Ohmic heating and pulsed vacuum effect on dehydration processes and polyphenol component retention of osmodehydrated blueberries (cv. Tifblue)

Blueberries are highly perishable fruits; therefore, emerging technologies focus on improving the bioactive compound retention and extending the shelf life. The aim of this study was to evaluate the effect of ohmic heating and vacuum pulses on the dehydration processes and polyphenol compound retention of osmodehydrated blueberries (cv. Tifblue). The treatments were performed using a 65% (w/w) sucrose solution, an electric field of 13 V/cm (100 V) at 30 °C, 40 °C or 50 °C for 300 min, and air drying at 50, 60 or 70 °C to obtain dried blueberries. The moisture content, soluble solids and phenolic compounds were analyzed. The combination of ohmic heating/pulsed vacuum treatments intensifies mass transfer in osmodehydrated blueberries, especially at higher temperatures. Nevertheless, the polyphenol retention was greater at lower temperatures; hence, the application of an intermediate process temperature (40 °C) was selected as a pre-treatment prior to further drying. The treated samples improve the retention of polyphenols after drying compared with untreated samples. Therefore, the results of this research study suggest that the use of a pulsed vacuum and ohmic heating in the osmotic dehydration (PVOD/OH) treatment at 40 °C for 240 min and subsequent drying at 60°C could be the best process for dehydrating blueberries, considering that it improved mass transfer, achieved lower losses of phenolic components and reduced the drying time.Industrial relevanceBlueberries are an important fruit due their high bioactive compound content, especially polyphenols. Studies that involve emerging technologies application could add value to blueberries. Ohmic heating and pulsed vacuum as pre-treatments improve the efficiency of dehydration processes, focused toward bioactive compounds retention and achieving commercial viability. In this work have been applied PVOD/OH treatments at moderated temperatures and subsequently dried at 60 °C, obtaining promissory results.     

Mathematical modeling of mass transfer in osmotic dehydration of onion slices

The study on osmotic dehydration of onion slices was carried out in order to remove the moisture prior to the further mechanical drying. Three salt concentration levels (5%, 12.5% and 20%), three temperature levels of osmotic solution (28 °C, 43 °C and 58 °C) and the observations on weight loss and solid gain were taken at an interval of 5 min up to first half an hour followed by interval of 10 min for next 1 h. The sample to solution ratio of 1:5, agitation of 100 shakes per minute, sample thickness of 4 mm and 0.2% potassium metabisulphite mixed with osmotic solution were used for the study. A two-parameter mathematical model developed by Azuara et al. was used for describing the mass transfer in osmotic dehydration of onions slices. The effect of time on mass transfer kinetics was investigated and the constants of two-parameter model and final equilibrium points for moisture loss as well as solid gain were found. The effect of solution concentration and solution temperature was also studied and it was found that equilibrium moisture loss and solid gain are related to solution concentration and solution temperature logarithmically. The optimum conditions of osmotic dehydration for further drying were found to be 20% salt concentration, 28 °C solution temperature and 1-h of osmosis.     

Modelling of red abalone (Haliotis rufescens) slices drying process: Effect of osmotic dehydration under high pressure as a pretreatment

Simultaneous application of osmotic dehydration and high pressure as a pretreatment to drying process on red abalone (Haliotis rufescens) slices was studied. During drying process the process time was reduced by increasing temperature from 40 to 60 °C along with the application of different pretreatments: high pressure (350 and 550 MPa), pressure time (5 and 10 min), and osmotic solution (10 and 15% NaCl). Effective moisture diffusivity was determined and varied from 4.35 to 9.95 × 10^− 9 m²/s, for both control and pretreated samples (R² ≥ 0.97). The Weibull, Logarithmic and Midilli–Kucuk models were applied to drying experimental data, where Midilli–Kucuk model was found to be the best fitting model. Furthermore, all drying curves were normalized and then modelled by the same three above models showing a R² ≥ 0.96. As to energy consumption and efficiency values for drying processes were found to be in the range of 777–1815 kJ/kg and 8.22–19.20%, respectively. Thus, knowledge on moisture transfer kinetics, energy consumption and data normalization, is needed to manage and control efficiently drying process under different pretreatment conditions.Industrial relevanceThis article deals with the mass transfer modelling and energy consumption during simultaneous high hydrostatic pressure treatment and osmotic dehydration as a pretreatment to drying process of abalone slices. Water and salt transfer during this combined process was satisfactorily simulated with the Midilli–Kucuk model. Results indicated that application of this combined innovative technology improved abalone slices dehydration rates compared to atmospheric pressure operation resulting in a dried abalone with intermediate moisture content ready to be used as input material of further processes. Furthermore, the different energetic features were determined in order to realize the importance of the changes that can influence to alter process time.     

