Drying Of Slices Research Articles

Improving the infrared drying and rehydration of potato slices using simple approaches: Perforations and ethanol

AbstractThe objective of this work was use ethanol and perforations as simple approaches to improve the infrared drying and rehydration of potato slices. Perforations were performed to study the effect of promoting routes to capillarity flow, while ethanol was impregnated in the samples to evaluate the effect of Marangoni flow. All pretreatments reduced the drying time compared to control treatment. However, a great time reduction was observed with P + E pretreatment: The synergistic combination of both treatments increased the drying rate in more than four times, reducing both drying time and the necessary energy by 44%. The samples with perforations (P and P + E) increased their rehydration rate as well as the water retention capacity. However, the pretreated samples with ethanol shows poor rehydration properties. Possible mechanisms were discussed. These results show simple approaches to enhance food drying and rehydration.Practical ApplicationsDrying is an ancient unit operation to obtain safe and stable food products. However, some challenges still face food process engineers, such as the long processing time and the low rehydration capacity. Consequently, different technologies have been explored to enhance food drying, such as pulsed electric fields, high pressure, and ultrasound. However, although interesting and effective, some of that approaches can be complicated or even expensive when considering the reality of drying vegetables such as fruits and starchy products, limiting their application. Therefore, this work purposes a simple but efficient technique based on the use of ethanol and the creation of channels through perforations to improve the infrared drying of potato slices, also evaluating the rehydration properties. Our results show that simple operations could be performed to create routes to water flow (through mechanical perforations) combined with drying accelerator (ethanol), improving both drying and rehydration of food products.

DESIGN NEW PROTOTYPE OF AN INDIRECT SOLAR- ELECTRICAL DRYER TO DRY WHITE ONIONS SLICES

In the present research, a new specific model of an indirect solar–electrical dryer for onions slices was designed and constructed at a Zagazig City , Sharkia Governorate, Egypt. Solar dryer consists of solar flat plate air collector with V- corriugated absorption plate. The total area of the collector is 1.75 m2. The size of the drying cabinet is (1.5 × 0.50 × 1) m (height, width and depth). An experiment was conducted to study drying of onions slices 5 and 10 mm. The qualitative analysis for drying of onions slices of 5 mm under three air velocities (1.5,2.2 and 3) m/s, showed that moisture content was reduced from (669.23db to 6.95, 8.69 and 14.41db), (4.27,5.26 and 9.89db) and (2.04, 3.09 and7.52db) for( Tray1, Tray2, Tray3) while it were (19.33,26.90 and 33.51db), (14.41, 21.35 and 27.71db) and (9.89, 16.27 and 21.95db) for onions slices 10 mm respectiviely.The average moisture content of open sun dry were 20.60 and 50.95 db for onions slices of 5and10 mm. The average percentage thermal efficiency for the collector was found to be 33.03, 49.96 and 65.45 % while it were 21.37,15.43 and 10.29% of the dryer for air speed 1.5,2.2 and 3 m/s,, respectiviely.The average percentage value of the collector 34.07,37.59 and 42.69% while it were be24.82, 32.55and 41.85% for the dryer at air velocities were1.5,2.2 and 3 m/s, respectiviely. In order to estimate and select the suitable form of solar drying curves, five different mathematical models, were compared according to their coefficient of determination R2, MBE, RMSE, %E and chi square X2 to estimate experimental drying curves. The Modified page model in this condition proved to be the best for predicting drying behavior of onions slices of 5 and10 mm with (R2 = 0.9961and0.9899) and (X2 = 0.000148 and0.000591). The effective moisture diffusivity (Deff) was obtained using Fick’s diffusion equation and its value varied from 1.72958× 10-9 to 2.37261× 10-9 m2/s and 4.31037× 10-9 to 5.61732× 10-9 m2/s while the value of activation energy ranged from 23.49 to 29.82 kJ/mol k and 16.09 to 18.01 kJ/mol k for onions slices of 5and10 mm. Finally an economic evaluation was calculated using the criterion of payback period which is found very small 1.05 years compared to the life of the dryer 25 years.

