J Agric Food Chem 50(2): 396-9. (Jan 16, 2002)
A Novel Zwitterionic Anthocyanin From Evergreen Blackberry (Rubus Laciniatus Willd.)
Florian C. Stintzing, Angela S. Stintzing, Reinhold Carle, Ronald E. Wrolstad

Abstract
A novel zwitterionic anthocyanin was isolated from evergreen blackberry (Rubus laciniatus Willd.) and structurally characterized as cyanidin 3-dioxalylglucoside. During short-term storage in acidified methanol, methyl esterification of the carboxyl group of the terminal oxalyl unit occurred, providing additional information for structural elucidation. Until now, oxalic acid as an acyl moiety of anthocyanins has been reported only in orchid flowers (Orchidaceae) but never in fruits or in the Rosaceae. This is the first report of an anthocyanin diacylated with oxalic acid, establishing a more widespread occurrence of anthocyanins substituted with aliphatic acids than hitherto believed.


Interestingly, the decrease of compound 6 during ripening was directly correlated to the increase of cyanidin 3-glucoside (9). This can be explained by the need for acylation for the anthocyanin transfer into the vacuole during pigment accumulation (30). Whereas evidence was given for succinyl and malonyl transport mechanisms (31, 32), oxalyl transferases have not been reported so far. From a chemical point of view, the ionic attraction between the positively charged flavylium core and the free carboxylic acid may account for the stabilization of these zwitterionic anthocyanins. Natural colorants and processed foods containing significant amounts of this class of pigments would be expected to benefit from the enhanced color stability.

 

Rose Pigments