Milk metabolite composition and its relation to nutritional and technological quality – A NMR metabolomic approach

The Danish Swedish milk Genomics Initiative aims at identifying genetically contingent differences in the metabolite profile of milk and its impact on nutritional and technological quality traits of bovine milk. For this purpose, we have collected milk and tissue samples from 1200 Danish Holstein Friesian, Danish Jersey and Swedish Red Breed. The metabolite composition of the milk was investigated by nuclear magnetic resonance spectroscopy (NMR), which has previously been proven valuable in the assessment of the metabolite composition of body fluids. The metabolite profile of the milk was then associated with coagulation properties, somatic cell counts, and genetic analyses. Milk quality is closely correlated to the specific milk metabolite composition. We have shown that coagulation properties of the milk, which is a substantial technological quality trait, are reflected in the metabolite composition. Using multivariate data analysis (MVDA) we were able to classify milk samples according to their ability to form a gel (non-, good and poor coagulation). Nutritional quality of milk is affected by the specific composition of essential small molecules. Furthermore, milk quality is also associated with milk somatic cell count (SCC). SCC is commonly associated with mastitis, and our NMR metabolite data indicate that several metabolites can be correlated with SCC. Relative quantification using NMR revealed that lactic acid, acetate, and β-hydroxybutyrate were significantly increased in milk samples with a high number of somatic cells, and these metabolites may be potential markers for SCC in milk. Recently, we have shown that many of the metabolites in bovine milk have a genetic component. The heritability was in the range of 0 for lactic acid to > 0.8 for orotic acid and β-hydroxybutyrate. In conclusion, we show that NMR metabolite profiling associated with rheological and genetic analyses are able to identify many interesting features. The MVDA and rheological analyses indicate novel metabolites correlated with coagulation properties, and accordingly cheese yield and quality, whereas the genetic analyses can elucidate metabolites that are regulated by a genetic component.

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