High-intensity Pulsed Electric Fields Treatment Research Articles

Effects of high intensity pulsed electric field processing conditions on vitamin C and antioxidant capacity of orange juice and gazpacho, a cold vegetable soup

Orange juice and gazpacho, a cold vegetable soup, were submitted to high intensity pulsed electric fields (HIPEF). The effects of electric field strength, treatment time, pulse frequency, width and polarity, as process parameters, on vitamin C retention and antioxidant capacity of both products were evaluated and compared to those in a heat pasteurization. Vitamin C was determined by HPLC and antioxidant capacity through the inhibition of the DPPH (1,1-diphenyl-2-picrylhydrazyl) radical. Orange juice and gazpacho retained a 87.5–98.2% and 84.3–97.1% of vitamin C, respectively, after HIPEF treatments. Pulses applied in bipolar mode, as well as a lower electric field strength, treatment time, pulse frequency and width, led to higher levels of vitamin C retention ( p < 0.05). HIPEF-treated orange juice and gazpacho always showed a vitamin C retention higher than that of the heat-pasteurized products. There were no differences ( p < 0.05) in antioxidant capacity between HIPEF-treated and untreated products, whereas heat-treated foods showed lower values of antioxidant capacity.

Enhancing Inactivation of Staphylococcus aureus in Skim Milk by Combining High-Intensity Pulsed Electric Fields and Nisin

High-intensity pulsed electric fields (HIPEF) can be used as a nonthermal preservation method that is believed to enhance the effect of nisin on microorganisms such as Staphylococcus aureus. The survival of S. aureus inoculated into skim milk and treated with nisin, with HIPEF, or with a combination of nisin-HIPEF was evaluated. Nisin dose, milk pH, and HIPEF treatment time were the controlled variables that were set up at 20 to 150 ppm, pH 5.0 to 6.8, and 240 to 2,400 μs, respectively. HIPEF strength and pulse width were kept constant at 35 kV/cm and 4 μs, respectively. No reduction in S. aureus concentration was observed in skim milk at its natural pH after treatment with nisin, but 1.1 log units were recovered after 90 min of treatment at pH 5.0 with 150 ppm nisin. A reduction in viable S. aureus counts of 0.3 and 1.0 log unit in skim milk treated with HIPEF at its natural pH was observed at 240 and 2,400 μs, respectively. The nisin-HIPEF treatment design was based on a response surface methodology. The combined effect of nisin and HIPEF was clearly synergistic. However, synergism depended on pH. A maximum microbial inactivation of 6.0 log units was observed at pH 6.8, 20 ppm nisin, and 2,400 μs of HIPEF treatment time, whereas a reduction of over 4.5 log units was achieved when pH, nisin concentration, and HIPEF treatment times were set at 5.0, 150 ppm, and 240 μs, respectively.

Effect of High-Intensity Pulsed Electric Fields Processing and Conventional Heat Treatment on Orange−Carrot Juice Carotenoids

Liquid chromatography (LC) was the method of choice for quantification of carotenoids (including geometrical isomers) to evaluate the effects of high-intensity pulsed electric field (HIPEF), a nonthermal preservation method, with different parameters (electric field intensities and treatment times), on an orange-carrot juice mixture (80:20, v/v). In parallel, a conventional heat treatment (98 degrees C, 21 s) was applied to the juice. HIPEF processing generally caused a significant increase in the concentrations of the carotenoids identified as treatment time increased. HIPEF treatment at 25 and 30 kV/cm provided a vitamin A concentration higher than that found in the pasteurized juice.

