Impact of Pulsed Electric Fields on the Dehydration and Physical Properties of Apple and Potato Slices

Abstract

The effect of pulsed electric fields (PEF) on drying and some physical properties of apple and potato was evaluated. Pulsed electric field intensities from 0.75 to 1.5 kV/cm with pulse duration within 100 and 300 μs were studied. The number of pulses applied was up to 120. Measurement of porosity and density were conducted using a mercury porosimeter. The drying process was carried out in a convective air oven at 70°C. The compressive strength of apples was reduced between 21 and 47% after treatment. The results show potential advantage for PEF enhanced juice extraction from the tissues even at moderate PEF treatment. PEF treatment increased porosity and particle density but decreased bulk density. Treating the apple samples with PEF resulted in generation of more pores of sizes in the order of cell wall thickness. Thus electric field application affected not only cell membranes but also cell wall integrity. PEF treatment enhanced drying rates of potato samples. Diffusion coefficients of PEF pretreated potato samples increased by up to 40%.     

Effect of Dipping Temperature and Dipping Time on Drying Rate and Color Change of Grapes

Thompson seedless grapes (Vitis vinifera) were pretreated in potassium carbonate and ethyl oleate solutions for 1, 2, and 3 min at 30, 40, 50, and 60°C and dried in a convective air dryer at 60°C. The effect of dipping time and solution temperature on drying rate and color kinetics were investigated. Grapes dipped into the solution at 60°C for 2 and 3 min had the fastest drying rate. Among the seven semi theoretical models compared, the Midilli equation best described the drying curves of grapes for all dipping pretreatments. Color data were obtained using a machine vision system in CIE L*a*b* color space. Regardless of the dipping time and temperature applied, all raisins had varying degrees of brown coloring. At all dipping times and temperatures the highest R ² value was obtained for a* values, which followed zero-order reaction kinetics during drying.     

The effect of pulsed electric field on drying kinetics,color, and microstructure of carrot

The aim of the study was to investigate the impact of pulsed electric field (PEF) treatment on the convective drying kinetics of a carrot and color and microstructure changes of the dried product. Samples were treated by PEF with the specific energy input equal to 5.63, 8 and 80 kJ · kg^?1. After PEF treatment, thermal conductivity and electrical conductivity were measured. Drying time of the PEF-treated samples was reduced up to 8.2% (W_s = 8 kJ · kg^?1, 5 kV · cm^?1; 10 pulses) in comparison to intact tissue. Statistical analysis showed that Midilli et al.’s model was considered to describe the kinetics of the process the most precisely. Pulsed electric field treatment increased the effective water diffusion coefficient up to 16.7%. Moreover, PEF treatment and drying caused the alteration of the sample color. After drying, the lightness and chroma were higher or unchanged in comparison to the intact tissue. The dried PEF-treated samples exhibited significantly higher redness (higher value of a^* parameter) in comparison to the untreated dried samples. Moreover, the visual inspection of scanning electron microscope images revealed that PEF pretreatment performed at high electric field intensity (5 kV · cm^?1, regardless of pulse number) provoked the material to form greater cavities during drying in comparison to the untreated material.     

Drying Kinetics and Bioactivity of Beetroot Slices Pretreated in Concentrated Chokeberry Juice and Dried with Vacuum Microwaves

Beetroot slices 18 mm in diameter and with a thickness of 9.6, 6.3, 3.35, or 2.6 mm were pretreated in 40°Bx chokeberry juice at a temperature of 50°C for 2 h and then dried by a vacuum-microwave (VM) method at different microwave power levels, such as 120, 240, 360, 480, and 480/120 W. The drying kinetics were described by a fitted model that incorporated contributions from the surface area of the samples, microwave power, and VM processing time. As the microwave power during VM drying increased, the bioactive potential decreased for untreated samples and increased for pretreated samples. Increasing the samples' specific surface area resulted in shorter drying time, lower temperature of the material during drying, and enhanced quality of the dried product. For osmotically pretreated beetroot slices with a specific surface area of 827 ± 18 m²m^?3, a final VM drying step at 240 W is recommended to produce high quality vegetable snacks.     

Optimization of pulsed electric field pretreatment parameters for preserving the quality of Raphanus sativus

Pulsed electric field (PEF) pretreatment can increase the drying rate of produce, but preserving product quality while minimizing energy consumption and maintaining food quality is a significant challenge. The goal of this study was to determine optimal PEF parameters for pretreatment of Raphanus sativus (radish) prior to the drying process. The effects of pulse intensity, treatment time, and pulse number on the drying rate, vitamin C (Vc) content, and ascorbic acid oxidase activity of R. sativus were characterized. Optimal PEF pulse parameter values were determined through quadratic orthogonal regression tests followed by multi-objective nonlinear optimization. The optimal PEF pulse parameters for pretreatment of R. sativus were: pulse intensity, 1446 V · cm^?1; reaction time, 28 μs; and pulse number, 87. This study provides reference values to guide application of PEF pretreatment in R. sativus processing.     

