The total polyphenolic content of the extracts was determined
using the Folin–Ciocalteu colorimetric method, as described by
Gao, Bjork, Trajkovski, and Uggla (2000). 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.