Insights into the structure and retrogradation behavior of pullulanase modified potato starch using asymmetrical flow field-flow fractionation

The retrograded starch (RS3) possesses the functional properties of dietary fiber and has attracted increasing interest in the food industry. In this study, the effects of pullulanase treatment (i.e., pH, enzyme content, treatment time, and temperature) on the structure and conformation of potato starch (PS) were systematically investigated using asymmetrical flow field-flow fractionation coupled online with multiangle light scattering (MALS) and differential refractive index (dRI) detectors (AF4-MALS-dRI). The PS treated by pullulanase (EPS) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). Furthermore, the retrogradation of PS and EPS was monitored by AF4-MALS-dRI. The AF4 results indicated that the short chain amylose (AM) molecules were generated via debranching amylopectin molecules by pullulanase treatment, which was consistent with XRD, FTIR, and DSC results. Moreover, the AF4 results suggested that the AM molecules with a random coil conformation produced by pullulanase treatment could be conducive to PS retrogradation. AF4-MALS-dRI was proved to be a useful method for monitoring debranching and retrogradation of PS. The data obtained in this study could offer a guidance for developing PS-based food with a low glycemic index.