Inactivation of plant pectin methylesterase by thermal or high intensity pulsed electric field treatments

A comparative study between new and traditional food preservation technologies was performed on pectin methylesterase (PME) inactivation from different plant sources. PME was extracted from carrots, tomatoes, bananas and oranges and was purified by affinity chromatography. Its inactivation was investigated during high intensity pulsed electric fields (HIPEF) and thermal treatments. Thermal treatment was performed at temperatures from 54 °C to 81 °C and up to 120 min treatment time. PME inactivation was adequately described by a first-order kinetic model for PME from bananas, carrots and tomatoes, whereas a biphasic model described adequately thermal inactivation of orange PME. The thermal stable fraction of orange PME was the least sensible to heat and carrot PME was the most thermally sensitive. HIPEF treatment consisted of 40-μs-square-wave pulses applied up to a total treatment time of 1.6 ms at 0.5 or 5 Hz and an electric field between 13.2 and 19.1 kV/cm. The higher the electric field, total treatment time or pulse frequency the higher the degree of PME inactivation from all sources. Maximum enzyme inactivation was: 87% for orange and tomato PME, 83% for carrot PME and 45% for banana PME at the most intense conditions. Industrial relevance Increasing studies show that using high intensity pulsed electric fields technology for fruit juices pasteurisation is feasible in the near future. A critical point on the fruit juice production and preservation is the pectin methyl esterase activity control. Consequently, the effect of HIPEF on PME activity has a great industrial relevance. This paper shows high inactivation percentages of PME from different plant sources with a HIPEF treatment carried out at moderate temperatures (55-65 °C) and offers an attractive alternative to the traditional heat treatment.

Comparative study on shelf life of orange juice processed by high intensity pulsed electric fields or heat treatment

The effects of high intensity pulsed electric fields (HIPEF) processing (35 kV/cm for 1,000 μs; bipolar 4-μs pulses at 200 Hz) on the microbial shelf life and quality-related parameters of orange juice were investigated during storage at 4 and 22 °C and compared to traditional heat pasteurization (90 °C for 1 min) and an unprocessed juice. HIPEF treatment ensured the microbiological stability of orange juice stored for 56 days under refrigeration but spoilage by naturally occurring microorganisms was detected within 30 days of storage at 22 °C. Pectin methyl esterase (PME) of HIPEF-treated orange juice was inactivated by 81.6% whereas heat pasteurization achieved a 100% inactivation. Peroxidase (POD) was destroyed more efficiently with HIPEF processing (100%) than with the thermal treatment (96%). HIPEF-treated orange juice retained better color than heat-pasteurized juice throughout storage but no differences (p<0.05) were found between treatments in pH, acidity and °Brix. Vitamin C retention was outstandingly higher in orange juice processed by HIPEF fitting recommended daily intake standards throughout 56 days storage at 4 °C, whereas heat-processed juice exhibited a poor vitamin C retention beyond 14 days storage (25.2–42.8%). The antioxidant capacity of both treated and untreated orange juice decreased slightly during storage. Heat treatments resulted in lower free-radical scavenging values but no differences (p<0.05) were found between HIPEF-processed and unprocessed orange juice.

Inactivation of Lactobacillus brevis in orange juice by high-intensity pulsed electric fields

High-intensity pulsed electric fields (HIPEF) is a non-thermal preservation method which is believed to be able to inactivate spoilage micro-organisms such as Lactobacillus brevis. The effects of HIPEF parameters (electric field strength, treatment time, pulse polarity, frequency and pulse width) and heat pasteurization (90 °C/1 min) were evaluated on samples of orange juice inoculated with L. brevis (10 8 cfu/ml). HIPEF as well as heat treatments were carried out in continuous flow equipments. Electron microscopy was performed in order to observe L. brevis cell damage induced by HIPEF treatment. HIPEF processing of orange juice was more effective in inactivating L. brevis than thermal processing. The extent of microbial inactivation depended on the processing parameters ( p < 0.01 ). L. brevis destruction was greater when the electric field strength and the treatment time increased, and also when the pulse frequency and the pulse width decreased. L. brevis was inactivated to a maximum of 5.8 log reductions when inoculated orange juice was processed at 35 kV/cm for 1000 μs using 4 μs pulse width in bipolar mode and 200 Hz at less than 32 °C. Mechanical breakdown of cell walls was observed in L. brevis when orange juice was processed by HIPEF.

