J. Sci. Food Agric. zyxwvutsrq 198 I, 32, 273-278 zyxwvut Saponin Content of Soya Beans and Some Commercial Soya Bean Products Dorothy E. Fenwick and David Oakenfull CSIRO Division of Food Research, PO Box 52, North Ryde, New South Wales 2113, Australia (Manuscript received 19 May 1980) Quantitative thin layer chromatography has been used to estimate the saponin content of whole soya beans (Glycine zyxwv max L. Merrill, cv. Williams) and a number of commercial soya bean products such as protein isolates and lecithin. Saponins were present in all these materials at concentrations ranging from 56 g kg-1 (on a dry weight basis) for whole soya beans to 3 g kg-1 for the protein isolate ‘Promine-D’. Previous estimates indicate a saponin content of whole soya beans of only about 5 g kg-l. It is suggested that this is an underestimate resulting from loss of material during the extraction procedures used in earlier methods of analysis. 1. Introduction Saponins are steroid or triterpenoid glycosides which occur in a wide variety of These compounds seem to be of considerable nutritional significance since dietary saponins lower plasma cholesterol concentrations in experimental animals4j5 and possibly have the same effect in man.6 Soya beans contain at least ten triterpenoid sap on in^^,^^* and the presence of these may account for the cholesterol-lowering effect of various soya bean products when present in human and animal Therefore, the saponin content of whole soya beans zyxwv (Glycine max L. Merrill, cv. ‘Williams’) and a number of commercial soya bean products have been estimated: protein isolate, tofu (bean curd), defatted flour, and lecithin. Essentially, the method of KartnigI2 was followed-using thin layer chromatography (t.1.c.) to separate the saponins from a crude extract of the plant material and a densitometer to estimate the quantity of saponins on the chromatogram. All the test materials contained significant amounts of saponins. diets.5,6.9-11 2. Experimental 2.1. Extraction of saponins The material was dried for 16 h at 110°C. zyxwv A weighed sample (about 20 g) was exhaustively extracted with acetone in a Soxhlet extractor to remove lipids, pigments, etc. The solvent was then changed to methanol and the extraction continued for at least 36 h. The methanolic extract was allowed to cool and made up to 200 ml with methanol. This solution contained the saponins, but also other compounds such as flavonoids. 2.2. Thin layer chromatography Standard samples (5-50 pl) of the methanolic extract were spotted on to pre-coated silica gel t.1.c. plates (Merck, Kieselgel 60 F-254). The plates were developed with zyx n-butanol-ethanol-concen- trated ammonia (3.5: 1 :2.5). To visualise the spots the plates were sprayed with a 100 ml litre-1 solution of sulphuric acid in ethanol and heated at 110°C for 30 min. A typical chromatogram is shown in Figure 1 in which an extract prepared from whole soya beans is compared with a purified commercial saponin (saponin white, Ajax Chemicals, Sydney). 0022-5~42/81/0300-0273$02.00 zyxwv @ 1981 Society of Chemical Industry zyx 213