The interaction of pulsed electric fields and texturizing ‐ antifreezing agents in quality retention of defrosted potato strips

The combination of pulsed electric fields (PEF) and texturizing and antifreeze agents on quality retention of defrosted potato strips were studied. Potato strips (10 mm thickness, 100 g) were placed in different solutions (1% w/v) of CaCl₂, glycerol, trehalose as well as NaCl and sucrose, treated with PEF (0.5 kV cm^?1, 100 pulses, 4 Hz). Then, all the samples were soaked in the same solutions for 10 min. After draining, samples were packed into polypropylene pouches and stored at ?18 °C for 12 h. Samples were thawed out at room temperature (20 °C) in 3 h. Untreated controls and PEF treated control samples were also frozen and thawed in similar conditions. To assess the potato strip quality, the thawed samples were analysed for moisture content, weight loss, firmness and colour attributes. The results indicate that PEF treatment by itself is not a suitable pre‐treatment method for frozen potato strips and should be assisted by CaCl₂ and trehalose treatment to prevent softening after defrosting. Firmness analyses determined that application of PEF alone results in 2.38 N. However, PEF in combination with CaCl₂ and trehalose result in 2.97 N and 2.99 N, respectively, which are both significantly firmer than the samples solely treated with PEF. CaCl₂ and trehalose were effective in not only maintaining the structural integrity of the cells, but also retaining colour attributes. The L* value was found to be higher (P < 0.05) in CaCl₂ and trehalose treated samples (58.95 and 57.21, respectively), as compared to PEF treated samples (53.97) denoting a darker colour. Application of CaCl₂ and trehalsoe in combination with PEF also resulted in significantly less weight loss after thawing.     

Effect of postharvest storage on potato (Solanum tuberosum L.) texture after pulsed electric field and thermal treatments

Pulsed electric field (PEF) and mild thermal pretreatments at 60 °C (T60) may help preserve texture of plant tissue during thermal processing through pectin modification. However, potato starch may counteract the adhesive role of pectin during thermal processing. Furthermore, postharvest storage of potatoes may result in compositional and textural changes. Therefore, the effect of postharvest storage on potato composition and on texture of untreated, PEF treated and thermally treated tissue was studied. The composition remained unchanged (p-value <0.05), whereas the fresh tissue hardness slightly decreased (p-value ≤0.0001–0.1387) during storage. Prolonged storage resulted in a softer texture after PEF treatments with total specific energy input (W_T) ≤ 0.6 kJ/kg at electric field strengths of 0.74–1.01 kV/cm, whereas the hardness was independent of the storage time if W_T > 0.6 kJ/kg. Slower texture degradation at 95 °C was observed after T60 and, especially, PEF-T60 pretreatment, independently of the storage time.     

Water-Holding Capacity in Hard-to-Cook Beans (Phaseolus vulgaris): Effect of pH and Ionic Strength

The effect of pH and ionic strength (IS) of soaking solution on the water holding capacity (WHC) of hard-to-cook (HTC) and control black beans (Phaseolus vulgaris) was evaluated. Beans were soaked 18 hr in solutions covering the pH range 1–7 at constant IS (1.0 M) or in solutions ranging in IS from 0.01 to 1.3M (prepared with either NaCl or CaCl₂) at pH 7. WHC was significantly reduced in the pH range 3.5 to 5.1 in control beans but the effect was not as pronounced with HTC samples which had a lower WHC at each pH. Solutions prepared with NaCl produced significantly lower WHC values than CaCl₂ solutions in the control but not in the HTC beans. WHC values in control beans tended to increase with higher IS, although this effect was not as apparent for HTC beans.     