Prediction of moisture content uniformity of microwave-vacuum dried mangoes as affected by different shapes using NIR hyperspectral imaging

The prediction of moisture content uniformity on mango slices as affected by four different shapes (square, rectangle, regular triangle, and round shape) during microwave-vacuum drying (MVD) was investigated using near-infrared hyperspectral imaging in combination with multivariate chemometric analysis. Applying spectral pretreatment of a 2nd derivative followed by mean-center to raw spectra was found to be greatly beneficial for the reduction of noise and scattering levels. Seven wavelengths (951, 977, 1138, 1362, 1386, 1420, and 1440 nm) with larger absolute values of regression coefficients derived from a partial least square regression model were identified as feature variables for moisture prediction. An optimized model based on the selected wavelengths was developed using multivariate linear regression, achieving a high prediction accuracy with R_p² = 0.993 and RMSEP = 1.282%. From the moisture distribution map, a similar non-uniform drying pattern was found on square, rectangle and regular triangle-shaped samples, while round-shaped mango slices achieved better drying results.Industrial relevanceThe current study suggested that NIR hyperspectral imaging was a promising technique in predicting the moisture content of mango slices during MVD, and non-uniformity of moisture distribution and the effect of sample geometry should be taken into account when the microwave-vacuum method is implemented in drying.     

Drying of edamames by hot air and vacuum microwave combination

The characteristics of hot air and vacuum microwave drying were compared using edamame as the raw material, and an optimized combination drying process was then established thereof so as to achieve increased drying rate and enhanced product quality. Edamame was subjected to 70 °C hot air drying for 20 min, and then microwave dried at power intensity 9.33 W/g for 15 min under −95 kPa (gauge pressure). The optimized combination drying process exhibited significantly shortened drying time as compared with conventional hot air drying, and greatly decreased mass loads on the vacuum microwave dryer.     

Modeling dehydration and rehydration of cooked soybeans subjected to combined microwave–hot-air drying

Pre-cooked soybeans were subjected to convective hot-air, microwave and combined microwave–hot-air dehydration. Three microwave levels (210, 300, 560 W) and three air temperatures (160, 180, 200 °C) were examined. Drying kinetics, rehydration kinetics and colour change were investigated relative to microwave level and air temperature. Combined microwave–hot-air drying decreased the drying time required when compared to drying with either hot-air or microwave energy alone. Predictive models were developed to describe dehydration and rehydration kinetics. Dehydration rate, rehydration rate and total colour change of rehydrated product generally increased with microwave level and air temperature. Within the studied range, optimal drying occurred for the lowest levels of both microwave and air temperature studied, i.e. microwave power = 210 W, air temperature = 160 °C.Industrial relevanceApplication of microwave energy simultaneously with convective hot-air drying to pre-cooked soybeans was up to four times faster when compared to convective drying alone, and up to twice as fast when compared to microwave drying alone. Rehydration time for soybeans subjected to combined microwave–hot-air drying was 50–60% less than for legumes subjected to either convective or microwave drying alone. Therefore, application of combined microwave–hot-air drying to pre-cooked soybeans resulted in significant saving in process time, while also producing a dehydrated product with fast rehydration properties.     

