Effects of debranching and repeated heat-moisture treatments on structure, physicochemical properties and in vitro digestibility of wheat starch

In this study, wheat starch (WS) was firstly debranched with pullulanase (PUL) and then subjected to repeated heat-moisture treatments (RHMT). The effects of PUL and RHMT on the structure, physicochemical properties and in vitro digestibility of WS were investigated. The proton nuclear magnetic resonance spectroscopy confirmed that the ratio of alpha-1,6 glycosidic linkage decreased. Raman and Fourier transform-infrared spectroscopy demonstrated that more ordered structure of starch was formed. Differential scanning calorimetry and X-ray diffraction analysis revealed that RHMT could enhance thermal stability and degree of crystal perfection of PUL-WS sample. Scanning electron microscopy results showed that more agglomerates appeared on the surfaces of RHMT starch granules. The swelling power and solubility significantly decreased after HMT. Additionally, the resistant starch (RS) content of RHMT samples significantly increased. These results suggest that debranching and RHMT can significantly change the physicochemical properties and digestibility of WS, and it's beneficial to the RS formation.