A Comparative Study on the Effects of Microwave and High Electric Field Pretreatments on Drying Kinetics and Quality of Mushrooms

This research evaluated the effects of microwave and high-voltage pretreatments on convective freeze drying of mushrooms (Agaricus bisporus) independently. The effect of the microwave (5 W/g for 5 min) and high electric field (HEF; 430 kV/m for 15 min) as pretreatments on enhancement of the drying rates during subsequent drying and the value addition due to the above pretreatments on the quality of the final dehydrated products were investigated. An exponential mathematical model was developed by fitting the drying kinetics to the Page equation to predict the effects of the pretreatments on the drying kinetics of the mushrooms. The parameters considered for the evaluation of product quality project included color, texture, shrinkage properties, and rehydration ratio of the dried mushrooms. The drying rate of HEF-pretreated mushrooms was found to be unaffected overall when compared to the control and the HEF pretreatment resulted in better quality product and less overall shrinkage. Freeze drying of the pretreated mushrooms was found to result in slower drying rate but better overall quality and rehydration ratio.     

Effects of Microwave-Assisted Hot Air Drying and Conventional Hot Air Drying on the Drying Kinetics,Color, Rehydration,and Volatiles of Moringa oleifera

In this study, the fresh Moringa oleifera pods (Drumsticks) were dehydrated by microwave-assisted hot air drying (MAHD) and conventional hot air drying methods. The samples were dried at three different temperatures, viz. 50, 60, and 70°C, with and without the application of microwaves. Microwave power density of 1 W/g was used for the MAHD. The final moisture content was targeted as 13% wb. The drying curves and drying rate curves were plotted and compared. The kinetics of drying obtained experimentally were correlated with the Page equation. The constants K and N of the Page equation were determined to predict the drying kinetics for varying conditions. The quality attributes, namely, color, rehydration ratio, and volatile compounds, were analyzed and compared with that of the fresh Moringa pods. The volatile compounds were analyzed using z-Nose (an electronic nose; Electronic Sensor Technology, Newbury Park, CA) and bioactive molecules were analyzed using gas chromatography–mass spectrometry. The results showed that the MAHD method had significantly (P < 0.05) reduced the loss of volatiles during drying. Also, MAHD preserved most of the bioactive molecules when compared to the conventional hot air drying method. The samples dried at 50°C using MAHD were the best in terms of all of the quality attributes tested in this study. Also, the results established that the z-Nose can be used as a quick and inexpensive means to assess the effect of different process parameters on the aromatic quality of the product and quantitatively classify quality based on aroma.     

Effect of High Pressure Pretreatments on Structural and Dehydration Characteristics of Aloe Vera (Aloe barbadensis Miller) Cubes

The effect of high-pressure (HP) pretreatments (300–500 MPa for 5–15 min) on dehydration characteristics of aloe vera cubes (AVC), dried at 50–70°C and air velocity of 1–2 m/s, was studied. Pretreatments resulted in higher drying rates, leading to a reduction in drying time compared to untreated ones. The drying rate and drying time were most significantly affected (p < 0.05) by the drying temperature, followed by air velocity, pressure level, and dwell time. HPP enhanced the firmness of AVC with a maximum of up to 21% for the sample treated at 500 MPa for 15 min. Microstructural analysis using scanning electron microscopy (SEM) indicated non-uniform structures in the pretreated and dried AVC samples. Semi-quantitative elemental detection (EDS) confirmed the presence of a considerable amount (14%) of calcium in aloe vera.     

Effect of Pretreatments and Drying Methods on the Properties and Fishy Odor/Flavor of Gelatin from Seabass (Lates calcarifer) skin

Effects of different pretreatments of seabass skin and various drying methods on properties and fishy odor/flavor of resulting gelatin were evaluated. All gelatins contained α- and β-chains as the predominant components. Generally, a higher gel strength was found in the freeze-dried gelatin, compared with spray-dried counterpart (p < 0.05). Gel strength of gelatin decreased as the inlet temperature for spray drying increased (p < 0.05). All gelatin samples had creamy whitish color but became more yellow as the inlet temperature for spray drying increased. All gelatin gels were sponge- or coral-like in structure. Gelatin from skin pretreated with citric acid had lower fishy odor/flavor than that from skin pretreated using acetic acid. The lower fishy odor/flavor with coincidentally lower abundance of volatile compounds, including aldehydes, ketones, and alcohols, etc., was found in gelatin obtained by spray drying, in comparison with its freeze-dried counterpart. The lower fishy odor/flavor in spray-dried gelatin was in accordance with the lower thiobarbituric acid reactive substances and peroxide values. Thus, spray drying in conjunction with an appropriated pretreatment could be an effective method for production of gelatin with negligible undesirable fishy odor and flavor.     

