Ultrasound pretreatment-enhanced OSA esterification of proso millet starch for application in low-fat mayonnaise

Ultrasonication (US) pretreatment (10 and 20 min) before octenyl succinic anhydride (OSA, 3 %) esterification significantly increased the degree of substitution (DS) in proso millet starch, increasing it from 0.0078 to 0.0115. This dual modification led to smaller, rougher starch particles due to US-induced fragmentation. Consequently, the pasting qualities, gelatinization temperature, swelling power, and relative crystallinity decreased, whereas the solubility, water absorption, and oil absorption increased. All starch gels exhibited shear-thinning behavior with dominant elastic properties (G' > G''), which are desirable in mayonnaise formulations with good spreadability, structural stability, and a consistent mouthfeel. When used as a fat substitute in mayonnaise, dual-modified starches, particularly the US20-OSA sample, demonstrated improved thickening and thermal stability, maintaining higher viscosity across temperatures than fully fat-based samples. Microscopy confirmed enhanced emulsion stability in the dual-modified samples due to the finer, more uniform oil droplet dispersion. This highlights the potential of dual-modified proso millet starch as an effective fat replacer.