Rhoeo spathacea (Swartz) Stearn leaves, a potential natural food colorant

Anthocyanins, a popular choice for natural food colorants, are unstable at low acidity or neutral pH. Thus, anthocyanins that are less affected by pH, such as those with multiple acylated groups, are highly desirable. One such source is from the leaves of Rhoeo spathacea (Swartz) Stearn, an herbal plant traditionally decocted and consumed orally. This study tests the stability of the purple-red colour of R. spathacea extract from pH 1.0 to 11.5 stored under refrigerated and room temperature conditions, in the presence and absence of light over a period of 60 days. The colour stability was also monitored in a solid food model (jelly) and a liquid food model (barley water) for a month. The colour was found to be remarkably stable in acidic pH, and completely stable in the food models. The primary anthocyanin in R. spathacea leaves was isolated and identified by NMR to be rhoeonin.