Effect of Alcoholic Fermentation on the Stability of Purple Sweet Potato Anthocyanins.

Abstract

Anthocyanin pigments (AN) extracted and purified from purple sweet potatoes (Yamagawamurasaki and Kankei 55) were studied for stability during alcoholic fermentation. The fermentation was continued for 7 days, followed by aging up to day 120. Analyses were performed to measure pH, sugar and alcohol contents, browning, relative absorbance at 525 nm, and hue, individual AN and alcohol by high-performance liquid chromatography (HPLC). Up to day 7 of fermentation: 1) pH decreased slightly; 2) browning increased; 3) absorbance increased; 4) the hue of Yamagawamurasaki AN underwent a positive shift in terms of both a* and b* values, taking on a deeper red color, and the Kankei 55 AN had a positive shift for a* values but no shift for b* values; 5) The structures of the major ANs of purple sweet potato were estimated as follows: A:3-O-(2-O-(6-O-caffeoyl [Caf]-β-D-glucopyranosyl [Glu]))-β-D-Glu-(5-O-(β-D-Glu))cyanidin [Cy], B:3-O-(2-O-(6-O-Caf-β-D-Glu))-(6--Caf-β-D-Glu)-(5-O-(β-D-Glu))Cy, C: 3-O-(2-O-(6-O-Caf-β-D-Glu))-(6-O-p-Hydroxybenzoyl [p-HB]-β-D-Glu)-(5-O-(β-D-Glu))Cy, D: 3-O-(2-O-(6-O-Caf-β-D-Glu))-β-D-Glu)-(5-O-(β-D-Glu))peonidin [Pe], 3-O-(2-O-(6-O-Caf-β-D-Glu))-(6-O-feruloyl [Fer]-β-D-Glu)-(5-O-(β-D-Glu))Cy, 3-O-(2-O-(6-O-Caf-β-D-Glu))-(6-O-Caf-β-D-Glu)-(5-O-(β-D-Glu))Pe, 3-O-(2-O-(6-O-Caf-β-D-Glu))-(6-O-p-HB-β-D-Glu)-(5-O-(β-D-Glu))Pe, 3-O-(2-O-(6-O-Caf-β-D-Glu))-(6-O-Fer-β-D-Glu)-(5-O-(β-D-Glu))Pe. 6) Compared to pre-fermentation values, both HPLC peak area of Yamagawamurasaki AN and Kankei 55 AN rapidly decreased became unstable on day 7 of fermentation. After the fermentation, major ANs aged were stably.