsed electric fields on apple juice peroxidase and polyphenoloxidase inactivation

Pulsed electric fields (PEF) were applied to freshly prepared apple juice using a laboratory scale continuous PEF system to study the feasibility of inactivating peroxidase (POD) and polyphenoloxidase (PPO). Square wave PEF using different combinations of electric field strength, pre-treatment temperature and treatment time were evaluated in this study and compared to conventional pasteurisation (72 °C; 26 s). Inactivation curves for the enzyme were plotted for each parameter and inactivation kinetics were calculated. Results showed the highest level of decrease in the enzymatic activity of 71% and 68%, for PPO and POD, respectively, were obtained by using a combination of preheating to 50 °C, and a PEF treatment time of 100 μs at 40 kV/cm. This level of inactivation was significantly higher (P < 0.05) than that recorded in juice processed by conventional mild pasteurisation where the activity of PPO and POD decreased by 46% and 48%, respectively. The kinetic data for the inactivation of both enzymes could be described using a 1st-order model (P < 0.001).     

Inactivation kinetics and secondary structural change of PEF-treated POD and PPO

Effects of pulsed electric fields (PEF) on the activity of peroxidase (POD) and polyphenol oxidase (PPO) in buffered solution were studied while the corresponding changes to their secondary structures was demonstrated by far-UV Circular dichroism (CD). The relative residual activity of POD and PPO decreased with the increase in electric field strength and treatment time, and PPO was more susceptible than POD to PEF treatment. The greatest reduction of the activity was achieved for POD at 25 kV/cm for 1740 μs and PPO at 25 kV/cm for 744 μs with reductions of 32.2% and 76.2%, respectively. The inactivation kinetic parameters D-value and Z_E value were calculated. The D-values of PPO were smaller than those POD at higher electric field strength, and Z_E values of POD and PPO were 36.9 and 16.2 kV/cm, respectively. The secondary structures of the two enzymes were changed following treatment by PEF. The intensity of negative peaks in the CD spectra decreased, and the CD spectra of PPO changed more significantly than that of POD; the reduction of the relative α-helix fractions for POD at 25 kV/cm for 124 μs was 22.63% while it was 50.72% for PPO at 25 kV/cm for 52 μs. The inactivation of PEF-treated POD and PPO was in close agreement with their secondary structure changes.     

Pulsed electric fields versus thermal treatment: equivalent processes to obtain equally acceptable citrus juices

Pulsed electric field treatment has been claimed to produce more acceptable chilled citrus juices than those obtained by conventional thermal treatment. The pectin methylesterase activity and the acceptability of nine juices obtained from Clementine mandarins, Valencia oranges, and Ortanique fruits (hybrid of mandarin and orange), untreated, pasteurized (85 degrees C for 10 s), and treated by pulsed electric fields (25 kV/cm for 330 micros), were evaluated. The treatments, selected to reach a similar level of pectin methylesterase inactivation, produced juices that did not differ in acceptability from each other for the three varieties and in all cases were less acceptable than the untreated juice.