Background and objectives: Kashk is a milk product that has been commonly prepared in most parts of the Middle East and especially in various parts of Iran since ancient times. Kashk is usually prepared in two forms: liquid or paste and dry. The basis of dry Kashk is milk, which is obtained by boiling, concentrating and drying yogurt, buttermilk and fermented buttermilk. The drying method has a great impact on the sensory and appearance as well as microbial properties of the product. For this purpose, Kashk was studied using different methods of oven, hot air, freezing and solar drying and its physicochemical, sensory and kinetic drying properties.Materials and Methods: In this study, after producing Kashk from pasteurized milk, four methods were used to dry Kashk: solar drying, hot air tunnel, oven, and the finally freeze-drying method. In order to investigate the effect of drying method on physicochemical properties of Kashk, factors such as solubility, acidity, moisture, fat, color and drying kinetics were investigated. To investigate the drying kinetics, moisture fraction (MR) was selected as a dimensionless factor for process analysis and appropriate fit was selected using empirical equations (Table 2-2) and MATLAB software. The experiments were performed in 3 replicates. Statistical analysis was performed using SAS 9.1 software and LSD test at a significance level of 5%.Results: During drying, acidity increased compared to the original sample, and the highest acidity with a value of 0.199 g/g of dry matter was related to the solar method and the lowest with a value of 0.123 g/g of dry matter was related to the freezing method. Also, in the oven and hot air methods, the type of method and temperature did not have a significant effect on the increase in acidity. The results show that the type of drying method is effective on the solubility of the whey, and among the different drying methods, the freezing method had the highest solubility with a value of 13.33. On the other hand, in the oven and hot-air drying methods, solubility also increases with increasing temperature. The L* index of the freeze-dried Kashk samples increased compared to the original sample, and in the oven and hot air methods, the L* index increased slightly with increasing drying temperature. The freeze-dried Kashk had the lowest a* and b* values, and in the drying methods using heat (oven and hot air), these indices increased with increasing temperature. The results of the changes in the whiteness index showed that the whiteness of the oven, hot air and solar dried samples decreased compared to the original sample, while it increased in the freeze-dried sample. In the sensory evaluation, the solar dried sample obtained the highest sensory score for odor, texture, mouthfeel, and overall acceptance. With increasing drying temperature in the oven and hot air methods, the sensory score of the samples decreased, so that the samples dried in the oven at 70 ° C obtained the lowest sensory score. In the study of experimental models for drying, the Medley model with the highest correlation coefficient and the lowest root mean square error for the oven, hot air and solar methods and the logarithmic model for the freeze dryer showed the best fit.Conclusion: According to the results, the freeze-drying method produces better samples in terms of most physicochemical properties, but the investment cost for this method is very high. On the other hand, the samples dried by the solar method obtained the best sensory score. Therefore, using solar-drying method is a suitable method for drying Kashk.

Potato is one of the most important agricultural crops and there is remarkable loss of this produce because of unfavorable storage conditions. Therefore, it is vital to convert raw potatoes into some processed products such as dried ones. Our aim was to evaluate three cultivated potatoes of Golestan province of Iran (so-called Agria, Satina and Kenebek) to find the best cultivar for dehydration. Also, we investigated the influence of drier type (Microwave oven and Hot air oven) and shelf life on the rehydration behavior of processed potatoes (powder and cubes). Total sugars, reducing sugars and ascorbic acid contents were analysed to evaluate the processing effect on product components. The factorial completely randomized design was selected as the statistical design and three replications were conducted for each treatment. In order to examine the quality and shelf life of products during storage, the analyses were continued until three months. Results revealed that there is significant difference (P<0.05) between microwave processed potatoes and hot air ones, due to different heat transfer mechanisms. For instance, ascorbic acid content in the former products was about 8.3 mg/100gr dry matter which was significantly (P<0.05) higher than hot air dried potatoes. Also water absorption of the cubes which were dried in microwave oven, was about 12% more than hot air ones. It was concluded that all the three cultivars were suitable for producing dehydrated products. Agria had the lowest amount of reducing sugars and the best color accepted by the panelists and Kenebek had the highest rehydration ratio but from from theoveral point of acceptability, Satina received the highest score amongst three cultivars.

