Molar absorptivities (ε) and spectral and colorimetric characteristics of purple sweet potato anthocyanins

Abstract

Purple sweet potato, a source of acylated cyanidin and peonidin derivatives, is commercially available as a food colorant. Our objectives were to determine molar absorptivities (ε), spectral and colorimetric properties of purple sweet potato anthocyanins. Anthocyanins were isolated by semi-preparative HPLC, weighed, dried, and redissolved in acidic methanol or water. Anthocyanins were diluted in pH 1–9; ε, spectra, and color were measured on the methanolic and aqueous solutions. Higher ε were obtained in 0.1% HCl methanol (10,797–31,257 L/(mol × cm)) than in aqueous solution pH 1 (8861–24,303 L/(mol × cm)). Peonidin-3-sophoroside-5-glucoside had greatest ε in pH 1, but in alkaline pH, ε of acylated Peonidin-3-sophoroside-5-glucoside derivatives were greatest. Generally monoacylation decreased ε while diacylation increased ε. Location of acylation also affected ε of two Peonidin isomers (pH 1: 15,999 and 21,011 L/(mol × cm)). All anthocyanins expressed red-pink hues (330°–13.2°) in acidic pH and blues (230°–262°) in alkaline pH.