REFRACTANCE WINDOWTM TECHNOLOGY

Practically, in food it is used to convert fruits, vegetables, herbs, and other material into value-added powders and concentrates (Nindo & Tang, 2007). This RW™ drying  technique is highly effective in reducing the energy consumption and retention of heat labile compounds with enhanced color than other traditional drying methods (Puente et al., 2020). In comparison to freeze drying technique, RW™ drying machinery requires 50–70% less capital investment and 50% less energy consumption for the equal quantity of material to be dried (Nindo & Tang, 2007). Hence, RW™ drying proved higher energy efficiency than the traditional dyers and freeze dryers (Baeghbali, Niakousari, Ngadi, & Hadi Eskandari, 2019). RW™ drying was patented by Magoon and developed by MCD Technologies Inc. .
On the other hand, heat transfer by conduction is the dominant one and the temperature of the product is kept below the temperature of the water (Ortiz-Jerez et al., 2015; Vega-Mercado et al., 2001; Zotarelli et al., 2015). This technology was applied to different fluid or solid laminated products, which, in short times, results in powders, flakes or natural leathers with good physicochemical properties (Raghavi et al., 2018; Waghmare, 2021). The evaluation of the impact of food processing on the nutrients and health benefits of vegetables and fruits Refractance Window Dryer is of high practical importance. In this short literature overview the refractance window drying technology, a novel contact drying technique, was compared with other drying techniques as the freeze drying technique to stabilize fruits and vegetables. The antioxidant capacity, phenolic or polyphenol content and carotenoids are important published quality properties. The RWD technology as mild drying process showed various opportunities to maintain the product quality and the nutrient content as well as their biological activity to a high degree.

However, these statements were not observed in Hungarian thyme. In this particular case, as the air temperature increased, the losses decreased. This behavior was attributed to the longer processing at lower temperatures compared to the shorter times required for higher temperatures . Volatile compounds retention was observed in studies on ginger when heat pump drying was applied. This is a positive effect with respect to other driers that usually loose the volatile compounds of the product .
The spectra were corrected for baseline  in the region of 400–4000 cm−1 using Origin 2022b software . These window dryers help to keep your room organized and dries quickly. Refractance window dryers are a simple way to cool the air inside of the home, and they maintain a low amount of air inside of the room.
The enzymatic browning occurs in fruits and vegetables due to the phenolic compounds oxidation by polyphenols oxidase, which starts the generation of the brown pigments called o-quinones. However, there are alternatives to prevent this degradation such as the previous inhibition of enzymatic system by using sulphites . Browning is accelerated when the level of water content is intermediate and decreases at very low or very high levels of moisture content. Consequently, browning is harsh close to the end of drying process due to the low levels of moisture remaining in the product. In carbohydrate dried foods , changes of color after dehydration are linked with the presence of high amount of reducing sugars such as glucose and fructose.

In another study, a solar dryer using a PV-T solar collector was used in a tomato drying system to provide the required electrical energy. The results showed that the electrical energy required to dry tomato slices is from 0.65 to 1.4 kWh. The results also showed that as the drying temperature decreases, both the solar heat fraction and the ratio of solar electricity to consumed electricity increased (Dorouzi et al., 2018).
Product quality shows good results as compared to drum drying, freeze-drying, spray drying, tray drying, etc. while being extremely energy efficient. Refractive window drying is a novel technology which can be use to dry the semi solid, puree and paste type of product. The advantage of this drying technology, its minimising drying time, and provides better quality product with higher retention of nutrients in comparison with other conventional drying techniques. Castoldi et al. investigated the drying of tomato powder using an RW dryer at different drying temperatures (65, 75, 85, and 95 °C) and two thicknesses . They showed that the lowest drying time was obtained at 95 °C temperature and 1 mm thickness.

Table 1 shows the estimated kinetic parameters of Newton and Midilli's models, including criteria to evaluate the fitting quality. Where N is the number of observations, z is the number of model parameters, MRexp is the experimental moisture ratio, and MRpre is the predicted moisture ratio. Where mt is the mass at a given time , rat is the apparent density at a given time (g/cm3) and R is the ratio of the papaya slices, equivalent to 0.015 m. Deff values were calculated with and without considering shrinkage. Energy utilization and microbial reduction in a new film drying system.
Through this process, evaporated water from the product is removed resulting in the formation of dried crystals. According to one embodiment, conditioned air is air that has a predetermined humidity and temperature.  The humidity and temperature of the conditioned air may be specific to the types of products being dried.
For pulp production, the dragon fruit slices were ground in a mixer and sieved using a 40-mesh size, with the resulting pulp spread out in a thin layer 5 to 8 mm thick. After drying, the texture of the dried product was analyzed using a texture analyzer (TA-XT plus model, Micro-Systems, UK). Then, the dried product was ground into powder using a mixer grinder . The resulting powder was sieved and packed into LDPE pouches for further analysis.

Papaya is a tropical fruit which originated from Mexico and Central America, and it is a good source of vitamins . Papaya is highly perishable, mainly due to its high moisture content (between 80 and 85% wb), so it is important to find alternatives for its preservation and/ or processing [3-5]. The cost of Refractance Window drying equipment is approximately one third to one half that of a freeze dryer to dry a similar amount of product, while the energy costs to operate RW dryers are less than half of freeze dryers. The RWD method has become attractive for applications in the food industry, especially because the dried products are of high quality and the equipment is relatively inexpensive. Besides its ability to handle a diverse liquid product, it can be used effectively to transform fruits, vegetables, herbs and other related products into value added powders and concentrates. Both capital investment and operating cost of refractance window drying is economical than other techniques.