Modelo matemático de la capa delgada de piña (Ananas comosus, L.): Experimento en un secador solar tipo invernadero a gran escala

The objectives of this research were two: first to investigate experimentally the behavior of pineappl (Ananas comosus, L.) thin layer drying in a greenhouse-type solar dryer and second to describe the best fitting kinetic and mathematical model taken from literature. A large scale greenhouse dryer designed and installed at Silpakorn University, Nakhon Pathom, Thailand was used to dry slices 1 cm width at temperature range between 25-60 °C with relative humidity between 50-90%. Nine statistical models, either empirical or semi-empirical, were tested in order to validate the experimental data. A non-linear regression analysis conducted by a statistical computer program was applied to evaluate the constants of all the models. The parameter values, root mean square error (RMSE), mean absolute error (MAE) and modelling efficiency (EFF) of the nine models were calculated. Comparison outcomes of two experiments are displayed between the predicted moisture content and the observed pineapple moisture content. Hasibuan and Daud drying model proved to describe the best pineapple solar drying curves. The two experiments were carried out on sunny days, the second experiment on the third day showed cloudiness decreasing the solar radiation. Mathematical models of pineapple drying in a greenhouse dryer have not been found so far in the literature. Drying curves obtained from experiments showed that the constant drying and the falling drying rate periods exist. Nine thin-layer drying models were fitted to two experimental data in order to describe the drying characteristics of pineapple founding that the Hasibuan and Daud model was the best fitting.

Modelo matemático de la capa delgada de piña (Ananas comosus, L.): Experimento en un secador solar tipo invernadero a gran escala

The objectives of this research were two: first to investigate experimentally the behavior of pineappl (Ananas comosus, L.) thin layer drying in a greenhouse-type solar dryer and second to describe the best fitting kinetic and mathematical model taken from literature. A large scale greenhouse dryer designed and installed at Silpakorn University, Nakhon Pathom, Thailand was used to dry slices 1 cm width at temperature range between 25-60 °C with relative humidity between 50-90%. Nine statistical models, either empirical or semi-empirical, were tested in order to validate the experimental data. A non-linear regression analysis conducted by a statistical computer program was applied to evaluate the constants of all the models. The parameter values, root mean square error (RMSE), mean absolute error (MAE) and modelling efficiency (EFF) of the nine models were calculated. Comparison outcomes of two experiments are displayed between the predicted moisture content and the observed pineapple moisture content. Hasibuan and Daud drying model proved to describe the best pineapple solar drying curves. The two experiments were carried out on sunny days, the second experiment on the third day showed cloudiness decreasing the solar radiation. Mathematical models of pineapple drying in a greenhouse dryer have not been found so far in the literature. Drying curves obtained from experiments showed that the constant drying and the falling drying rate periods exist. Nine thin-layer drying models were fitted to two experimental data in order to describe the drying characteristics of pineapple founding that the Hasibuan and Daud model was the best fitting.

Ion wind from yield corona discharge and its application to drying of Turmeric slices (Curcuma domestica Val)

Turmeric (Curcuma domestica Val) is a native Indonesian medicinal plant. Drying sliced turmeric is an important process to get the basic herbal ingredient of a durable herb. The purpose of this study was to apply the ion wind of corona discharge to dry the turmeric slices and its characterization.The corona discharge is generated by using a pin-three of ring electrode which is subjected to a high voltage DC with positive pin electrode polarity and a negative concentric three-ring electrode. The ion will flow from the pin electrode to the three-ring electrode and a portion will be forwarded through the gap between three concentric rings. The drying of the turmeric slices is carried out at distance between electrodes which is constant. It is placed just below the concentric three-ring electrode and the distance between electrode is 2 mm. The drying of turmeric slices is time-varying 5 to 65 minutes with a time interval of 5 minutes. The study result of drying of turmeric slices is obtained drying rate and mass shrinkage is inversely proportional to a drying time. While the efficiency of drying is inversely proportional to the drying rate.

Thin layer drying kinetics of Banana var. Monthan (ABB): Influence of convective drying on nutritional quality, microstructure, thermal properties, color, and sensory characteristics

