A Review on Quality Preservation and Energy Efficiency in Refractance Window Drying
This higher lipoxygenase activity can be attributed to the duration of time . Similar findings have been reported by Fu et al. in drying walnuts using sun drying, direct oven drying methods and intermittent oven drying for walnut . So, the Refractance Window Drying Technology has Refractance Window Dryer an important advantage in terms of dried products exposed to low temperatures. The nutritional quality of the product is protected in quite a high proportion with the RWD technique. Moreover, the powder properties of dried products are comparable level with freeze dried products.
The technique is already reportedly used for commercial applications by MCD Technologies, Tacoma and Mt. Capra, Washington for drying of whey and other products . Commercial dryers also dry a range of products; including brine shrimps, micro-algae and herbal formulations . Unlike certain other drying technologies, RW™ drying does not require high operational pressures. Also, there is limited scope to oxidation and free radical formation and RW™ dried products offer improved shelf life.
While conduction, convection and radiation occur at the hot water-film interface, conduction and radiation occur through the film and convection occurs at the air-film interface. Thus, moisture ratio is the dependent variable, which relates the gradient of the sample moisture content in real-time to both initial and equilibrium moisture content. Experimental data were expressed in terms of the MR and were calculated according to Equation . Then, the integrated equation of Fick’s second law was also used for long time periods and thin-layer in one dimension, representing the first term in the development of the series, from which the diffusional coefficient is obtained for each temperature. The moisture effective diffusivity was calculated according to Equation . Food and feed dryers are often the most complex in the dryer family, and today these are the beneficiaries of major innovations.
The kinetic parameters of empirical models can be observed in both RW™ method without IR and IR-assisted RW™ drying method in Table 3 and Table 4, respectively. The parameter k, ko, and k1 values increase as drying temperature increases, this behavior is observed for most of the models and for each RW™ drying process. The other empirical parameters (n, a–c) did not present significant variations despite increasing the temperature, this could occur due to the food matrix structure that is dried. Furthermore, some authors have found the n parameter not to vary with the temperature, as well as showed an air velocity linear dependence of this parameter n . The authors proposed that particularly for parameter n, this empirical parameter could be affected in the case of drying fruit slices with or without skin, increasing accordingly the shell thickness. Since this study presented a fruit purée drying by RW™ method, these empirical parameters would not be affected by the presence of the shell, despite the temperature being increased, as well as IR radiation included.
Again, a cooling system arrangement is usually done by cooling the water in a tank below the conveyer belt of the dryer. Drying is a common technique as it consumes more energy and an optimized appropriate choice may lead us towards economic savings. The drying concept implies that the product passes through warm or hot air for dehydration . The questionable area is how to reduce energy costs and maintain the quality of the product. In the 1990s, the system named Refractance window was invented by MCD technology company Tacomafor the first time .
The heat from the cistern’s water is conducted by way of a “refractance window” through the Mylar belt to the water present in the raw material laying on the belt’s surface. The objective of this work was to study the influence of the drying temperature, infrared radiation assistance, and the Mylar™ film thickness during Physalis fruit puree drying by the Refractance Window™ (RW™) method. For this, a RW™ dryer layout with a regulated bath at working temperatures of 60, 75, and 90 °C, Mylar™ thicknesses of 0.19, 0.25, 0.30 mm and IR radiation of 250 W for assisting RW™ drying process was used. Effects of natural convection and forced convection of air in RW dryer was studied by Ortiz-Jerez & Ochoa-Martínez11in a study on drying pumpkin slices.
Conductive hydro-drying also known as Refractance Window drying is a relatively new drying technology, which uses hot water to carry thermal energy to materials to be dehydrated. It has a high retention of heat sensitive quality parameters with better energy efficiency than freeze-drying as well as many other conventional drying methods. A new ultrasound and infrared assisted conductive hydro-dryer was developed to increase drying rate while reducing required hot water temperature and increasing the drying material thickness. The goal of this study was to evaluate the performance of the new dryer and to compare the performance of a pilot scale continuous UIACHD with a freeze-dryer and a cabinet dryer in drying apple slices.
& Takhar, P. S. Rheological properties of blueberry puree for processing applications. & Tang, C.-H. Microfluidization as a potential technique to modify surface properties of soy protein isolate. & Sun, D. Preparation of highly stable concentrated W/O nanoemulsions by PIC method at elevated temperature. & Santiago, L. G. Characterisation of freeze-dried flaxseed oil microcapsules obtained by multilayer emulsions. The textural feature contrast is a measure of the intensity contrast between a pixel and its neighbour over the whole image. It measures the local variation in the GLCM.
The water activity of RW and HA dried UGBF was 0.28 ± 0.05 and 0.39 ± 0.07, respectively. The RW drying showed a higher whiteness index of 90.26 ± 0.30, whereas HA drying showed 87.04 ± 0.45. The SEM analysis showed the presence of oblong and sphere-shaped starch granules with a smooth surface in the case of RW dried UGBF. The crystallinity of RW and HA dried UGBF were found to be 9.61% and 8.73%, respectively by using x-ray diffractograms. The gelatinization temperature and enthalpy of UGBF obtained by RW and HA drying were found to be 80.92 °C and 2.05 Jg−1K−1; 75.74 °C and 2.64 Jg−1K−1, respectively.
