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.     

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.     

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.     

Ultraviolet and Pulsed Electric Field Treatments Have Additive Effect on Inactivation of E. coli in Apple Juice

ABSTRACT: Apple juice inoculated with Escherichia coli ATCC 23472 was processed continuously using either ultraviolet (UV), high‐voltage pulsed electric field (PEF), or a combination of the PEF and UV treatment systems. Apple juice was pumped through either of the systems at 3 flow rates (8, 14, and 20 mL/min). E. coli was reduced by 3.46 log CFU/mL when exposed in a 50 cm length of UV treatment chamber at 8 mL/min (2.94 s treatment time with a product temperature increase of 13 °C). E. coli inactivation of 4.87 log CFU/mL was achieved with a peak electric field strength of 60 kV/cm and 11.3 pulses (average pulse width of 3.5 μs, product temperature increased to 52 °C). E. coli reductions resulting from a combination treatment of UV and PEF applied sequentially were evaluated. A maximum E. coli reduction of 5.35 log CFU/mL was achieved using PEF (electrical field strength of 60 kV/cm, specific energy of 162 J/mL, and 11.3 pulses) and UV treatments (length of 50 cm, treatment time of 2.94 s, and flow rate of 8 mL/min). An additive effect was observed for the combination treatments (PEF and UV), regardless of the order of treatment (P > 0.05). E. coli reductions of 5.35 and 5.30 log CFU/mL with PEF treatment (electrical field strength of 60 kV/cm, specific energy of 162 J/mL, and 11.3 pulses) followed by UV (length of 30 cm, treatment time of 1.8 s, and flow rate of 8 mL/min) and UV treatment followed by PEF (same treatment conditions), respectively. No synergistic effect was observed.     

Inactivation of in Apple Juice by Radio Frequency Electric Fields

ABSTRACT: Heat pasteurization may detrimentally affect the quality of fruit and vegetable juices; hence, nonthermal pasteurization methods are actively being developed. Radio frequency electric fields processing has recently been shown to inactivate yeast in water at near-ambient temperatures. The objective of this study was to extend the radio frequency electric fields (RFEF) technique to inactivate bacteria in apple juice. A converged-field treatment chamber was developed that enabled high-intensity RFEF to be applied to apple juice using a 4-kW power supply. Finite element analyses indicated that uniform fields were generated in the treatment chamber. Escherichia coli K12 in apple juice was exposed for 0.17 ms to electric field strengths of up to 26 kV/cm peak over a frequency range of 15 to 70 kHz. The population of E. coli was reduced by 1.8 log following exposure to an 18 kV/cm field at an outlet temperature of 50 °C. Raising the temperature increased inactivation. Intensifying the electric field up to 16 kV/cm increased inactivation; however, above this intensity, inactivation remained constant. Radio frequencies of 15 and 20 kHz inactivated E. coli better than frequencies of 30 to 70 kHz. Inactivation was independent of the initial microbial concentration between 4.3 and 6.2 log colony-forming units (CFU)/mL. Applying 3 treatment stages at 50 °C increased inactivation to 3 log. The electric energy for the RFEF process was 300 J/mL. The results of the present study provide the 1st evidence that RFEF processing inactivates bacteria in fruit juice at moderately low temperatures.     

Inactivation of E. coli 8739 in Enriched Soymilk Using Pulsed Electric Fields

ABSTRACT: Soymilk enriched with dairy proteins was subjected to pulsed electric fields (PEF) to evaluate the inactivation of Escherichia coli 8739 and the extension of microbial shelf-life. The maximum thermal exposure level of sample was 60 °C for 1.6 s during a PEF treatment. A 5.7-log reduction was achieved using PEF at 41.1 kV/cm for 54 μs. PEF inactivation of E. coli 8739 followed a 1st-order kinetic model. D-values of E. coli 8739 were 31.9,18.6, and 11.0 μs at 30,35, and 40 kV/cm, respectively. PEF treatment at 41.1 kV/cm for 54 μs significantly extended the microbial shelf-life at 4 °C ( P < 0.05). No significant change in brightness and viscosity of PEF-treated samples was observed during a 30-d storage at 4 °C. PEF was found effective in inactivation of E. coli in and extension of microbial shelf-life of enriched soymilk.     

Inactivation of Listeria innocua in liquid whole egg by pulsed electric fields and nisin

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.     

