Sulfonation of Monascus pigments to produce water-soluble yellow pigments

Red Yeast Rice, a kind of Monascus pigments produced by fermentation of Monascus species on rice, is a traditional Chinese medicine and food colorant. Chemical modification of natural pigments is a common strategy to diversify the pigments to meet various demands. Herein, native Monascus pigments as well as some of their derivates were prepared. Sulfonation of Monascus pigments with conjugated double bonds adjacent to a carbonyl group was carried out to produce novel water-soluble yellow pigments (WSYPs). The chemical structure of novel WSYPs, i.e., an addition of H2SO3 to the double bond at the side-chain of Monascus pigments, was elucidated by MS and NMR analysis. The introduction of H2SO3 into Monascus pigments makes WSYPs exhibit yellow color and high water solubility. The yellow color, high water solubility, as well as relatively high stability in a wide pH range contribute the novel WSYPs as a potential food colorant.