Total phenolics (TP) content
A calibration curve of gallic acid (0.04 – 0.40 mg/ml) in methanol was
prepared. One ml of a standard solution of gallic acid, 6 ml of
methanol, 2.5 ml of the Folin-Ciocalteau reagent, and 5 ml of 7.5%
Na2CO3 were added to a 50-ml volumetric
flask and reached the final volume with distilled water. The solutions
were maintained overnight and the absorbance was read at 765 nm. To
measure TP, 2.5 g of oil was diluted with 2.5 ml of n -hexane and
extracted three times by 5-min centrifugations (5000 rpm) with
CH3OH:H2O (80:20 v/v). The extract was
added to 2.5 ml of Folin-Ciocalteau reagent and 5 ml of 7.5%
Na2CO3 in a 50-ml volumetric flask
reaching the final volume with distilled water. Results were expressed
in mg of gallic acid per kg of oil (Capannesi et al., 2000).