Red beetroot as a rich source of bioactive and health enhancing compounds has a high potential for use in a wide range of foods and its powder with containing these compounds, can be used as a natural antioxidant and colorant in the food industry. In the present study, red beetroot pulp powder was produced by foam-mat drying technique. Drying kinetics, physicochemical and microstructural properties of the resulting powder were investigated. To prepare foam, 2% ovalbumin (w/v) was added to the red beetroot pulp and stirred for a specific time and speed. Prepared foam was spread on aluminum plates at thicknesses of 5, 6 and 7 mm and then dried in a hot air cabinet dryer at 50 º C and constant air velocity of 1 m/s. Results showed that increasing foam thickness from 5 to 7 mm had no significant effect on moisture content and moisture ratio but significantly (p <0. 05) reduced the drying rate by about 29. 63%. The effective moisture diffusion coefficient was significantly affected by the foam thickness and ranged between 5. 550 × 10− 9 and 7. 388 × 10− 9 m2/s. Also, with increasing foam thickness, due to increasing drying time and more denaturation of proteins, an increase in Carr index and Hausner ratio was observed, resulting in a decreasing trend in the flowability of the powders. Bulk and tapped densities of powders were significantly decreased due to the change in moisture content, caused by the increase in foam thickness. Thickness had no significant effect on water solubility index and water absorption index. The microstructure analysis of the produced powders by field emission scanning electron microscope showed that with increasing foam thickness, cracking and surface roughness of powder particles increased. The results of this study and further studies can lead to optimization of red beetroot powder production as a natural food coloring and better preservation of its nutritional and functional properties.

Introduction: Due to the nutritional status and health effects of raspberry as a fruit rich in nutrients such as anthocyanins and phenolic compounds, the resulting powder can while have these compounds, increasing the variety and consumption of raspberry products (Si et al., 2016). However, because of its high moisture content and vulnerable texture, raspberry fruit corrupts very quickly and is difficult to keep fresh, even in cold storage conditions. Therefore, maintaining the quality of raspberry fruit after harvest and also increasing its storage time is one of the goals of raspberry growers around the world (Palonen and Weber, 2019). The drying process of fruits and vegetables prevents chemical and biochemical spoilage of the products and increases their shelf life by reducing the moisture content. However, some undesirable physical and chemical changes such as loss of color, texture and nutritional value may also occur during drying, which reduce consumer acceptance (Dehghannya et al., 2017; Kayran and Doymaz, 2017). Foam mat drying is an alternative method of drum dryer, spray dryer and freezer dryer for the production of food powder. Food products become a stable foam by adding foaming agents and stirring in the presence or absence of foam stabilizers and are dried using different heat streams. Therefore, with the proper selection of foaming agents and drying conditions, a high quality powder can be obtained (Qadri et al., 2010; Javed et al., 2018). Despite the impact of air velocity on drying kinetics and other process parameters and consequently on the qualitative and functional characteristics of the dried product, few studies have been done on the effect of air velocity on foam mat drying of agricultural and food products. Therefore, according to the potentials of raspberry fruit and foam mat drying method, the aim of the present study was to evaluate the effect of drying air velocity (2 to 4 m/s) on the effective moisture diffusion coefficient, drying kinetics and also on the physicochemical properties of raspberry powder produced by the foam mat drying method. Material and methods: Black raspberry fruit after being prepared from the local market in the north of the Iran (Gilan province) was stored at a temperature of 4 C. The raspberry fruit was first completely crushed by a food processor and passed through mesh number30. Ovalbumin and methylcellulose with a concentration of 0. 5%were used as foaming agent and foam stabilizing agent, respectively and added to the raspberry pulp. The resulting mixture was mixed with an electric stirrer at maximum speed for 10 minutes and the resulting foam was spread in a thickness of 7 mm on an aluminum plate. Drying was performed with a convective hot air dryer at a temperature of 70 C and an air velocity of 2 to 4 m/s. Drying kinetics and effective moisture diffusion coefficient, as well as physicochemical properties of raspberry powder such as bulk and tap density, powder flowability, absolute density, water solubility index (WSI) and water absorption index (WAI), powder mass porosity, moisture content and color were evaluated according to the methods described by Dehghannya et al (Dehghannya et al., 2018, 2019). Results and discussion: In the present study, the drying kinetics of raspberry by the foam mat drying method and the physicochemical properties of the resulting powder under the influence of air velocity were investigated. The results showed that the effective moisture diffusion coefficient (Deff) was in the range of 1. 391  10-8 to 1. 723  10-8 2 m /s and the increase of drying air velocity from 2 to 3 m/s and 3 to 4 m/s had a significant effect on it (p<0. 05). However, increasing the drying air velocity had no significant effect (p> 0. 05) on moisture content, moisture ratio and drying rate of the product during drying. Changes in Carr index and Hausner ratio at different drying velocities were statistically significant (p <0. 05) and increasing the air velocity from 2 to 3 m/s reduced their values, which indicated the improvement of the powder flowability at air velocity of 3 m/s. Furthermore, the mean values of MC, WSI, WAI, Chroma index and brightness of raspberry powder significantly increased with increasing drying air velocity (p <0. 05). However, the bulk and tap density and absolute density and the overall color difference of raspberry powder decreased with increasing drying air velocity (p> 0. 05). Conclusion: The results of this study showed that the hot air velocity used in the drying process can be effective on the effective moisture diffusion coefficient and thus on the quality characteristics of the produced powder. So that, its effect on effective moisture diffusion coefficient, bulk and tap density, flowability, absolute density, WSI, WAI, moisture content and brightness of powder were significant. It should be noted, that the effect of air velocity in different values and in accordance with other process conditions, on different parameters is variable. Raspberry powder produced by foam mat drying method, due to its high anthocyanin content, can be used as a natural additive in dairy products, desserts, jams, jellies and other food products and the results of this study can increase the quality of the powder and improve its nutritional and functional properties by optimizing the drying process.

