Polyphenolic composition of raisins

The polyphenolics of raisins were extracted, separated by HPLC, and charact erized by their UV-vis spectra, and their concentrations measured. Color me asurements and browning indices were also determined. Samples (n = 20) incl uded sun-dried, dipped, and golden raisins. Comparisons were also made with fresh and frozen Thompson Seedless grapes. Golden raisins (which are treat ed with SO2) had the highest amount of hydroxycinnamic acids and the highes t lightness values. In comparison with fresh grapes, percent losses of the two major hydroxycinnamics (caftaric and coutaric acids) in sun-dried, dipp ed, and golden raisins were on the order of 90%. Flavonols were not influen ced by processing as much as hydroxycinnamics, while procyanidins and flava n-3-ols were completely degraded in all raisin samples. Formation of hydrox ymethylfurfural and loss of amino acids in sun-dried and dipped raisins are ascribed to Maillard browning reactions.