Understanding the molecular weight distribution, in vitro digestibility and rheological properties of the deep-fried wheat starch.

The effects of frying temperature on the properties of wheat starch were investigated, including the microstructure, weight-average molar mass (M), crystalline properties, functional groups, in vitro digestibility, static rheological properties, swelling power and solubility. SEM micrographs showed that the disc-shaped starch granules ruptured after being fried, and formed a continuous and dense gel structure. With the increasing frying temperature, the starch molecules underwent violent degradation, and the M decreased from 3.04 × 10 g/mol to 0.80 × 10 g/mol. The XRD and FTIR data indicated the formation of starch-lipid complexes during the frying process. In vitro digestion analysis revealed that the digestion rate of starch decreased, while the content of resistant starch (RS) increased after being fried. Besides, the shear stability of fried starch increased, whereas its swelling power and solubility decreased. These significant variations in physicochemical properties of starch could provide scientific basis for further improving the quality of instant noodles.