Validation of a high-performance liquid chromatography-ultraviolet method to quantify soy sapogenols A and B in soy germs from different cultivars and in soy isoflavone-enriched supplements

An increasing number of studies investigating the health effects of soy phytochemicals has led to the commercialization of many soy-based products. Due to its particularly high concentration in many secondary metabolites, the use of soy germ as raw material is emerging for the processing of soy dietary supplements. However, the soybean seeds and germs do not exhibit the same major phytochemical profiles. This is particularly the case for soy saponins. Due to their structural diversity, the analysis of each individual soy saponin remains difficult. In this study, the total amount of these health-protective phytochemicals was determined through the quantification of their aglucon precursors, soy sapogenols A and B. A simple and rapid analytical method was developed using high-performance liquid chromatography coupled with an ultraviolet detection. The within-day and between-day variabilities of total soy sapogenol concentration were 7.3% and 10.9% in the whole seed and 3.3% and 4.7% in the germ, respectively. The total soy sapogenol contents investigated among the germs from 43 cultivars ranged from 32.8 mu mol/g to 63.1 mu mol/g: High amounts of soy saponins were also observed in several soy-based dietary supplements; from 5:5 mu mol/g to 107.8 mu mol/g, with an A/B ratio varying from 0.3 to 8.6, showing large differences between the raw materials and concentration process used. These results indicate that these compounds have to be clearly determined when discussing the biological activity of dietary supplements issued from soy.