Effects of pulsed vacuum osmotic dehydration (PVOD) on drying kinetics of figs (Ficus carica L)

Drying kinetics of non-pretreated (fresh) and pretreated Sarılop (Ficus carica L.) variety figs were compared. In experiments, figs were performed as a whole (unsliced and unpeeled). Pretreatment was pulsed vacuum osmotic dehydration (PVOD). Osmotic dehydration was performed in sucrose solution at 50 °Brix and 50 °C with a solution/fruit mass ratio of 4/1. Vacuum impregnation in osmotic dehydration was applied at 130 mbar for 15 min then the osmotic treatment continued at atmospheric pressure for 165 min, therefore the total pretreatment period lasted for 180 min (15 min (130 mbar) + 165 min (P_atm)). Pretreated and non-pretreated figs were dried at 55, 65 and 75 °C in a convective oven. Results showed that increasing of drying temperature shortened the drying time for both non-pretreated and pretreated figs. Drying period of pre-treated figs lasted shorter than non-pretreated figs, thus PVOD shortened the drying period. Non-pretreated (fresh) figs had greater shrinkage than the pretreated figs. Effective moisture diffusivity (D_eff) values of pretreated figs are greater than the non-pretreated figs during the drying at all three temperatures. D_eff increased with drying temperature for both pretreated and non-pretreated figs. D_eff values of non-pretreated and pretreated figs ranged 2.75·10^− 10–5.69·10^− 10 m²/s and 3.57·10^− 10–10.25·10^− 10 m²/s, respectively. Activation energy (E_a) of non-pretreated and pretreated figs were obtained 34.68 (kJ/mol) and 50.27 (kJ/mol), respectively. Also, sensory evaluation of color, flavor, odor, texture and overall acceptability of the samples was made.Industrial relevanceThe use of PVOD technique is relevant for food industry. So that, PVOD treatment shortened the drying period of figs. Thus, this result can cause the economic advantage as reducing the further costs for drying process. Additionally, results of sensory evaluation show that there was no significant difference (p > 0.05) between the pretreated and traditional dried figs except for flavor. Sensory properties of pretreated figs may be improved by changing conditions of pretreatment.     

Thin-layer drying characteristics and modelling of mint leaves undergoing microwave treatment

The effect of microwave drying technique on moisture content, moisture ratio, drying rate, drying time and effective moisture diffusivity of mint leaves (Mentha spicata L.) were investigated. By increasing the microwave output powers (180–900 W) and the sample amounts (25–100 g), the drying time decreased from 12.50 to 3.0 min and increased from 6.60 to 16 min, respectively. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content versus drying time. Among of the models proposed, the semi-empirical Midilli et al. model gave a better fit for all drying conditions applied. By increasing the microwave output powers and decreasing the sample amounts, the effective moisture diffusivity values ranged from 3.982 × 10⁻¹¹ to 2.073 × 10⁻¹⁰ m² s⁻¹ and from 9.253 × 10⁻¹¹ to 3.162 × 10⁻¹¹ m² s⁻¹, respectively. The activation energy was calculated using an exponential expression based on Arrhenius equation. The relationship between the drying rate constant and effective moisture diffusivity was also estimated; and gave a linear relationship.     

Relation between mechanical properties and structural changes during osmotic dehydration of pumpkin

This work presents the changes in the mechanical properties of pumpkin (Cucurbita pepo L.) fruits when submitted to osmotic dehydration processes. Cylinders of the parenchymatic tissue were dehydrated with sucrose solutions, varying the concentration (30–60% w/w) and temperature (12–38 °C) of the osmotic solution and process time (0–9 h). As an opposite process to dehydration, water soaking of some cylinders was also performed. Samples were submitted to uniaxial compression until rupture, and four parameters were analyzed: apparent modulus of elasticity, true stress at failure, Hencky strain at failure and failure work (toughness). Values of these mechanical properties for fresh material ranged from 0.96 to 2.53 MPa for apparent modulus of elasticity, 250–630 kPa for failure stress, 0.42–0.71 for failure strain and 85–285 kJ/m³ for toughness. Mechanical properties of osmodehydrated samples showed no dependence on concentration of the osmotic solution and process temperature, whereas they were found to be dependent on moisture content: apparent elastic modulus decreased and failure strain increased during dehydration; toughness and failure stress initially decreased with moisture content, and increased at advanced stages of the process. Water soaked samples showed a decrease in failure strain, failure stress and toughness, but the apparent elastic modulus increased. Simultaneous structural observation during compression showed that the material fails in the contact zones of its fibres. This fact and the observed structural profiles during dehydration could explain the changes in the failure properties (strain, stress, toughness) along the studied processes. Changes in the apparent modulus of elasticity were likely related with the changes in the turgor pressure of cells.     

