Reactions of OH-radicals with hydroxylated and methoxylated benzoic acids and cinnamic acids. Radiation-induced chemical changes in mushrooms

In the first part of this work the radiation induced chemical changes of methoxylated and hydroxylated benzoic acids and cinnamic acids were investigated. Methoxylated compounds were also used as model components for acid derivatives with no free-OH groups. The latter are essentials parts of vegetable foodstuff. A comparison of the radiolytic behaviour of single substituted methoxy- and hydroxybenzoic acids was given at first, data of literature was included. The priority of the investigation was the hydroxylation process induced by OH-radicals. The OH-adduct distribution is generally the same for the hydroxy- as well as for the methoxybenzoic acid isomers. This could be proved by oxidation of these OH-adducts with K3Fe(CN)6. In the presence of air 68-77 % of the hydroxybenzoic acids are converted into hydroxylation products, whereas with the methoxylated acids this reaction leads only to about 10%. An explanation gives the different decay pathways of the intermediate peroxylradical. The multiple methoxy- and hydroxybenzoic acids show three different reaction possibilities: hydroxylation, replacement of -OCH3 by -OH and -in case of the cinnamic acids-oxidative decomposition of the rest of the propenic acid under formation of the corresponding benzaldehydes. All these reactions can be expected when irradiating foodstuff, containing these acid compounds. The characteristic formation of these components and their linear dose/concentration relationship make these substrates very promising for the use as markers for irradiation treatment of foodstuff. The second part of this work deals with the gamma-radiation induced chemical changes in mushrooms. The irradiated and non-irradiated samples were freeze-dried and purified from matrix components chromatographically on polyamid columns. In case of the phenolic compounds for 4-hydroxybenzoic acid and three unknown components linear dose/concentration relationships could be obtained. Two of these unknown compounds seem to be promising for a use as marker for irradiation treatment of mushrooms. (author)