A study on quality retention of dried carrot puree showed that RW drying is a much better method than drum drying to dry carrot puree . The color of the RW-dried carrot purees was comparable to fresh puree (Abonyi et al., 2002). Another research on RW drying of carrots have also demonstrated similar results (Hernández-Santos et al., 2016).
The technique is already reportedly used for commercial applications by MCD Technologies, Tacoma and Mt. Capra, Washington for drying of whey and other products . Commercial dryers also dry a range of products; including brine shrimps, micro-algae and herbal formulations . Unlike certain other drying technologies, RW™ drying does not require high operational pressures. Also, there is limited scope to oxidation and free radical formation and RW™ dried products offer improved shelf life.
While conduction, convection and radiation occur at the hot water-film interface, conduction and radiation occur through the film and convection occurs at the air-film interface. Thus, moisture ratio is the dependent variable, which relates the gradient of the sample moisture content in real-time to both initial and equilibrium moisture content. Experimental data were expressed in terms of the MR and were calculated according to Equation . Then, the integrated equation of Fick’s second law was also used for long time periods and thin-layer in one dimension, representing the first term in the development of the series, from which the diffusional coefficient is obtained for each temperature. The moisture effective diffusivity was calculated according to Equation . Food and feed dryers are often the most complex in the dryer family, and today these are the beneficiaries of major innovations.
The kinetic parameters of empirical models can be observed in both RW™ method without IR and IR-assisted RW™ drying method in Table 3 and Table 4, respectively. The parameter k, ko, and k1 values increase as drying temperature increases, this behavior is observed for most of the models and for each RW™ drying process. The other empirical parameters (n, a–c) did not present significant variations despite increasing the temperature, this could occur due to the food matrix structure that is dried. Furthermore, some authors have found the n parameter not to vary with the temperature, as well as showed an air velocity linear dependence of this parameter n . The authors proposed that particularly for parameter n, this empirical parameter could be affected in the case of drying fruit slices with or without skin, increasing accordingly the shell thickness. Since this study presented a fruit purée drying by RW™ method, these empirical parameters would not be affected by the presence of the shell, despite the temperature being increased, as well as IR radiation included.
Again, a cooling system arrangement is usually done by cooling the water in a tank below the conveyer belt of the dryer. Drying is a common technique as it consumes more energy and an optimized appropriate choice may lead us towards economic savings. The drying concept implies that the product passes through warm or hot air for dehydration . The questionable area is how to reduce energy costs and maintain the quality of the product. In the 1990s, the system named Refractance window was invented by MCD technology company Tacomafor the first time .
The heat from the cistern’s water is conducted by way of a “refractance window” through the Mylar belt to the water present in the raw material laying on the belt’s surface. The objective of this work was to study the influence of the drying temperature, infrared radiation assistance, and the Mylar™ film thickness during Physalis fruit puree drying by the Refractance Window™ (RW™) method. For this, a RW™ dryer layout with a regulated bath at working temperatures of 60, 75, and 90 °C, Mylar™ thicknesses of 0.19, 0.25, 0.30 mm and IR radiation of 250 W for assisting RW™ drying process was used. Effects of natural convection and forced convection of air in RW dryer was studied by Ortiz-Jerez & Ochoa-Martínez11in a study on drying pumpkin slices.
Conductive hydro-drying also known as Refractance Window drying is a relatively new drying technology, which uses hot water to carry thermal energy to materials to be dehydrated. It has a high retention of heat sensitive quality parameters with better energy efficiency than freeze-drying as well as many other conventional drying methods. A new ultrasound and infrared assisted conductive hydro-dryer was developed to increase drying rate while reducing required hot water temperature and increasing the drying material thickness. The goal of this study was to evaluate the performance of the new dryer and to compare the performance of a pilot scale continuous UIACHD with a freeze-dryer and a cabinet dryer in drying apple slices.
& Takhar, P. S. Rheological properties of blueberry puree for processing applications. & Tang, C.-H. Microfluidization as a potential technique to modify surface properties of soy protein isolate. & Sun, D. Preparation of highly stable concentrated W/O nanoemulsions by PIC method at elevated temperature. & Santiago, L. G. Characterisation of freeze-dried flaxseed oil microcapsules obtained by multilayer emulsions. The textural feature contrast is a measure of the intensity contrast between a pixel and its neighbour over the whole image. It measures the local variation in the GLCM.
The water activity of RW and HA dried UGBF was 0.28 ± 0.05 and 0.39 ± 0.07, respectively. The RW drying showed a higher whiteness index of 90.26 ± 0.30, whereas HA drying showed 87.04 ± 0.45. The SEM analysis showed the presence of oblong and sphere-shaped starch granules with a smooth surface in the case of RW dried UGBF. The crystallinity of RW and HA dried UGBF were found to be 9.61% and 8.73%, respectively by using x-ray diffractograms. The gelatinization temperature and enthalpy of UGBF obtained by RW and HA drying were found to be 80.92 °C and 2.05 Jg−1K−1; 75.74 °C and 2.64 Jg−1K−1, respectively.
A study on quality retention of dried carrot puree showed that RW drying is a much better method than drum drying to dry carrot puree . The color of the RW-dried carrot purees was comparable to fresh puree (Abonyi et al., 2002). Another research on RW drying of carrots have also demonstrated similar results (Hernández-Santos et al., 2016).
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