Inactivation of Saccharomyces cerevisiae Suspended in Orange Juice Using High-Intensity Pulsed Electric Fields

Saccharomyces cerevisiae is often associated with the spoilage of fruit juices. The purpose of this study was to evaluate the effect of high-intensity pulsed electric field (HIPEF) treatment on the survival of S. cerevisiae suspended in orange juice. Commercial heat-sterilized orange juice was inoculated with S. cerevisiae (CECT 1319) (108 CFU/ml) and then treated by HIPEFs. The effects of HIPEF parameters (electric field strength, treatment time, pulse polarity, frequency, and pulse width) were evaluated and compared to those of heat pasteurization (90°C/min). In all of the HIPEF experiments, the temperature was kept below 39°C. S. cerevisiae cell damage induced by HIPEF treatment was observed by electron microscopy. HIPEF treatment was effective for the inactivation of S. cerevisiae in orange juice at pasteurization levels. A maximum inactivation of a 5.1-log (CFU per milliliter) reduction was achieved after exposure of S. cerevisiae to HIPEFs for 1,000 μs (4-μs pulse width) at 35 kV/cm and 200 Hz in bipolar mode. Inactivation increased as both the field strength and treatment time increased. For the same electric field strength and treatment time, inactivation decreased when the frequency and pulse width were increased. Electric pulses applied in the bipolar mode were more effective than those in the monopolar mode for destroying S. cerevisiae. HIPEF processing inactivated S. cerevisiae in orange juice, and the extent of inactivation was similar to that obtained during thermal pasteurization. HIPEF treatments caused membrane damage and had a profound effect on the intra-cellular organization of S. cerevisiae.

High intensity pulsed electric fields and heat treatments applied to a protease from Bacillus subtilis. A comparison study of multiple systems

The effects of several thermal treatments and high intensity pulsed electric fields (HIPEF) processing on a protease from Bacillus subtilis, suspended in simulated milk ultrafiltrate (SMUF) or milk, were evaluated. This protease did not show high resistance to conventional thermal treatments since, in milk, a high reduction of protease activity was achieved with both LTLT (low temperature long time; 63 °C–30 min) and HTST (high temperature short time, 75 °C–15 s) pasteurization treatments. The enzyme was more heat resistant suspended in SMUF than in milk. HIPEF affected the activity of the studied protease in different ways when treatments up to 500 kJ/l were applied using several types of equipment. Only when HIPEF treatment was applied with a continuous flow device and coaxial electrodes did the enzyme activity vary, changing from a slight inactivation when suspended in SMUF to some enhancement of activity when suspended in milk.

Lessening polygalacturonase activity in a commercial enzyme preparation by exposure to pulsed electric fields

The effect of high-intensity pulsed electric field (HIPEF) treatments on polygalacturonase (PG) activity in an aqueous solution of a commercial enzyme preparation was evaluated. HIPEF treatments reduced PG activity notably. Exponentially decaying pulses of 40 and 160 μs generated by a laboratory scale device were applied in a batch processing and bipolar mode. Electric fields ranged from 5.18 to 19.39 kV/cm. The number of pulses ranged up to 400. Temperature was always below 25 °C. Maximum inactivation of PG activity (98%) required 32.4 ms HIPEF treatment at 10.28 kV/cm. PG activity depleted exponentially because of HIPEF treatments. The first order rate constants ranged from 32 to 590 μs-1 and increased exponentially with electric field intensity. PG activity decreased exponentially with input electric energy density.

Reduction of Protease Activity in Simulated Milk Ultrafiltrate by Continuous Flow High Intensity Pulsed Electric Field Treatments

ABSTRACT:A protease from Bacillus subtilis suspended in simulated milk ultrafiltrate (SMUF) was subjected to high intensity pulsed electric field (HIPEF) treatments of up to 6787 kJ/l, applying field strengths ranging from 19.7 to 35.5kV/cm up to 896 μs to evaluate the feasibility of this treatment on inactivating the enzyme. In addition, the influence of the pulse repetition rate (67, 89, and 111 Hz) and pulse width (4 and 7 μs) on the effectiveness of HIPEF treatments was tested. Protease activity was considerably reduced; a maximum inactivation of 62.7% was achieved after an 896‐μS treatment at 35.5 kV/cm and 111 Hz. Protease activity decreased exponentially with increase of input energy density, treatment time, field strength, and pulse repetition rate when exposed to HIPEF processing.

