High-intensity Pulsed Electric Field Processing Research Articles

The Application and Optimization of HIPEF Technology in the Processing of Juice from Strawberries Harvested at Two Stages of Ripeness.

The aim of this study was to investigate the influence of high intensity pulsed electric field (HIPEF) technology on the stability of total phenols, anthocyanins, hydroxycinnamic acids, flavonols, and condensed tannins in strawberry juices (Fragaria x ananassa Duch. cv. ‘Albion’) with different ripening stages (75% and 100%) and stored at +4 °C for 7 days. The HIPEF parameters studied were: (i) electric field strength (40 and 50 kV cm−1), (ii) frequency (100 and 200 Hz), and (iii) treatment duration (3 and 6 min). Of the HIPEF parameters studied, electric field strength and frequency had a statistically significant effect on the content of all phenolic compounds. Treatment duration showed no statistically significant effects on phenolic compounds except for flavonols and condensed tannins. Storage had a positive effect on the stability of most of the phenolic compounds, with the exception of flavonols. Optimization of HIPEF processing showed that strawberry samples at both ripeness levels were suitable for HIPEF treatment to obtain functional fruit juices with a high content of polyphenols.

Screening the Antioxidant Activity of Thermal or Non-Thermally Treated Fruit Juices by In Vitro and In Vivo Assays

The health benefits of fruit juices have been associated with their high content of antioxidant compounds. Commercial juice has been traditionally heat-processed to destroy microorganisms and enzymes. However, high temperatures induce undesirable changes in the nutritional value of the juice. High-intensity pulsed electric fields (HIPEF) are being studied as an alternative to heat treatments. In addition, in vitro and in vivo methods have been recommended to determine the antioxidant potential of juices in a complementary manner. Thus, the antioxidant activity of untreated, high-intensity pulsed electric fields (HIPEF) or heat-treated fruit juices (tomato, apple, pineapple and orange) was studied using in vitro (TEAC, DPPH, FRAP and Folin-Ciocalteu) and in vivo assays (Saccharomyces cerevisiae). Vitamin C and total phenolic compounds in these juices were determined. The highest antioxidant activities (12.01 mmol of Trolox/L) were obtained through the Folin-Ciocalteu assay in orange juices. The lowest values (0.119 mmol of Trolox/L) were found in apple juice analysed by the FRAP assay. Vitamin C content varied from 10 mg/L (orange juice) to 344 mg/L (orange juice). The highest concentration of total phenolic compounds was determined in orange juice (1238 mg/L), whereas the lowest value was found in tomato juices (149 mg/L). The effect of HIPEF and thermal processing on the antioxidant potential of juices depended on the fruits used to prepare the juices and the antioxidant activity assay conducted. Vitamin C concentration was directly related to the antioxidant activity analysed by Folin-Ciocalteu and FRAP methods and the S. cerevisiae growth rate. S. cerevisiae yeast can be used as a feasible in vivo assay to further determine the antioxidant activity of fruit juices.

In vitro bioaccessibility of isoflavones from a soymilk-based beverage as affected by thermal and non-thermal processing

High Pressure Processing (HPP) and High Intensity Pulsed Electric Fields (HIPEF) are non-thermal processing technologies used for obtaining safe and high-quality foods and beverages. In the present work, the changes on both the concentration and the bioaccessibility of isoflavones from treated (thermally and non-thermally) and untreated soymilk-based beverages were evaluated. Thermal treatment (TT) was applied at 90 °C for 1 min, HPP: 400 MPa at 40 °C for 5 min and HIPEF: 35 kV cm−1 with 4 μs bipolar pulses at 200 Hz for 1800 μs. Later, beverages were subjected to an in vitro gastrointestinal digestion for obtaining the bioaccessibility. Thermal and non-thermal processing increased the isoflavone concentration up to 25–26% in TT and HIPEF treated beverages, and up to 38.52% in HPP treated. After in vitro digestion, the concentration of isoflavones in non-thermally processed beverages was higher (70.55% for HIPEF and 98.77% for HPP) than that TT processed (18.52%). HIPEF processing and HPP increased the isoflavone bioaccessibility up to 35.40 and 47.32%, respectively, regarding the untreated product. These results demonstrate that both non-thermal processing technologies HIPEF and HPP are suitable for obtaining high quality and nutritious beverages by improving their isoflavone bioaccessibility.

