Varietal specificity of polyphenols, free phenolics and antioxidant potential in hops

Many studies have confirmed hops (Humulus lupulus L.) as the source of a number of physiologically active polyphenols, important for both brewing and potentially pharmaceutical purposes. The three-year screening of polyphenols and 23 free phenolics profile (HPLC/coulometric detection) showed a significant association of polyphenols and free phenolics with DPPH antioxidant potential and the genetically determined specificity of free phenolics composition in hops. Varieties of American origin have a different profile compared to European varieties. For the first time, the free phenolics hydroxycoumarins were detected in hops. The DPPH strongly correlated with total polyphenols and flavanoids (n = 95, r = 0.92, 0.93 respectively) and correlated negatively with alpha acids (n = 95, r = -0.73). The polyphenols and the DPPH decrease with increasing alpha acids both among varieties and within one variety. These findings can serve as a useful tool for hop selection in brewing or pharmaceutical production.

An Original HPLC Method with Coulometric Detection to Monitor Hydroxyl Radical Generation via Fenton Chemistry

Hydroxyl radicals (•OH) can be generated via Fenton chemistry catalyzed by transition metals. An in vitro Fenton system was developed to test both the inhibition and stimulation of •OH formation, by monitoring salicylate aromatic hydroxylation derivatives as markers of •OH production. The reaction was optimized with either iron or copper, and target analytes were determined by means of an original HPLC method coupled to coulometric detection. The method granted good sensitivity and precision, while method applicability was tested on antioxidant compounds with and without chelating properties in different substance to metal ratios. This analytical approach shows how Fenton’s reaction can be monitored by HPLC coupled to coulometric detection, as a powerful tool for studying molecules′ redox behavior.