Improving colorimetric properties and stability of acylated anthocyanins through UV irradiation

Research poster
Yucheng Zhou
Monica Giusti
Department of Food Science and Technology

Anthocyanin-based food colorants are usually acylated with hydroxycinnamic acids, which occur in nature predominantly in the trans-configuration, with cis-configuration rarely found. The trans- and cis-isomers have different colorimetric properties and stability. Trans-isomers can isomerize to cis under UV irradiation in methanol.

Our goal was to explore the effects of coumaric acid configuration on spectral and colorimetric properties of acylated cyanidin-derivatives and determine the effects of solvent, anthocyanin purity and concentration on the UV-induced transcis conversion process.

Cis- and trans-isolates were extracted from American elderberry and isolated by semi-prep HPLC. 100 to 800 M crude extracts or purified trans-isolates were irradiated by UV light (254nm) in acidified water, methanol or ethanol until reaching equilbrium. The conversion rate was monitored by uHPLC. Color and spectra of UV-irradiated crude extract, cis- and trans-isomers were monitored over 72hr at pH1-9.

Cis-isomers were more stable, with shaper spectra, larger max and higher absorbance at all pH, with more color at pH4-6 and bluer hues at pH7-9. Transcis conversion occurred in trans-isolates and crude extract with similar efficiency. A plateau was reached at trans:cis ratio 5:4 in alcohol and 10:3 in water. The conversion was faster in low anthocyanin concentration, but more cis-isomers were produced at high anthocyanin concentration. The crude extract displayed bluer hues at pH7-9 after UV irradiation.

UV irradiation could be a novel and safe way to trigger acylated anthocyanin transcis conversion, to improve anthocyanin stability, and potentially produce promising anthocyanin-based colorants for food industry.