Ultrasound-Assisted Extraction of Okra Mucilage: Rheological Properties of its Aqueous Solutions

Abstract

Using chemical and physicochemical techniques, we extracted the mucilaginous component of okra (Abelmoschus esculentus L.) by the ultrasound-assisted extraction method, then evaluated the resulting polysaccharide extract's rheological properties. Our investigation encompassed examining the flow behavior of polysaccharides extracted under different okra to distilled water ratios (1:10 and 1:30) and various polysaccharide concentrations (1, 2, 3 and 4%, w/v) over a temperature range of 10°C to 80°C. Employing the power law model, we derived parameters and found that okra polysaccharides displayed non-Newtonian pseudoplastic flow characteristics. The flow behavior index ranged from 0.234 to 0.947, with the consistency coefficient ranging from 4.37 to 244.50 mPa.s. Increasing temperature resulted in a decrease in both the consistency coefficient (K) and flow behavior index (n), while concentration elevation led to higher consistency coefficient values. However, the flow behavior index did not exhibit consistent trends with concentration variations. Three statistical parameters; correlation coefficient (R2), root mean square error (RMSE) and chi-square (χ2) were used to evaluate the fit of the power law model to the experimental data. Our study further explored temperature’s impact on the apparent viscosities of okra polysaccharide samples and modeled the influence of temperature on the consistency index using the Arrhenius equation. Samples with solid-to-solvent ratios of 1:10 and 1:30 showed increasing activation energy with concentration rise, with the highest value recorded at 275.84 kJ/mol for the 1:10 ratio sample with a 4% concentration. In SEM images, okra polymers exhibit irregular, wavy, rough textured surface, and amorphous appearance. These findings hold promise for optimizing ultrasound extraction protocols and enhancing the industrial utilization of mucilages through their rheological properties.