Optimisation and kinetic study of the ultrasonic-assisted extraction of total saponins from alfalfa (Medicago sativa) and its bioaccessibility using the response surface methodology

The ultrasonic-assisted extraction of total saponins from alfalfa leaves was optimised by the simultaneous maximization of the yield and bioaccessibility as a factor with increasingly great relevance in the biological activity by Response Surface Methodology. The kinetics of total saponins and bioaccessibility were investigated for the optimum ultrasound-assisted method compared to conventional method by the pseudo-first order model. The optimum extraction conditions were of solvent/raw material ratio of 11.4 mL/g, extraction time of 2.84 h, extraction temperature of 76.8 °C, ultrasound power of 112.0 w and ethanol concentration of 78.2%. The yield of total saponins and bioaccessibility was 1.61 and 18.6%, respectively. The yield rate constant for the ultrasound extraction was almost two times more than that of the heat-reflux method. Ultrasonic-assisted extraction, comparing to conventional method, had greater efficiency for the extraction yield and bioaccessibility of total saponins.