Pulsed electric field treatment prior to freezing carrot discs significantly maintains their initial quality parameters after thawing

The interaction of pulsed electric fields (PEF) with different cryoprotectant and texturizing agents in quality retention of carrot discs was analysed. Increasing the permeability properties by PEF may lead to better accessibility of intracellular materials to freezing and thus reducing the freezing time, leading to better maintaining the texture after thawing. Carrot discs of 5 mm thickness were immersed in different solutions of CaCl₂, glycerol, trehalose and tap water, and subsequently were treated with PEF (1 kV/cm, 100 pulses, 4 Hz). Then, the samples were drained and packed along with a control group in separate prepared polypropylene pouches. All the samples were frozen at ?18 °C for 24 h and thawed during 3 h at ambient temperature (20 °C) the following day. The quality of the thawed carrot discs was certified by measuring weight loss, firmness, microscopic studies and CIE colorimetric attributes. All the PEF‐treated samples, no matter what solution they were soaked in, could significantly (P < 0.05) maintain the firmness as well as colour attributes. However, it was deducted that application of CaCl₂ in conjunction with PEF can result in a firmer texture. Firmness analyses determined that application of PEF alone results in 5.84 N, while its combination with CaCl₂ leads to higher value of 6.63 N. Firmness in control samples was found to be 3.46 N. The SEM studies supported the results of firmness analysis and depicted more integrity in the cell walls of the samples treated with CaCl₂ and glycerol. The weight loss values varied among different samples, and the highest amount and lowest amount were reported in CaCl₂ and solely PEF‐treated samples, respectively. There was no significant difference between the colour attributes measured in different groups including control sample (P > 0.05).     

Effects of Pulsed Electric Field Processing on Quality Characteristics and Microbial Inactivation of Soymilk

Effects of pulsed electric fields (PEF) on quality characteristics and microbial inactivation of soymilk were studied with different PEF parameters. PEF did not affect significantly the values of pH, “a” (an indicator of redness ranging from “?a” to “+a”, ?a?=?green, +a?=?red) and electric conductivity. The values of “L” (white if “L”?=?100, black if “L”?=?0) increased slightly, whereas values of viscosity and “b” (an indicator of yellowness ranging from “?b” to “+b”, ?b?=?blue, +b?=?yellow) decreased slightly as PEF time increased from 0 to 547 μs. Cysteine, tyrosine, phenylalanine, and serine reduced with the increase of PEF time. The relative activities of soybean lipoxygenase (SLOX) decreased with PEF time increasing from 0 to 1,036 μs. When PEF time and strength increased, the inactivation of Escherichia coli and Staphylococus aureus increased significantly (p?<?0.05), achieving a maximum of 5.20 and 3.51 log₁₀ cycles reduction at PEF time 547 μs and pulsed electric strength 40 kV/cm, respectively. The inactivation of E. coli, S. aureus, and SLOX as a function PEF time followed Weibull distribution. This study demonstrated that PEF could inactivate efficiently E. coli, S. aureus, and SLOX without affecting the quality characteristics of soymilk. Thus, this technique could be an advantageous alternative to heat treatment for pasteurization of soymilk.     

The selected quality aspects of infrared-dried black soldier fly (Hermetia illucens) and yellow mealworm (Tenebrio molitor) larvae pre-treated by pulsed electric field

Drying is one of the most important steps in processing of edible insects biomass for their potential utilisation in food applications. In this study, the impact of pulsed electric field (PEF) pre-treatment (at E = 1.07 kV/cm and W_spec = 5 and 20 kJ/kg) on infrared-assisted air drying kinetics of black soldier fly (Hermetia illucens) and yellow mealworm (Tenebrio molitor) larvae has been evaluated. Moreover, microbial load and physical quality parameters of dried matter have been analyzed. The results show that PEF enhances the kinetics of water evaporation from insects biomass, especially in the range of the moisture ratio (MR) from 1.0 to 0.2. For instance, in the case of having been drying H. illucens larvae for 20 min, MR equalled 0.86, 0.75, and 0.72 for the untreated sample, 5 kJ/kg PEF-treated and 20 kJ/kg PEF-treated one, respectively. The effect of the PEF treatment was less visible in the case of H. illucens larvae and for low MR values. The PEF pre-treatment did not affect the water binding properties of dried insect biomass, regardless of species. However, the PEF pre-treated matter exhibited the same or even higher hygroscopic properties than the untreated ones. The difference in optical properties between untreated and PEF-treated samples was marginal. Nevertheless, for microbial contamination, 20 kJ/kg PEF treatment reduced the total number of microorganisms by 0.5–1.0 log cycle in comparison to the dried matter that had not been pre-treated. Nevertheless, the total number of microorganisms was too high to be feasible for food production purposes which would require additional operations to ensure food safety.Industrial relevanceThe interest in utilisation of insects as an alternative source of macronutrients for food and feed is growing tremendously. Drying is one of the most popular first steps in further processing technology applicable to insect biomass. Since air drying is one of the longest and the most energy consuming unit operation, there is a need to seek alternative methods that can be coupled with pre-treatment to enhance the process kinetics. In this paper, the combination of infrared drying of two species of insects preceded by pulsed electric field treatment has been discussed.     

