The origin of the volatile metabolites found in mastitis milk

The possibility to detect mastitis pathogens based on their volatile metabolites was previously studied. Because the origin of the metabolites is unknown, the formation of volatile metabolites by five mastitis pathogens inoculated in milk of healthy cows was studied. The volatile metabolites from inoculated samples were compared to those of mastitis milk samples from which the inoculated pathogens were isolated. Most metabolites formed in the inoculated samples were similar to the metabolites formed in mastitis samples, both in presence and in amount. Prediction by a neural network showed that the similarity between the inoculated samples and mastitis samples was sufficient for correct prediction of the pathogen in the inoculated sample. The main difference between the inoculated samples and the mastitis samples was the absence of ethyl esters of free fatty acids in inoculated samples. This could be explained by disturbance of the milk–blood barrier, allowing the transfer of esterase from the cows’ blood to the milk in cows with mastitis.