title: Suitability of tryptophan radiation products as markers for the detection of gamma-irradiated protein rich food.
abstract: During gamma-irradiation (5 kGy) of aqueous tryptophan (Trp) solutions small amounts of 5-, 6-, and 7-hydroxytryptophan (OH-Trp) (0.04-0.08 Mol-%) are formed. Protein rich food like shrimps contain reasonable amounts of non-protein bound Trp (100 mg/kg). In order to detect the treatment of shrimps with gamma-irradiation a method for the determination of OH-Trp in gamma-irradiated shrimps was developed. After homogenization, squeezing of shrimp samples and protein precipitation, a two-step-SPE-clean up was performed using a C18-cartridge and a propylsulfonic acid cation-exchange SPE followed by HPLC analysis with electrochemical detection (750 mV). Results showed that 5-OH-Trp contents in shrimp samples increased with applied doses up to 3 kGy and then decreased with higher doses. Other OH-Trp isomers were not detectable in the irradiated shrimps. Similarly no formation of 4-, 6-, and 7-OH-Trp was detected in model solutions containing the same amino acid composition as in shrimps. This indicates a suppression of the reaction of OH-radicals with Trp by the 300 fold molar excess of other amino acids acting as well as radical scavengers. Therefore, non-physiological OH-Trp isomers formed from free Trp are not suitable as markers for the detection of gamma-irradiated protein-rich foodstuff.
authors.affiliation: University of Hamburg, Department of Food Chemistry, Grindelallee 117, D-20146 Hamburg.
authors.forename: Kim Karen
authors.initials: KK
authors.lastname: Kleeberg
authors.forename: Andre
authors.initials: A
authors.lastname: Müller
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Simat
authors.forename: Hans
authors.initials: H
authors.lastname: Steinhart
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D033501:Crangonidae / Q000737:chemistry / Q000528:radiation effects; D004044:Dietary Proteins / Q000032:analysis / Q000528:radiation effects; D005514:Food Irradiation; D006900:Hydroxylation; D007536:Isomerism; D017747:Seafood / Q000528:radiation effects; D014364:Tryptophan / Q000031:analogs & derivatives / Q000737:chemistry / Q000528:radiation effects*
chemical_list: D004044:Dietary Proteins; D014364:Tryptophan