Further understanding the unique structure derived from interaction of soy proteins with acylated starch of various chain-length short-chain fatty acids

Waxy maize starch was acylated via different chain-length of short-chain fatty acids (SCFAs) (referred to AS, PS and BS, respectively), followed by investigation of their structural characteristics of complexes formed between the acylated starch and soy protein isolate (SPI) via FTIR, NMR, XRD and CLSM, etc. This is the first time to reveal that ζ-potential value of the complexes between two polymers was proportional to chain length of SCFAs. The occurrence of new peak at 1580 cm⁻¹ in AS-SPI, PS-SPI and BS-SPI might imply the interaction between NH₂ group of SPI and hydroxyl group of acylated starch. Consistently, disappearance of characteristic peaks OH-2, 3 (5.40, 5.50 ppm) from ¹H-shift in NMR further evidenced covalent reactions between two polymers. Interestingly, although acylation reduced crystallinity, new diffraction peaks at 7.5°, 14.5° and 19.8° of WMS-PS and WMS-BS revealed the formation of V-type crystalline structure rather than WMS-AS, indicating the importance of chain length of SCFAs for manipulating complexes structure. Furthermore, G′ of BS-SPI complexes was greater than G″ under various frequency, but not for other types of complexes. Meanwhile, BS-SPI complexes demonstrated a better encapsulation wall for probiotics protection against gastrointestinal digestion, which might indicate association of structural characteristics with functionality.