Residues of Antimicrobial Growth Promoters

As has been demonstrated by stability experiments at 100 C in aqueous buffer solutions, lasalocid is relatively stable to heat in neutral and acidic conditions, but unstable in alkaline conditions (95). Thus, the drug exhibits stability at pH 

5 and 7.0, but instability at pH 10.0 with a half-life of 30 min. Lasalocid is also not stable in sunflower cooking oil heated at 180 C, with a half-life of 15 min. 

In incurred chicken muscle, lasalocid residues were found to be stable to cooking. Residues in raw tissue from the treated chickens were found to be evenly distributed in edible muscle. Chicken was cooked by microwaving, boiling, roasting, frying, and grilling. Less than 5% of the residue was found in juices that came out of the meat when it was cooked by microwave and roasting. 

Unlike with muscle, cooking decreased the amount of residues measured in eggs. Frying decreased residues by 59%, whereas scrambling reduced it by 27%. 

These results are consistent with the mentioned pH-dependence of lasalocid stability chicken muscle is known to be at about pH 5.7, egg yolk at about pH 6.0-6.8, whereas egg white pH can be as high as 9.0-10.0. The loss of lasalocid in egg should therefore be due to the base-catalyzed hydrolysis of lasalocid. 

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