Impact of critical high‐intensity pulsed electric field processing parameters on oxidative enzymes and color of broccoli juice

This research evaluated the influence of high-intensity pulsed electric field (HIPEF) processing parameters, electric field strength, treatment time, and polarity on color difference (∆E*), polyphenol oxidase (PPO), and lipoxygenase (LOX) activities in broccoli juice. An optimization of HIPEF processing was accomplished and compared with thermal treatment (90°C/60 s). The lowest RALOX (68.71%) and RAPPO (36.11%) were reached at the strongest HIPEF conditions (35 kV/cm for 2,000 µs in bipolar mode). Bipolar mode pulses showed lower RALOX and RAPPO than monopolar mode. However, polarity did not show a significant effect on ∆E*. LOX was always more resistant to HIPEF treatment than PPO. The optimization process (26.35 kV/cm for 1,235 μs in bipolar mode) showed around 60% of enzyme inactivation and ∆E* = 0.69. Thermally processed broccoli juice exhibited the greatest color difference (∆E* = 7.89). HIPEF processing could be an appropriate technology to preserve the color properties and reduce the enzyme activity of broccoli juice. Practical applications Vegetable juices, in particular broccoli juice is attracting the food industry attention because it contains high amounts of nutrients; however, this fact increase their susceptibility to endogenous enzymes. HIPEF is a nonthermal technology for liquid food preservation that inactivates microorganisms and enzymes without compromising the nutritional and sensorial features of foods. Consequently, this technology could be used in the food industry as an alternative for thermal treatment to inactivate deteriorative enzymes in vegetable juices, offering to consumers a high quality product.

Effect of Pulsed Electric Field Processing on Flavor and Color of Liquid Foods†

This review shows that pulsed electric field (PEF) is a non-thermal preservation method that uses electric pulses to inactivate microorganisms and most especially high-intensity pulsed electric field (HIPEF) treatment involving application of pulses of high voltage (typically 20–80 kV/cm) to foods placed between two electrodes could achieve better flavor preservation and color retention in liquid foods than heat processing. HIPEF processing has been shown to deliver safe and chill-stable fruit juices with fresh-like sensory and nutritional properties. In addition, studies have shown that hurdle application of the different non-thermal treatments offers synergistic advantage over separate application of the individual treatment. PEF treatment in combination with other hurdles (such as microfiltration with large pore ≥1.2 µm, ultraviolet irradiation, high-intensity light pulses, etc.) has the potential to increase the preservation of liquid foods while retaining sensory attributes. Practical Applications Non-thermal technology is one of the food processing and preservation methods that currently have been explored on a global scale. Pulsed electric fields (PEF) is a non-thermal preservation method that uses electric pulses to inactivate microorganisms and causes little or no change in food qualities. It is an efficient process that is employed to inactivate microorganisms and decrease the activity of enzymes without major undesirable effects on the organoleptic qualities of food products. PEF technology has not only proven to be effective in eliminating food microorganisms and inactivate enzymes, it also has a higher flavor and color retention properties than thermally processed foods.

Influence of high-intensity pulsed electric field processing parameters on antioxidant compounds of broccoli juice

Abstract The effect of high-intensity pulsed electric field (HIPEF) processing parameters (electric field strength, treatment time, and polarity) on broccoli juice carotenoids, vitamin C, total phenolic (TP) content and antioxidant capacity (AC) was evaluated. Results obtained from HIPEF-processed broccoli juice were compared with those of thermally treated (90 °C/60 s) and untreated juices. HIPEF processing parameters influenced the relative content (RC) of bioactive compounds, and the relative AC (RAC). Maximum RC of lutein (121.2%), β-carotene (130.5%), TP (96.1%), vitamin C (90.1%) and RAC (5.9%) was reached between 25 and 35 kV/cm and from 2000 μs to 500 μs. The highest RAC and RC of bioactive compounds were observed in HIPEF treatments applied in bipolar mode, except for vitamin C. HIPEF-treated broccoli juice exhibited greater RC of bioactive compounds and RAC than juice treated by heat. HIPEF technology could be considered a promising option for preserving the antioxidant quality of broccoli juice. Industrial relevance Vegetable juices are becoming more and more popular because of their wide range of health-related compounds. Particularly, broccoli juice is attracting the food industry attention because it contains high amounts of vitamins, carotenoids and phenolic compounds, among other bioactive compounds. Broccoli juice requires treatment conditions that protect its microbial, nutritional and sensorial quality. HIPEF is a non-thermal technology for liquid food preservation that inactivates microorganisms and enzymes without compromising the nutritional and sensorial features of foods. Consequently, this technology could be used in the food industry as an alternative for thermal treatment to preserve the bioactive compounds present in vegetable juices, offering to consumers a healthy product.

