Milk may be among our most familiar and venerable parts of the human diet, but its complex chemistry still holds a few mysteries and surprises. Most analyses have focused on the macronutrients, the proteins, fats, and carbohydrates that make up this product. The latest generation of metabolomics methods, however, bring powerful technologies such as mass spectrometry and nuclear magnetic resonance to bear on the longstanding question of what makes up milk. The answer, according to University of Alberta Biological Sciences Professor David Wishart: a lot more than you might think.
“We used our very big hammer to hit milk,” he says, referring to the extensive facilities at his disposal as a member of The Metabolomics Innovation Centre, a facility outfitted with more than $26 million of state-of-the-art analytical hardware and the staff to carry out detailed studies on thousands of different chemicals. With support from Alberta’s dairy industry and Genome Canada, he and many of his students have spent several years applying these resources to the contents of a common glass of milk.
Among the surprises they found were a wide range of free amino acids, as well as a large number of organic acids, specifically citric, lactic, and butyric acid. The findings also revealed no fewer than 160 different lipids. Some findings were even counter-intuitive.
“Historically, people felt that milk had high lactic acid and we found that was not the case,” explains Wishart. “That surprised a few milk researchers.”
All told the team measured more than 660 different compounds in milk. The information was incorporated with other measurements already found in the scientific literature to become the basis of the Milk Composition Data Base, a freely available on-line archive of some 2,355 milk metabolites, that also includes publications pertaining to each chemical entry and searchable details about its respective mass, spectral features, and physical structure.
The results of this work were also published recently in the Journal of Agriculture and Food Chemistry, where Wishart and his colleagues recount the particular approaches that were employed in this work. They cast the findings as an example of the powerful potential that metabolomics can bring to the analysis of materials that might otherwise be regarded as completely characterized.
“The results presented here also have implications far beyond the field metabolomics, especially given the economic importance of bovine milk in the food industry and its importance in human and animal nutrition,” the paper concludes. “We expect these data to serve as a benchmark in comparing various technologies and assessing future methodological improvements in bovine milk research.”