Influence of mastitis on D-amino acid content of milk.

The California Mastitis Test was used as an indicator of mastitis in this study. Five cows were chosen for each of the five test scores (from 0 = healthy to 4 = severe mastitis). Milk samples were analyzed for free AA and free D-AA. The contents of free AA, free D-AA, and the ratio of free D-AA to free AA increased significantly as the California Mastitis Test score increased. The free D-AA content of foremilk (first milk jets) from healthy cows (test score = 0) was approximately five times that in samples drawn later from the same udders. Contents of free AA and free D-AA were highly associated with test score and udder inflammation. Very low concentrations of free D-AA are normal for raw milk. Higher concentrations of free D-AA could be attributed to inclusion of foremilk and milk from cows having subclinical mastitis in the bulk tank milk.

Age determination based on amino acid racemization: A new possibility.

A method has been developed to determine the age of fossil bone samples based on amino acid racemization (AAR). Approximately one hundred fossil bone samples of known age from Hungary were collected and analysed for D- and L-amino acids. As the racemization of amino acids is affected by temperature, pH, metal content of the soil, and time passed since death, these factors were eliminated by comparing the estimated age to age determined by the radiocarbon method. Determining the D- and L-amino acid contents in samples of known age, determining the half life of racemization and plotting the D/L ratio as a function of time, calibration curves were obtained. These curves can be used for the age estimation of samples after determining their D- and L-amino acid content. The D/L ratio for 2 to 3 amino acids was determined for each sample and the mean value of estimated ages based on calibration curves was considered to estimate age of the fossil samples.

Separation of D- and L-amino acids by ion exchange column chromatography in the form of alanyl dipeptides.

A method of ion exchange column chromatography was developed for the determination of D- and L-amino acids in the form of diastereomeric dipeptide. First the protein containing samples were hydrolyzed with 6 molar hydrochloric acid, then the single amino acids were separated in an LKB automated amino acid analyzer with the LKB fraction collector. Following lyophilization, the single amino acids were transformed into alanyl dipeptides with tertiary-butyloxycarbonil-L-alanine-N-hydroxy-succinimide (t-BOC-L-Ala-ONSu) active ester. The alanyl dipeptides were easily separated from one another and the initial amino acids. Determination of the D- and L-amino acids in this form is relatively accurate and reproducible but takes some time (33-38 min). Accuracy of the determination is satisfactory. The coefficient of variation amounts to 3-5%. The use of the method is suggested to laboratories having an amino acid analyzer and wish to determine D-and L-amino acids in synthetic-amino acids complements, peptides or natural materials.