Water droplet surface tension method - An innovation in quantifying saponin content in quinoa seed

Quinoa surface borne saponins are bitter tasting anti-nutritional compounds that must be removed before consumption of the seed. To determine saponin content, the currently available standard afrosimetric foam test method only determines the presence of saponin via a rating of either ‘acceptable’ or ‘unacceptable’. A water droplet surface tension (WDST) based innovative method was developed that can quantify saponin content in aqueous solutions with greater accuracy. The method comprised four steps: solution preparation, droplet creation, image capture and image analysis using Axisymmetric Drop Shape Analysis computer software. The method applied satisfactorily to saponin content up to 0.2 mg.ml⁻¹ as higher concentrations did not further reduce the surface tension. Results demonstrated that saponin concentration may be measured in the range 0.05 to 0.15 mg.ml⁻¹ (0.05 – 0.15% saponin by weight of seed). Validation of the WDST method on commercial and experimental samples offers quinoa processors an accurate inexpensive way of measuring saponin concentration to satisfy current seed quality specifications.