Soyasaponins I and bg in raw and cooked legumes: determination by SPE-HPLC-MS and its bioaccesibility by an in vitro digestion model

Legumes represent an important component of human diet in several areas of the world, especially in the developing countries where they complement the lack of proteins from cereals (Kalogeropoulos et al., 2010). Legumes include lentil (Lens culinaris L.), bean (Phaseolus vulgaris L.), pea (Pisum sativum L.), chickpea (Cicer arietinum L.), lupin (Lupinus albus) and others. Legumes are low in fat and rich in proteins, exhibiting lower glycaemic index compared to other starchy foods. In addition, legumes contain a rich variety of phytochemicals, including phytosterols, natural antioxidants and bioactive molecules such as soyasaponins (SSs). SSs are triterpenoidal glycosides (group A, monodesmosidic and group B, bidesmosidic) that possess multiple health-promoting properties such as lowering of cholesterol. Although the mechanism is not completely clarified, a proposed theory is based on the formation of non-absorbable complexes between SSs and cholesterol in the gut lumen. Notably, the hypocholesterolemic action was referred to SSs belonging to group B, such as SS I and SS g, that are particularly abundant in legumes (Sagratini et al., 2009). The aim of this work was the quantification of SS I and SS g in raw and cooked legumes of difference provenience and variety (60 samples) by a SPE-HPLC-MS method developed in our lab. The total level of SS I and g in raw seeds was in the range 1200-2500 mg kg-1. The cooking process produces a small loss of SSs in water, i.e. 5.6-7.6%, depending on time cooking and legume type. The bioaccessibility of SS I and g contained in lentils was determined by using an in vitro digestion model. References G. Sagratini, Y. Zuo, G. Caprioli, G. Cristalli, D. Giardinà, F. Maggi, L. Molin, M. Ricciutelli, P. Traldi, S. Vittori. 2009. Quantification of Soyasaponins I and bg in italian lentil seeds by solid-phase extraction (SPE) and high performance liquid chromatography-mass spectrometry. J. Agric. Food Chem. 57:11226-11233. N. Kalogeropoulos, A. Chiou, M. Ioannou, V.T. Karathanos, M. Hassapidou, N.K. Andrikopoulos. 2010. Nutritional evaluation and bioactive microconstituents (phytosterols, tocopherols, polyphenols, triterpenic acids) in cooked dry legumes usually consumed in the Mediterranean countries. Food Chem. 121(3): 682-690.