Solid–solvent ratio in the ultrasound-assisted extraction of total saponins from quinoa husk (Chenopodium quinoa Willd.)

Abstract

This study evaluated the effect of the solid-to-solvent ratio on the ultrasound-assisted extraction of total saponins from quinoa husk (Chenopodium quinoa Willd.), with the aim of identifying an efficient operating range for further optimization studies. Saponin quantification was performed using the vanillin-sulfuric acid spectrophotometric method, employing commercial saponin from Quillaja saponaria as a standard. Calibration curves with high linearity (R2 > 0.996) and adequate reproducibility were obtained. Screening assays were carried out under fixed extraction conditions (40% v/v ethanol, 60 °C, 50% ultrasonic amplitude, and a 30 s ON–30 s OFF pulse cycle), evaluating five solid-to-solvent ratio levels (0.01–0.10 g of quinoa husk/mL solution). The results showed a significant increase in the total saponin content of the extract with increasing solid-to-solvent ratio, reaching concentrations of up to 20.27 mg total saponins/mL of extract. A reduction in the progressive increase in yield was observed at treatments above 0.075 g/mL, attributed to physical limitations of the system. Based on these results, an optimal operating range was established between 0.050 and 0.100 g of quinoa husk/mL of solution, which provides a technical basis for the subsequent application of a Box-Behnken design for multivariable process optimization. This study contributes relevant experimental criteria for the sustainable valorization of quinoa husk using ultrasound-assisted extraction technologies.