Characterization of Anthocyanins and Pyranoanthocyanins from Blood Orange [Citrus sinensis (L.) Osbeck] Juice

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Abstract
Anthocyanins from blood orange [Citrus sinensis (L.) Osbeck] juices were isolated and purified by means of high-speed countercurrent chromatography and preparative high-performance liquid chromatography. Structures of the pigments were then elucidated by electrospray ionization multiple mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. The major anthocyanins of the juice were characterized as cyanidin 3-glucoside and cyanidin 3-(6‘ ‘-malonylglucoside). Furthermore, six minor anthocyanins were detected and identified as cyanidin 3,5-diglucoside, delphinidin 3-glucoside, cyanidin 3-sophoroside, delphinidin 3-(6‘ ‘-malonylglucoside), peonidin 3-(6‘ ‘-malonylglucoside), and cyanidin 3-(6‘ ‘-dioxalylglucoside). The occurrence of the latter compound in blood oranges is reported here for the first time, together with full NMR spectroscopic data. Further investigations revealed the presence of four anthocyanin-derived pigments, which are formed through a direct reaction between anthocyanins and hydroxycinnamic acids during prolonged storage of the juice. These novel pyranoanthocyanins were identified as the 4-vinylphenol, 4-vinylcatechol, 4-vinylguaiacol, and 4-vinylsyringol adducts of cyanidin 3-glucoside through comparison of their mass spectrometric and chromatographic properties with those of synthesized reference compounds. Keywords: Blood orange; Citrus sinensis (L.) Osbeck; anthocyanins; cyanidin 3-(6‘ ‘-dioxalylglucoside); oxalic acid; anthocyanin-derived pigments; pyranoanthocyanins; vinylphenol; aging products