Refractance Window drying of goldenberry (Physalis peruviana L.) pulp: A comparison of quality characteristics with respect to other drying techniques

Refractance window drying (RWD) is a novel drying technique, in which heat transfer is by conduction and radiation. In this study, RWD technique has been performed in a static mode at a temperature of 70 °C that is lower than that used in common practice, which led to a consequently prolonged drying time of 180 min to reach equilibrium. Goldenberry (Physalis peruviana L.) pulp was dried under these RWD conditions and several quality characteristics were assessed and compared to the products from freeze-drying, convective drying and infrared radiation drying. It was found that RWD even under a prolonged drying time produced a high-quality product, comparable in many aspects to freeze-dried products; total phenolics contents were not significantly different, while total flavonoid and total carotenoid contents were only slightly lower. RWD samples maintained a color closer to that of the fresh sample than did freeze-dried product. Antioxidant activity determined by DPPH and ORAC assays was maintained at a high level. Amino acid profiles of RWD and freeze-dried samples were similar. The capacity of RWD samples to inhibit α-glycosidase is of the same order as displayed by the dried products from the other drying techniques.