Effects of pulsed infra-red radiation followed by hot-press drying on the properties of mashed sweet potato chips

Abstract

This study attempted to develop an additive-free dried sweet potato snack. To provide a crispy texture, sweet potatoes were dried by a two-stage process. At the first drying stage, steamed sweet potatoes were semi-dried for 6 h using hot-air convection or pulsed infra-red (IR) radiation, and drying rate was compared under varying sample thicknesses and drying temperatures. The IR exhibited enhanced drying speed, particularly the IR radiation at 60 °C was favorable for application to the drying of sweet potatoes with large thickness. For the secondary drying, the IR-dried sweet potatoes with varying moisture content were applied to hot-press (HP) drying at 180 °C for 2 s. The quality of final products indicated that the crispy texture of the products was generated when the semi-dried sample had a moisture content lower than 0.5 kg/kg dry base (d.b.). When the moisture content of samples prior to HP process was lower than 0.3 kg/kg d.b., the final product was easily broken with discoloration to dark-brown. Considering the entire processing procedure, the present study demonstrated that IR radiation at 60 °C for 5 h followed by HP was an effective combination for the mass production of a crispy sweet potato snack.