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.

Background and Objectives: Drying, one of the traditional food preservation technique, is a complex process defined as a simultaneous heat and mass transfer steps under transient conditions, which leads to significant changes in physicochemical properties of the foodstuffs. The objective of the present study was to assess effects of ovalbumin concentration (as a foaming agent) at three levels of 1, 2 and 3% on green banana drying kinetics and qualitative and quantitative properties of the produced powder using foam-mat drying method. Materials and Methods: Ovalbumin, as a foaming agent, and 0. 5% (w/w) methyl cellulose, as a stabilizer, were used for the preparation of foams. In this study, effects of ovalbumin concentration (1, 2 and 3% w/w) at 70 ° C with foams of 3-mm thickness were assessed on drying kinetics of immature banana pulp and physicochemical properties of the produced powder like bulk density, glass transition temperature and water solubility index. Statistical analysis was carried out using completely randomized design with three replications. Means were compared using Duncan’ s multiple range test at 5% levels. Results: Results showed that increases in ovalbumin concentration caused significant increases in effective moisture diffusion coefficient, decreased the foam density and increased the porosity, expansion and stability of the foam. Bulk density and water absorption index decreased with increasing concentration of the foaming agent. Moreover, Carr index and Hausner ratio respectively increased and decreased by increasing ovalbumin concentration from 1 to 2 and 2 to 3%. The lowest glass transition temperature was achieved at 2% ovalbumin concentrations. Conclusion: Study of physicochemical properties of the final product showed that the powder produced at 1% ovalbumin concentrations included the highest flowability. Unripe banana pulp powder rich in resistant starch produced by foam-mat drying can be used as a natural product enriched with egg white protein and fiber source, mainly in production of functional products.

This paper aims to investigate the effect of the amount of calcium carbonate as foaming agent on the physical and mechanical properties of LM13 aluminum foam. Aluminum alloy LM13 foams have been made using calcium carbonate (CaCO3) as foaming agent and calcium metal (Ca) as stabilizing particles with densities from 0. 3 to 0. 5 gr/cm3 (relative density from 0. 12 to 0. 18) and the pores size from 0. 25 to 0. 92 mm. The effects of the amount of foaming agent on the size of the pores, the minimum thickness of the walls and the density have been evaluated. Furthermore, the mechanical behavior of foams has been investigated using uniaxial compression test. The influences of the amount of foaming agent on compressive strength, elastic characteristics and energy absorption capacity of foams have been investigated. According to the obtained results, the use of more foaming agent leads to the production of foams with larger average pores size and less density. Also, increasing the amount of foaming agent reduces the compressive strength of foams in the uniaxial compression test and their energy absorption capacity.

Fumed Silica nanoparticles are widely used as fillers in various industries such as aerospace, building, transportation, health, and more. Considering the lightweight, thermal insulation properties and suitable compressive strength and, the use of this filler as an increaser of resin viscosity to glue different parts in the aerospace industry, in this study, the effect of Fumed silica nanoparticles filler on the mechanical and electrical properties of epoxy/Fumed silica polymer Nano composite has been investigated. To achieve optimal properties, samples with different weight percentages were made. To determine the mechanical properties of the produced composites, the tensile test and the three-point bending test were performed, and to determine the electrical properties of the samples, the dielectric constant test was performed. In the end, the mechanical and electrical properties of the samples with different weight percentages were compared with the pure epoxy resin sample. The results showed that the maximum tensile strength of pure resin samples, Fumed silica 5% and 9% are 18, 16, and 10 MPa, respectively. The maximum flexural strength for pure resin, Fumed silica 5%, and 9% were 109, 85, and 67 MPa, respectively. The maximum dielectric constant measured for pure resin, Fumed silica 5% and 9% were obtained as 2.95, 2.97, and 3.09 respectively. The maximum Loss tangent measured for pure resin, Fumed silica 5% and 9% were obtained as 0.16, 0.17, and 0.23 respectively. The results of electrical properties indicate that the addition of Fumed silica filler to the resin did not affect the electrical properties of the resin.

Heat transfer of polymeric foams is consisting of three different mechanisms including heat transfer through a solid phase, gas phase, and thermal radiation. Thermal insulation properties of polymeric foams are affected by different structural properties. Also, these structural properties have a different influence on the different heat transfer’ s mechanisms. Therefore, it is necessary to use theoretical models. Several theoretical models have been presented so far, meanwhile, providing theoretical models that can estimate the thermal conductivity using the easiest measurable properties along with sufficient accuracy and reliability can be very helpful. In this regard in the present study, a theoretical model based on cell size and foam density is developed in order to predict the thermal properties of polymeric foams. It was concluded that the error of the developed theoretical model is lower than 8% in comparison to the experimental results. In the following, the effect of most important structural parameters i. e. foam density and cell size on the thermal conductivity is investigated. Based on the results, determining the optimum density is necessary to achieve the lowest thermal conductivity. Also, the gas thermal conduction has the most contribution to the overall thermal conductivity and achieving the nanometer cell sizes can be useful in order to decrease it.