Radio frequency drying and puffing of composite purple sweet potato chips

Abstract

Radio frequency (RF) heating is a novel technology applied to drying and puffing. In the previous study, the optimal conditions for RF drying and puffing of composite purple sweet potato chips were 60% initial moisture content, 1 mm sample thickness, and 110 mm electrode gap. The effects of RF treatment temperature (50–110 °C) on the quality, physicochemical properties, and starch structure of composite purple sweet potato chips were further studied in this research. With the increase in RF treatment temperature, the protein, starch, and anthocyanin content in the samples were significantly reduced. However, the reducing sugar content, gelatinization degree, water absorption index (WAI), and water soluble index (WSI) were greatly improved. No new functional groups were produced after RF treatment. The starch changed from A-type to B-type crystal structure at temperature of 65 °C, which may result in the formation of a new double helix structure. Moreover, a larger irregular structure was observed at low temperatures of 50–65 °C, while this structure disintegrated into debris at high temperatures of 80–110 °C. This study provided a theoretical foundation for applying RF drying and puffing technology to starchy foods.