Effects of pulsed electric fields (PEF) treatment on physicochemical properties of potato starch

Potato starch–water suspensions (8.0%, w/w) were subjected to pulsed electric fields (PEF) treatment at 30 kV·cm^− 1, 40 kV·cm^− 1 and 50 kV·cm^− 1, respectively. The physicochemical properties of PEF-treated potato starch samples were investigated using scanning electron microscopy (SEM), laser scattering technique, X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and the Brabender rheological method, with native potato starch as reference. It has been concluded from SEM analysis that dissociation and damage of PEF-treated potato starch granules appeared. Some granules aggregated with each other and showed gel-like structures. It was revealed from particle size analysis that there was an obvious increase of the granule size after PEF treatment. This has been attributed to the aggregation among granules. It was also demonstrated from other analysis that relative crystallinity, gelatinization temperatures, gelatinization enthalpy, peak viscosity as well as breakdown viscosity of modified samples all decreased with increasing electric field strength.

Industrial relevance

In this study, the effect of PEF treatment (up to 50 kV·cm^− 1) on physicochemical properties of potato starch has been investigated. The results from SEM images showed that dissociation, denaturation and damage of potato starch granules had been induced by the PEF treatments. Some of granule fragments showed gel-like structures, and congregated with each other or with other starch granules. Laser scattering measurements of particle size revealed that an obvious increase of granule size under electric field strength of 50 kV·cm^− 1, which was attributed to the aggregation of the starch granules. The X-ray diffraction pattern showed an obvious loss of crystalline structure after the PEF treatment at 50 kV·cm^− 1, which induced a trend of transformation from crystal to non-crystal in potato starch granules. DSC analysis showed a decrease in gelatinization temperatures (T_o and T_p) and gelatinization enthalpy (ΔH_gel) with increasing electric field strength. Brabender rheological method has been used to show that the peak viscosity and breakdown viscosity decrease with increasing electric field strength of PEF treatment. All the results reveal that the PEF treatment can lead to an intragranular molecular rearrangement of potato starch granules, which induces changes of various physicochemical properties of the treated starch thus may endow it some new characteristics and functions. This phenomena may warrant further more detailed study.     

The inactivation of Listeria monocytogenes by pulsed electric field (PEF) treatment in a static chamber

An experimental analysis of the effect of pulsed electric field (PEF) energy on the inactivation of Listeria monocytogenes was conducted using a custom-designed static chamber and a gel suspension medium for treatment. This allowed PEF energy to be delivered to the suspension under near isothermal conditions. The effects of variations in the number of pulses (5–50 pulses), electric field strength (15–30 kV/cm), temperature (0–60°C) and media bases (water and skim milk) on the inactivation of L. monocytogenes were examined. At temperatures less than 50°C a maximum of 1 log reduction was obtained for L. monocytogenes regardless of pulse number or electric field strength within the ranges examined. In skim milk no reduction occurred. At 50°C and 55°C synergy between PEF and thermal energy was observed. The experimental approach separated the contribution of PEF and thermal energy to total kill and thus allowed this synergy to be quantified. At 55°C the kill due to PEF energy increased to 4.5 logs with another 4.5 logs reduction attributable to thermal energy. It appears that under the conditions of this study PEF alone has a very limited effect on the reduction of L. monocytogenes. However, the addition of thermal energy not only contributed to the kill, but also increased the susceptibility of L. monocytogenes to PEF energy.     