Reduction of Protease Activity in Milk by Continuous Flow High-Intensity Pulsed Electric Field Treatments

High-intensity pulsed electric field (HIPEF) is a nonthermal food processing technology that is currently being investigated to inactivate microorganisms and certain enzymes, involving a limited increase of food temperature. Promising results have been obtained on the inactivation of microbial enzymes in milk when suspended in simulated milk ultrafiltrate.The aim of this study was to evaluate the effectiveness of continuous HIPEF equipment on inactivating a protease from Bacillus subtilis inoculated in milk. Samples were subjected to HIPEF treatments of up to 866μ of squared wave pulses at field strengths from 19.7 to 35.5 kV/cm, using a treatment chamber that consisted of eight colinear chambers connected in series. Moreover, the effects of different parameters such as pulse width (4 and 7μ), pulse repetition rates (67, 89, and 111Hz), and milk composition (skim and whole milk) were tested.Protease activity decreased with increased treatment time or field strength and pulse repetition rate. Regarding pulse width, no differences were observed between 4 and 7μ pulses when total treatment time was considered. On the other hand, it was observed that milk composition affected the results since higher inactivation levels were reached in skim than in whole milk. The maximum inactivation (81%) was attained in skim milk after an 866-μs treatment at 35.5 kV/cm and 111Hz.

Application of High-Intensity Pulsed Electrical Fields in Food Processing

High-intensity pulsed electric fields (HIPEF) treatment is gaining popularity as a nonthermal processing technology due to its instant penetration characteristics and short processing time. It is evolving as a potential alternative to other thermal and chemical unit operations in food processing. In recent years, numerous research groups have demonstrated the possibility of inactivation of a range of microorganisms and food quality-related enzymes. This article focuses on the potential to use the HIPEF treatment as a preservation technology and as an adjunct to other processing steps, such as extraction, osmotic dehydration, air dehydration, and rehydration.

Microbial and Enzymatic Changes in Fruit Juice Induced by High-Intensity Pulsed Electric Fields

High-intensity pulsed electric fields (HIPEF) treatment is a nonthermal technology that has been studied in the last few years as an alternative to heat treatments. It consists of applying pulses of high electric field (kV/cm) during a short time (μsec or msec) at low or moderate temperature. Because of their properties, fruit juices are appropriate products to be processed by HIPEF. Studies on the effects of HIPEF on microorganisms show that this treatment destroys microorganisms at levels of heat pasteurization with lower destruction of vitamins, flavor compounds, and other micronutrients. The majority of enzymes that are responsible for adverse biological reactions in fruit juices are inactivated by HIPEF. The effects of HIPEF, as for thermal treatments, are mainly described by first-order models. Furthermore, others models are also proposed to fit some effects of HIPEF on the enzymatic activity or microorganisms population. Fewer works are focused on the effects on organoleptic, physical, and chemical properties of fruit juices, but results show that most of the properties remain unchangeable. The changes, if they occurred after a HIPEF treatment, are always less important than those produced by heat.

Control of Enterobacter aerogenes by high-intensity, pulsed electric fields in horchata, a Spanish low-acid vegetable beverage

High-intensity pulsed electric fields (HIPEF) is a non-thermal technology used in the processing of liquid foods. Inactivation of foodborne micro-organisms by this novel technology is an important alternative to traditional thermal methods with a great potential for new liquid products. However, the existence of a resistant proportion of microbial population presents a problem to establish the parameters that can guarantee the safety during the shelf-life of each food. The aim of this study was to investigate the influence of field strength, substrate inoculum size (initial cell concentration) and storage conditions after HIPEF treatment to evaluate the potential growth and subsequent spoilage by Enterobacter aerogenes in horchata, a Spanish low-acid vegetable beverage. Although no more than 1.1-log reductions were obtained by any of the HIPEF conditions applied, E. aerogenes growth in both substrates (horchata and a standard broth) at 10°C, 12°C and 16°C was affected by HIPEF treatments compared to untreated samples. The specific growth rate of the bacteria after HIPEF treatment was not modified, but the lag period was increased. A synergistic effect of HIPEF treatment, low temperature (10°C) and low inoculum size on the delay in lag phase was observed.

Effect of high intensity pulsed electric fields and heat treatments on vitamins of milk.