Introduction: Basil contains high phenolic compounds and its seeds contain mucilages. By investigation the essential oils of this plant, and especially its phenylpropanoid compounds, have been identified as the main medicinal product. Materials and Methods: In this research, basil leaves were dried by three methods: shadow, drying oven method at 40 and 60° C and microwave method at 180 and 360 W. In order to increase the heat transfer in short time some effective factors concerned with the leaves, namely moisture, iron, potassium, vitamin C and polyphenol contents were determined. Results: The first stage of drying rate is constant and controlled by external factors, was seen only in the shadow drying method. In two other methods, this stage has been almost eliminated. Forced convection heat transfer coefficients is higher than natural convection coefficient. Therefore in the oven drying method, mass transfer rate is higher than the other methods. With increasing microwave power, drying time decreased. The determined amounts of iron, potassium and vitamin C showed that there is a significant difference between different drying methods (P <0. 05). The longest drying time was in shadow with1800 minutes and the highest amount of vitamin C, iron and phenolic compounds was in the dried treatment in the shade. Conclusion: According to the results, it can be stated that the drying of the basil leaf using shade drying and microwave drying at 180 W, are desirable because the amount of active ingredients in the plant is considerably retained.

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.

Introduction: Dehydration is one of the methods employed for food preservation. In this study the effect of drying on the quality characteristics of apricots consisting of browning, shrinkage, rehydration, hardness and residual sulfites has been investigated.Materials and Methods: Ripened apricots with 83-87% initial moisture content were employed. Statistical analysis concerned with the effect of heat variations on quality indices namely browning, water absorption, texture hardness and residual SO2 were carried out using MINITAB and SAS software.Results: The results indicated that the effects of drying methods on browning, rehydration, residual sulfite of dried apricots were highly significant, but the methods had no significant effects on shrinkage and hardness.Conclusion: This investigation indicated that hot air drying at 60oC was found to be the most suitable condition.

The aim of this paper is to identify the unknown properties of an industrial hot air gun using inverse heat transfer approach. A combination of experiments and numerical analyses is used to define the convection coefficient and the produced temperature of this device. A numerical solver is developed by employment of a straightforward and powerful inverse heat transfer method: “The conjugate gradient method for parameter estimation”.The variation of temperature versus time in a fixed point of a steel-304 rod is sensed by a thermocouple and is given as an input to the numerical solver. The produced temperature of the hot air gun and the variation of convection heat transfer coefficient of this device as a function of distance between gun and rod are estimated in this research. Two non dimensional distances between hot air gun and head of rod, H/D, are considered in this research: 2 and 6. These distances are chosen based on the hot jet potential core, the former is inside the potential core and the latter is outside it. The identifications of this gun are used in the process of determining unknown thermal properties of insulating and ablative materials, which are essential components of ablative heat shields, by inverse heat transfer methods.

In this research, the drying process of papaya slices was conducted at three temperature levels of 40, 50 and 60 °C and three thicknesses of 3, 5 and 7 mm in a hot-air oven. The velocity, relative and absolute humidity of the hot-air used were 1±0.1 m/s, 30% and 0.6±0.02 g water/kg dry air, respectively. An osmotic solution containing 50% sucrose solution was used for dehydration of papaya slices with 5 mm thickness. The osmotic parameters of water lost (WL), solid gain (SG) and weight reduce (WR) increased with increasing immersion time. The osmotic dehydration process was modeled by Plege, Azuara and Weibull models. In addition the kinetics of hot-air drying was modeled by 8 well-known thin layer mathematical models. The results demonstrated that the Plege and Azuara’s models with R2 and RMSE amounts of 0.992 and 0.179, respectively, had more precision to predict the SG values. Also, the two terms and exponential two terms models had the highest and lowest amounts of R2 and RMSE, respectively, to estimate the MR (moisture ratio) values during hotair drying. Increase in temperature resulted in an increase in the effective diffusivity coefficient, so that this coefficient reached to 7.58×10-10m2/s at 60 °C from the initial value of 2.28×10-10m2/s at 40 oC. The activation energy (Ea) calculated for the papaya slices were 48.61 kJ/mol. Analysis of variance results showed that the drying temperature had a significant effect on the color parameters compared to the control sample, and also the influence of temperature on shrinkage was significant (p<0.05).

In this study, the combination of infrared - hot air dryer was used for drying of button mushroom. The effect of infrared lamp power (150, 250 and 375 W), hot air temperature (50, 60 and 70oC) and hot air rate (1, 2 and 3 m/s) on drying of button mushroom were investigated. The results of infrared-hot air drying of button mushrooms showed that by increasing of lamp power from 150 to 375, the drying rate increased. With the increase in hot air temperature from 50 to 70oC, and hot air rate from 1and 3 m/s, weight loss increased 10.3% and 13.9%, respectively. Also process modeling were done with the genetic algorithm–artificial neural network (GA-ANN) method with 4 inputs (lamp power, hot air temperature and rate, drying time) and 1 outputs for prediction of weight loss. Sensitivity analysis results by optimum GA-ANN showed the drying time of mushroom was the most sensitive factor for controlling of weight loss. The results of modeling by GA-ANN showed that a network with 7 neurons in the hidden layer with sigmoid activation function can predicted the weight loss (R=0.99) of button mushrooms dried by infrared system-hot air method.