Effect of ultrasonication on OSA esterified surface modification of sorghum (Sorghum bicolor (L.) Moench) starch

The present study investigates the effect of ultrasonication (US) amplitude (30 %, 50 %, and 70 %, time- 45 min) followed by octenyl succinic anhydride (OSA, 3 %) esterification on morphological, structural, functional, and rheological properties of sorghum starch. The increase in US amplitudes significantly (p < 0.05) increased the degree of substitution (DS) of esterified starch (0.0094 to 0.0170). US treatment promotes the fragmentation of starch granules, resulting in smaller particle sizes with higher surface roughness that was further enhanced with dual modification (USOSA). The contact angle (35.681° to 79.377°) increased with both DS and surface roughness. Dual modification decreased the pasting properties, gelatinization temperature ranges, swelling power (13.11-12.17 g/g), and relative crystallinity (29.88 to 21.58 %) of starch, whereas the increase in solubility (10.06 to 13.81 %), water absorption capacity (0.92 to 1.62 g/g), and oil absorption capacity (2.17 to 3.17 g/g) were observed. The rheological assessment demonstrated a shear-thinning behavior (n < 1), with decreasing consistency indices as amplitude increased. The storage modulus (G') consistently exceeded the loss modulus (G") and damping factor (tanδ <1), indicating elastic behavior. Overall, the findings suggest that the combined US and OSA modification techniques significantly improve the properties of sorghum starch which can be used for various food applications.