Rehydration kinetics and soluble solids lixiviation of candied mango fruit as affected by sucrose concentration

Rehydration behaviour of candied mango samples was studied. The influence of candy process conditions and rehydrating medium on the rehydration kinetics was studied. In this sense, water gain, solute loss and compositional changes in the fruit liquid phase were fitted using Peleg’s model. Mango cubes were candied using two osmotic dehydration steps (applying vacuum impregnation in the first) plus air drying at 35 °C till 80% or 90% soluble solids was obtained. Four combinations of sucrose solutions (^°Bx) was used in the osmotic steps: 25–65, 45–45, 45–65 and 65–65. Rehydration process were carried out at 10 °C for 8 h on sucrose solutions (0, 10, 20 and 30^°Bx). Candied samples using 45^°Bx sucrose in the two osmotic steps showed the highest solute retention at equilibrium. A higher drying level of candied fruit also implied the greatest solute retention.     

Retention of Physicochemical and Antioxidant Properties of Dehydrated Bael (Aegle Marmelos) and Palmyra (Borassus Flabellifer) Fruit Powders

Present study was carried out to evaluate the effect of various dehydration techniques such as sun drying, solar drying, drying after freezing (Freeze for one hour followed by mechanical drying at 55 °C), vacuum drying and drying using lab scale air oven on proximate composition and retention of antioxidants in different fruit powder prepared from Bael (Aegle marmelos) and Palmyra (Borassus flabellifer). Moisture content, Total Ash, Crude fiber %, Fat %, Crude protein %, total phenolic content,β –Carotene and antioxidant activity were tested. The antioxidant activity was measured based on the ability of fruit extract to scavenge 1, 1- diphenyl-2-picrylhydrazyl (DPPH). Among different drying treatments the highest fat percentage recorded by the solar dried palmyra fruit powder and there is no significant difference (α= 0.05) between sun drying and vacuumed drying. Higher concentration of β -Carotene and total phenolic content were recorded in vacuum dried samples both in bael and Palmyra fruit powders and it significantly different (α= 0.05) from other treatments. The scavenging activity of bael fruit powder in vacuum drying was ranged from 65.36% to 81.33% of the concentration 200 μg/ml to1000 μg/ml and the palmyra fruit powder was recorded 57.32% to 83.25% of the concentration 200 μg/ml to1000 μg/ml. Vacuum dried fruit powders of palmyra and bael were given highest radical scavenging activity and the scavenging activity of palmyra fruit powder is higher than the bael. Therefore vacuum drying can be recommended as the most effective drying method to protect chemical characteristics and retention of antioxidant properties of fruit powders.     

Radiant energy under vacuum (REV) technology: A novel approach for producing probiotic enriched apple snacks

The feasibility of vacuum impregnation in combination with air drying + radiant energy vacuum (REV) drying to produce shelf stable probiotic enriched apple slices was evaluated. The shelf life of the products was monitored at 25 and 4 °C. The results demonstrated that bacterial stability at 25 °C depended on the dehydration techniques; with the longest shelf life in air drying +REV drying followed by freeze drying and air drying. Storage at 4 °C showed no significant changes in bacterial population up to 180 days in all samples. Sensory properties of the air drying +REV and freeze dried apple slices remained above the acceptable level for 30 days at 25 °C and 180 days at 4 °C. The results also revealed that dried apple slices were able to provide prominent protection to the cells in acidic gastric juice.     

