A novel green synthesis approach for natural bluish-violet pigments derived from water extracts of Vaccinium bracteatum Thunb. leaves

Vaccinium bracteatum Thunb. leaves (VBTL) is a historical source of pigments exhibiting potential applications for food and cosmetics. Some iridoid glycosides which could react with primary amines to form bluish-violet pigments were identified as the precursor compounds of VBTL pigments in previous study. However, the original preparing method of VBTL pigment limited further application. In this study, the fraction with higher color formation capability was obtained from the water extracts of VBTL. Some amino acids were selected as the fundamental substrates for preparing the VBTL-derived pigments for the first time. The results showed that the 60% ethanol fraction (Fr-60%) was selected to be the optimum substrate to produce pigments with amino acids. Two iridoid glycosides and chlorogenic acid were the main components in Fr-60%. The preparing parameters of pigments were optimized as follows: reaction temperature, 70 °C; reaction time, 3 h; reaction system pH, 4.0. Isoleucine, glutamine, and glycine had been proved to have high efficiency in the production of bluish-violet pigments. In addition, the storage stabilities under thermo-accelerated condition showed that these three bluish-violet pigments were more stable at lower H+ concentration (pH 4.0∼6.0).