The Influence of Refractance Window Drying on Qualitative Properties

The phase II design improvements targeting the commercialization of RW drying will be facilitated by prototyping and testing auxiliary and alternative product application, product conditioning, and product removal equipment. In October, fresh walnuts harvested with the green hull (Juglans regia L.) were procured Refractance Window Dryer from the Tral area of Jammu and Kashmir . The outer green hull and shell were removed before drying. The initial moisture content was determined in triplicates by the simple hot air oven method at 105 ± 2 °C. A laboratory-scale Refractance Window drying equipment was developed for drying purposes.
The “window” aspect of the transparent sheet allows infrared energy from the hot water to pass rapidly and directly into the slurry. Heat is also conducted through the belt, which helps to evaporate moisture in the product. Evaporate is carried away by mechanically boosted airflow. The transfer of infrared energy through the transparent sheet slows as the product loses moisture, creating a controlled drying process that retains nutrition, flavor, color and aroma. Ascorbic acid is an important vitamin and an essential nutrient  for humans and  some animal species. It is found in many fruits and vegetables but it is very sensitive to heat and oxidation (Burdurlu, Koca, & Karadeniz, 2006).

The nutrition found in fresh, whole foods is unparalleled. In a perfect world, we would get all that we need from fruits and vegetables while they’re still fresh. Tontul, İ, Kasimoglu, Z., Asik, S., Atbakan, T. & Topuz, A. Functional properties of chickpea protein isolates dried by refractance window drying. Nindo, C. I., Sun, T., Wang, S. W., Tang, J. & Powers, J. R. Evaluation of drying technologies for retention of physical quality and antioxidants in asparagus (Asparagus officinalis, L.).
By extending shelf life and safety, drying also facilitates transport and storage. Refractance Window is a relatively new film drying technique and it is characterized by high-quality products, short drying times, low cost, high energy efficiency and high evaporation capacity. RW dryer can retain product quality in terms of heat sensitive vitamins, phytochemicals content, color and antioxidant activity equal or greater than those of the freeze-dried products. Early understandings heat transfer mechanism in RW drying have concluded that thermal radiation from hot water transfers to the moist material by the use of a thin plastic sheet that allows creates a “window” for transfer of infrared radiation. This “window” gradually closes as the material dries out cutting off radiation. Drying technologies belong to first, second, third or fourth generation.
As the material travels down the conveyor, the water in the material evaporates through the “window” in the matter of few moments, with the “window” closing in proportion to the rapid dissipation of water in the material. Because the Mylar conveyor belt is a poor heat conductor, once the material dries, the “refractance window” closes, and only a minuscule amount of heat is transferred to the product as it is carried to the end of the conveyor system. In a matter of a few moments, the water in the material on the plastic membrane’s surface evaporates, and the “window” of infrared energy closes and “refracts” back into the heated water source, no longer exposing the material to heat. Investigating dehydration of different food materials including microorganisms , leaf vegetables, meat and marine products.

The effective diffusion coefficient values obtained (2.89 × 10−9 to 8.84 × 10−9m2/s) using Dincer and Dost analytical approach had higher R2 (0.980–0.991) and lower RMSE (0.029–0.053) values. RW drying at 90 °C resulted in higher ascorbic acid retention (~76–78%) with the least total colour change (3.4–6.9) compared to other studied conditions. Besides, retention of total phenolic (10.3 mg GAE/g dm) and flavonoid contents (3.4 mg QE/g dm), as well as antioxidant capacity (58.8 mM TE/g dm), were also better in samples dried at 90 °C. The study suggested that drying at a higher temperature during RW not only reduces drying time but also improves retention of quality attributes.
Dehydration is one of the most effective means to preserve foods in a stable and safe condition for an extended shelf life. Loss of heat sensitive nutrients and other health promoting compounds in dried foods are major concerns in the design and operation of food drying equipment. Scientific information is lacking on the operation of the Refractance Window drying process. Lipoxygenase activity is shown in Table 1 for sun-dried and RW-dried samples at different temperatures. The lipoxygenase activity was observed to increase with an increase in temperature.

Drying reduces moisture content and lowers water activity in perishable products  to safe levels, thereby prolonging shelf life and adding value. Compared to products produced with other preservation methods, dehydrated products have almost unlimited shelf-life and substantially lower transportation, handling and storage costs. In the United States, they provide opportunities for maximum convenience, flexibility, and economics as industrial and food service ingredients, whereas in other countries they are also frequently consumer products, as well. In this work, unripe green banana flour was dried by using Refractance window drying and Hot Air oven drying, and various properties were evaluated.
To dry a similar amount of product, the cost of the RW equipment is about one-third of the cost of a freeze-dryer ; while energy consumption of RW is less than half of the energy consumption for a FD (C. I. Nindo & Tang, 2007). Variable hab was significantly affected by flake thickness, microfluidization pressure and formulation. Drying is one of the most efficient methods for conserving food, as reducing aw reduces microbial growth and decreases the speed of degradation reactions, the latter being of great interest for drying products having antioxidant activity.
While  swimming underwater, I looked up to see that the water’s surface acted like a mirror, only allowing me to see something floating on it but almost nothing else. I knew water was the best heat transfer medium in nature and wondered if perhaps water could be used to provide the energy needed to dry products. If so, it might do so more efficiently and without damaging the delicate and valuable nutrients in the food. Modeling of drying process in RW dryer and investigating the role of different parameters and heat transfer mechanisms in the process. Authors who have researched food area-related contact angles have based their work on studying the properties of materials’ surfaces in response to contact with liquid foodstuffs (i.e. interfacial interactions). Their usefulness as a mechanism for predicting interactions between liquids and solid surfaces (i.e. biofilms, membranes, heat interchange or packed food surfaces) has been studied by authors like Güleç et al.47.