Objective: Potato is the fourth important food crop after wheat, rice and maize. Shrinkage of food materials has a negative consequence on the quality of the dehydrated product. The main objective pursued in this paper is to investigate the shrinkage amount of potato slices during drying process using vacuum-infrared method.Methods: In this work, the effect of the infrared radiation powers (100, 150 and 200 Watt) and absolute pressure levels (20, 80, 140, 760 mmHg) at different thickness (1, 2 and 3 mm) on bulk volumetric shrinkage were investigated.Results: Data analysis showed that shrinkage percentage decreased with decrease of sample thickness and increase of infrared power. It was found that either thickness or infrared power had any significant effects (P<0.01) on shrinkage of potato slices in this drying system. The regression model is a three-variable linear that Coefficient of determination is 0.532 and implies that the model can explain 53.2 % of the volume ratio changes

Introduction: Dunaliella salina unicellular alga belonging to the Chlorophyceae family has been introduced as a extensive source of carotenoids (Zenouzi et al., 2013; Mendiola et al., 2008). The Carotenoids are strong antioxidants and bright pigments, and for this reason are used as human food and aquatics diets pigments (Denery et al., 2004). Investigations have shown that increasing the drying temperature will decrease the volatile and phenolic compounds of algae, and by decreasing the drying temperature, the amount of these compounds in the algae will be increased (Ling et al., 2015). According to the other research, the amount of beta-carotene after drying has been greatly decreased in conventional drying methods. (Ihns et al., 2011; Karabulut et al., 2007). The supercritical drying is an extraction process, that the supercritical fluid is the extraction solvent and water is the soluble substance (Brown 2010). The advantage of this drying method is that it is possible to prevent vapor-liquid contact in the homogeneous phase. For this reason, the tensile stress caused by the capillary that occurs during the air drying process does not exist in supercritical drying, and protects the structure of the material (Namatsu et al., 1999). In addition, carbon dioxide easily reached to critical temperature (31.1°C), so operating at low temperature (significantly lower than common dryers) prevents thermal damage (Brown 2010). Also Ultrasonic power at low frequency (20 to 100 kHz) is used for bacterial inactivation, improving process speed, heat and mass transfer, and water removal. In addition, the phenomenon of cavitation occurs in this composition and it causes an increase in the micro-mixing and communication between the solvent and microorganisms, and as a result, water exit and bacterial inactivation are improved (Morbiato et al., 2019). Non-contact ultrasonic, such as airborne processes, in which there is no contact surface or liquid to connect the transducer and the desired surface, can be used in various applications, including food drying. This system in combination with the other methods can overcome the limitations. For example, high temperature drying can damage the components of the material (color, texture, volatile compounds, etc.), while the combination with airborne can decrease the temperature and thus reduce the drying time, and the quality of the product and its nutritional ingredients should be maintained. The present work focused on investigation of the kinetics and drying rate of the Dunaliella salina algae by the supercritical carbon dioxide method in combination with airborne ultrasonic power, as well as the modeling of drying using mathematical and response surface methods.Materials and methods: The studied algae in this research was Dunaliella salina, which was obtained from the Artemia & Aquaculture Research Institute of Urmia University. In this research, 2.8 grams of algae paste with a thickness of 3 mm was placed in the drying vessel and methanol was added directly to the sample as a co-solvent. And the Suprex (MPS/225) in combination by airborne ultrasonic was used. The vessel that used in devise was made by stainless steel 316. Face center design consisting of 20 experimental runs with six replications at the central point was utilized to determine the effects of three independent variables in three levels: -1, 0, +1. The independent variables were Pressure at three levels (80, 110, 140 bar), temperature at three levels (40, 50, 60 °C) and airborne ultrasonic power at three levels (0, 20, 40 w) and the samples were weighed in dynamic mode in 30 minute intervals. The software of Design-Expert 13.0.5 (Stat-Ease, Minneapolis, MN, USA) was used for design experiment, data analysis and surface responsible diagram.Results and discussion: In 80 bar of pressure, the reduction of moisture content was constant for 150 min in temperature of 40 °C and without ultrasonic power and then was reduced. In other treatment the reduction of moisture content was continued for 120 min. In this pressure, after 180 min the moisture content in 40°C reached to 52% and in 60 °C and 40 w ultrasonic power reached to 31%. In 110 bar of pressure, the lowest moisture reduction was reached to 44% at 40 °C and 20 w. and the highest moisture reduction was 33% at 60°C and 20 w. The moisture reduction was constant for 120 min in temperature of 40°C and 20 w, while in temperature of 60°C and 20 w, the moisture content was constant for 90 min. in pressure of 140 bar, the maximum of moisture content was in 40 °C and without ultrasonic power and the minimum moisture content was 22% in 60 °C and 40 w. These results are due to the low viscosity, high diffusion rate and the near-absence of surface tension of the supercritical fluid. These properties allow the supercritical fluid to easily penetrate into the micro pores and surface and internal cells. Furthermore, new pores or channels could have been made by the supercritical fluid (Lee et al., 2011). The Midilli et al. model was the best ftting model. The highest values of R2, and the lowest values of SSE and RMSE obtained for the Midilli et al. model were 0.99925, 0.00023 and 0.0004, respectively. In RSM modeling, the results show that the changes of pressure, temperature and ultrasonic power had significant effect on moisture ratio in weighting time. While the interaction effect of independent variables had no significant effect on the factors. and the model has been investigated linearly. In the drying rate curve, at the beginning, drying was increased with a great slope, and then the curve decreases with a lower slope. The lowest drying rate at a pressure of 80 bar was occurred, in temperature of 40°C and the without ultrasonic power. And the highest drying rate was observed, in 60 °C and 40 w. the lowest drying rate in pressure of 110 bar was occurred in 40°C and 20w.Conclusion: According to the results, the supercritical carbon dioxide method in combination with airborne ultrasonic power was suitable for dunaliella salina drying at low pressure and temperature. But in order to reduce the drying time and final moisture content, the pressure, temperature and ultrasonic power can be increased.