The effects of high intensity pulsed electric field (HIPEF) treatments at room or moderate temperature on water-soluble (thiamine, riboflavin, ascorbic acid) and fat-soluble vitamins (cholecalciferol and tocopherol) were evaluated and compared with conventional thermal treatments. Vitamin retention was determined in two different substrates, milk and simulated skim milk ultrafiltrate (SMUF). Samples were subjected to HIPEF treatments of up to 400 micros at field strengths from 18.3 to 27.1 kV/cm and to heat treatments of up to 60 min at temperatures from 50 to 90 degrees C. No changes in vitamin content were observed after HIPEF or thermal treatments except for ascorbic acid. Milk retained more ascorbic acid after a 400 microstreatment at 22.6 kV/cm (93.4%) than after low (63 degrees C-30 min; 49.7% retained) or high (75 degrees C-15s; 86.7% retained) heat pasteurisation treatments. Retention of ascorbic acid fitted a first-order kinetic model for both HIPEF and thermal processes. First-order constant values varied from 1.8 x 10.4 to 1.27 x 10(-3) micros(-1) for the HIPEF treatments (18.3-27.1 kV/cm) and, for thermal processing ranged from 5 x 10(-3) to 8 x 10(-2) min(-1) (50-90 degrees C). No significant differences were found between the results obtained after applying HIPEF treatments at room or moderate temperature. However, results depended on the treatment media. A beneficial effect of natural skim milk components, mainly proteins, was observed on the preservation of ascorbic acid, since skim milk retained more ascorbic acid than SMUF after HIPEF treatments.

Effects of High Intensity Pulsed Electric Field and Thermal Treatments on a Lipase from Pseudomonas fluorescens

Milk and dairy products may contain microorganisms capable of secreting lipases that cause sensory defects and technological problems in the dairy industry. In this study, the effects of thermal and high-intensity pulsed electric field (HIPEF) treatments on an extracellular lipase from Pseudomonas fluorescens, suspended in a simulated skim milk ultrafiltrate (SMUF) have been evaluated. Heat treatments applied were up to 30min from 50 to 90°C. HIPEF treatments were carried out using pilot plant facilities in a batch or continuous flow mode, where treatment chambers consisted of parallel and coaxial configuration, respectively. Samples were subjected to up to 80 pulses at electric field intensities ranging from 16.4 to 37.3kV/cm. This resulted in a lipase that was quite resistant to heat and also to HIPEF. High (75°C-15s) and low pasteurization treatments (63°C-30min) led to inactivations of 5 and 20%, respectively. Using the batch-mode HIPEF equipment, a 62.1% maximum activity depletion was achieved after 80 pulses at 27.4kV/cm. However, when HIPEF treatments were applied in the continuous flow mode, an inactivation rate of just 13% was achieved, after applying 80 pulses at 37.3kV/cm and 3.5Hz. The results of both heat and HIPEF treatments on enzyme inactivation were adjusted with good agreement to a first-order kinetic model (R2>62.3%).

Inactivación de formas esporuladas de Bacillus subtilis mediante campos eléctricos pulsantes de alta intensidad en combinacion con otras tecnicas de conservacion de alimentos/Inactivation of Bacillus subtilis spores using high intensity pulsed electric fields in combination with other food conservation technologies

The inactivation of Bacillus subtilis spores using high intensity pulsed electric fields (HIPEF) was investigated. Spores were not inactivated when HIPEF treatment (60 kV/cm, 75 pulses) was used alone. The combination of-HIPEF and moderate temperatures around 60°C, and/or the activation of spore suspension prior to HIPEF treatment, and/or the use of up to 5000 IU/ml lysozyme, did not inactivate spores. High hydrostatic pressure (1500 atm, 30 min, 40°C) resulted in the initiation of germination of more than five log cycles in the number of spores, making them sensitive to subsequent pasteurization heat treatment, whereas they were not sensitive to subsequent HIPEF treatment at temperatures less than 40 °C. An intermediate step is needed which allows the outgrowth of spores to vegetative cells. Thus, the combination of high hydrostatic pressure and HIPEF treatment offers an attractive alternative to the stabilization of food products by heat to inactivate spores.