The role of phenolic compounds during formation of turbidity in an aromatic bitter

An aromatic bitter produced from alcoholic extracts of botanicals were studied over 2½ years. The concentrations of gallic acid and the flavonoids catechin, epicatechin, eriodictyol, and taxifolin decreased during the first year of storage in the presence of oxygen, whereas the turbidity stayed below the limit for visible detection. After one year the turbidity increased linearly with time and the total concentration of phenolic compounds decreased. In contrast, the concentrations of eugenol and phenolic acids with two or one hydroxyl groups remained constant or increased, and these compounds are probably not involved in formation of turbidity. The oxidative properties of the phenolic compounds were evaluated in an assay based on iron-catalysed Fenton reactions and spin trapping of radicals. The fresh bitter and bitter stored for one year increased the amount of radicals detected in the assay, demonstrating an overall prooxidative effect of the phenolic compounds. It is concluded that easily oxidised phenolics in the bitter are converted into soluble intermediates that slowly react with proteins and carbohydrates forming haze and deposits.