Thermal inactivation of L-thyroxin.
We assessed the extent of inactivation of L-thyroxin induced by exposure to heat in the presence of two vehicles. Preparations of L-thyroxin in the dry powder form, or dispersed in the solvents propylene glycol (water-like) or ethoxylated castor oil (oil-like), were heated at temperatures ranging from 65 to 160 degrees C, for 5- to 15-min periods. Heating L-thyroxin to a temperature below that of cooked bovine ground meat (72 degrees C) produced less than 10% degradation. Thermal degradation was pronounced only above 90 degrees C, and was almost completed at 160 degrees C. L-Triiodothyronine was the only thermal degradation product identified after L-thyroxin was heated at 125 degrees C. In a separate experiment we measured the melting point of L-thyroxin, 148.81 degrees C. This value agrees closely with the observed thermal sensitivity. We conclude that L-thyroxin is not significantly degraded under conditions encountered during cooking of ground bovine meat for short times at moderate temperatures.
Wortsman
J
J
Department of Medicine, Southern Illinois University, Springfield.
Papadimitriou
D C
DC
Borges
M
M
Defesche
C L
CL
D000818:Animals; D002152:Calorimetry, Differential Scanning; D002368:Castor Oil / Q000031:analogs & derivatives; D002417:Cattle; D004355:Drug Stability; D006358:Hot Temperature; D008460:Meat; D011208:Powders; D019946:Propylene Glycol; D011409:Propylene Glycols; D012997:Solvents; D013816:Thermodynamics; D013974:Thyroxine; D014284:Triiodothyronine
D011208:Powders; D011409:Propylene Glycols; D012997:Solvents; D014284:Triiodothyronine; C023040:polyethoxylated castor oil; D019946:Propylene Glycol; D002368:Castor Oil; D013974:Thyroxine