Black goji as a potential source of natural color in a wide pH range.

Lycium ruthenicum Murr. is a traditional Chinese herb widely distributed in Tibet. The fruit, known as black goji, is popular in traditional Chinese medicine. The objective of this study was to investigate its anthocyanin profile (by HPLC coupled to PDA and MS detectors) and the colorimetric and spectrophotometric properties. Black goji extracts contained abundant petunidin derivatives, with cis and trans isomers of petunidin-3-p-coumaroyl-rutinoside-5-glucoside. The colorimetric and spectrophotometric traits of black goji anthocyanins were significantly impacted by solid-phase-extraction, pH, and acylation. MCX cartridge removed considerable polyphenolics from fruit extracts, but attenuated the saturation of color expression. Petunidin-3-trans-p-coumaroyl-rutinoside-5-glucoside contributed most of the color expression of the black goji extract, and showed superior stability compared to other extracts over time. Acylation strengthened the petunidin derivatives color retention, and enhanced the color intensity and stability. Black goji anthocyanins produced various vivid hues over wide ranges of pH, making them promising candidates for natural colorants.