flavonoids. Unlike O-glycosides, the intact aglycone of C-glycosides
is not efficiently cleaved from the parent ion. Also, the fragments at
m/z 353 and 383 are, respectively, indicative that the molecular
weight of the aglycone is 270 Daltons, in keeping with apigenin.
Based on previous published data (Liu, Qiu, & Beta, 2010) and because
flavone C-glycosyl bonds have been found only at 6- and
8-positions (Cuyckens & Claeys, 2004), peaks 10–12 were tentatively
identified as apigenin-6/8-C-pentoside-8/6-C-hexoside isomers.
These flavone conjugates are known to occur in red rice
grains (Hirawan, Diehl-Jones, & Beta, 2011).