Structure and in vitro digestibility on complex of corn starch with soy isoflavone

Abstract

Rapid starch digestion rate is negative for the normal level of human blood glucose. This study investigated the protective effects of corn starch (CS) complexed with soy isoflavone (SI) on the control of starch digestibility and glycemic index (GI). The structure of the corn starch–soy isoflavone (CS-SI) complexes was characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA), and Differential scanning calorimetry (DSC), and the complexes digestibility was evaluated using in vitro digestion model. The results of FT-IR spectrum showed that, compared with corn starch, new characteristic peaks were not occurred in CS-SI complexes, and the value of R1047/1022 was decreased, which indicated the short-range structure of CS-SI complexes had been reduced. The V-shaped structure characteristic peaks occurred obviously in CS-SI complexes detected by XRD patterns, which formed a new crystalline structure. The thermal stability was improved in CS-SI complexes revealed by TGA and DTG curves that the thermal cracking temperature increased from 315°C to 320°C. The enthalpy (ΔH) of CS-SI complexes decreased from 2.34 J/g to 1.75 J/g showed by DSC data, which indicated that the ordered structure of starch was destroyed. Furthermore, the content of resistant starch increased from 10.53% to 21.78% and predicted glycemic index (pGI) reduced in CS-SI complexes. In conclusion, the digestibility and pGI of starch can be improved by complexed with soy isoflavone.