Determination of o-Tyrosine Production in Aqueous Solutions of Phenylalanine Irradiated with Gamma Ray, Using High Performance Liquid Chromatography with Automated Pre-column Derivatization and LASER Fluorometric Detection.

Abstract

Tyrosine isomers produced by gamma radiation of aqueous phenylalanine solutions at mid dose levels (1-10kGy) were examined to obtain basic information for irradiated food detection using a new high performance liquid chromatography (HPLC) analytical procedure. The procedure was established using an automated pre-column derivatization with 4-fluoro-7-nitro 2, 1, 3-benzoxadiazole (NBD-F) followed by reverse phase HPLC and LASER fluorometric detection. The limit of detection (LOD) was 0.06ng on-column and the linear range for calibration was 0.06 to 50ng for the tyrosine derivatives. The relative standard deviation was 10% to 12%. The amounts of the tyrosine isomers increased with levels of irradiation. Irradiation at low temperature with reduced oxygen decreased the isomer yields. In the pH range of 5 to 7, the amount of product was not changed significantly by pH, outside this range, the pH did have an effect on product generation. At constant dose levels the yields of tyrosine isomers initially increased with phenylalanine concentration, although, with further increases in phenylalanine a reduction in the absolute amounts was observed. Dose rates varying from 0.5kGy/h to 10kGy/h had no significant effect on tyrosine isomer formation if a total of 10kGy was used in each case. In addition, demonstrating the usefulness of this new analytical technique for o-tyrosine determination, these studies suggest that the presence of o-tyrosine is another parameter indicative of gamma irradiation.