(626a) Redox Properties of Food-Derived Polyphenols

Polyflavanols (procyanidins), anthocyanins, and phenolic acids are known naturally-occurring antioxidants.  Polyphenolic structures of these antioxidants enable one-electron transfer reactions to quench radicals; the reaction is reversible if the antioxidant forms stable semiquinone radicals.  Because of its aromatic, polyphenolic structures, procyanidin extracted from sorghum reportedly have several-fold greater peroxyl radical-quenching ability than phenols and Trolox.  Limited information is available on the chemical constituents responsible for the antioxidant activity of sugarcane extracts.  For example, kokuto, “black sugar” in Japanese, is produced by evaporating water from sugarcane juice at elevated temperature.  Like sugarcane molasses, kokuto contains phenolic acids, phenyl glycosides, phenyl propanoid glycosides, and phenyl propanoids.  The objective of this study was to understand the relationships between the structure (by solid-state NMR and fluorescence/UV-visible spectrophotometry) and redox property of naturally occurring antioxidants: grape seed, evaporated sugarcane juice, and sorghum grain.  Fully oxidized and reduced forms of sugarcane, sorghum, and grape seed extracts were prepared using Fremy’s salt.   Solid and liquid-state NMR techniques were then utilized to investigate the structural components responsible for the redox reactivity.  Iron (III) reduction kinetics was examined, and compared with DPPH, acid-butanol, and vanillin assays.