Determination of total flavonols
The content of total flavonols was determined following the Yermakov
method (Mickelsen & Yamamoto 1958). Rutin hydrate (Sigma Aldrich,
purity ≥ 94%) was used as standard solution. Briefly, 200 μL of sample
or rutin standard was mixed with 200 μL AlCl3 (20 g
L-1 in ethanol, Sigma Aldrich) and 600 μL sodium
acetate (50 g L-1; Sigma Aldrich). Samples and
standards were incubated at 20 °C for 2.5h, and absorbance measured at
440 nm using a spectrophotometer (Agilent Technologies, Cary Series 100
UV-VIS Spectrophotometer, Italy). Results were expressed as µmol rutin
equivalent.