Effects of Infrared-Assisted Refractance Window Drying on the Drying Kinetics

To perform the scanning electron microscopy , Physalis purée samples, from the drying experiments, were fixed with 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer for 2 h, after this period they were washed 3 times × 5 min in double distilled water. This process allowed to remove all water molecules through CO2 blast and ensured the maximum structural Refractance Window Dryer preservation for the samples. Finally, the samples were mounted on Aluminum holders and metalized with gold in denton vacuum desk metallizer. Microphotographs were obtained using a scanning electron microscope operating at 15.0 kV. Another aspect of food dryers that is receiving increasing attention is improving operating efficiency through heat recovery.
Bulgaricus and Streptococcus thermophilus in the yoghurt powders produced by RW drying at 50 °C was higher than those produced by RW drying at 60 °C and 70 °C. Figure 4D–F shows dried Physalis purée peel by IR-assisted RW™ drying method, where these drying experiments maintained the tendency to compare it with the fresh Physalis purée peel obtaining a rough surface, with an evident loss of water from the cells. This could be present with a more marked tendency than in those obtained in Figure 4A–C. In the same way this can also be observed when comparing the same drying temperatures with and without the use of infrared energy. Figure 4A shows a dried peel with a smoother surface than Figure 4D, indicating in both situations described above the incidence of infrared assisted RW™ drying. Likewise, the tendency towards rough surfaces is maintained in Figure 4E, also observing the emergencies described above.

Just as in most of the drying processes, during RW drying the product that is being dried initially goes through a constant drying rate period which is also mainly dependent on the product thickness. RW drying mainly follows type III patterns of moisture isotherm (Zotarelli et al. 2017). Nindo et al. reported the reduction in moisture content of pumpkin puree by around 80% at 95°C hot water temperature with 2.98 m/min conveyor belt speed in 4.5 minutes of drying. The reflectivity value of pulp increases and the absorptivity values drop during the drying process . No chemical additives are used in RW drying. In a study on drying of green asparagus using different methods, microwave assisted spouted bed drying was the fastest and resulted in highest retention of total antioxidant activity among the methods where heated air was used.
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.
The above suggest that drying nanoemulsions at low temperatures could a more heterogeneous flake structure as the IDM values obtained for these temperatures decreased. Image analysis represents a particularly useful tool for characterising food morphology. Many food materials present highly irregular structures that elude precise quantification by conventional techniques. This methodology enables measurements to be obtained from digitalised images15,16.

This technique has been widely used and represents a highly efficient method for producing nanoemulsions containing small-sized droplets (100–500 nm)8. It uses high pressure to force fluid into specially configured microchannels9. Apart from inertia regarding turbulent flow, laminar elongational flow and cavitation also contribute to droplet break-up10. Lipoxygenase activity was measured as per the protocol followed by (Fu et al. ) using linoleic acid as substrate. Two grams of ground sample was centrifuged for 2 min at RCF of 10,000 in presence of 10 mL of 0.2 M sodium phosphate buffer (pH 7.8) solution under refrigerated conditions.
The structural properties of the product depend on the type of drying technique, operative variables, and food microstructure formed during the process . Walnut (Juglans regia L.) is a hard-shelled and temperate-climatic fruit species within the Juglandaceae family. There are almost 60 different species in the world and among them, 21 are in the Juglans genus . Walnut (J. regia) cultivation started in Central Asia. In global nut production walnuts (Juglans regia L.) are ranked second after almonds.

Importantly, product temperatures are kept low and rapid drying occurs as all three modes of heat transfer are involved. Refractance window drying has found several applications not only in food industries but also in pharmaceutical, nutraceutical, cosmetic and pigment handling industries. The objective of this work is to present the recent trends in refractance window drying of foods with emphasis on the underlying mechanism and effect on product quality.
Topuz, A., Dincer, C., Özdemir, K. & Kushad, M. Influence of different drying methods on carotenoids and capsaicinoids of paprika (Cv., Jalapeno). Increased nanoemulsion drying temperature was thus mainly responsible for improving the parameters regarding image texture as a more homogeneous and regular texture was thereby obtained at higher temperatures. Table S1 of Supplementary file, gives the prediction equations for the texture parameters from the model’s parameters for formulations A and B. Similar results were obtained by Barrera et al.67 when evaluating mechanical damage to wheat starch granules. They concluded that damaged granule surface had lower IDM values than those for native starch granules, suggesting that the mechanical process decreased IDM.
This product was featured at a recent Technology and Market Assessment Forum sponsored by the Energy Solutions Center. In this dryer design, a slurry of liquid product is evenly applied to the top surface of a continuous sheet of transparent plastic. This impervious conveyor belt floats on a surface of hot water at temperatures of 210°F or less.