Microwave assisted drying of short-cut (ditalini) macaroni: Drying characteristics and effect of drying processes on starch properties

Macaroni samples were dried by conventional hot air, microwave alone and hot air followed by microwave drying methods. The drying of macaroni samples took place in the falling rate period. Higher drying rates were observed with a higher microwave power level. A diffusion model was employed to fit the experimental drying data in order to characterize the drying rate of samples. Drying only with microwave energy (70 and 210 W) or hot air–microwave energy (70 and 210 W) resulted in substantial shortening of the drying time. The reduction was 61.8%, 87.3%, 61% and 78%, respectively, of the time to dry with hot air. All starch granules of semolina and hot air dried macaroni displayed a clear “Maltese cross” under polarized light. Starch granules of macaroni samples dried with microwave (70–210 W) and combined hot air–microwave (70–210 W) had irregular shapes but retained birefringence in about half or whole of each granule. The starch gelatinization enthalpies of macaroni samples dried with hot air, microwave alone (70 and 210 W) and combined hot air and microwave (70 and 210 W) drying were lower than that of semolina sample. This confirms that starch is not completely gelatinized during drying.     

Use of dried pumpkins in wheat bread production

Pumpkins belong to the family of Cucurbitaceae. They are classified to Cucurbita pepo, Cucurbita moschata, Cucurbita maxima and Cucurbita mixta, according to the texture and shape of their stems. The nutritional value of pumpkin fruits is high, varies from one species or cultivar to another. Pumpkins are reach in vitamins C, B₁, B₆, K, and in mineral substances. There are no data found about vacuum microwave dried pumpkin application in wheat bread production. The main purpose of the research was to evaluate quality parameters of microwave vacuum dried pumpkins and to verify its application in wheat bread production. Following quality parameters of pumpkins and bread made with pumpkin additive were evaluated: moisture content (oven – drying method), vitamin C content (iodometric), carotenoid content (spectrophotometric), reducing sugars (LVS 252:2000), colour changes (ColorTec- PCM), total fat content (ISO 6492:1999), degree of bread liking (ISO 4121:2003), bread baking loss and dry off. Quality parameters of non dried pumpkins were: content of reducing sugars − 2.40 g⋅100 g^-1, vitamin C – 0.26 g⋅100 g^-1, carotenoids – 0.50 mg % (in dry matter). The technological parameters for pumpkins drying in vacuum microwave drier were used: pressure (70–50 mmHg), speed of tumbler – 6 rpm, one working cycle and three stages. During the pumpkins drying process a decrease in the following parameters was observed: moisture content – 10.5 times, vitamin C content – 2.0 times; increase of yellowness (b*) value – 1.5 times. The optimal dried pumpkin additive to the wheat dough was 10% of the total flour amount. The wheat bread sample with dried pumpkins additive is richer in carotenoids and reducing sugars comparing to control wheat bread sample. The results of sensory analyses using hedonic rating demonstrated that a higher degree of liking was attributed to the bread sample with dried pumpkins additive (7.3) comparing to control wheat bread sample (6.7).     

Anthocyanin infused watermelon rind and its stability during storage

Anthocyanins from Garcinia indica Choisy was impregnated in watermelon rind (WMR) through osmotic dehydration. The impregnation of anthocyanin was enhanced by application of pretreatments like vacuum and sonication (from 24 to 32 mg/100 g). Application of pretreatment during impregnation changes the tissue architecture of the WMR which helps in retaining the infusate during candy making process. The developed product from WMR was highly acceptable w.r.t. texture, taste and appearance. Moisture sorption study indicated that the WMR product was quite stable at ambient temperature upto 75% RH. Storage of the sample in LDPE (low density polyethylene pouches) and PET/LDPE (Polyethylene terephthalate/low density polyethylene pouches) did not show any significant difference in moisture content, anthocyanin degradation, texture, taste and appearance of the product. The WMR product was stable for 90 days at ambient storage conditions.Industrial relevanceThe knowledge provided by this work may be useful the development of new product (watermelon candy) from watermelon rind impregnated with anthocyanin. The extent and rate of infusion of anthocyanin was enhanced by application of pretreatments like vacuum and sonication. The developed product had highly acceptable texture, taste and appearance. The product was quite stable at ambient temperature upto 75% RH in LDPE (low density polyethylene pouches) and PET/LDPE (Polyethylene therapthalate/low density polyethylene pouches) pouches without significant difference in moisture content, anthocyanin degradation, texture, taste and appearance of the product. The WMR product was stable for 90 days at ambient storage conditions. This technique may be helpful in producing foods with enriched bioactive compounds, besides providing diversified products in terms of taste and nutrition.     

