Comparison of the reactions induced by ultrasound and gamma rays in aqueous lactose solutions

The products obtained in aerated aqueous lactose solutions after irradiation with ultrasound and gamma rays were compared. The dose rate of gamma irradiation equivalent to the effect of ultrasound in our experiments was determined to be 1.384 kGy h^-1 using the Fricke dosimeter. Separation and identification of the products were performed by gas chromatography-mass spectrometry. Three methods for the derivation of products were used: (1) trimethylsilylation of the OH-groups; (2) methoximation of the carbonyl groups followed by trimethylsilylation of the OH-groups; and (3) reduction of the carbonyl and carboxyl groups to alcohols by sodium borohydride and sodium borodeuteride. The formation of products for both types of irradiation was identical, showing only minor deviations in the yield. The main reaction was oxidative splitting of the glucosidic bond, resulting in the formation of galactonic acid, glucose and galactose. Hexosuloses, gluconic acid, hexulosonic acids and glucuronic acid were detected as secondary products still containing the intact monosaccharide units. In addition, oxidation products with three to five carbon atoms were observed. The main product still containing 12 carbon atoms was lactobionic acid.