15A-9 |
Free D-amino acids in milk as related to psychrotrophic bacteria |
C. H. KIM1, Y. M. Song, S. C. Baick, and W. H. Chung. (1) Seoul Dairy Cooperative, Institute of Dairy Food Research, 1059 Shingil-Dong, Ansan, Kyunggi-Do, Korea, 425-839, South Korea It is generally believed that in mammals naturally occurring amino acids are of the L-configuration. Free D-amino acids(DAAs) are common in nature as constituents of bacterial cell walls and several antibiotics. Recent reports have demonstrated the presence of small amounts of free DAAs in milk. The presence of free DAAs may be affecting the food quality by decreasing the nutritional value. Our objective was to examine whether the free DAAs came from psychrotrophic bacteria Free DAAs was produced by treatment raw milk inoculated with Pseudomonas spp. The samples were extracted with sulphosalicylic acid and derivatization with AccQ-TagTM reagent. The analysis was carried out by reverse-phase HPLC. We tested correlations of the content of free DAAs with bacterial growth. The significant amount of free D-alanine, D-proline have been found in Pseudomonas spp. inoculated raw milk. The increase of D-alanine, D-proline appeared to be mainly related to the presence of Pseudomonas fluorescens. These results suggest that free DAAs may be considered as an indicator of psychrotrophic bacterial contamination in milk.
Session 15A, Dairy Foods
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