Convective air,microwave, and combined drying of potato pre-treated by pulsed electric fields

Abstract

The effects of pulsed electric field (PEF) treatment on drying of potato have been investigated. The convective air (CA) (T?=?50?°C), microwave (MW), and combined (CA?+?MW or MW?+?CA) drying was applied. The drying curves, progression of temperature inside samples, microstructure, and capillary imbibition capacity of untreated (U) and PEF treated samples were compared. The PEF treatment noticeably affected the CA and MW drying characteristics and structure of dried samples. It reflected impact of electroporation on the heat and mass transfer processes during the different drying periods. The different progressions of temperatures inside U and PEF samples for the MW mode of drying were revealed. The highest and smallest rehydrations were observed for the U samples for individual CA and MW modes of drying, respectively. The observed behavior was explained accounting for the absence of starch gelatinization for the CA mode of drying and presence of it for the MW mode of drying.     

Effect of Osmotic Dehydration with Pulsed Vacuum on Hot-Air Drying Kinetics and Quality Attributes of Cherry Tomatoes

The effects of osmotic dehydration (OD) with or without pulsed vacuum (PV) on hot-air drying kinetics and quality attributes of cherry tomatoes were investigated. Both OD and PVOD pre-treatments were performed for 3 h at 50°C in 50 and 70^o Brix sucrose solutions with a solution-to-fruit mass ratio of 4:1, and PVOD was applied for 15 min before OD at atmospheric pressure. Samples were further dried at air temperature of 70°C. Effective moisture diffusivity (D _eff) of osmotically dehydrated samples increased gradually while the D_eff curve of fresh samples had a plateau stage during hot air drying. Lower glass transition temperature, T_g, values of osmotically dehydrated samples indicated that they needed a lower storage temperature. Both OD and PVOD pre-treatments had advantages in shortening drying cycles and improving quality of products. Compared with air drying, osmo-air drying decreased the total drying time, color change, and hardness of dried samples by 32.26%, 18.11%, and 88.21%, respectively, and increased volume ratio and vitamin C retention rate by 72.31% and 125.82%. As compared with OD, PVOD decreased color change and hardness by 28.48% and 45.17%, increased volume ratio and vitamin C retention rate by 27.41% and 17.77%, but there was no significant difference shown in drying time. Therefore, osmotic pre-treatment can shorten the total dehydration time, and improve the general quality of dried cherry tomatoes.     

Drying Kinetics of Apple Tissue Treated by Pulsed Electric Field

The aim of this work was to study the influence of pulsed electric field (PEF) on the drying kinetics of apple tissue. Therefore, mathematical models that are commonly used in the literature were applied to describe the process. PEF treatment of the samples was carried out at an intensity of E = 5–10 kV/cm and 10–50 pulse numbers. Subsequently, the apples were convectively dried at 70°C and air velocity of 2 m/s. Based on electrical conductivity measurement, the cell disintegration index Z _p was computed. Midilli et al.'s(Drying Technology, Vol. 20, pp. 1503–1513, 2001) model was evaluated as the most adequate to describe the moisture transfer in PEF-treated and intact samples. PEF pretreatment induced a reduction in drying time of up to 12% when 10 kV/cm and 50 pulses were applied. For instance, after 60 min of drying, the dimensionless moisture ratio for PEF-treated (10 kV/cm, 50 pulses) samples was 0.18 compared to 0.26 for the untreated apples. The effective moisture diffusivity, calculated on the basis of the Fick's second law, was 1.04 × 10^?9 m/s for intact samples and from 1.09 × 10^?9 to 1.25 × 10^?9 m²/s for PEF-treated samples at 10 pulses at 5 kV/cm and 50 pulses at 10 kV/cm, respectively.     

