Formation mechanism of polyphenol-Tartary buckwheat starch complexes and their Pickering emulsifying capacity

The complexes of gallic acid (GA), epigallocatechin-3-gallate (EGCG) and tannic acid (TA) with Tartary buckwheat starch (TBS) were prepared using the autoclaving method, and the effects of polyphenol structure on the bound polyphenol amount and the Pickering emulsifying ability of the complexes were evaluated. The molecular structure and size of polyphenols determine their different binding modes and binding amounts with TBS. The semi embedded (partially exposed) binding modes of EGCG have a positive impact on the binding amount and emulsifying capacity. The complexation altered the morphology and crystalline structure of TBS. Molecular docking analysis confirmed that the binding mode of polyphenols to starch significantly influenced the emulsifying capacity of the complexes. EGCG-TBS complexes with contact angle of 90.88° demonstrated optimal efficacy in reducing oil-water interfacial tension. It could stabilize Pickering emulsions with the oil phase volume fractions (φ) of 50 % and 60 % when the concentration (c) was 3.0 %. GA-TBS was difficult to construct stable Pickering emulsions, due to the fully embedded binding mode that is unable to alter the surface hydrophobicity of TBS. While TA-TBS could only stabilize the Pickering emulsions with φ = 50 % and 60 % at c = 4.0 %, due to the lowest binding amount and the inferior emulsifying capacity to TBS. Therefore, the difference in complex structure and binding mode affects the emulsifying performance of Pickering emulsions, which contribute to improve the emulsification theory of polyphenols and proteins.