Preparation and Structural Characterization of Rice Flour with High Content of Resistant Starch Based on Extrusion Method

In order to produce nutritious rice flour with high content of resistant starch and anti-digestive properties, the extrusion method was used to investigate the effects of high-temperature extrusion, low-temperature extrusion combined with ambient and low-temperature storage on the formation, structure and in vitro digestive properties of starch-lipid and starch-lipid-protein complexes in rice flour, using broken rice (BR) as raw material and with the addition of lauric acid (LA) and β-lactoglobulin (βLG). The optimal preparation method of rice flour containing high resistant starch was explored by taking the viscosity value of the pasting cooling peak, the differential thermal scanning enthalpies (ΔH) and the relative content of resist starch of in vitro digestion as the indicators for the formation effect of the complexes. The structural properties of the complexes were characterized by Fourier infrared spectroscopy bands and V-shaped peaks of X-ray diffraction. The results showed that different extrusion and storage treatments had a large effect on the pasting and thermal properties of rice flour, and the BR-LA-βLG group treated with low-temperature extrusion combined with low-temperature storage had the largest the pasting cooling peak viscosity value of 636 cP, indicating that the BR-LA-βLG treated with low-temperature extrusion-low-temperature storage produced the largest number of complexes, and had the highest ΔH and relative contents of resist starch in the thermal properties, which were 27.69% and 28.08%, respectively. The short-range ordering determination found that the infrared absorption peaks appeared at 1 710 cm^-1 and 2 855 cm^-1 in the BR-LA group and BR-LA-βLG group, and the intensity of the absorption peak of BR-LA-βLG group at 1 710 cm^-1 was significantly lower than that of BR-LA group. The analysis of the crystal structure showed that the Va-type crystals were formed by starch with LA and βLG under different extrusion and storage temperatures. The crystallinity of the BR-LA-βLG group treated with low-temperature extrusion combined with low-temperature storage was the highest, which was 13.77%. The processing method of low-temperature extrusion combined with low-temperature storage could be used to obtain nutritious rice flour with relatively high content of resistant starch. The research aimed to enrich the source of staple food for diabetic people, and provide some reference for the raw material production of food with high content of resistant starch.