Certification of reference materials for analysis of isoflavones genistin and genistein in soy products†
Soy isoflavones are a class of secondary metabolites in the growth process of soybeans or other legumes. Many studies support their roles in the prevention and treatment of cancer, arterial sclerosis, osteoporosis and menopausal syndrome. Genistin and genistein, the two highest amount active ingredients in soy isoflavones, were developed into two new certified reference materials (CRMs) in this work. According to the guidelines of development of CRMs, mainly ISO Guides 34:2009 and 35:2005, studies on sample preparation, homogeneity, stability, characterization, and uncertainty estimation were carried out. In the characterization, two methods based on different theories, namely differential scanning calorimetry (DSC) and coulometric titrimetry (CT), were employed. Genistin and genistein CRM certified values and corresponding expanded uncertainties, obtained from the combined standard uncertainty multiplied by the coverage factor (k = 2), for a confidence level of 95%, were 99.7 ± 0.3% and 99.3 ± 0.5%. The mass balance (MB) method was employed to cross-check the results. Genistin and genistein CRMs have been approved and assigned as a grade primary reference material by the National Administrative Committee. These CRMs can be applied to the analysis of soy isoflavones in related products, such as (fermenting) soybean foods or medicines.