Pearl millet starches were modified at pH 8.0 using 3.0% octenyl succinic anhydride (OSA), and their pasting, rheological properties, and in vitro digestibility were analyzed. The degree of substitution (D.C.) of OSA-modified starches varied from 0.010 to 0.025. The amylose content decreased after modification, while the reverse was observed for swelling power. After OSA modification, the pasting viscosities (peak, trough, setback (cP)) of the modified starches increased compared to their native counterparts. G′ (storage modulus) and G″ (loss modulus) decreased significantly (p < 0.05) compared to their native counterparts during heating. Yield stress (σo), consistency (K), and flow behavior index (n) varied from 9.8 to 87.2 Pa, 30.4 to 91.0 Pa.s., and 0.25 to 0.47, respectively. For starch pastes, steady shear properties showed n < 1, indicating shear-thinning and pseudoplastic behavior. The readily digestible starch (RDS) and slowly digestible starch (SDS) contents decreased, while the resistant starch (R.S.) content increased. After OSA treatment, the solubility power of the starches increased; this property of OSA starches speeds up the biodegradability process for the films, and it helps to maintain a healthy environment.
Keywords: OSA; coatings; digestibility; film; pasting; pearl millet; rheology; starch.