Drying of Chestnuts (Castanea sativa Mill.) after Osmotic Dehydration with Sucrose and Glucose Solutions

Chestnuts were dehydrated by using a combined method of osmotic dehydration followed by air drying. Samples were osmotically pretreated with sucrose (60% w/w) and glucose (56% w/w) for 8 h, air-dried at temperatures of 45, 55, and 65°C, at a relative humidity of 30% and at a velocity of 2.7 m·s^?1 and the experimental data of the drying kinetics were obtained. Whole samples were dried with different peelings: (a) removal of endocarp and pericarp (peeled) and (b) additionally the internal rough surface (cut). In all cases, cut chestnuts show greater drying rates than peeled samples, indicating that a significant mass transfer resistance in the layer nearest to the surface takes place. Peeled samples pretreated with sucrose solutions behave in a similar way to untreated samples. For the rest of the samples, the cut samples osmotically treated with sucrose solutions and all the samples treated with the glucose solution, the drying rates decrease during drying. Drying kinetics are successfully modeled by employing a diffusional model that takes the shrinkage into account. The effective coefficient of water diffusion was evaluated and correlated with temperature. The quality of the final product was monitored by color change. In spite of the fact that the total color difference is not modified by the osmotic treatment, the L?, a?, and b? color coordinates of cut samples treated with sucrose and glucose solutions do undergo changes; the L? and a? coordinates change less than the b?.     

Comparison of Water Blanching and High Hydrostatic Pressure Effects on Drying Kinetics and Quality of Potato

Abstract

Drying kinetics and quality parameters of potato cubes were evaluated as affected by high pressure processing and hot water blanching. The potato cubes in 1% citric acid solution as immersion medium were pressure treated at 400 MPa for 15 min. Hot water blanching was conducted in boiling water for 3 min. Drying kinetics and quality parameters (i.e., rehydrability, texture, color and apparent density) were assessed for the high pressure–treated and water-blanched samples and for dehydrated and rehydrated samples. Drying rates were found to be higher (p < 0.05) in the initial period of drying for the pressure treated samples. The Page model was found to better fit drying data of the thermally treated samples, and the two-terms model better described the drying behavior of high pressure–treated samples. High pressure–treated samples had a similar rehydrability to thermally treated samples. It was found that pressure–treated samples had a hardness value close to that of fresh samples, whereas thermal treatment resulted in a softer texture. After rehydration, samples of both treatments returned their texture before drying. The total color difference for the thermally blanched samples was higher (p < 0.05) than for pressure–treated samples before drying and after drying. High pressure–treated and dried potato cubes had a color close to that of fresh potato cubes. High pressure–treated and air-dried samples were found to have higher (p < 0.05) apparent density than thermally treated samples.     

Drying Characteristics of Pulsed Electric Field-Treated Carrot

This study was designed to establish the interaction effect of various components of pulsed electric field (PEF) system on drying characteristics of carrot, a vegetable rich in carotenoid. Carrots were treated in PEF system of 0.5, 1, and 1.5 kV/cm electric field strength, 0.5 and 1 μF capacitance, and pulse numbers of 10, 30, and 50. The samples were subsequently dried at 70°C until reaching an acceptable moisture content level. Drying rates were significantly (P < 0.05) influenced by PEF treatment. Variation in drying constant was not significantly influenced by the interaction effect of electric field components but by the energy per pulse. The Henderson and Perry model was fitted to the drying curve and it gave correlation coefficients ranging between 0.86 and 0.96.     

Influences of Pretreatments and Drying Process Including Fluidized Bed Puffing on Quality Attributes and Microstructural Changes of Banana Slices

Healthy snacks have received more attention because of their low fat content. Color and texture are important to snack quality. Effects of chemical pretreatment, thickness, blanching, and puffing temperature on quality of banana slices were therefore investigated. Banana slices (2.5 and 3.5 mm thickness) were chemically treated by citric acid and sodium metabisulfite, blanched, and dried at a temperature of 90°C to an intermediate moisture content of 25% db. They were then puffed in a fluidized bed dryer at 160 and 180°C for 2 min and dried again at the same drying temperature as the first drying step. Blanching, puffing temperature, and thickness strongly affected the degree of shrinkage, effective moisture diffusivity, morphology, textural properties such as hardness and crispiness, and color, but the chemical treatment did not affect those qualities. Blanching can improve the product appearance; the color was uniform and shiny throughout the surface and golden yellow. However, the textural attributes of the blanched sample had higher hardness and less crispiness than those of unblanched sample.     

