Fractionation of Colored Maillard Reaction Products from Dark Specialty Malts

Maillard reaction products that are responsible for the color of dark specialty malts are poorly characterized. To study these compounds, Congress wort was brewed with different dark malts and evaluated with several fractionation techniques. Capillary zone electrophoresis showed that colored Maillard compounds were mainly negatively charged over a broad pH range, including wort and beer pH. Moreover, ethanol precipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), ultrafiltration, and gel permeation chromatography proved to be effective methods for the separation of colored malt components. Fractionation by ultrafiltration and gel permeation chromatography revealed the existence of two groups of colored Maillard reaction products, one group containing low-molecular-weight (LMW) compounds and the other group containing high-molecular-weight (HMW) compounds. The molecular weight (MW) distribution of malt colorants depended on malt type and color. In pale malts, colored compounds were mainly of LMW (<10 kDa), colorants of brown caramel malts were of LMW and HMW, whereas the color of black roasted malt originated almost exclusively from HMW compounds (>100 kDa). Furthermore, SDS-PAGE and gel permeation chromatography demonstrated that melanoidins from roasted malt were of higher MW than the largest melanoidins from other dark malts. By using a column with an exceptionally broad fractionation range, roasted malt melanoidins were found to have an average MW of 320 kDa. In comparison with colored products from other malts, colorants of roasted malt were not only of higher MW, but also were more intensively colored and characterized by a different color shade as observed by the absorption spectra and the Commission Internationale de l'Eclairage (CIE) L*a*b* parameters of diluted wort.