Total carbohydrates concentration in water-soluble sunflower seed extracts was determined with the phenol/sulfuric acid colorimetric method (DuBois, Gilles, Hamilton, Rebers, & Smith, 1956). Briefly, to a 2 mL aliquot of a carbohydrate solution 1 mL of 5% aqueous solution of phenol was mixed in a test tube. Subsequently, 5 mL of concentrated sulfuric acid was added rapidly to the mixture. Test tubes were shaken in an ultrasonic bath for 10 min and then left to stand at room temperature for 20 min for colour development. The absorbance of the acquired solution was measured at 490 nm on a UV–Vis spectrophotometer. A reference solution was prepared in identical manner as explained above, except that the
2 mL aliquot of carbohydrate solution was replaced by deionised water. The quantification was done based on a calibration curve obtained with glucose. Total carbohydrates in water soluble extracts (wGLU) were expressed in mg of glucose per g of extract (mg GLU/g ext.).