Sustainable dehydration of onion slices through novel microwave hydro-diffusion gravity technique

Onion is a semi-perishable commodity having prominent nutritional value. The deterioration of onion during storage can lead to huge amount of post-harvest losses. Shelf life can be increased through drying, which also facilitates transportation, storage, and packaging due to reduced weight and volume. In the present study, a novel microwave-assisted drying technique called microwave hydro-diffusion gravity was investigated for process optimization and compared with conventional drying techniques. Results indicated that 400 W and 14 min of process were the best combination for drying that removed 80% moisture present in slices. The overall drying time of onion slices was significantly reduced (about six times) compared to hot air oven and freeze-drying methods. MHG dehydration prevented the burning of onions and maintained their sensorial attributes especially color and texture. Similarly, MHG in combination with hot air oven consumed only 0.5 MJ energy as compared to 3.24 and 3 MJ energy used by hot air oven and freeze drying, respectively. In short, results proved that MHG technique is much better than conventional techniques in terms of end product quality and process efficiency.Industrial relevanceMicrowave hydro-diffusion technology is optimized for onion drying. This technology will help in reducing the use of energy and will avoid the loss of water soluble components. These bioactive components have great importance in the field of pharmaceutical. Thus, this technology simultaneously dries the product and extracts the valuable components. It will increase the process efficiency and reduce the processing cost.     

Combined effect of γ-irradiation and osmotic pretreatment on mass transfer during dehydration

The combined effect of γ-irradiation (3.0–9.0 kGy) and osmotic pretreatment (10 and 50°B) on dehydration kinetics was studied. The exposure to irradiation pretreatment resulted in an increase in cell wall permeabilization, leading to softening of tissue, which in turn resulted in faster dehydration. The effective diffusion coefficient of water in case of potato during dehydration, considering Fickian diffusion, increased from 2.38 × 10⁻⁹ to 4.14 × 10⁻⁹ m²/s at 9.0 kGy, whereas the osmotic pretreatment resulted in lower dehydration rates due to infusion of solute from osmotic solution, which resulted in lower mass transfer rates. Even though the effective diffusion coefficients decreased from 2.38 × 10⁻⁹ to 1.55 × 10⁻⁹ m²/s (up to 50°B), the osmotic pretreatment improves nutritional, sensorial and functional properties of food without changing its integrity, apart from partial removal of water present in food. The combining of γ-irradiation treatment with osmotic pretreatment resulted in increased mass transfer rates during air dehydration, offering a feasible solution for satisfactorily enhancing the mass transfer rates.     

Microwave irradiation of hazelnuts for the control of aflatoxin producing Aspergillus parasiticus

In this study, the effects of microwave treatment on hazelnuts artificially contaminated with aflatoxigenic fungi were evaluated qualitatively and quantitatively. The physical quality attributes (color, moisture loss, and sensory attributes) of microwave treated hazelnuts were also evaluated. A significant 3-log reduction in Aspergillus parasiticus contamination was observed after 120 s treatment, no or similar changes were observed during the storage of microwave treated hazelnuts under the storage conditions. While taste and odour of microwaved in shell hazelnuts were unaffected during treatment and subsequent storage, microwave treatment duration of 120 s was found to be capable of reducing fungal count of A. parasiticus on in-shell hazelnut without any noticeable change in nutritional and organoleptic properties of nuts. Based on this and the earlier study, a hybrid process is proposed, where UV-C surface treatment and vacuum assisted microwave are combined with air drying to increase the shelf life and control the quality.Industrial relevanceA hybrid industrial process is proposed, where UV-C surface treatment and vacuum assisted microwave treatment are combined to increase the shelf life and control the quality of hazelnuts.     

