SOLID-STATE C-13 NMR INVESTIGATIONS OF INSOLUBLE DEPOSITS IN AROMATICBITTERS

Insoluble deposit formed in aromatic bitters produced from alcoholic e xtracts of about 30 different botanical materials with a dry matter co ntent of 1.67% and 38 vol% alcohol and a characteristic astringent fla vour was shown by C-13 NMR spectroscopy to be a coprecipitate of plant polyphenols, proteins and carbohydrates. The polyphenols in the depos it were flavonoids such as anthocyanidins and anthocyanins, with gluco se as the principal carbohydrate and derivatives of cinnamic acid. The deposit formation in the aromatic bitters was accelerated by addition of the radical initiator 2,2'-azobis(2-amidinopropane) dihydrochlorid e or by addition of hydrogen peroxide in combination with iron(III) ni trate and ascorbic acid as a Fenton reagent. Polymerization of catechi n and pelargonidin was shown, in model experiments, to be oxidative an d to be accelerated by exposure to light. A mechanism involving oxidat ive polymerization of polyphenols followed by coprecipitation of polym erized polyphenols, proteins and carbohydrates is proposed for formati on of deposits in alcoholic beverages of the bitters type.