Refractance window drying: A new approach for producing high-quality powdered dairy products

Refractance window drying is an emerging technology that allows the development of new dried foods with an acceptable shelf life from products widely consumed in the world with high nutritional content and health benefits, such as dairy products. The present study aimed to determine the effect of temperature and product thickness during refractance window drying in a laboratory-scale dryer on the physicochemical properties of whole bovine milk and commercial flavored yogurt using an optimal design model. The drying temperature range was between 40°C and 80°C, and the evaluated thickness ranged from 1 to 3 mm. Energy consumption, pH, moisture, water activity, color, solubility, hygroscopicity, and protein denaturation were determined by reconstitution of the powders obtained and employing techniques such as gravimetric analysis, color analysis, and Fourier-transform infrared spectroscopy. Based on the results obtained, the drying temperatures and thicknesses studied did not affect the secondary structure of proteins; the optimal operational conditions were 64.7°C and 0.001 m for whole milk and 63.7°C and 0.001 m for yogurt. These findings suggest that refractance window drying is a suitable technology for obtaining dried dairy products, particularly for viscous foods such as yogurt.