PULSED ELECTRIC FIELD INACTIVATION of MICROORGANISMS and PRESERVATION of QUALITY of CRANBERRY JUICE

Cranberry juice was treated either by high voltage pulsed electric field (PEF) at 20 kV/cm and 40 kV/cm for 50 and 150°s, or by thermal treatment at 90C for 90s. Higher field strength and longer treatment time reduced more viable microbial cells. the overall volatile profile of the juice was not affected by PEF treatment but it was affected by thermal treatment. No Significant difference in color was observed between the control and PEF treated samples. the application of 40kV/cm for 150 1ts resulted in no growth of molds and yeasts during storage at 22 and 4C, and no growth of aerobic bacteria during storage at 4C. PEF is an alternative process to thermal pasteurization for cranberry juice.     

Inactivation of Pseudomonas fluorescens in skim milk by combinations of pulsed electric fields and organic acids

Pseudomonas fluorescens suspended in skim milk was inactivated by application of pulsed electric fields (PEF) either alone or in combination with acetic or propionic acid. The initial concentration of microorganisms ranged from 10(5) to 10(6) CFU/ml. Addition of acetic acid and propionic acid to skim milk inactivated 0.24 and 0.48 log CFU/ml P. fluorescens, respectively. Sets of 10, 20, and 30 pulses were applied to the skim milk using exponentially decaying pulses with pulse lengths of 2 micros and pulse frequencies of 3 Hz. Treatment temperature was maintained between 16 and 20 degrees C. In the absence of organic acids, PEF treatment of skim milk at field intensities of 31 and 38 kV/cm reduced P. fluorescens populations by 1.0 to 1.8 and by 1.2 to 1.9 log CFU/ml, respectively. Additions of acetic and propionic acid to the skim milk in a pH range of 5.0 to 5.3 and PEF treatment at 31, 33, and 34 kV/cm, and 36, 37, and 38 kV/cm reduced the population of P. fluorescens by 1.4 and 1.8 log CFU/ml, respectively. No synergistic effect resulted from the combination of PEF with acetic or propionic acid.     

Reduction in levels of Escherichia coli O157:H7 in apple cider by pulsed electric fields.

Many studies have demonstrated that high voltage pulsed electric field (PEF) treatment has lethal effects on microorganisms including Escherichia coli O157:H7; however, the survival of this pathogen through the PEF treatment is not fully understood. Fresh apple cider samples inoculated with E. coli O157:H7 strain EC920026 were treated with 10, 20, and 30 instant charge reversal pulses at electric field strengths of 60, 70, and 80 kV/cm, at 20, 30, and 42 degrees C. To accurately evaluate the lethality of apple cider processing steps, counts were determined on tryptic soy agar (TSA) and sorbitol MacConkey agar (SMA) to estimate the number of injured and uninjured E. coli O157:H7 cells after PEF treatment. Cell death increased significantly with increased temperatures and electric field strengths. A maximum of 5.35-log10 CFU/ml (P < 0.05) reduction in cell population was achieved in samples treated with 30 pulses and 80 kV/cm at 42 degrees C. Cell injury measured by the difference between TSA and SMA counts was found to be insignificant (P > 0.05). Under extreme conditions, a 5.91-log10 CFU/ml reduction in cell population was accomplished when treating samples with 10 pulses and 90 kV/cm at 42 degrees C. PEF treatment, when combined with the addition of cinnamon or nisin, triggered cell death, resulting in a reduction in E. coli O157:H7 count of 6 to 8 log10 CFU/ml. Overall, the combination of PEF and heat treatment was demonstrated to be an effective pasteurization technique by sufficiently reducing the number of viable E. coli O157:H7 cells in fresh apple cider to meet U.S. Federal Drug Administration recommendations.     

Inactivation of Saccharomyces cerevisiae and Bacillus cereus by pulsed electric fields technology

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.     

