OSA-Starch Production – Improved Esterification by Sonication

Esterification of starches with octenyl succinic anhydride (OSA) is a widely applied modification technique, especially relevant in the food industry for creating functional starches with improved properties. However, traditional OSA starch modification under alkaline conditions is time-consuming and can limit the efficiency and feasibility of the process. Ultrasonically assisted esterification is an effective alternative approach to accelerate the esterification of starches with OSA. By applying sonication, a higher degree of substitution (DS) and reaction efficiency (RE) is achieved when compared to conventional alkaline OSA esterification. This means sonication allows for an expansion and the applicability of esterified starches in the food industry. The results of scientific studies underscore sonication-assisted esterification as an efficient, eco-friendly advancement in starch modification.

Ultrasonic Esterification of Octenyl Succinic Anhydride Starch

Starches are essential polysaccharides in the food industry, widely used as thickeners, stabilizers, and emulsifiers due to their unique properties. However, the functional limitations of native starches often necessitate modifications to enhance their performance. Esterification with octenyl succinic anhydride (OSA) is a chemical modification process that introduces hydrophobic groups, enhancing the emulsifying and stabilizing capabilities of starch. Despite its effectiveness, conventional OSA esterification under alkaline conditions is a lengthy process. Ultrasonically assisted esterification is a green technology that can potentially increase the degree of substitution (DS) and reaction efficiency (RE) of OSA starches, improving time and resources.

Sonication improves the esterification of OSA starch. Effect of ultrasound intensity on the microstructure of the OSA-esterified annatto seed starch.
Study and images: ©Keven Silva et al. 2022

Case Study: Ultrasonic Esterification of OSA Potato Starch

In the study by Martínez et al. (2024), Andean native potato starches were subjected to both conventional alkaline OSA esterification and ultrasound-assisted (US-OSA) esterification. They analyzed the granule morphology, molecular characteristics, thermal properties, and rheological behaviors of the resulting starches to determine the potential advantages of ultrasound-assisted esterification.

Starch Samples and Esterification Procedure

Andean native potato starches were esterified using two methods:

• Conventional OSA Esterification (OSA) – conducted under alkaline conditions with octenyl succinic anhydride.
• Ultrasonically Assisted OSA Esterification (US-OSA) – where ultrasonic waves were applied during the esterification to enhance the reaction rate and effectiveness.

Degree of Substitution (DS) and Reaction Efficiency (RE)

The ultrasonically assisted esterification process produced starches with a significantly higher degree of substitution (DS) and reaction efficiency (RE) compared to conventional methods. This enhancement is crucial, as DS reflects the extent of hydrophobic group substitution on the starch molecule, directly influencing its emulsifying properties.
The high reaction efficiency in ultrasonically modified OSA starches suggests that ultrasonic waves enhance molecular collisions and the penetration of OSA molecules into starch granules, potentially due to cavitation effects, which improve mass transfer and promote more efficient esterification.

Morphological Characteristics

Microscopic examination of granule morphology revealed notable differences between OSA and ultrasonically modified OSA starches. While both modified starches retained granule integrity, ultrasonically modified OSA granules showed peeled surfaces with some pores, indicating the ultrasonic treatment had a mild impact on surface structure. This structural modification, albeit slight, suggests improved accessibility of starch granules for esterification without compromising granule integrity.
Additionally, ultrasonically modified OSA starches displayed lower span values, indicating a narrower size distribution and more uniform granule population. This consistency could benefit specific food applications where precise texture and stability are essential.

Molecular Features

IR spectroscopy and XRD analysis showed minimal structural differences between OSA and ultrasonically modified OSA starches. Both starch types retained the characteristic starch structure, with no detectable changes in crystallinity patterns, confirming that ultrasound-assisted treatment did not disrupt the native structure of starch significantly.
This molecular stability is advantageous, as it ensures that ultrasound-assisted esterification enhances functionality without altering the starch’s fundamental molecular framework, which is critical for maintaining desirable textural properties in food applications.

Thermal Properties

The thermal behavior, specifically gelatinization enthalpy, differed between conventional OSA and ultrasonically modified OSA starches. The ultrasonically modified OSA starches exhibited a lower gelatinization enthalpy compared to conventional OSA starches, suggesting a reduced energy requirement for gelatinization. This finding implies that the ultrasound treatment may facilitate easier hydration and gelatinization, potentially enhancing the modified starch’s processability in food applications that involve thermal processing.

Rheological Properties

Ultrasonically esterified OSA starches demonstrated favorable rheological properties, with viscosity profiles similar to or slightly enhanced compared to conventional OSA starches. Such properties can improve their performance in applications requiring stable emulsions or consistent viscosity under varying processing conditions.

Case Study: Ultrasonically Esterified OSA-Starch from Annatto Seeds

The study by Silva et al. (2013) investigated the effect of sonication intensity on the esterification of annatto seed starch with octenyl succinic anhydride (OSA), aiming to create a novel emulsifier for colloidal systems. Ultrasound was applied at varying intensities (0, 5, 10, and 20 W/cm²) for a brief processing time (5 minutes). Key findings included an increase in the degree of substitution (DS) with higher sonication intensity, reaching a maximum degree of substitution of 0.139 ± 0.031 at 20 W/cm². The sonication treatment also boosted amylose content by 1.24–1.36 times compared to samples without sonication.
Granule morphology revealed smooth surfaces and well-defined elliptical particles at higher sonication intensities, which reduced granule aggregation. The X-ray diffraction patterns showed no significant qualitative differences, indicating that ultrasound did not alter the starch’s crystalline structure. The modified starches were effective at stabilizing annatto seed oil-in-water emulsions, achieving larger Sauter mean diameters (14 ± 2 μm) but displaying greater kinetic stability over time compared to commercially modified starches. Overall, ultrasonically-assisted OSA modification proved to be a rapid and effective approach for enhancing the functional properties of annatto seed starch as an emulsifier.

Sonicators for OSA-Starch Esterification

Hielscher industrial sonicators are high-performance ultrasonic devices used to enhance OSA-esterification of starches, a process that introduces hydrophobic octenyl succinic anhydride (OSA) groups to starch molecules. Through ultrasonic cavitation, these sonicators create microjets and intense shear forces in the starch suspension, improving the diffusion and reaction efficiency of OSA into starch granules. This results in a higher degree of substitution (DS) and improved reaction efficiency, often achieved in significantly shorter times compared to conventional methods. Hielscher sonicators are ideal for industrial-scale applications, offering precise control over parameters like intensity, frequency, and duration to optimize the esterification process, ensuring consistent quality in modified starch products for enhanced emulsifying and stabilizing properties.

Design, Manufacturing and Consulting – Quality Made in Germany

Hielscher ultrasonicators are well-known for their highest quality and design standards. Robustness and easy operation allow the smooth integration of our ultrasonicators into industrial facilities. Rough conditions and demanding environments are easily handled by Hielscher ultrasonicators.

Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators: