New Metalloanthocyanin from Blue Petals of Salvia uliginosa

Abstract

Blue, violet, red, orange colors of flower are mostly composed of anthocyanins, betalains and carotenoids. Among them, the anthocyanins are widely used as natural food colorants additives because the anthocyanins are thought to be safe as food additives. Anthocyanin changes its color with pH change; in strongly acidic medium, it shows orange to red color, whereas reddish violet to violet color appears in weakly acidic or neutral solutions. Blue color can be produced only in alkaline pH.Willsta tter, who determined the basic structure of anthocyanin around 1913, attributed the variety of flower colors to pH variation in flower cell sap. However, most blue flower cell sup is weakly acidic and never basic, and the blue color could not be explained by the Willsa tter's pH theory. Extensive studies on the correlation between the structure of the anthocyanins and flower color variation have been carried out and several proposals have been presented, i.e. metalloanthocyanin, copigmentation of anthocyanin and flavone, and intracellular sandwich-type stacking. In nature, there are many blue flowers, and it is not necessarily clear that each pigment of the all blue flower colors is suited to which one of the above proposals. Because of wide use of anthocyanin for food additives, the structure of each anthocyanin is very important to understand the mechanism of coloring and to understand the stability of anthocyanins in food. We have been interested in the flower color of Salvia uliginosa and found that its pigment contains magnesium and clarified that for the blue color expression, magnesium is essential. This paper describes about a new metalloanthocyan from blue petals of S. uliginosa.