Acta Scientiarum Polonorum Technologia Alimentaria

Background. Biopolymers can be modified to induce and enhance complexation with other molecules. This study aimed to: (a) obtain insoluble complex coacervates (ICC) via electrostatic interactions between native (N) and modified amaranth protein (AP) using pH shifting (pH 12) and ultrasonication (US), or dual treat­ment (pH 12-US) with gelatinized octenyl succinic anhydride-modified corn starch (CS_OSA); and (b) evaluate the structural, rheological, thermal, morphological and digestibility properties of the ICC variants.
Material and methods. Protein-polysaccharide ICC variants were prepared via electrostatic interactions at pH 3.5 and designated as AP_N-CS_OSA, AP_US-CS_OSA, A_PpH12-CS_OSA and AP_pH12US-CS_OSA. These variants were evaluated for ζ-potential, secondary structure and starch band, in vitro digestibility, rheology, calorimetry, morphology, sulfhydryl groups and disulfide bonds.
Results. Protein modification significantly influenced the starch band and the proportions of major second­ary structure components (β-sheet, random coil, α-helix and β-turn) in the ICC variants. In vitro protein digestibility was highest in AP_N-CS_OSA (98.1 ±0.52%) and AP_pH12US-CS_OSA (98.3 ±0.91%). All ICC variants showed a significant increase in the slowly digestible starch fraction. The pasting temperature was highest for AP_N-CS_OSA (88 ±0.8°C) and lowest for AP_pH12-CS_OSA (55 ±1.3°C). Starch retrogradation was lowest for AP_pH12US-CS_OSA (43 ±0.37%) and highest for AP_N-CS_OSA (63 ±1.1%).
Conclusion. Vegetable by-products, such as proteins and starch, can be effectively used to form ICCs. How­ever, they require prior modification through chemical and/or physical methods to optimize their techno-functional properties and digestibility.