Effect of stearic acid modification on properties of pearl millet starch

Abstract The present study aims Pennisetum glaucum (commonly known as pearl millet) starch modification with stearic acid at various concentrations (2.4, 2.6, and 4.8%) to improve starch functionality. The interaction of stearic acid and starch was verified by X-ray diffractogram which showed peaks at 15.1°, 23.2°, and a doublet with peaks at 17.1° and 18°confirming that an A-type crystalline starch was successfully isolated from pearl millet. The crystallinity pattern of the starch-stearic acid complex was similar to native starch, but there was a slight increase in peak intensity, and an additional peak at 21.42° (SSA3) was recorded, which might be due to aggregates of stearic acid. The surface of the starch granules was slightly dented and punctured as a result of the stearic acid modification, which SEM confirmed. DSC pattern showed that compared to native starch, the starch-stearic acid complex had higher peak temperatures of 123.21 °C (SSA3), demonstrating greater thermal stability. Complex formation was also interpreted from the FTIR spectrum, which showed a small peak at 1698 cm −1 in starch-stearic acid composite samples, which might be due to the stretching vibration of C═O of stearic acid. The complexing index of the sample increased from 26.81 to 90.32% on increasing the stearic acid concentration from 2.4 to 4.8%, respectively. This characterization confirmed the reaction between the hydroxyl group of starch and stearic acid, which showed an increase in thermal stability and can also help improve hydrophobicity, which implies that this complex has the potential for usage in food packaging with improved barrier properties. Graphical abstract