Effects of High-Intensity Pulsed Electric Fields Processing Parameters on the Chlorophyll Content and Its Degradation Compounds in Broccoli Juice

The influence of high-intensity pulsed electric fields (HIPEF) parameters including electric field strength (15–35 kV/cm), treatment time (500–2,000 μs), and polarity (monopolar or bipolar mode) on the content of chlorophylls (Chls), pheophytin (Phe), chlorophyllide (Chlide), and pheophorbide (Phb) and chlorophyllase activity (Chlase) in broccoli juice were assessed. A significant effect of HIPEF parameters on Chlase, Chls, and Chls degradation compounds was observed through a response surface methodology design. However, polarity did not exert influence neither on Chl a nor on Chl b. The optimum HIPEF treatment was found to be 35 kV/cm for 1,980 μs in bipolar mode, where the highest content of Chls was kept, the lowest Chlase residual activity was reached, and the minimal quantities of Chls degradation compounds content were formed. Additionally, at these HIPEF conditions, broccoli juice exhibited greater content of Chls than thermally treated or untreated juice. These outcomes demonstrated that HIPEF processing could be a suitable technology to maintain the Chls content in broccoli juice.

Changes in Water-Soluble Vitamins and Antioxidant Capacity of Fruit Juice–Milk Beverages As Affected by High-Intensity Pulsed Electric Fields (HIPEF) or Heat during Chilled Storage

The effect of high-intensity pulsed electric fields (HIPEF) or thermal processes and refrigerated storage on water-soluble vitamins and antioxidant capacity of beverages containing fruit juices and whole (FJ-WM) or skim milk (FJ-SM) was assessed. Peroxidase (POD) and lipoxygenase (LOX) inactivation as well as color changes were also studied. High vitamin C retention was observed in HIPEF and thermally treated beverages, but a significant depletion of the vitamin during storage occurred, which was correlated with antioxidant capacity. HIPEF treatment did not affect the concentration of group B vitamins, which also remained constant over time, but thermally treated beverages showed lower riboflavin (vitamin B2) concentration. With regard to enzyme activity, thermal processing was more effective than HIPEF on POD and LOX inactivation. The color of the beverages was maintained after HIPEF processing and during storage. Consequently, HIPEF processing could be a feasible technology to attain beverages with fruit juices and milk with high vitamin content and antioxidant potential.

Changes on phenolic and carotenoid composition of high intensity pulsed electric field and thermally treated fruit juice–soymilk beverages during refrigerated storage

The effects of high intensity pulsed electric fields (HIPEF) (35kV/cm with 4μs bipolar pulses at 200Hz for 800 or 1400μs) or thermal (90°C, 60s) treatments over phenolic and carotenoid compounds of a fruit juice–soymilk (FJ–SM) beverage stored at 4°C were evaluated and compared, having the untreated beverage as a reference. Coumaric acid, narirutin and hesperidin were the most abundant phenolic compounds in the FJ–SM beverage, while the main carotenoids were lutein, zeaxanthin and β-carotene. Immediately after HIPEF or heat processing, hesperidin content of the beverage showed a huge rise, resulting in a significant increase on the total phenolic concentration. Regarding carotenoid concentration, HIPEF or thermal treatment lead to a significant decrease; lutein, zeaxanthin and β-cryptoxanthin being the most affected compounds. In contrast, the content of some individual phenolics and carotenoids increased with time, while others tended to decrease or remained with no significant changes with regards to their initial values. Total phenolic concentration seemed to be highly stable during storage; while, total carotenoid content gradually diminished, irrespectively of the treatment applied. Overall, the changes observed in HIPEF treated FJ–SM beverage were less than those in the heat processed one. Hence, HIPEF is a feasible technology to obtain FJ–SM beverages with extended shelf-life and a similar profile of antioxidant compounds to freshly made beverages.

