Preparation and Characterization of Acetylated Submicron Starch Derived from Broken Rice

Abstract

Broken rice is an underutilized agro-industrial by-product with high starch content and potential for value-added applications. However, native starch has several limitations, including high hydrophilicity and relatively large particle size, which may restrict its broader functional use. This study investigated the modification of broken rice starch through acetylation followed by sulfuric-acid hydrolysis to obtain acetylated starch with reduced particle size. Acetylation was carried out using two acetic anhydride levels, namely 10 and 20 g/100 g starch, and reaction times of 15, 30, and 45 min. The modified starches were evaluated for acetyl content and degree of substitution (DS), and were further characterized by Fourier transform infrared spectroscopy (FTIR), particle size analysis, zeta potential measurement, and scanning electron microscopy (SEM). Increasing acetic anhydride level and reaction time increased acetyl content and DS, with the highest DS value of 0.119 ± 0.004 obtained at 20 g/100 g starch and 45 min. After acid hydrolysis, the DS decreased to 0.055 ± 0.002. FTIR spectra indicated structural changes after acetylation and subsequent hydrolysis. The acid-hydrolyzed acetylated starch showed an average particle size of 557.72 ± 3.18 nm, a polydispersity index (PDI) of 0.08 ± 0.03, a zeta potential of 3.10 ± 0.40 mV, and irregular surface morphology. These findings indicate that sequential acetylation and acid hydrolysis of broken rice starch produced an acetylated starch material with reduced particle size and altered surface characteristics. However, the low zeta potential suggests limited colloidal stability, indicating that further optimization is required before further application-related evaluation.