Optimisation of pulsed electric fields processing parameters for developing biodegradable films using zein,chitosan and poly(vinyl alcohol)

This study investigated the feasibility of using pulsed electric fields (PEF) to develop biodegradable films from biopolymers (zein, chitosan) and biosynthetic polymers (poly(vinyl alcohol), polyethylene glycol). Various responses including the viscosity, loss modulus, particle size and polydispersity index of the dispersions were determined after PEF processing at various electric field strengths (0.9–3.5 kV/cm), pulse frequencies (50–300 Hz), and specific energies (80–650 kJ/kg). The structure-function relationship between the PEF processed colloidal dispersions, and the effect of PEF on the resulting films was evaluated using the tensile strength, Young's modulus, and erosion index. The viscosity and loss modulus decreased, but the particle size increased at a field strength above 2.4 kV/cm and specific energy below 200 kJ/kg. The films showed higher tensile strength and Young's modulus but low erodibility at a field strength/frequency/specific energy of 2.4 kV/cm/<100 Hz/<100 kJ/kg, respectively. The optimum tensile strength (maximised) (32.89 MPa) and erosion index (minimised) (33.42%) were obtainable at a field strength/frequency/specific energy of 3.4 kV/cm/50 Hz/100 kJ/kg, respectively. The results of scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry depicted improvements in the compatibility and nature of intra−/intermolecular interactions between biomacromolecules, as evidenced by the modifications in the morphology, crystallinity and thermal properties. These findings demonstrate the potential of using PEF as a pre-treatment technique during the production of biodegradable films from colloidal dispersions.Industrial relevance.The combinations of PEF processing parameters investigated in this study can be employed to elicit microstructural modifications of colloidal dispersions. PEF-induced effects on colloidal systems can be translated into a functional modification of assembled biological materials (e.g. biodegradable films). The study illustrates possible designs for a PEF process for utilisation of agro-based co-products to meet the demand for eco-friendly materials.     

Process optimisation of pulsed electric fields pre-treatment to reduce the sous vide processing time of beef briskets

This study used multiple regression to model the effect of pulsed electric field (electric field strengths 0.7, 1.0 or 1.5 kV cm⁻¹) and sous vide (60 °C for either 12, 18 or 24 h) processing on the quality parameters (tenderness, cooking loss, colour, lipid stability) of beef brisket. Pulsed electric fields (PEF) at 0.7 kV cm⁻¹ and 1.5 kV cm⁻¹ followed by sous vide processing for 12–20.2 and 20.8–23.7 h, respectively gave the lowest values for hardness (<20.2 N), shear force (100.5 N mm⁻¹ s⁻¹) and cooking loss (<17.4%). PEF treatment prior to sous vide processing had no significant effect on lipid oxidation, colour stability, cooking loss or in vitro protein digestibility of sous vide-processed brisket. Increasing the electric field strength and/or prolonging the sous vide time significantly increased collagen solubilisation in the sous vide brisket. This study demonstrated that a PEF pre-treatment can reduce sous vide processing time while enhancing the tenderness of tough meat cuts.     

Effect of pulsed electric fields on the structure and frying quality of “kumara” sweet potato tubers

The aim of this research was to study the effect of pulsed electric fields (PEF) on the microstructure of “kumara” sweet potato (Ipomoea batatas cv. Owairaka) and its quality after frying. Whole sweet potato tubers were treated at different electric field strengths ranging from 0.3 to 1.2 kV/cm with specific energy levels between 0.5 and 22 kJ/kg. Cell viability was determined using tetrazolium staining to investigate the uniformity of the PEF effect across tubers. Based on the patterns of viable cells it was observed that the effect of PEF was not homogeneous across the tuber. This result was also supported by the pattern of enzymatic browning due to PEF facilitating the reaction of polyphenoloxidase and phenols. PEF treatment resulted in significant softening of the ground tissues, but not on the dermal tissues, as determined by texture analysis. With respect to frying quality, tubers pre-treated with PEF at electric field strength of 1.2 kV/cm and fried at 190 °C had an 18% lower oil content than non-PEF treated samples. The kinetics of browning as a function of frying time could be described by a fractional conversion model. The activation energy (Ea) of the browning rate during frying increased (more temperature sensitive) due to PEF pretreatment at 0.5 kV/cm and 1.2 kV/cm. It implies that PEF pretreatment allows frying the potato chips at lower temperature in order to achieve the same brown colour intensity as the non-PEF treated tubers. This study shows clearly that PEF could reduce the energy required for cutting and frying of kumara.Industrial relevanceThis study provides evidence that the effect of PEF processing on whole kumara tubers is not uniform, demonstrating heterogenous distribution. These findings provide important information for food industry to design appropriate PEF processing conditions for solid materials. More importantly, PEF treatment reduced the energy required for cutting and frying of kumara, and reduced the oil content in the fried kumara chips.     

