Impact of soy protein isolate addition on corn starch during gelatinization: exploring the mechanism behind physicochemical property changes

Background: Effective food quality management requires an understanding of starch-protein interactions, as many pre-prepared foods rely on partial gelatinization for their texture and stability. The aim of this study was to examine the interactions between soy protein isolate (SPI) and normal corn starch (NCS) at various stages of the starch gelatinization process and to assess their effects on the physicochemical qualities of the resulting composite. 

Results: Rheological analysis suggested that hydrogen bonding was the primary mode of interaction in NCS-SPI composites during the gelatinization process. Experiments on the leaching of amylose starch and iodine binding demonstrated dose-dependent and temperature-dependent interactions between SPI and the leached amylose. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analyses revealed that SPI increased the quantity of hydrogen bonds inside the starch, enhancing both the short-range molecular arrangement and long-range structural order of NCS during the gelatinization process. When the heating temperature was adjusted from 50 to 65 °C, the relative crystallinity (RC) of NCS decreased by 8.02% (from 24.71% to 16.69%) whereas the RC of NCS-SPI decreased by only 1.37% (from 20.43% to 19.06%). Microstructural observations also provided visual evidence of SPI adhering and scattering on the surface of starch granules. 

Conclusion: Interactions between SPI and NCS during the gelatinization process significantly impeded the gelatinization of NCS and altered its physicochemical and functional properties. These findings provide valuable insights into starch-protein interactions during the gelatinization process, contributing to research and quality control with regard to starch-based foods.