Refractance Window drying of pomegranate juice: Quality retention and energy efficiency

Refractance Window (RW) drying system utilizes circulating hot water as a means to carry thermal energy to materials to be dehydrated. Products are spread on a transparent plastic conveyer belt that moves over circulating water in a shallow trough. In this study the quality retention characteristics of pomegranate juice (PJ) concentrate dried in a continuous pilot scale RW drying system were evaluated against freeze drying and spray drying methods. Samples of PJ concentrate (Brix 64) mixed with Gum Arabic as a carrier (35%, dry basis) were dried by the RW drying, freeze drying and spray drying methods. Physicochemical properties including moisture content, solubility, bulk density and color parameters of samples dried using different methods were compared. Chemical analysis and color measurements of reconstituted samples showed that RW dryer can produce high-quality products with anthocyanins content, anthocyanins color and antioxidant activity equal or greater than those of the freeze dried and spray dried samples. Energy consumption of the RW dryer was about one third and 1/40 of those of spray drying and freeze drying systems, respectively.