Total phenolic acid content was determined using the Folin–Ciocalteu method
by reading the absorbance at 725 nm against a methanol blank. As briefly described,
samples (20lL, water added to 1.6 mL) were added to tubes containing 100lL
Folin–Ciocalteu reagent and 300lL sodium carbonate (20%). After incubation at
40C for 40 min, the absorbance at 725 nm was measured.