AbstractBanana with good amount of resistant starch (RS) offers greater benefit to human health. Studying the dehydration mechanism of the raw banana slice is very important for subsequent processes and quality of the product. Thus the study was aimed to investigate the influence of varying temperatures viz., 45, 55, and 65°C in a convective dryer on thin layer drying kinetics and to infer their influence on the rheological properties coupled thermal and sensory quality. Time for reducing the moisture content from the initial 71.2 ± 0.2% to a final 4.66–6.13% was found to be 270, 210, and 150 min for the drying temperatures 45, 55, and 65°C, respectively. Moisture ratio decreased exponentially with an increase in drying time. Page and logarithmic models obtained highest r2, lowest chi‐square values and least root mean square error and better reflected drying mechanism of banana slices. Improved rehydration ratio (1:2.4) and RS content (36.26%) was observed with the drying temperature of 55°C. Higher water absorption capacity (WAC) was observed in 55°C (4.86%). Swelling power of the flour was maintained to 4–6% till 70°C but it reached to 22% with the increase in temperature to 90°C. Thermal properties and microstructure of flour differed significantly with the temperatures. The lower value for whiteness index with low temperature drying reflected the better drying than at higher temperatures. Dehydration at 55°C was superior with nutrients like ascorbic acid. The banana flour had the rod shaped starch granules and traces of protein in its surface as evidenced. Irregular spherical shape, surface dents, and shrinkages were observed in powders dehydrated with high temperature (>65°C). Equilbrium relative humidity (ERH) studies revealed that 13.27 and 15.23% were the danger and critical point, respectively, for the banana flour. Descriptive sensory scores of the banana flour endorsed that dehydration at 65°C was found superior to other temperatures.Practical applicationsBanana flour offers greater potential to increase the resistant starch (RS) content in the food products besides adding minerals and basic nutrients. Drying process should retain the characteristics of fresh fruits by minimizing the cellular and structural changes during the drying. Mathematical modeling offers scope to set the variables which are influencing the drying of banana slices. The dried banana flour could be a replacement or supplement for various formulations. With the better physical properties like swelling capacity and enthalpy along with high RS, banana flour allow the formation of low bulk, high‐fiber products like pasta, noodles, and healthy functional foods with improved sensory descriptors. Banana flour‐based enterprises could be started in places where banana is cultivated and large sum of produced bananas are getting wasted due to poor postharvest management.

Mathematical modelling of far-infrared vacuum drying of apple slices

In this study, a mathematical model of far-infrared vacuum drying of shrinkage body is presented. The system of two coupled PDE for heat and mass transfer with appropriate initial and boundary conditions are solved numerically with used of the finite difference method. On the basis of the numerical solutions a computer program for calculation of temperature profiles, transient moisture content, mid-plane temperature, and the volume averaged moisture content changes for different drying regime was developed. For verification of a mathematical model a series of numerical calculations were carried out with experimental conditions similar to those in the realized experiments of far-infrared vacuum drying of apple slices. Very good agreement between the experimental and numerical temperature and moisture content changes during the drying was obtained.

Effect of air recirculation and heat pump on mass transfer and energy parameters in drying of kiwifruit slices

The simultaneous transfer of mass and heat in the drying process has turned it into a complicated process with respect to mass transfer and moisture removal. A hot-air dryer equipped with an auxiliary heat pump and air recirculation system was used to dry kiwifruit slices at three different temperatures (45, 55 and 65 °C) to determine mass transfer and activation energy using two different models, namely Dincer-Dost and Crank's models. When the heat pump was on, compared with 45 °C and air recirculation rate (0%) at higher temperature (65 °C) and higher air recirculation rate (100%) the drying rate constant increased from 1.113 × 10−4 s−1 to 2.357 × 10−4 s−1and the effective moisture diffusion coefficient increased from 1.94 × 10−9 m2/s to 7.12 × 10−9 m2/s. When the heat pump was off, both parameters decreased with increasing recirculation (from 0 to 100%) and increased with rising the temperature (from 45 to 65 °C). When the heat pump was turn off and on, at 65 °C and 100% recirculation the change in the range of activation energy, convective mass transfer coefficient, specific energy consumption, drying efficiency and specific moisture extraction rate (SMER) were 14.04–20.39 kJ/mol, 4.12–8.55 × 10−7 m/s, 1.08–1.49 kWh/kg, 9.84–12.15% and 0.11–0.15 kg/kWh, respectively.

Optimization of convective drying by response surface methodology

In this work, response surface methodology (RSM) is applied to state an optimized system for convective drying of apple slices using desirability function. The interaction of the independent parameters including air temperature (T = 70–90 °C), air velocity (V = 4–5 m/s), and apple slice geometry (G = circle, square, and triangle) with the dependent variables consist of drying time, energy consumption, and shrinkage is determined. Minimum drying time, energy consumption and shrinkage is regarded as the optimizing drying conditions of apple slices. Experimental results are adapted by a second-order polynomial model where analysis of variance is utilized to define model compatibility and optimal drying conditions. The optimal conditions of combined optimized responses were 90 °C inlet temperature, 5 m/s inlet velocity, and square geometry which designated by maximum desirability function (D = 0.781). The air temperature had a notable influence on total responses, but the effect of air velocity and apple slice geometry were important in shrinkage. Generally, the results marked that a greater desirability value could be obtained in the higher air temperature and higher air velocity with the square geometry.