Modifications in the physicochemical properties of flour “fractions” after Pulsed Electric Fields treatment of thermally processed oat

This research aimed to investigate the physicochemical properties of thermally processed oat flour (TPOF) “fractions” (Supernatant, Top/S1, Middle/S2, Bottom/S3) after Pulsed Electric Fields (PEF) treatment of TPOF at 2 and 4 kV/cm between 50 and 451 kJ/kg. Supernatant from PEF-treated TPOF displayed a generally higher β-glucan content than untreated TPOF. No major changes were observed in chemical composition (in terms of total starch, protein, and fat contents) amongst “fractions”. However, S1 obtained from PEF-treated TPOF exhibited an increase in particle size, while both gelatinisation enthalpy and percent relative crystallinity were significantly lower compared to untreated counterpart. S1 from PEF-treated TPOF at 422–451 kJ/kg also manifested severe changes in granule morphology. S2 exhibited the highest gelatinisation enthalpy and S3 registered the least degree of observed changes in particle size. Findings of this study suggest the potential of PEF treatment application to produce oat “fractions” with varying physicochemical properties.Industrial relevanceThis study provides indispensable scientific information that could be utilised to further investigate industrial production of customised fractionation of oat flour with targeted physicochemical properties through PEF treatment. This opens new opportunities to strategically diversify the range of oat flour ingredients based on their targeted unique properties in the food industry.     

Pulsed electric field-assisted glycation of bovine serum albumin/starch conjugates improved their emulsifying properties

In this study, pulsed electric field (PEF, at electric field strengths from 3.5 to 8.1 kV/cm, pulse duration (τ) = 50 μs) was used to assist the glycation between soluble potato starch and bovine serum albumin (BSA). Moreover, the physicochemical and stability of BSA/starch conjugates emulsions were characterized. Spectroscopic investigations (A₄₂₀ and UV–Vis spectra) proved that PEF treatment (3.5–5.7 kV/cm) facilitated Maillard reaction between BSA and soluble starch. Moreover, the grafting degree (%) and the protein solubility of BSA/starch conjugates increased after PEF treatment but declined at higher electric field strengths. PEF treatment (at 3.5–5.7 kV/cm) decreased the particle sizes, surface hydrophobicity and fluorescence emission intensity of BSA/starch conjugates. Furthermore, emulsions stabilized by PEF-treated conjugates (at electric field strengths 3.5–5.7 kV/cm) exhibited smaller droplet sizes and higher adsorbed protein (AP%), indicating improved emulsion stability. Similarly, emulsions stabilized by PEF-induced conjugates (at electric field strengths 3.5–5.7 kV/cm) had better stability at pH = 4.6 and against different ionic strengths (150-300 mM NaCl). Differential scanning calorimetry (DSC) patterns showed that emulsions stabilized by PEF-treated conjugates had better freeze-thaw stability. In conclusion, PEF as a green technology could assist glycation and enhance the emulsifying properties of protein-polysaccharides conjugates.Industrial relevanceApplying green technologies in the food industry is critical for sustainable food production. As an eco-friendly food processing approach, PEF has been utilized in food industries to inactivate enzymes and microorganisms without affecting the nutritional quality of treated foodstuffs. Moreover, emulsions are widely applied in the food, drug delivery, and pharmaceutical industries. In our research, PEF could facilitate the Maillard reaction between soluble starch and BSA and improve the emulsifying properties of BSA/soluble starch conjugates. The results of this work could provide fundamental information on the mechanism of PEF-induced Maillard reaction and how PEF can improve the emulsifying properties of the conjugates. Thus, this work could help for increasing PEF applications in the food industries.     

