Total phenolic compounds in water-soluble sunflower seed extracts were determined according to the Folin–Ciocalteu colorimetric method (Škerget et al., 2005).
Briefly, to a 0.5 mL aliquot of water-soluble sample solution 2.5 mL of Folin–Ciocalteu reagent (diluted ten times with water) and 2 mL of 75 g/L Na2CO3 were added.
The temperature of the solution was then elevated in a water bath at 50 C for 5 min. After cooling at room temperature
for 30 min, the absorbance of the solution was measured at 760 nm by an UV–Vis spectrophotometer.
A reference solution was prepared in identical manner as explained above, except that the 0.5 mL aliquot of extract solution was replaced by deionised water.
The quantification was done by calibration curve prepared with gallic acid. Total phenolics in water soluble extracts (wGA)
were expressed in mg of gallic acid per g of extract (mg GA/g ext.).