Evaluation of the effects of surface treatments on the cathodic delamination and anticorrosion performance of an epoxy-nanocomposite on steel substrate

The St-37 type steel substrates were pretreated with Cr(VI) and Cr(III) conversion coatings where the latter was then post-treated with Co(II) and Ni(II) chemical treatments. The epoxy coatings containing 3.5 wt% nano-sized ZnO particles were applied over the chemically treated steel samples. The corrosion resistance of the samples was studied by a DC polarization technique. A scanning electron microscope (SEM) was utilized to investigate the morphology of the pretreated and post-treated samples. Electrochemical impedance spectroscopy (EIS) was utilized to investigate the corrosion resistance of the epoxy nanocomposites for different immersion times in 3.5 wt% NaCl solution. The adhesion strengths of the coatings were measured before and after 120 days of immersion in the corrosive electrolyte using a pull-off test. The cathodic delamination (CD) of the painted samples was also investigated. Results showed that conversion coatings can significantly increase the corrosion resistance and adhesion strength of the epoxy coating on the steel, and also reduce the rate of CD in comparison with an untreated sample. The adhesion strength and corrosion resistance of the epoxy coating on the Cr(III) pretreated samples were significantly greater than on the Cr(VI) sample. The increase in adhesion strength and corrosion resistance was more pronounced on the samples that were post-treated with Co(II) and Ni(II) chemical treatments. The cathodic disbonded areas of the Cr(III)–Co(II) and Cr(III)–Ni(II) post-treated samples were significantly lower than the Cr(III) and Cr(VI) pretreated samples. Results showed that Cr(III)-based conversion coatings can improve the anticorrosion performance and reduce CD compared with those with Cr(VI).     

Drying kinetics and quality of carrots subjected to microwave-assisted drying preceded by combined pulsed electric field and ultrasound treatment

Abstract

In the study the impact of combined pulsed electric field and ultrasound pretreatment on microwave-assisted air drying kinetics and quality of dried carrot was evaluated. Pretreatment of samples has been realized through sequential application of PEF followed by US or vice versa. Sonication was performed using either the contact or immersive method whereas PEF treatment was carried out at 5?kV·cm^?1 and 10 pulses. After pretreatment the samples were subjected to microwave-assisted convective drying. Combined pretreatment reduced drying time by 27–49%. The highest retention of carotenoids (93.7%) was noted for samples subjected to PEF treatment followed by contact sonication. Optical properties of pretreated carrots were similar to reference samples (without pretreatment) and total color change ranged from 2.8 to 5.8. Application of immersive sonication, regardless of the sequence, resulted in the highest rehydration capacity and the highest loss of soluble solids. Despite samples subjected to combined pretreatment exhibited the most porous structure, the hygroscopic properties remained almost unchanged in comparison to the reference sample.     

Influence of number of puffing times on physicochemical,color, texture,and microstructure of explosion puffing dried apple chips

The impact of number of puffing times during explosion puffing drying (EPD) on drying characteristics and qualities of apple chips was studied. Physicochemical characteristics, antioxidant capacity, color, texture, expansion ratio, rehydration ratio, hydroscopicity, and microstructure of apple chips dried by EPD with 0 (vacuum drying, VD), 1, 3, 5, 7, and 9 puffing times were analyzed. The apple chips dried by EPD with 3 and 5 puffing times exhibited better color (ΔE 7.27–7.70) and texture (hardness 40.5–40.8 N, crispness 8.8–9.3 N/mm), as well as higher expansion ratio (104.4–109.7%) compared to VD and EPD with fewer or more puffing times. The samples dried with 3 and 5 puffing times also showed relatively higher rehydration ratio and hygroscopicity, and acceptable retention of total phenolic content (0.32–0.37 mg/g) and ascorbic acid content (1.66–1.89 mg/100 g), as well as considerable antioxidant abilities (DPPH 79.45–81.17 AEAC µM/g, FRAP 66.54–68.25 TEAC µM/g, ABTS 73.36–79.21 TEAC µM/g) compared to VD dried samples. In conclusion, experiments with apple chips indicated that EPD drying with 3 to 5 puffing times yielded superior overall quality than that with more or fewer puffing times.     

Effects of ultrasound pretreatment on drying kinetics and quality parameters of button mushroom slices

The aim of this study was to investigate the utilization of ultrasound as a pretreatment method prior to drying to improve the quality of button mushroom slices during both hot air drying and far infrared drying processes. The effects of ultrasound and blanching pretreatments upon drying were analyzed. The ultrasound frequency was 40 kHz, the power was 0.4 W/cm², and the ultrasound energy was applied for 3 and 10 min, respectively. The ultrasound treatment caused reduction of the drying time by 9.5% in comparison to untreated samples. The drying kinetics of button mushroom slices were improved by ultrasound application, which involved an improvement of mass transfer coefficient and effective moisture diffusivity. The logarithmic model showed the best fit to the experimental drying data. For ultrasound treated samples, the parameters including hardness, crispness, rehydration ability, shrinkage, microstructure, and nutrient composition had remarkable changes compared with blanched and untreated samples.