Microbial and enzymatic stability of fruit juice-milk beverages treated by high intensity pulsed electric fields or heat during refrigerated storage

The influence of high intensity pulsed electric fields (HIPEF) treatment (35 kV/cm, bipolar 4 μs square wave pulses at 200 Hz) on the inactivation of Listeria innocua in fruit juice–whole (FJ–WM) or skim milk (FJ–SM) beverages was assessed. As well, the effects of HIPEF or conventional thermal (90 °C 60 s) processing in terms of microbial and enzymatic stability and changes on physicochemical parameters of the beverages during refrigerated storage were also studied. HIPEF and thermal processing ensured the microbial stability of the beverages during 56 days at 4 °C without significant changes on pH, acidity and soluble solid content values. Thermal processing was more effective than HIPEF in reducing Pectin Methyl Esterase (PME) activity in FJ–SM and FJ–WM beverages since its activity was reduced by 70.66% and 87.33%, respectively. With regards to Polygalacturonase (PG), HIPEF treatment reduced by 26.92% and 20.93% the enzyme activity in the FJ–WM and FJ–SM beverages, respectively, whereas thermal treatment did not inactivate PG in both beverages. HIPEF or thermally-treated samples showed higher viscosity than the untreated ones, being this increment more pronounced in the beverages with whole milk. Therefore, HIPEF processing may be a feasible technology in order to obtain shelf stable and fresh-like fruit juice-milk beverages.

Isoflavone profile of a high intensity pulsed electric field or thermally treated fruit juice-soymilk beverage stored under refrigeration

Abstract A fruit juice-soymilk (FJ-SM) beverage was treated by high intensity pulsed electric fields (HIPEF) (35 kV/cm with 4 μs bipolar pulses at 200 Hz for 800 or 1400 μs) or heated (90 °C, 60 s) in order to evaluate and compare the effects of both technologies on the isoflavone profile along the storage at 4 °C. Total isoflavone content was determined by quantification of aglycone and glucoside forms analyzed with HPLC. Immediately after treatments, all the evaluated samples showed a higher concentration of glucosides than aglycones, genistin being the most abundant glucoside. Heat treated samples showed higher initial concentration of glucosidic forms as compared to the untreated or HIPEF treated beverages. No significant changes were observed in total isoflavone content after the increasing HIPEF treatment time from 800 to 1400 μs. During the storage, genistein, daidzein and daidzin content increased; while genistin showed a slight decrease, irrespective of the treatment applied. In this way, total isoflavone content tend to increase throughout the time in all the evaluated samples. After 56 days of storage, there was no significant difference in HIPEF treated and fresh FJ-SM beverages, the latter being slightly higher in those thermally treated. As a result, HIPEF could be a good technology in order to obtain FJ-SM beverages with a high content of isoflavones and fresh-like characteristics. Considering the great concentration of isoflavones in untreated and treated FJ-SM beverages, their consumption could be a good way to increase the isoflavone daily intake of the population. Industrial relevance HIPEF processing could be a competent technology in order to obtain FJ-SM beverages with fresh-like appearance and similar isoflavone content than just made products. The fruit juice-soymilk beverage evaluated in the present research has a great isoflavone content regarding to commercial soy based beverages. Its consumption could increase the current isoflavone intake of the population. Industry could apply this non-thermal technology in order to meet current consumers' claims for quality foods with high nutritional values.

High‐Intensity Pulsed Electric Fields Processing Parameters Affecting Polyphenoloxidase Activity of Strawberry Juice

High-intensity pulsed electric fields (HIPEF) were applied to strawberry juice to study the feasibility of inactivating polyphenoloxidase (PPO). Response surface methodology was used to evaluate the effect of HIPEF processing, in which total treatment time (1000 to 2000 μs), pulse frequency (50 to 250 Hz), pulse width (1.0 to 7.0 μs), and polarity (monopolar or bipolar) were the controlled variables at a constant electric field of 35 kV/cm. The proposed 2nd-order response functions were accurate enough to fit experimental results. Strawberry juice PPO was strongly reduced within the range of assayed conditions. HIPEF treatments were more effective in bipolar than in monopolar mode in inactivating PPO. Treatments of longer duration resulted in reductions of the enzyme activity. Moreover, it was feasible to minimize residual PPO activity (down to 2.5%) by selecting bipolar treatments at frequencies higher than 229 Hz and pulse widths between 3.23 and 4.23 μs for a constant total treatment time of 2000 μs.

