Extruded corn soy blends: physicochemical and molecular characterization

Corn soy blends (CSB), the typical high protein fortified blended food (FBF), has been extensively used to help feed the undernourished people of the developing world. In the present study, CSB binary blends were prepared using pilot-scale single & twin screw extruders. The physicochemical properties and the molecular features of the produced CSB binary blends under different extrusion conditions were investigated and their relationships were explored. Results from differential scanning calorimetry (DSC) suggested that over 93% of the starch gelatinized for each of the extruded samples. Samples treated with higher specific mechanical energy (SME) demonstrated higher water solublility index. The water absorption index showed an increasing trend at initial stage while decreasing afterward with the increase of SME. Bostwick flow rate (BF) was affected by both viscosity and gelling properties of the CSB which were reflected by both RVA analysis and dynamic rheological test. BF of extruded CSB was significantly improved (p < .05) compared to non-extruded sample. However, among the extruded samples, BF could only be partially predicted by SME. Results from HPSEC and HPAEC showed an obvious degradation of starch molecules after extrusion; harsher extrusion process resulted in more cleavage of the starch molecules.