Effects of ultrasound pretreatments on the kinetics of moisture loss and oil uptake during deep fat frying of sweet potato (Ipomea batatas)

The possibility of ultrasound assisted pretreatments of sweet potato to lower the moisture content and oil uptake during deep fat frying and its effects on the mass transfer rate was investigated. Sweet potato samples prior to frying were immersed in distilled water with ultrasound (UD), osmotic dehydration without ultrasound (OD) and ultrasound assisted osmotic dehydration (UOD). Ultrasound probe having frequency of 28 kHz at 300 W maximum power and time of 30 min was used for the pretreatment. The control (without pretreatment) and the pretreated samples were fried using sunflower oil at temperature of 130, 150 and 170 °C for 2, 4, 6, 8 and 10 min. The first order kinetic model was used for the mass transfer rate for moisture loss and oil uptake. The lowest moisture content was found in fried samples pretreated in UOD and OD while the lowest oil uptake was obtained in fried samples pretreated in UD having 65.11 and 71.47% oil reduction at temperature of 150 and 170 °C, respectively, compared to the untreated sample. The k values of all pretreated samples were higher than that of the untreated at 150 and 170 °C. The highest activation energy for moisture loss was found in untreated samples while the lowest activation energy for oil uptake was found in samples pretreated in UOD. The results from this work proved that ultrasound is a good pretreatment that can be used to obtain a low moisture content and oil uptake during deep fat frying of sweet potato.Industrial relevanceUltrasound is a novel technology that is widely used in the food industries because of its numerous advantages over conventional methods. Its application in the frying of foods could also help in the reduction of oil uptake, thus making safe the consumption of fried foods. The information about frying kinetics could also help in the design and optimization of the process in the food industry.     

Influence of ohmic heating/osmotic dehydration treatments on polyphenoloxidase inactivation,physical properties and microbial stability of apples (cv. Granny Smith)

The combined effect of ohmic heating (OH) and osmotic dehydration (OD) with vacuum impregnation (VI), on the polyphenoloxidase (PPO) inactivation, physical properties and microbial stability of apples stored at 5 °C or 10 °C was analyzed. The treatments were performed using a 65% (w/w) sucrose solution and with ohmic heating at 13 V/cm at 30 °C, 40 °C or 50 °C for 90 min. Examination of the dehydrated samples showed that the water loss and the solid gain were greater with the OD/OH and VI/OH treatments at 50 °C. PPO was completely inactivated by the OD/OH and VI/OH treatments at 50 °C. There was a correlation between the PPO activity, the color change and the browning index of the treated and stored samples; the values for these parameters were stable when PPO was inactivated. The lowest loss of firmness and color was obtained with the VI/OH treatment at 50 °C. The shelf-life of the apples treated with VI/OH at 50 °C and stored at 5 °C was extended to more than 4 weeks. Therefore, the VI/OH treatment at 50 °C was determined to be the best process for dehydrating apples.Industrial relevanceThe aim of this research was 1 to study the combined effect of ohmic heating (OH) and osmotic dehydration (OD) with vacuum impregnation (VI) on the polyphenoloxidase inactivation and microbial stability of osmotically dehydrated apples stored at either 5 °C or 10 °C. Two technologies, OH and OD were performed at 30, 40 or 50 °C with an electric field intensity of 13 V/cm and conventional heating for 90 min. The results showed a correlation between the PPO activity, the color change and the browning index of the treated and stored samples; the values were stable when PPO was inactivated. PPO was completely inactivated by the OD/OH and VI/OH treatments at 50 °C. The shelf-life of the apples treated was extended to more than 4 weeks. Under the investigated conditions, VI/OH treatment at 50 °C and stored at 5 °C may be considered the better minimal processing that preserves the fresh-like properties.