Optimizing critical high-intensity pulsed electric fields treatments for reducing pectolytic activity and viscosity changes in watermelon juice

A response surface methodology was used to determine the combined effect of high-intensity pulsed electric fields (HIPEF) variables such as frequency, pulse width and polarity on the inactivation of pectolytic enzymes involved in viscosity changes of juices. Pectin methylesterase (PME) and polygalacturonase (PG) activities as well as viscosity were determined in watermelon juices processed at pulse frequencies from 50 to 250 Hz and pulse widths ranging from 1.0 to 7.0 μs in monopolar or bipolar mode. Electric field strength and total treatment time were maintained constant in all treatments at 35 kV/cm and 1,000 μs. Second-order expressions were accurate enough to fit the experimental results. The great PME reduction contrasted with the low impact of HIPEF on the PG activity of watermelon juice within the range of assayed conditions. Minimal residual PME activity values (15%) were obtained by selecting pulse widths higher than 5.5 μs at 250 Hz in bipolar mode, whereas the lowest PG residual activities (60%) were achieved after applying 7.0-μs bipolar pulses at 250 Hz. Moreover, watermelon juice viscosity increased throughout the range of studied conditions. The highest viscosity observed in the juice after applying 7.0-μs bipolar pulses at 250 Hz was related to the lowest PME activities obtained in the product treated under those conditions. Hence, the HIPEF processing optimization through frequency, pulse width and polarity could contribute to assure enzymatic inactivation while keeping valuable attributes of juices.

Volatile compounds and changes in flavour-related enzymes during cold storage of high-intensity pulsed electric field- and heat-processed tomato juices

The effects of high-intensity pulsed electric field (HIPEF) processing (35 kV cm(-1) for 1500 micros, using 4 micros bipolar pulses at 100 Hz) on the production of volatile compounds and flavour-related enzymes in tomato juice were investigated and compared with those of thermal processing (90 degrees C for 30 or 60 s). Tomato juice treated by HIPEF showed lower residual lipoxygenase (LOX) activity (70.2%) than juice heated at 90 degrees C for 60 s (80.1%) or 30 s (93.2%). In contrast, hydroperoxide lyase (HPL) was almost completely inactivated when the juice was subjected to 90 degrees C for 60 s, whereas roughly 50% of the control tomato juice was depleted after HIPEF treatment or thermal processing at 90 degrees C for 30 s. A slight decrease was observed in the initial LOX activity of treated and untreated samples during storage, whereas initial HPL activity was strongly affected over time. HIPEF-treated juice exhibited higher levels of compounds contributing to tomato aroma than untreated and heat-treated juices throughout storage. Thus HIPEF processing can preserve flavour quality and stability of tomato juice compared with conventional thermal treatments.

Impact of high intensity pulsed electric field on antioxidant properties and quality parameters of a fruit juice–soymilk beverage in chilled storage

The effects of high-intensity pulsed electric fields (HIPEF) treatment (35 kV/cm, 4 μs bipolar pulses at 200 Hz for 800 or 1400 μs) on the microbial stability, quality parameters and antioxidant properties of a fruit juice–soymilk (FJ–SM) beverage along the storage time at 4 °C were compared to those obtained by thermal pasteurization (90 °C, 60 s). HIPEF processing for 800 μs ensured the microbial stability of the beverage during 31 days; however, longer microbial shelf-life (56 days) was achieved by increasing the treatment time to 1400 μs or by applying a thermal treatment. Peroxidase and lipoxygenase of HIPEF treated beverages were inactivated by 17.5–29% and 34–39%, respectively; whereas thermal treatment achieved 100% and 51%. During the storage, vitamin C content and antioxidant capacity depleted with time, and they were higher in FJ–SM beverages processed by HIPEF than in those thermally treated. Instead, total phenolic content of beverages did not present significant changes over the time, and it was higher in the 1400 μs-HIPEF treated beverages. In general, color, soluble solids, pH, and acidity values were not significantly affected by the processing treatments. Beverage viscosity increased over time, regardless of the treatment applied. Hence, application of HIPEF may be a good alternative treatment to thermal processing in order to ensure microbiological stability, high nutritional values and fresh-like characteristics of FJ–SM beverages.