Drying kinetic of quince (Cydonia oblonga) fruit slices with the thickness 3, 5 and 7mm were dried at three temperature 60, 70 and 80oC using convection hot air dryer studied. For evaluating drying kinetic of quince fruit slabs used from effective diffusivity coefficient (Deff) parameter. Deff changed in 2.77×10-8 – 8.12×10-8 m2/s that amount of Deff in various thickness had difference significant (P<0.01). For mathematical modeling used from among 10 different models with which these models were compared, the coefficient of determination (R2), Mean relative percent deviation (MRPD), Root mean squares error (RMSE) and reduced chi-square (c2) parameters and finally the chosen model, with the best compatibility from drying process was midlli model.

The drying characteristics of unbleached Kraft pulpboard have been studied in convective drying equipment under different hot air temperatures and velocities. In this work, the drying experiments were conducted in the range of 80-100℃ and 1. 87-2. 48m/s, respectively. The results indicated that high air temperature and velocity are beneficial to increasing drying rate and decreasing drying time. Ten thin-layer drying models were evaluated to describe the drying kinetic of unbleached Kraft pulpboard for its suitability. Based on the statistical analysis, the Yun model could predict the pulpboard drying kinetic better than others in terms of fitting performance. Through calculation and fitting, the effective moisture diffusivity varied from 2. 077 10-10 to 3. 631 10-10m2/s over the investigated temperature range and the average activation energy for moisture diffusion was 22. 818kJ/mol.

Introduction: Drying is one of the oldest methods for preservation of agricultural products and it is aimed and tried to effectively increase the drying rate by heat and humidity transfer.Materials and Methods: In this study, drying process for quince fruit slices with 3, 5 and 7 mm thickness at 60–80°C to reach a maximum of diffusion effects (Deff) and decrease drying time using response surface methodology have been optimised.Results: The results showed that Midli model had minimum amounts of RMSE, MRPD and c2 and a maximum of R2. Optimization of drying process indicated that the application of 71°C for 7mm thickness had the most diffusion effect with least drying time. Conclusion: Hot air drying method removes the moisture from the fruit and generally is suitable for drying quince fruit.

In this study, a hot air-microwave dryer equipped to imaging system was used for modeling of drying kinetics of strawberry slice. The experiments were conducted at three levels of hot air temperature of 50, 60, and 70 C with 0. 5 m/s air velocity as well as three levels of microwave power density of 2. 7, 3. 5 and 5 W/g with 40 C air temperature. In order to estimate the drying curve, seven different thin layer mathematical drying models were fitted to experimental data and according to the obtained results, Page’ s model could satisfactorily describe the drying curve with highest R2 value (0. 9945-0. 9987) and lowest RMSE (0. 0097-0. 0213) of microwave data and Logarithmic model could describe the drying curve with highest R2 value (0. 9945-0. 9987) and lowest RMSE (0. 0097-0. 0213) of hot air drying data. Also Δ E color kinetic demonstrated that highest color changes were happened in the initial drying stage and remained constant in the other drying stage in microwave and finally the Δ E value changed in any power density near 10. But in hot air drying the color changes occurred progressively during drying process and reached upper than 15.

