Refractance Window Drying: An Emerging Technology for Heat-Sensitive Food Products

RW Drying time of pulp was more influenced by thickness of the pulp than by temperature of drying . In the last phase of drying, heat transfer by conduction becomes more dominant and heat transfer to the product slows down (Baeghbali & Niakousari, 2018; Nindo & Tang, 2007; Topuz, Feng, & Kushad, 2009). Due to these advantages, the RW method is a drying technique suitable for foods that are dried in thin layers such as pulp. RW drying is a novel drying technique for liquid and semi liquid foods such as vegetable purees and juices. In a recent paper, Raghavi, Moses, and Anandharamakrishnan reviewed studies on RW drying. In this technique, drying was achieved in a very short time due to effective heat transfer by both radiation and conduction, with no or little effect on colour and nutritive values of dried materials (Tontul & Topuz, 2017a).
The diffusion coefficient was higher when not considering shrinkage. These findings show that the RW™ technique is highly suitable for papaya drying; it makes it possible to dry the product reaching a Revolutionizing Food Drying: The Advantages of Refractance Window Dryer low moisture content in shorter times, reducing the aw to values below 0.4 and preserving a similar color. This drying technology totally depends on Mylar film, which is the heart of this technology.

The hot water beneath the film is recirculated to improve thermal efficiency. The belt moves at the desired speed while the drying process takes place. The drying rate curves for RWD, oven drying, and solar drying are shown in Figure 2. The figures indicate that the drying rate rapidly increases with time to a maximum value and then decreases.
The survival of beneficial microorganisms in kefir powders by refractance window drying was higher at 50°C than other drying temperatures. This suggests that refractance window drying at low temperatures can be used in probiotic-rich products. Cornellian cherry pulp, a rich source of bioactive compounds was dried by both refractance window drying and convective drying. Refractance window drying not only provided a less drying time of minutes but also resulted in better quality in terms of colour, ascorbic acid, and total monomeric anthocyanin content. Additionally, it did not cause the formation of HMF, which is a heat-induced contaminant.
A RW dryer can preserve color,9heat sensitive vitamins and phytochemicals that some of them will be discussed in the following section. Ochoa-Martínez, C.I.; Quintero, P.T.; Ayala, A.A.; Ortiz, M.J. Drying characteristics of mango slices using the Refractance WindowTM technique. Quality retention in strawberry and carrot purees dried with refractance window system. Antioxidant activity for dried passion fruit was 367.6 mg vitamin C equivalent/100 g of powder. For the uncertainty analysis the Monte Carlo procedure was used to statistically quantify… Order fitted the reaction processes to best represent the mechanical extraction. Removal of TMP in the secondary effluent by Fe was achieved.

Effects of natural convection and forced convection of air in RW dryer was studied by Ortiz-Jerez & Ochoa-Martínez . Pumpkin slices were dried in this study and temperatures were measured at three levels during drying. The most common drying processes used for the preservation of the food materials are conventional thermal drying, which proved to be a high energy consuming process. With the world progressing towards the application of green technology and sustainable methods, the use of alternative energy efficient drying systems are of paramount importance. Fresh white dragon fruit was purchased from a local fruit supplier in the Kokrajhar market, India.
An aliquot of sample supernatant (0.5 ml) was added to 2.5 ml diluted Folin–Ciocalteu reagent (0.2 N). After 5 min, 2 ml sodium carbonate solution (7.5%) was added to the mixture and kept in dark at room temperature for 1.5 h. Absorbance of the solution was measured using UV visible spectrophotometer at wavelength 765 nm (Liu et al. 2013).

The use of the modified Midilli and Gompertz model allowed observing that there is a correlation between the drying rate and the cellular inactivation rate . When the drying temperature increases, kd and k increase, which indicates that the faster the moisture in the product is lost, the faster the cell death rate increases  in the product. The above is consistent with the phenomena aforementioned, where it is stated that cell death can be caused by the migration of water from the microorganism to the environment.
The coefficient of determination and root mean square error values were used as major criteria in selecting the best equation to describe the experimental data . Open sun, Solar + thermal shelf Black turmeric The hybrid system consists of a solar heater and thermal energy storage system. Mint leaves are cut into a cylindrical shape (around 30 to 35 mm thick × 5 to 6 mm). Initial moisture 73.4% It took 1110 min to 2790 min to obtain a final moisture content of 8.5% . The best models to describe the drying curves were two terms and Page .
Finally, a parametric sensitivity analysis of some key parameters is carried out to study the effects of their variability as affecting moisture loss from the material being dried. Refractance Window™ (RW™) drying is a more recent method for drying heat-sensitive products such as fruit and vegetable purees, slices, juices into powders, flakes or sheets. Retention of color, flavor, aroma, vitamin and antioxidants can be improved in this drying process and product quality can generally be comparable to or, in some instances, better than what can be achieved in freeze drying. The technique is also used to dry pharmaceuticals, nutraceuticals, cosmetic and pigments.

In recent years, much attention has been given to expanding this imaging technique to food science in order to help in the study of food microstructure, including fresh and dried products. Recently, XMT has been successfully applied for highly porous products to determine the shrinkage, cracking, and the internal moisture of different products such as dried banana, carrots, chokeberries, apples etc. . Maintaining of natural color in dried food products is very important as the visual appearance is one of the first judgments made by consumers. Color together with size, gloss, shape, etc. form the appearance and represent a valuable indicative parameter used in quality control.