Effect of ultrasound on the processing of oleoresin emulsions from Capsicum peppers and saponins

This study aimed to produce emulsions with Capsicum oleoresin in the oil phase and quillaja saponins aqueous solution by ultrasound-assisted emulsification. It was expected that the emulsification of oleoresin (micrometric scale emulsions) could increase the bioavailability of the compounds presented in the oleoresin. Initially, the ultrasound equipment's effective power was determined by experiments to compare the nominal power with the dissipated power. The rated powers of 150 (20%), 300 (40%), 450 (60%), and 600 W (80%) were evaluated at 3, 6, and 9 min. The condition of 60% nominal power (450 W) and 6 min resulted in better emulsification performance. Subsequently, emulsions were obtained by mixing the quillaja saponins water solutions (0.01; 0.1; 0.5; 1.0; 1.5 and 2.0% w/w) with an oil phase (10% w/w) composed of commercial oleoresin from Capsicum pepper under fixed conditions of 6 min and 450 W. Emulsions were characterized by zeta potential, microscopy, and droplet size. For the concentration of 1.0% w/w, the average size of emulsion droplets remained practically constant; therefore, this concentration was selected for the following experiments. After that, the ultrasound power was set at 450 W to evaluate the effect of the time variable (2, 4, 6, 8, and 10 min) on the characteristics of the emulsions. The droplets had a significant size reduction in the first 6 min, starting from 0.75 μm (2 min) to 0.35 μm (6 min), and from 6 to 10 min, there was no significant variation in the droplet size of the emulsions. Finally, based on the previous result, the ultrasound emulsification time was set at 6 min and the nominal power varied at 150, 300, 450, and 600 W. In a similar way to what was observed for the influence of the processing time on the droplet size, it was verified that there was a reduction in the size of the droplets with the increase of the ultrasound power up to 450 W (60% of the rated power), remaining practically constant from 450 to 600 W. The results made it possible to select the best experimental conditions for producing emulsions with smaller droplet sizes using 450 W of nominal power for 6 min and with a surfactant concentration in the aqueous phase of 1% w/w. This result agrees with what was previously verified when the performance of the ultrasound equipment was evaluated. In this way, emulsions with smaller diameters were obtained under ultrasound conditions with the highest ratio between rated power and dissipated power.