Introduction: Broccoli is a rich source of minerals such as potassium, phosphorus, calcium and sodium. Additionally, broccoli provides vitamins, especially vitamin C, vitamin A and folic acid. In addition, it has been reported as a one of the main sources of natural antioxidants such as phenolic compounds, glucosinolates and isothiocyanates. Because of the high corruptibility of broccoli, it is very important to keep its effective components as much as possible. Drying is the most common method for enhance the shelf life of food products. The foam mat drying method was developed in the 1960s. This method involves mixing pulp or fruit and vegetable juices with a foaming agent and a foam stabilizer to prepare a stable foam that is spread and dried on a tray, then the dried product is ground to a powdered product. In this technique, due to increasing of the material area, the drying rate is high. Convective hot air is generally chosen as the drying medium of the foam mat method. The disadvantage of this drying method is the poor heat transfer of the air around the foam. Microwave heating, with its ability to produce volumetric heat inside the material, can overcome this limitation. Microwave energy can penetrate directly into the foamed pulp to evaporate moisture inside the foam,continuously generated vapors stimulate foam bubbles, which expand the evaporation level and speed up the drying process even more. There are many strategies to improve the quality of microwave-dried products, such as combining microwave and convective hot air, intermittent drying, and microwave-vacuum drying. The combination of microwave and convective hot air has been used successfully for a number of agricultural products such as garlic, grapes, carrots, kiwis and blueberries. The combination of these two methods has a shorter drying time than single convective hot air, and the final sample will have higher quality. Material and methods: Broccoli was purchased from the local market of Tabriz and its enzymes were inactivated by blanching in 90°, C hot water for 4 minutes and then immediately cooled in ice water for 5 minutes. It was then pulped and stored in a freezer at minus 18°, C until drying experiments were performed. Broccoli pulp was first thawed before drying experiments. 3% (w/w) egg white as foaming agent and 0. 5% (w/w) methyl cellulose solution as stabilizer agent were used to prepare the broccoli foam. The foam was spread to a thickness of 5 mm on a glass plate and then it was dried with different drying methods including convective hot air (at 40°, C and air velocity of 1m/s), microwave (90w) and combination of microwave and convection as pre and post treatment (MWCHA and CHA-MW). The moisture content of samples was measured at 10 minute intervals (in CHA method) and at 2 minute intervals (in MW method), and the drying process was terminated when moisture content of the samples reached 0. 04 g water/g dry solids. The produced powders were then scratched off by a special spatula and were immediately ground in a crucible in order to prevent further moisture absorption and kept in the refrigerator until further testing. Results and discussion: The combination of microwave and convective hot air (in both pre and post treatment) compared to microwave method, had lower effective moisture diffusivity coefficient and drying rate but higher energy consumption. The average of moisture content and moisture ratio was also affected by drying method and the combination of microwave and convective hot air (MW-CHA and CHA-MW). In MW-CHA, the average of moisture content and moisture ratio was higher than MW and CHA drying method, but in CHA-MW, the average of moisture content and the moisture ratio was the lowest obtained. Among the four drying methods, the hot air drying method had the lowest drying rate due to the hardening of the surface due to the loss of surface moisture. This phenomenon slows down the exit of moisture from the product and reduces the drying speed. In the microwave method, in the early stages of drying, the samples have high humidity. High humidity is the main reason for volumetric heating in the microwave method, in that bipolar molecules absorb a significant part of the microwave energy and lead to an increase in product temperature and rapid transfer of moisture to the surface. The flow of water vapor from the inner parts to the surface of the product creates a porous structure, resulting in faster evaporation of moisture, and ultimately increases the drying speed. Therefore, the highest drying rate was observed in the microwave drying method. The passage of time and the reduction of moisture in the product reduce the absorption of microwave power and, as the drying process progresses, leads to a slowdown in the drying speed. Compared to the combined drying methods, due to the prevention of surface drying in the microwave-hot air (MWCHA) method, this method had a higher drying rate than the hot air-microwave (CHA-MW) method and hot air alone. The mean drying time were from low to high: microwave (48 minutes), hot airmicrowave (70 minutes), microwave-hot air (102. 16 minutes) and hot air (120 minutes), respectively. The effective moisture diffusion coefficient of all four drying methods was significantly different from each other at the level of 5% probability and were from high to low related to microwave, hot air-microwave, microwave-hot air and hot air, respectively. The high effective diffusion coefficient of moisture in microwave drying is related to its volumetric heating mechanism. In a microwave field, the core temperature of the product rises, creating a pressure difference between the core and the surface of the product (Junkoria et al. 2017), creating a more porous structure and more vapor permeability, and ultimately increasing the effective moisture diffusion coefficient due to faster heating. (Dehghani Khiavi et al. 1399). Hot air method has the lowest effective moisture diffusion coefficient value, due to the low air temperature (40°, C), because there is a direct relationship between the effective diffusion coefficient of humidity and temperature, and on the other hand, the hot air energy for moisture exit is lower than other methods, so the effective moisture diffusion coefficient in this method is at its lowest value compared to other drying methods, and this is the reason for the slower drying speed in this method. In the combination of hot air and microwave, when hot air (as a pre-treatment) is applied at the beginning of the process, the drying and dehumidification process is controlled by the microwave and the effective moisture diffusion coefficient in this method are higher than hot air. When hot air is applied at the end of the process (as a post-treatment), the drying process is controlled by hot air and the effective moisture diffusion coefficient are lower than hot airmicrowave, but higher than hot air alone. Conclusion: According to the least energy consumption, drying time, moisture content, moisture ratio and the most effective moisture diffusivity coefficient and drying rate, MW and CHA-MW were the optimum methods for drying the broccoli foam (with 0. 88 and 0. 7 desirability, respectively). The use of microwave energy as a pretreatment for hot air (CHA-MW) was able to significantly reduce the average moisture content and moisture ratio compared to the microwave method alone, and produce a powder with lower moisture content and longer shelf life.