Quantitative determination of protein of bacterial origin

Abstract

Several methods have been developed for the determination of the proportion of nitrogen-containing substances of microbial origin in the digestive tracts of cattle. These include assays that use nucleic acids and adenosine triphosphate as indicators, radioisotopes 35S, 15N, 32P and 33P incorporated into bacterial protein and phospholipids, duodenal amino acid composition with amino-ethylphosphonic acid, diaminopimelic acid and d-alanine (d-Ala) contents as indicators. On the basis of the data in the literature on d-amino acid content of milk and milk products the authors came to the conclusion that d-glutamic acid (d-Glu) and d-aspartic acid (d-Asp) can be considered as markers for proteins of bacterial origin. To demonstrate this, experiments have been carried out and some of the results are reported here.