Differences in element content between organic and conventional milk

The importance of microelements in food, including elements occurring in ultra low concentrations, has been increasingly acknowledged in relation to positive as well as negative health aspects. However, due to difficulties in measuring elements with ultra low concentrations limited knowledge exists on the content of and sources of variation of microelements in food, including milk.

Analysis of elements in organic and conventional milk

By means of high-resolution inductively coupled plasma mass spectrometry the concentration of 45 trace elements and 6 major elements were quantified in milk from 10 organic dairy herds and 10 conventional ones in Denmark. Each group of herds included 7 herds of Danish Holstein and 3 herds of Jersey cows, and samples were collected 8 times per herd during one year.

To our knowledge this is the most comprehensive determination of trace elements in milk, and in particular regarding possible difference between organically or conventionally produced milk.

Few differences related to system

For a number of trace elements the concentration was affected by breed and system. The differences related to system are given in Table 1.

The concentration of Mo was significantly elevated in organic milk whereas the concentrations of Ba, Eu, Mn, and Zn were significantly reduced compared with conventional milk. The differences in Mo and Ba between organic and conventional milk is in particular interesting since the system-related variation was much higher than the variation related to herd within system or time of sampling, and even higher than the variation related to breed.

The explanation for this difference is not obvious, but it is known that the concentration of Mo is dependent on dietary intake. In addition antagonistic interaction between minerals regarding uptake by the cow may be an explanation. For instance the content of cobber tended to be lowered in organic milk (54 vs 60 ppm P<0.10) and it is well known that antagonistic interactions exists between these two elements.

In a huge number of trace elements no significant differences related to system were observed. These were: Al, As, Au, Bi, Ce, Cr, Cs, Dy, Er, Fe, Ga, Gd, In, La, Lu, Nb, Nd, Pb, Pr, Rb, Sb, Se, Si, Sm, Sr, Tb, Te, Th, Ti, Tl, U, V, Y, Zr.

Profiles of trace elements may reveal organic origin

Although the differences between organic and conventional milk measured for certain trace elements – in particular Mo and Ba - were highly significant, none of these trace elements in itself seems sufficient to use as indicators of organic origin, but it might be anticipated that the profile of trace element concentrations could be used at least for screening purposes. This, however, remains to be verified.

Further reading

Hermansen, J.E., Badsberg, J.H., Kristensen, T. and Gundersen, V. 2005. Major and trace elements in organically or conventionally produced milk. J. Dairy Res. 72 362-368.