Influence of microwave and microwave‐convective drying on the drying kinetics and quality characteristics of pomelo

The present study investigated the effects of microwave (90 and 160 W) and combined microwave‐convective (90 W–55 °C, 90 W–65 °C, 90 W–75 °C, 160 W–55 °C, 160 W–65 °C and 160 W–75 °C) drying techniques on the drying kinetics, color parameters (L∗, a∗, b∗, C, α° and Δe), total phenolic content (TPC), and antioxidant capacity (ATC) of pomelo samples. The drying data were fitted to 10 typically used thin‐layer drying models to select a suitable model for drying of pomelo. Comparing the statistical parameters of applied models, the Diffusion Approach, Midilli et al., and Page models were found to be the best‐fitting models in describing drying kinetics of the pomelo samples. It was observed that the drying temperature and/or microwave power changed significantly the all color parameters, TPC, and ATC. The combined microwave‐convective drying resulted in shorter drying times with higher drying rates and high‐quality dried pomelo samples. PRACTICAL APPLICATIONS: A significant improvement in the quality retention of combined microwave‐convective drying of pomelo slices was achieved. This piece of work will provide a novel method to produce microwave‐convective‐dried pomelo fruits with a significantly improved product quality. A practical implication is that drying of pomelo slices with an optimum condition by combined microwave‐convective process can be used to get a high‐quality product with a higher ATC, TPC, and color.

Experimental investigation and numerical modeling of heat transfer during solar drying of carrot slices

The knowledge of heat transfer analysis during drying is critical for process design, quality control and energy saving. In this study, convective heat transfer coefficient, hc during solar drying of carrot slices was determined experimentally. Carrot slices of 0.03 m diameter and 0.005 m thickness were dried in laboratory scale natural convection direct, indirect and mixed mode solar dryers. It was observed that samples dried in mixed-mode solar dryer achieved higher values of $$ \overline{h_c} $$ (24.95 W/m2 °C) followed by indirect (15.80 W/m2 °C) and direct solar dryer (13.52 W/m2 °C). Heat transfer correlations were developed during drying of carrot slices in different dryers through standard dimensionless numbers in the form of an equation Nu = C(Ra)n. The results of uncertainty analysis in the $$ \overline{h_c} $$ was observed to be in the range of 0.073%–2.7%. A numerical 2D finite element model was developed to analyse the temperature distribution inside carrot slices during drying period by using COMSOL Multiphysics simulation program. The numerical results were compared against experimental data and the outcome suggested that the sample temperatures are in close agreement with the model predictions. Lower values of statistical parameters showed better acceptability of the simulation model for predicting solar drying behaviour of carrot slices.

Modeling and simulation of moisture transfer during solar drying of carrot slices

AbstractCarrot slices of 0.03 m diameter and 0.005 m thickness were dried in direct, indirect and mixed mode type natural convection solar dryers. Thin layer drying behavior of carrot slices was studied using 10 empirical and semi‐empirical mathematical models. Wang and Singh model described the drying behavior of carrot accurately with maximum values of coefficient of determination (R2) and minimum reduced chi‐square (χ2), and root mean square error (RMSE). The effective diffusivity (Deff) and convective mass transfer coefficient (hm) of carrot slices ranged from 2.59 × 10−8−6.36 × 10−8 m2/s and 3.15 × 10−7 to 4.28 × 10−7 m/s, respectively, with maximum values obtained for mixed mode solar dried samples followed by direct and indirect solar dried samples. The diffusivity of carrot slices dried in direct, indirect and mixed‐mode solar dryer were expressed as a function of temperature using Arrhenius relation. Finite element model was developed using COMSOL Multiphysics software to simulate moisture ratio during drying. The developed model predicted the transient moisture migration phenomenon inside the samples precisely during the drying process.Practical applicationsThe ever increasing worriment on climate change and growing demand for enactment of clean energy technologies in food industries is the motivation for investigating the solar drying behavior of carrot slices. It is well known that the physico‐chemical and sensorial changes during drying are very much dependent on the moisture content of food product. In this regard, proper understanding and controlling of the solar drying process by accurately predicting moisture distribution inside the product will result in superior quality dried products. Moreover, mathematical models will assist in predicting the drying behavior of food product by analyzing the influence of process parameters and will be helpful to minimize the cost of drying process and deterioration of quality attributes of the product. The use of solar dryers is a proven technology and the food industry should promote its practical applications in food processing sector.

