Impact of octenyl succinic anhydride (OSA) esterification on microstructure and physicochemical properties of sorghum starch

Sorghum starch granules were esterified with octenyl succinic anhydride (OSA) to obtain modified starches with different degrees of substitution (DS) (0.0028–0.011). The reaction took place more in the amorphous rather than crystalline regions of the starch granules. This did not change the crystalline morphology of the starch and had no significant effect on the particle size and appearance of the starch, but might affect the strength of the amorphous region. OSA modification of starch could increase its swelling power and water solubility during its swelling procedure. Rheological experiments showed that the strength of starch gels decreased with increasing substitution and the gelatinization temperature decreased from 72.2 to 61.5 °C. OSA-modified sorghum starch was effective in stabilizing O/W Pickering emulsions, and the ratio of oil to water phase had a large effect on emulsion stability. Under high oil phase conditions (ϕ = 0.6–0.65) the emulsions were stable and formed self-standing gel emulsions. Sixty-day storage and centrifugation experiments demonstrated that increasing the DS resulted in a decrease in the size of the formed emulsion droplets and an increase in the stability of the emulsions. This study presents a potential application of OSA-esterified sorghum starch as a novel emulsifier to stabilize Pickering emulsions. • OSA-sorghum starches with various degrees of substitution were prepared. • The structural properties of OSA-sorghum starches were characterized. • Increasing the degree of substitution decreases the starch gelatinization temperature. • OSA-modified sorghum starch was effective in stabilizing O/W Pickering emulsions. • Appropriate oil volume fraction enhanced the stability of the emulsion.