Assessment of plant tissue disintegration degree and its related implications in the pulsed electric field (PEF)–assisted aqueous extraction of betalains from the fresh red beetroot

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

Quality characteristics of horchata (a Spanish vegetable beverage) treated with pulsed electric fields during shelf-life

The application of pulsed electric fields (PEF) is one of the new non-thermal technologies being studied to evaluate their potential as alternative or complementary processes to thermal pasteurization. “Horchata de chufa” (tiger nut milk or earth almond milk) is of high nutritional quality and therefore has great potential in the food market, limited by its very short shelf-life. The present work studies whether PEF can be used to obtain a quality horchata and increase its shelf-life while maintaining its organoleptic characteristics. In order to do so we determined pH, total fat, peroxide index, thiobarbituric acid-reactive substances index, formol index, and peroxidase activity in natural (untreated) horchata and horchata subjected to various PEF treatments and studied their stability during refrigerated storage (2–4 °C). After PEF treatment, only peroxidase activity decreased significantly (p < 0.05). This parameter and pH varied during the shelf-life of the horchata, and a negative correlation was obtained between pH and peroxidase activity.     

Effect of pulsed electric field (PEF)-treated kombucha analogues from Quercus obtusata infusions on bioactives and microorganisms

Pulsed electric field (PEF) is a promising non-thermal food preservation technology. The objective was to study inactivation of yeasts in PEF-treated kombucha analogues prepared from Quercus obtusata infusions. Fermentation conditions of infusions from Q. obtusata were time (7 days), sugar (10%), starting culture (10%), and inoculum (2.5%, at 25 °C). The PEF treatment considered using square waves, an electric field strength (37.3–53.4 kV/cm), PEF processing time (445.3–1979.2 μs), an output temperature (18.31 ± 0.98 °C), an input energy (21.2 - 136.5 KJ/L), and two feed flow rates (51.42 and 102.85 L/h). pH, °Brix, color determinations, microbiological testing, total phenolic, flavonoid content, DPPH test, and UPLC/ESI/MS/MS analysis were done. No changes at different PEF conditions were observed for pH and °Brix. Higher color changes were observed at higher specific energies. Acid-acetic bacteria were more sensitive to PEF than yeasts. Lower specific energies render products with higher polyphenolic content and antioxidant capacity.Industrial relevancePulse electric field is an interesting alternative to preserve kombucha analogues from oak leave infusions with minimal changes in physicochemical characteristics, antioxidant activity and bioactive compounds. The present work describes the effect of feed flow and specific energy on the several characteristics of fermented beverages, determining conditions for best processing.     

Effect of pulsed electric fields on cricket (Acheta domesticus) flour: Extraction yield (protein,fat and chitin) and techno-functional properties

Edible insects are an important source of proteins, fat, and chitin, which need to be extracted to develop tailored products with a controlled composition. Pulsed electric fields (PEF) is a non-thermal technology that can enhance the extraction. This study explores the effect of PEF on the extraction of protein, fat and chitin from cricket flour, as well as the material's functional properties. House crickets (Acheta domesticus) were treated with PEF at several conditions (4.9–49.1 kJ/kg). PEF treatment with 4.90 kJ/kg increased the extraction yields of protein (>18%) and fat >40%), while the treatment at 24.53 kJ/kg increased the oil binding and emulsifying capacity and antioxidant activity of the cricket flour by 28.10, 64.88 and 58.20%, respectively. Water binding capacity and foaming capacity were not affected by the PEF treatment. These results outline PEF as a suitable pretreatment for the valorization of house cricket biomass with possible industrial application.     