Application of artificial neural network method for prediction of osmotic pretreatment based on the energy and exergy analyses in microwave drying of orange slices

In the present study, artificial neural network (ANN) method was applied for predicting osmotic pretreatment based on the energy and exergy analyses in microwave drying of orange slices. For this purpose, the oranges were cut into slices with a thickness of 4 mm and treated with salt (NaCl) and distilled water solution (7% by weight) for 30, 60, and 90 min as osmosis pre-treatment. Then, they were dried in three replicates using a microwave dryer and at three powers of 90, 360, and 900 W. The statistical analysis results showed that the osmosis time is significant for the energy efficiency and exergy efficiency and specific exergy loss at 1% level. The highest energy and exergy efficiency was observed at 900 W and in the osmosis time of 90 min. The highest energy and exergy efficiency was observed at 42.1% and 31.08%, respectively. The maximum exergy loss was seen at 360 W and osmosis time of 60 min. The osmosis time did not affect the specific energy loss. The microwave power was statistically significant for all the parameters (energy and exergy) such that with increasing the microwave power, the energy and exergy efficiency increased, while the specific exergy and energy loss decreased. Overall, with increasing osmosis time and microwave power, the energy and exergy levels of the microwave dryer increased. The maximum coefficient of determination (R2) in a network containing 6 neurons in the hidden layer was 0.999 for energy efficiency, R2 = 0.871 for specific energy loss, R2 = 0.999 for specific exergy loss, and R2 = 0.972 for exergy efficiency. This amount was seen in a network containing 4 neurons in the hidden layer.

Ultrasound as pretreatment for drying garlic slices in microwave and convective dryer.

The effects of ultrasound pretreatment (US) before hot air drying (HAD) and microwave drying (MWD) of garlic slices were investigated. For this aim ultrasonic bath at 30°C for 30min (35kHz), microwave oven at 540W power and tray dryer at 60°C and with 1.0m/s air flow rate were used to reach the final moisture content of 5%. Drying rate increased in the US + HAD and the US + MWD groups by 19.30% and 13.82% respectively in comparison with control groups. The effective moisture diffusivity (Deff) of garlic slices were calculated from Fick's diffusion model for the HAD, US + HAD, MWD and the US + MWD groups as 1.420 × 10-10, 1.826 × 10-10, 1.177 × 10-8, 1.363 × 10-8 m2/s respectively. The rehydration rates increased, and bulk densities were decreased in the US + HAD and the US + MWD compared to the control groups. The color values were significantly affected after ultrasound pretreatment. Redness, and yellowness increased most in the US + HAD group.

Batch drying of sliced tomatoes at specific ambient conditions

Abstract In this work, drying of tomato slices was studied in a laboratory scale batch dryer working at conditions specific for geographical locations with low ambient pressure and low relative humidity of air. Tomato is a perishable farm product with high moisture content. Despite their high value, tomatoes are subjected to wastage and spoilage during their seasonal period; to last longer after harvested, they need to be treated by drying. Drying is one of the most widely used methods of tomato preserving for a longer period of time. This study involves experimental work on tomatoes drying in a tray laboratory batch dryer with the dimensions of (490 × 330 × 310) mm, a load cell-force sensor (range: 0–5 kg), fan (speed: 0–2500 rpm), air flow sensor (0–150 l/min) and a temperature and humidity monitoring system. This study was aimed at the development of a suitable drying method for the production of dehydrated agricultural products under specific air properties and climate conditions such as low ambient pressure and low relative humidity. During the experiment, the average ambient pressure was 82 kPa, and the average relative humidity of air was 20 %. Drying characteristics of tomato slices were determined at three temperature levels, namely: 50 °C, 60 °C and 70 °C,and three air flow rates: 30 l/s, 40 l/s and 50 l/s, for each temperature level. In this study, the effect of temperature, air flow rate, and ambient conditions on the drying rate of tomato slices were studied. The results indicate that during the experiments, tomatoes were dried to the final moisture content of 32.2 % from 92 %. Drying time at 50 °C, 60 °C and 70°C, and air flow of 30 l/s was 17.80 h, 15.80 h, and 14.08 h, respectively. For the air flow rate of 40 l/s, the drying time was 15.0 h, 12.9 h and 11.7 h and for the air flow rate of 50 l/s, the drying time of tomato slices was 14.0 h, 11.6 h and 10.2 h, respectively.

Influence of applied time and power of ultrasonic pretreatment on convective drying of potato slices.

