Extraction kinetics of saponins from quinoa seed (Chenopodium quinoa Willd)

Abstract

Quinoa has higher protein content (11-16% m/m) and better amino acid profile than cereals and represents a valuable resource for healthy nutrition. The aim of this work was to study the saponins extraction kinetics during washing of soaked quinoa. The experimental curves of saponins content as a function of time was measured at water temperatures of 20, 40, 60, and 70ºC. A spectrophotometric method was proposed to determine total saponins content, while an unsteady state diffusional model was applied to this extraction problem, assuming strict internal control to the mass transfer rate. As a first analysis, the complete analytical solution for constant diffusion coefficient (D_eff) using the initial radius (R₀) provided an accurate predicted curve at each temperature. The diffusion coefficients (around 10⁻¹⁰ m²s^-1), were correlated with temperature using an Arrhenius-type relationship to obtain an activation energy E_a  of 16.9 kJ mol^-1.  The preliminary values of E_a and preexponential factor (D₀) thus obtained were used as initial values of a second, more robust fitting where the whole dataset of saponins concentrations as a function of time for all temperatures. The Arrhenius equation was directly inserted into the diffusional solution. The following parameters were obtained: E_a= 17.2 kJ mol^-1 and, D₀= 3.232×10⁷ m² s^-1, respectively with an overall r²=0.985. Saponins content agreed well with experimental values. As the equation is capable of predicting saponin extraction times for various operating conditions, it can be used within equipment design schemes.