Sugar boiling pre-treatment improves radio frequency explosion puffing quality on modifying the physicochemical and functional properties of purple sweet potato flour

The effects of sugar boiling pretreatment (SBP) with different maltitol concentrations (20 %, 30 %, and 40 %) and boiling time (0 - 6 min) on the physicochemical and functional properties of purple sweet potato flour and the radiofrequency explosion puffing (RFEP) quality were investigated. The results showed that the volume ratio, crispness, anthocyanin retention rate and overall acceptability of the samples were maximized after boiling for 6 min at 40 % maltitol concentration achieving increases of 78.63 %, 437.50 %, 392.25 % and 552.94 %, respectively compared to the control (p < 0.05). Fourier transform-infrared spectroscopy and X-ray diffraction analyses revealed that the flour underwent hydrogen bond breaking and formed hydrogen bonds with maltitol at high temperatures, forming maltitol starch-protein / lipid complexes, resulting in decreased crystallinity, short-range ordering, random coil, -helix and enthalpy, while the non-crystalline region area and -sheet increased. Additionally, the viscosity and storage modulus of the flour increased following pregelatinization. Conversely, as maltitol concentration increased, both viscosity and storage modulus decreased, facilitating the expansion of puffing volume due to the instantaneous total drainage of water upon pressure release. Furthermore, SBP effectively preserved the color and anthocyanin content of the chips. These findings may provide valuable insights for regulating oil-free puffing quality of starchy foods.