Spectrophotometric determination of oleanolic acid and saponins from quinoa (Chenopodium quinoa Willd, Kancolla variety)

Saponins were extracted from quinoa (Chenopodium quinoa Willd, Kancolla variety) by refluxing with a methanol-water (4:1) mixture. Once the methanol was evaporated, the remaining residue was treated following Honerlagen and Tretter's method with only slight modifications. The extract was then hydrolyzed with 12N sulfuric acid in a 1:1 dioxane-water system at 110 degrees C for 1.5 hr. The sapogenins were extracted with chloroform, concentrated and some microliters (equivalent to 121 mg of quinoa) were spotted, against an oleanolic acid standard, on a silicagel g plate and developed with a chloroform-acetone-benzene (80:20:10; v/v) mixture. The spots were located by iodine vapor, and the band whose Rf was similar to that of the oleanolic acid, was scraped into a glass column, eluted with chloroform, dried out, dissolved in 1 ml of glacial acetic acid, treated with 4 ml of (1:1; v/v) sulfuric acid:glacial acetic acid mixture, heated in a water bath at 60 degrees C for 25 minutes, cooled and taken to the spectrophotometer where it was read at a wave length of 527 nm against a reagent blank. Under the same conditions, the oleanolic acid employed as a standard showed a linearity in the range of 60 to 480 micrograms. The oleanolic acid percentage has been determined (0.269 +/- 0.025) in quinoa, and the content of saponins estimated using a conversion factor found by gas chromatography and expressed in the following relationship: % Saponin = (8.5204) x (% oleanolic acid) The sapogenin extract obtained - analyzed by this method - showed an error of 10.7% in relation to its gas chromatography determination.