Tetracycline residues in meat and bone meals. Part 2: the effect of heat treatments on bound tetracycline residues.

The stability of bound tetracycline residues during heat treatments at 133 degrees C and 100 degrees C for up to 45 min was investigated. An intermediate product from a rendering plant was mixed with bone splinters that contained bound tetracycline (TC) and chlortetracycline (CTC) residues. The mixture was heated in an autoclave at 133 degrees C for 20, 30 and 45 min and at 100 degrees C for 20 and 30 min and subsequently dried at 103 degrees C for 4 h. Two different extraction procedures with hydrochloric acid were used, one with and one without the previous sedimentation of bone particles. Tetracycline concentrations were determined by HPLC analysis before and after the heat treatment. A complete destruction of tetracyclines during heat treatment at 133 degrees C could not be demonstrated, but there was a significant decrease of TC by about 50%. CTC was less resistant to the same temperature, which brought about a reduction of 90-100%. Treatment at 100 degrees C did not bring about any reduction, except for CTC after extraction without sedimentation. The possible toxicological relevance of the findings is discussed. Further research has to be done on possible degradation products of the tetracycline derivatives.