Impact of octenyl succinic anhydride esterification on Kodo millet starch-commercial protein blends functionality and Pickering emulsion properties

This study was designed to investigate the morphological, structural, rheological, functional, and emulsifying properties of native (NKS) and octenyl succinic anhydride (OSA)-esterified Kodo millet starch (EKS) blended with commercial pea protein (PP), soy protein (SP), and whey protein (WP). The effects of esterification and blending on the stabilization of oil-in-water Pickering emulsions were also evaluated. Morphological analysis revealed significant starch-protein interactions, causing deformation and surface irregularities in the NKS and EKS blends, with stronger interactions in the esterified blends due to hydrophilic and hydrophobic forces. Structural characterization revealed similar crystalline structures in starch-protein blends, with increased X-ray diffraction peaks after protein addition. However, esterification reduced the pasting temperature (PT) from 88.80 °C (NKS) to 83.25 °C (EKS), and protein addition further decreased the PT by 0.5-4.80 % for the NKS blends and 0.25-1.62 % for the EKS blends, indicating reduced swelling resistance and thermal stability. Rheological tests of starch-protein blend suspensions revealed shear-thinning flow and elastic-dominant (G' > G'') behavior, with EKS-protein blends exhibiting stronger gel networks. NKS-protein blends had relatively high water absorption capacities (2.37-2.43 g/g), whereas EKS-protein blends showed higher oil absorption capacities (2.32-2.37 g/g). The emulsifying activity index (11.03 to 12.76-16.21) and emulsifying stability index (70.49 min to 93.85-99.62 min) increased after blending, with Pickering emulsions remaining stable for a minimum of two weeks. However, emulsion stability was highest for the EKS-SP blends, which remained stable for up to 25 days. Overall, the esterification of starch increased its compatibility with proteins, leading to improved emulsifying properties and more stable emulsions.