• Journal of Animal Science and Technology
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• v.46 no.1
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• pp.91-96
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• 2004

It is generally believed that amino acids occurring naturally in mammals are of the L-configuration. D-amino acid(DM) are common in nature as constituents of bacterial cell walls and several antibiotics. Recent reports have demonstrated the presence of small amounts of free DM in milk. The presence of free DM may affect the food quality by decreasing the nutritional value. Our objective was to examine whether the free DM carne from psychrotrophic bacteria. Free DM was produced by treating raw milk with Pseudomonas spp. The samples were extracted with sulphosalicylic acid and derivatized with AccQ-$Tag^{TM}$ reagent when the analysis was carried out by reverse-phase HPLC. We tested correlations of the content of free DM with bacterial growth. Significant amounts of free D-a1anine and D-proline have been found in the raw milk inoculated with Pseudomonas spp. The increase of D-alanine and D-proline appeared to be mainly related to the presence of Pseudomonas fluorescens. These results suggest that free DM may be considered as an indicator of psychrotrophic bacterial milk contamination.