PROCESSING OF YOGURT-BASED PRODUCTS WITH PULSED ELECTRIC FIELDS: MICROBIAL, SENSORY AND PHYSICAL EVALUATIONS

Yogurt-based products similar to a dairy pudding dessert were formulated and processed by mild heat and pulsed electric fields (PEF) to investigate the effects of combined mild heat and PEF treatment on the microbial stability and quality of high viscosity foods. Commercial plain low fat yogurt was mixed with fruit jelly and corn syrup and processed by mild heat treatment at 60C for 30 s and 30 kV/cm electric field strength for 32 μs total treatment time using OSU-2C pilot plant scale PEF system. Control and processed products were aseptically packaged and stored at 4 and 22C. Mild heat combined with PEF treatment significantly decreased the total viable aerobic bacteria and total mold and yeast of yogurt-based products during storage at both 4 and 22C (P ≤ 0.05). Mild heat treatment alone without any PEF treatment did not prevent the growth of microorganisms in yogurt-based products. Sensory evaluation indicated that there was no significant difference between the control and processed products (P ≤ 0.05). Color, pH and °Brix were not significantly affected by mild heat and PEF processing conditions.     

Influence of treatment time and pulse frequency on Salmonella Enteritidis, Escherichia coli and Listeria monocytogenes populations inoculated in melon and watermelon juices treated by pulsed electric fields

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   

INACTIVATION OF SELECTED MICROORGANISMS AND PROPERTIES OF PULSED ELECTRIC FIELD PROCESSED MILK

Raw skim milk and ultra-high-temperature (UHT) skim milk inoculated with Pseudomonas fluorescens, Lactococcus lactis and Bacillus cereus were processed by pulsed electric field (PEF) treatment. A continuous PEF bench scale system was set to deliver 35 kV/cm field strength with 64 pulses of bipolar square wave for 188 μs. The flow rate of milk was 1 mL/s. Milk temperature was raised to 52C and cooled to 22C during PEF treatment. Pasteurization at 73C for 30 s was used for comparison. Microbial inactivation and cell morphology were investigated. Analyses for protein, total solids, color, pH, particle size, density and electrical conductivity showed no significant effects (P > 0.05) in the PEF processed milk. PEF treatment accomplished a 0.3 to 3.0 log reduction of P. fluorescens, L. lactis and B. cereus in UHT milk and of total microorganisms in raw milk.     

Pasteurization of Milk Using Pulsed Electrical Field and Antimicrobials

The inactivation of naturally occurring microorganisms in raw skim milk by pulsed electric field (PEF) treatment alone and combined with the antimicrobial agents nisin and lysozyme, added both singly and together, was investigated. A 7.0‐log reduction of microorganisms found in raw skim milk was achieved through a combination of PEF treatment (80 kV/cm, 50 pulses), mild heat (52 °C), and the addition of both the natural antimicrobials nisin (38 IU/mL) and lysozyme (1638 IU/mL). The combination of PEF, mild heat, and antimicrobials resulted in a much higher microbial inactivation than the sum of the individual reductions achieved from each treatment alone, indicating synergy. Varying the pH from 6.7 to 5.0 had no effect on microbial inactivation.     

Inactivation of Escherichia coli O157:H7 and Salmonella enteritidis in Liquid Egg White Using Pulsed Electric Field

ABSTRACT: The effects of temperature and pulsed electric field (PEF) intensity on inactivation of pathogens such as Escherichia coli O157:H7 and Salmonella enteritidis in egg white was investigated. Liquid egg white inoculated with 10⁸ colony-forming units (CFU)/mL of each pathogen was treated with up to 60 pulses (each of 2 JAS width) at electric field intensities of 20 and 30 kV/cm. The processing temperatures were 10°C, 20°C, and 30°C. After treatment, uninjured and total viable cells were enumerated in selective and nonselective agars, respectively. Maximum inactivations of 3.7 and 2.9 log units were obtained for S. enteritidis and E. coli O157:H7, respectively, while injured cells accounted for 0.5 and 0.9 logs for E. coli O157:H7 and S. enteritidis , respectively. For both bacteria, increasing treatment temperature tended to increase the inactivation rate. There was synergy between electric field intensity and processing temperature. The inactivation rate constant k _T values for E. coli O157:H7 on both selective and nonselective agars were 8.2 × 10^-3 and 6.6 × 10^-3/μS, whereas the values for S. enteritidis were 16.2 × 10^-3 and 12.6 × 10^-3/μS, respectively. The results suggest that E. coli O157:H7 was more resistant to heat-PEF treatment compared with S. enteritidis.     