Ultrasound is a novel technology that can be applied as a pretreatment for the convective drying in order to reduce its undeniable shortcomings. The objectives of the present study are to ascertain the influence of sonication time (10, 20, and 30min) and sonication power (100 and 300W) on the performance of drying potato slices with regard to the drying kinetics and energy efficiency as well as the final product quality. The results showed that the application of ultrasound pretreatments significantly increased the drying rate of potato slices during the initial period of the drying process. Furthermore, ANOVA showed that the decrease in the sonication time and power gave rise to a significant reduction in drying time, specific energy consumption (SEC), and shear strength. In addition, compared to the control (pure convective drying), ultrasound pretreatments reduced the drying time, SEC, and the shear strength of dried potato slices.

Infrared drying of kiwifruit slices

ABSTRACTThe effect of different infrared powers on drying of kiwifruit slices was investigated in infrared dryer at 50, 62, 74, 88, and 104 W infrared powers. Results showed that drying, rehydration, and color behaviors of kiwifruit slices were greatly influenced by infrared power. Six different thin-layer drying models were evaluated for moisture ratios using nonlinear regression analysis. The results of regression analysis indicated that the Midilli & Kucuk model is the best to describe the drying behavior with the lowest P, χ2, RMSE and highest R2 values. The Fick’s diffusion model was used to calculate the effective moisture diffusivity (Deff) of kiwifruit slices. The value of Deff varied from 9.43 × 10−10 to 2.58 × 10−9 m2/sec. The activation energy was estimated by a modified Arrhenius type equation as 2.9 kW/kg.

Modeling of drying and ameliorative effects of relative humidity (RH) against β-carotene degradation and color of carrot (Daucus carota var.) slices.

Drying and β-carotenes retention kinetics were predicted using models in relative humidity (RH) drying condition. This was achieved by drying carrot slices using RH-convective hot-air dryer at 60, 70 and 80°C under RH (10% 20% and 30%) conditions at 2.0m/s air velocity. Three mathematical models describing thin layer were compared to their goodness of fit in terms of coefficient of correlation (R2), root mean square error (RMSE) and reduced Chi square ( ). The Wang and Singh model could satisfactorily describe RH-convective drying of carrot slices with R2, RMSE and in the ranges of 0.996-0.999, 5.4 × 10-4-9.4 × 10-4 and 0.0150-0.03353 respectively. The results reveal that a range of 3.61-8.2% retention of β-carotene was observed for every 10% increase in RH in various drying air temperature. In summary, higher temperatures were mainly responsible for β-carotenes degradation however this can be mitigated when drying is conducted under higher RH.

Low pressure superheated steam drying of onion slices: kinetics and quality comparison with vacuum and hot air drying in an advanced drying unit.

Pungency is important characteristics of onion and during processing it is generally reduces. Low pressure superheated steam drying (LPSSD) is gaining importance due to energy and product benefits. It results in better retentions of bioactive components. So, in current study onion slices were dried using low pressure superheated steam, and compared with vacuum and hot air drying at different temperature in NIFTEM advance drying unit. Among the selected models, Page's model gave a better prediction and satisfactorily described drying characteristics of onion slices. The Activation energy was found to be 41.87kJ/mol in LPSSD. Quality of product, i.e. retention of color, rehydration ratio, thiosulphinate content, total phenol content and antioxidant activity, were better at 70°C using LPSSD, at 60°C using VD and HAD, as compared to other drying temperature in respective drying technologies used. Significant differences in quality of the dried product were also observed due to drying temperature in different drying techniques.

Ethanol and ultrasound pre-treatments to improve infrared drying of potato slices

Abstract Ethanol and ultrasound (US) were applied as pre-treatments to improve the infrared (IR) drying of potato slices. Pre-treatments included Control samples (Without any pre-treatment), samples immersed in ethanol (Ethanol treated) and treated with US using ethanol (Ethanol + US) and water medium (Water + US). Effects on microstructure, drying, rehydration, and viscoelasticity were studied. Microstructure analyses suggested that ethanol affected the potato cell wall. The Water + US pre-treatment impacted the starch granules dispersion inside cells. However, higher modifications were observed when Ethanol + US was applied. Compared to the Control, all pre-treatments decreased the drying time, while Ethanol + US provided the highest reduction. In contrast, a slight decrease in rehydration properties was observed. The dried and rehydrated samples presented similar viscoelasticity among them but differed significantly with the in-natura (fresh potato) samples. Possible mechanisms were discussed. The results open new perspectives about an innovative method to improve drying.