Rye flavonoids - Structural profile of the flavones in diverse varieties and effect of fermentation and heat on their structure and antioxidant properties.

Flavones are important bioactive flavonoids in cereal grains, but are poorly characterized. This study investigated rye flavone profile as influenced by phenotype (grain color), sourdough fermentation, and subsequent heat processing. Twelve rye varieties belonging to 4 phenotypes were characterized using UPLC-tandem quadrupole MS before and after fermentation and baking. Antioxidant properties were also assessed. Rye flavones (range 57-137 μg/g) were dominated by O-glycosides (50-68%), present as derivatives of tricin (exclusively O-glycosides), chrysoeriol (O-/C-glycosides), and apigenin (exclusively C-glycosides). Phenotype did not influence flavone content. Fermentation partially hydrolyzed O-glycosides to their aglycones, but did not affect C-glycosides. Extractable phenols and antioxidants increased 1.9-3.6X after 96-h fermentation; baking further increased these components by 36-96% in fermented samples, likely via enhanced cell wall disruption. The high proportion of flavone-O-glycosides in rye is of interest due to their known higher bioavailability relative to typical cereal grain C-glycosides.