Recovery of lycopene from industrially derived tomato processing by-products by pulsed electric fields-assisted extraction

The influence of pulsed electric fields (PEF) pre-treatment at different field strength (E = 1–5 kV/cm) and energy input (W_T = 5–10 kJ/kg) on the recovery yield of lycopene in either acetone or ethyl lactate from industrial tomato peels residues, was investigated. The rate of lycopene extraction in both solvents decreased with time and was predicted rather satisfactorily (R² = 0.96–0.99) by the Peleg's model. Micrograph of tomato peels showed that PEF induced size reduction and separation between the plant cells likely due to pore formation and leakage of intracellular matter. Coherently, PEF treatment (5 kV/cm, 5 kJ/kg) significantly enhanced the extraction rate (27–37%), the lycopene yields (12–18%) and the antioxidant power (18.0–18.2%) in either acetone and ethyl lactate extracts, as compared with untreated samples. However, acetone gave the highest lycopene yield. HPLC analyses revealed that all-trans lycopene was the main carotenoid extracted and no degradation/isomerization phenomena occurred. The results obtained in this work suggest that the application of PEF prior to solid-liquid extraction with environmentally friendly solvents could represent a sustainable approach for the valorization of industrial tomato peels residues.Industrial relevanceIndustrial processing of tomatoes generates large amount of by-products, mainly peels, which represent a cheap and abundant source of natural carotenoids, especially lycopene. The recovery lycopene from tomato peels residues is a crucial step for use in a wide range of industrial applications in food, cosmetic and pharmaceutical sectors as natural pigment and antioxidant. PEF pre-treatment allows to intensify the extractability of lycopene from of tomato processing by-products using environmentally friendly solvents, thus adding new value to the tomato processing chain, improving economic performances and decreasing waste problems.     

Equivalent processing for pasteurization of a pineapple juice–coconut milk blend by selected nonthermal technologies

Identifying equivalent processing conditions is critical for the relevant comparison of food quality attributes. This study investigates equivalent processes for at least 5-log reduction of Escherichia coli and Listeria innocua in pineapple juice–coconut milk (PC) blends by high-pressure processing (HPP), pulsed electric fields (PEF), and ultrasound (US) either alone or combined with other preservation factors (pH, nisin, and/or heat). The two blends (pH 4 and 5) and coconut milk (pH 7) as a reference were subjected to HPP at 300–600 MPa, 20°C for 0.5–30 min; PEF at an electric field strength of 10–21 kV/cm, 40°C for 24 µs; and US at 120 µm amplitude, 25 or 45°C for 6 or 10 min. At least a 5-log reduction of E. coli was achieved at pH 4 by HPP at 400 MPa, 20°C for 1 min; PEF at 21 kV/cm, 235 Hz, 40°C for 24 µs; and US at 120 µm, 45°C for 6 min. As L. innocua showed greater resistance, a synergistic lethal effect was provided at pH 4 by HPP with 75 ppm nisin at 600 MPa, 20°C for 5 min; PEF with 50 ppm nisin at 18 kV/cm, 588 Hz, 40°C for 24 µs; and US at 45°C, 120 µm for 10 min. The total soluble solids (11.2–12.4°Bx), acidity (0.47%–0.51% citric acid), pH (3.91–4.16), and viscosity (3.55 × 10⁻³–4.0 × 10⁻³ Pa s) were not significantly affected under the identified equivalent conditions. HPP was superior to PEF and US, achieving higher ascorbic acid retention and lower color difference in PC blend compared to the untreated sample.     

Physicochemical properties of sugar beet pulp pectin by pulsed electric field treatment

This research focused on pulsed electric field (PEF) modification of pectin from sugar beet pulp. Experimental parameters including electric field intensity (18–30 kV cm^?1) and pulse time (806–2418 μs) were used, and the physicochemical properties of PEF‐treated pectin were evaluated by various instrumental techniques such as scanning electron microscopy, X‐ray diffraction, dynamic light scattering and Fourier transform infrared spectroscopy. The results showed that the degree of esterification, viscosity average molecular weight and particle size of pectin decreased with the increase in electric field intensity and pulse time. Meanwhile, some sharp interstices were shown on the surface of pectin, and its crystalline regions were destroyed after being treated with PEF. Results revealed that PEF technology is an effective method to obtain low‐molecular‐weight pectin with different degrees of esterification and obtain a desired production in food application.