Isolation, identification, and color characterization of cyanidin-3-glucoside and cyanidin-3-sophoroside from red raspberry

The major anthocyanins were isolated by Amberlite XAD-7 and Sephadex LH-20 column chromatography from the acidified, methanolic extracts of red raspberry, their purity was over 85%. Moreover, the major anthocyanins were identified as the cyanidin-3-glucoside (Cy-3-glu) and cyanidin-3-sophoroside (Cy-3-soph) using HPLC-PDA and HPLC/ESI-MS. Their UV–vis absorption spectra and color index were also investigated. Cy-3-glu and Cy-3-soph had the similar UV–vis absorption spectra in all investigated pH values, the bathochromic shift occurred progressively in the spectra with pH increase. However, the molar absorptivity of Cy-3-soph was lower than that of Cy-3-glu as pH increased except at pH 4.6 and 5.7. The color index of Cy-3-glu and Cy-3-soph in buffer solution were described by CIEL*a*b* coordinates L* (lightness), C* (chroma) and H° (hue angle). The L* and C* values had the similar change behavior. With increasing pH, the L* and C* values of Cy-3-glu and Cy-3-soph increased and reached a maximum at pH 5.7. Afterwards, the L* and C* values presented a decrease with increasing pH from 6.5 to 7.6. However, H° decreased for Cy-3-glu and Cy-3-soph with pH increasing from 1.0 to 5.7, respectively. Afterwards, H° kept constant and nearly identical for Cy-3-glu and Cy-3-soph although pH value continued increasing from 5.7 to 7.6. It could be concluded that the glucosyl and sophorosyl substitution at 3-position of cyanidin had no significant effect on spectra characteristics and color indices of anthocyanins except the molar absorptivity and the C* value.