Inactivation of Listeria innocua in skim milk by pulsed electric fields and nisin

Pulsed electric fields (PEF) is an emerging nonthermal processing technology used to inactivate microorganisms in liquid foods such as milk. PEF results in loss of cell membrane functionality that leads to inactivation of the microorganism. There are many processes that aid in the stability and safety of foods. The combination of different preservation factors, such as nisin and PEF, to control microorganisms should be explored. The objective of this research was to study the inactivation of Listeria innocua suspended in skim milk by PEF as well as the sensitization of PEF treated L. innocua to nisin. The selected electric field intensity was 30, 40 and 50 kV/cm and the number of pulses applied was 10.6, 21.3 and 32. The sensitization exhibited by PEF treated L. innocua to nisin was assessed for 10 or 100 IU nisin/ml. A progressive decrease in the population of L. innocua was observed for the selected field intensities, with the greatest reduction being 2 1/2 log cycles (U). The exposure of L. innocua to nisin after PEF had an additive effect on the inactivation of the microorganism as that exhibited by the PEF alone. As the electric field, number of pulses and nisin concentration increased, synergism was observed in the inactivation of L. innocua as a result of exposure to nisin after PEF. The reduction of L. innocua accomplished by exposure to 10 IU nisin/ml after 32 pulsed electric fields was 2, 2.7, and 3.4 U for an electric field intensity of 30, 40, and 50 kV/cm, respectively. Population of L. innocua subjected to 100 IU nisin/ml after PEF was 2.8-3.8 U for the selected electric field intensities and 32 pulses. The designed model for the inactivation of L. innocua as a result of the PEF followed by exposure to nisin proved to be accurate in the prediction of the inactivation of L. innocua in skim milk containing 1.2 or 37 IU nisin/ml. Inactivation of L. innocua in skim milk containing 37 IU nisin/ml resulted in a decrease in population of 3.7 U.     

Combined effect of temperature and pulsed electric fields on soya milk lipoxygenase inactivation

Pulsed electric fields (PEF) were applied to freshly prepared soya milk using a laboratory scale continuous PEF system to study the feasibility of inactivating lipoxygenase (LOX). Square wave PEF using different combinations of pre-treatment temperature, electric field strength and treatment time were evaluated in this study. Inactivation curves for the enzyme were plotted for each parameter and inactivation kinetics were calculated and modelled. Results showed the highest level of inactivation (84.5%) was obtained using a combination of preheating to 50 °C, and a PEF treatment time of 100 μs at 40 kV/cm. Inactivation of LOX activity as a function of treatment time could be described using a first order kinetic model. Calculated D values following pre-heating to 50 °C were 172.9, 141.6 and 126.1 μs at 20, 30 and 40 kV/cm, respectively.     

Combined effect of temperature and pulsed electric fields on pectin methyl esterase inactivation in red grapefruit juice (<Emphasis Type="Italic">Citrus paradisi</Emphasis>)

Pulsed electric fields (PEF) were applied to freshly prepared grapefruit juice using a laboratory scale continuous PEF system to study the feasibility of inactivating pectin methyl esterase (PME). Square wave PEF using different combinations of pre-treatment temperature, electric field strength and treatment time were evaluated in this study. Inactivation curves for the enzyme were plotted for each parameter and inactivation kinetics were calculated. Results showed that the highest level of inactivation (96.8%) was obtained using a combination of preheating to 50 °C, and a PEF treatment time of 100 μs at 40 kV/cm. Inactivation of grapefruit PME activity could be described using an exponential decay model. Calculated D-values following a 50 °C preheat were 77.5, 76.0 and 70.4 μs at 20, 30 and 40 kV/cm, respectively. The activation energy for the inactivation of PME by PEF was 36.2 kJ/mol.     

Effects of Pulsed Electric Fields and Thermal Processing on the Stability of Bovine Immunoglobulin G (IgG) in Enriched Soymilk

ABSTRACT: To investigate influences of pulsed electric field (PEF) on bovine IgG immunoactivity, soymilk enriched with hyperimmunized dairy milk protein concentrate was subjected to PEF and thermal treatments. Thermal treatment at 78.8 °C for 120 s inactivated 5.1 logs in natural flora and resulted in 86% decrease in IgG activity PEF at 41 kV/cm for 54 μS inactivated 5.3 logs of natural flora and resulted in no significant change ( P > 0.05) in bovine IgG activity. Specific antigen-binding activity of bovine IgG against Salmonella enteritidis showed parallel correlation with the measurement of IgG concentration. No further significant change in IgG immunoactivity was observed during a 10-wk storage at 4°C in PEF-, thermally-, or un-treated samples.