An Estimate of the Nonflavonoid Phenols in Wines

Abstract

A new and improved technique has been developed for the quantitative estimation of flavonoid and nonflavonoid phenols in wine and other plant extracts. It is based upon the determination of the phenol content before and after precipitation and removal of the flavonoids through reaction with formaldehyde under selected conditions (low pH, room temperature, etc.). Under the selected conditions phenols lacking a meta-dihydroxy grouping (nonflavonoids in plants) did not precipitate. Reproducible values were obtained on a series of wines with a coefficient of variability of about 2.5%. The nonflavonoid content of sweet and dry, white and red wines was very similar (183-322 mg/l as gallic acid) in spite of initial total phenol contents of a wide range (205-1421 mg/l as gallic acid). This verities the hypothesis that the caffeic acid derivatives and other nonflavonoids of grapes are located almost exclusively in the juice and therefore do not require extraction from firmer tissues into wine. Conversely, the flavonoid constituents are nearly absent in juice and wines derived from juice, but high in wines made under conditions affording extraction from grape skins and other pomace solids.