STABLE ISOTOPE-DILUTION GC MS FOR THE QUANTIFICATION OF FOOD CONTAMINANTS

6 Each replicate contained seven pork chops; one-half of the replicates were fried after irradiation. The data obtained from the analyses of the sam- ples described above were used to develop re- sponse surface equations which would predict the effect of the irradiation dose and temperature on each vitamin over the entire area covered by the design. From the equation for the response surface for thiamin loss the predicted losses in pork chops irradiated at 0 'C and then cooked were as follows: 0 kGy, -1.5% (-0.04%); 0.50 kGy, -10.1% (14.3%); 3.5 kGy, -48.7% (54.3%); and 7.0 kGy, -65.9% (69.7%). The values given in parentheses represent the average of the actual observed val- ues. There was no loss of thiamin in the control on a sample weight basis upon cooking, but there was an overall weight loss of about 30%. The effect of temperature on the degradation of thiamin can be illustrated by comparison of the predicted results obtained at a dose of 3.5 kGy, losses of 32.7 (34.9%) and 63.3% (60.2%) at -20' and +20'C respectively. The fit of the predicted values to the measured values is indicated by a R' value of 0.90 for the equation for the response surface. The effect of radiation on thiamin was different in poultry from that observed in pork. The re- sponse surface equation for thiamin loss in chicken breasts cooked after irradiation predicted the fol- lowing losses of thiamin at 0 'C: 0 kGy, + 3.2%; 1.0 kGy, -0.38%; 2.0 kGy, -2.2%; 3.0 kGy, -5.9%; 3.5 kGy, -7.4%; and 7.0 kGy, -34.9%. Thus, in the range of greatest interest for the con- trol of salmonella contamination (3.0 kGy) the loss of thiamin was very low especially when compared to losses in pork chops irradiated and cooked in the same manner.