The total polyphenolic content of the extracts was determined
using the Folin–Ciocalteu colorimetric method, as described by
Gao, Bjork, Trajkovski, and Uggla . Potato extract (0.1 ml)
and Folin–Ciocalteu reagent (0.2 ml) were pipetted into cuvettes.
After 3 min, 1 ml of a 20% aqueous solution of sodium carbonate
(Na2CO3) and 2 ml of distilled water were added. The absorbance
at 765 nm was measured after 1 h, and the results were expressed
as mg of gallic acid equivalents per 1 g of dry matter (DM). Data are
reported as the mean value for four measurements.