Color and viscosity of watermelon juice treated by high-intensity pulsed electric fields or heat

Abstract The effects of high-intensity pulsed electric field (HIPEF) processing (35 kV/cm for 1727 μs applying 4-μs pulses at 188 Hz in bipolar mode) on color, viscosity and related enzymes in watermelon juice were evaluated during 56 days of storage and compared to thermal treatments (90 °C for 60 s or 30 s). HIPEF-treated juice maintained brighter red color than thermally treated juices along the storage time. In addition, the application of HIPEF as well as heat at 90 °C for 60 s led to juices with higher viscosity than those untreated for 56 days of storage. On the other hand, peroxidase (POD) was inactivated more efficiently after HIPEF processing than after applying heat treatments. However, the thermally processed juice at 90 °C for 60 s kept the lowest residual POD activity values beyond day 7 of storage. Differences in lipoxygenase (LOX) activity among treatments were not appreciated at day 0. However, storage time had a strong reducing influence on the enzyme activity of heat-treated samples. A substantial loss of pectin methylesterase (PME) activity (more than 50%) was observed in all the treated juices, whereas a slight reduction in polygalacturonase (PG) activity was only achieved after the HIPEF treatment. The use of HIPEF technology could be an alternative to thermal treatments and could contribute to better maintain valuable attributes of watermelon juice. Industrial Relevance HIPEF processing is a feasible alternative to thermal treatments to obtain watermelon juice, achieving optimal inactivation of deleterious microorganisms and quality-related enzymes. HIPEF-treated watermelon juices exhibit better physical properties such as color or viscosity than thermally treated juices throughout storage. Thus, HIPEF technology can help processors to obtain juices that keep their fresh characteristics, thus being better accepted by consumers.

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

AbstractBACKGROUND:The effect of high‐intensity pulsed electric field (HIPEF) processing (35 kV cm−1for 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 × 10−2and 3.5 × 10−2day−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

Review: Potential of High-Intensity Pulsed Electric Field Technology for Milk Processing

Among nonthermal treatments, high-intensity pulsed electric field (HIPEF) has received special attention on account of its potential use in treating liquid foods and its feasible application in continuous-flow processing. Improving the food quality of milk and dairy products with HIPEF processing may be a relevant consideration in product development research. However, the future implementation of HIPEF equipment on an industrial scale may require more studies into the effects of the process parameters on the shelf-life of milk, the optimization of the HIPEF process with specific emphasis on the degree of microbial inactivation and energy consumption, more accurate design of the HIPEF equipment used for milk processing and a sensorial and nutritive evaluation of the treated product.

Flavour retention and related enzyme activities during storage of strawberry juices processed by high-intensity pulsed electric fields or heat

Abstract The effects of high-intensity pulsed electric fields (HIPEF) processing (35 kV/cm for 1700 μs using pulses of 4 μs at 100 Hz in bipolar mode) and thermal treatments (90 °C for 30 s or 60 s) on lipoxygenase (LOX) and β-glucosidase (β-GLUC) activities as well as on the production of volatile compounds were assessed in strawberry juice for 56 days of storage. HIPEF-treated juice kept higher residual LOX activity than heat-treated juices during the first 28 days of storage. Moreover, β-GLUC increased its initial activity just after HIPEF processing. The concentration of DMHF in HIPEF-processed strawberry juice was above those of untreated and heat-treated juices during the first 14 days of storage. On the other hand, concentrations of ethyl butanoate and 1-butanol obtained after HIPEF processing were better maintained than after thermal processing. However, thermally-treated samples showed an increase in the amount of 1-butanol beyond day 35, causing an unpleasant flavour to the product. Thus, flavour stability in HIPEF-processed strawberry juice was greater than in thermally-treated samples during storage.

Effects of high-intensity pulsed electric field processing conditions on lycopene, vitamin C and antioxidant capacity of watermelon juice

Abstract Watermelon juice was subjected to high-intensity pulsed electric fields (HIPEF). The effects of process parameters including electric field strength (30–35 kV/cm), pulse frequency (50–250 Hz), treatment time (50–2050 μs), pulse width (1–7 μs) and pulse polarity (monopolar/bipolar) on lycopene, vitamin C and antioxidant capacity were studied using a response surface methodology. Lycopene content was measured spectrophotometrically, vitamin C was determined by HPLC and antioxidant capacity through the inhibition of DPPH (1,1-diphenyl-2-picrylhydrazyl) radical. Watermelon juice exhibited high retention of lycopene and antioxidant capacity when high electric field strengths, frequencies and pulse widths were applied. However, severe HIPEF treatments reduced vitamin C content. Maximal relative lycopene content (113%), vitamin C (72%) and antioxidant capacity retention (100%) were obtained when HIPEF treatments were set up at 35 kV/cm for 50 μs using 7 μs bipolar pulses at 200 Hz.