Characterisation of sorbate geometrical isomers

trans,trans Isomers of sorbic acid, its potassium salt and ethyl sorbate is omerise under UV irradiation. All four geometrical isomers of the acid, sal t and ester were separated using high-performance liquid chromatography on a nonpolar reversed-phase column (C-18) and the ester also by gas chromatog raphy on a VOCOL capillary column. The limit of detection and the interval of linearity were determined for all chromatographic methods. Individual is omers were identified with NMR analysis. Resolved chemical shifts of proton s adjacent to the double bonds enabled qualitative and quantitative determi nation of isomers in the mixture. Antimicrobial activity of potassium sorba te isomers was tested on yeast Saccharomyces cerevisiae. Results show that the pure trans,trans isomer has a higher antimicrobial activity than the mi xture of isomers. (C) 2001 Elsevier Science B.V. All rights reserved.