INFLUENCE OF TEMPERATURE AND OXYGEN CONCENTRATION ON THE RADIATION-INDUCED OXIDATION OF PHENYLALANINE

The formation of tyrosine isomers by gamma-radiolysis of neutral aqueo us phenylalanine solutions was found to be strongly dependent on oxyge n concentration and temperature. Changing the dose rate did not influe nce the degradation process. In the presence of 0.25 x 10(-3) mol dm(- 3) oxygen at room temperature the yields of o-tyrosine as well as of m - and p-tyrosine drop from G (o-Tyr) = 0.5 and G(m-Tyr) = G(p-Tyr) = 0 .4 at a dose of 0.3 kGy to 0.18 and 0.16 at 2.5 kGy, respectively, In solutions containing 1.25 x 10(-3) mol dm(-3) oxygen the initial yield s remain unchanged but decrease at 2.5 kGy only to G (o-Tyr) = 0.3 and G (m-Tyr) = G (p-Tyr) = 0.20. Under the latter reaction conditions al so 3,4-dihydroxyphenylalanine was found. Samples irradiated in frozen state did not show remarkable radiolysis of phenylalanine and tyrosine formation. In the range between 5 and 20 degrees C no essential influ ence of temperature on the phenylalanine radiolysis and tyrosine yield s was observable. The obtained results are important for methods using the tyrosine yields as markers for the detection of irradiated food. Storage conditions and irradiation temperature play an essential role on radiation induced changes of food.