Low-frequency ultrasound-assisted esterification of Bixa orellana L. seed starch with octenyl succinic anhydride

This study aimed to evaluate the impact of the ultrasound intensity (0, 5, 10, and 20 W/cm²) on the esterification of annatto (Bixa orellana L.) seed starch with octenyl succinic anhydride (OSA) employing a short processing time (5 min) to produce a novel emulsifier. OSA-esterified annatto seed starches were examined according to their degree of substitution (DS), amylose content, granule size distribution, microstructure, and X-ray diffractogram. Also, the performance of the OSA-modified annatto seed starch to stabilize colloidal systems was compared to commercial samples of OSA-modified starches. For this, annatto seed oil-in-water emulsions were produced and characterized according to their droplet size distribution, microstructure, and kinetic stability. Increasing ultrasound intensity from 5 W/cm² to 20 W/cm², DS values reached up to 0.139 ± 0.031. Likewise, these treatments yielded approximately 1.24-1.36 times more amylose content than the sample without ultrasound application. Most of the starch granules presented smooth surfaces without visible fissures. The higher ultrasound intensity hindered the aggregation of starch granules, thus forming well-defined elliptical particles. On the other hand, the increase of the ultrasound intensity did not change Brouckere mean diameter of the starch granules. No significant qualitative differences were seen in the X-ray diffractograms in terms of diffraction angle and peak intensity, indicating that the main functional characteristics of starches were not altered with ultrasound treatment. Furthermore, modified annatto starch was able to stabilize annatto seed oil-in-water emulsions. When compared to two commercial modified starches, OSA-esterified annatto starch produced a colloidal system with a larger Sauter mean diameter (14 ± 2 μm). However, the emulsion stabilized with modified annatto starch was more kinetically stable during the storage time in comparison to those stabilized with commercial starches.