The rising number of food-adulteration and authenticity issues highlighted in the media has increased the public’s concerns over the safety of what they eat. This has led to an increasing number of people switching to organic products, one of which is milk.
This shift is evidenced by a 17% increase in sales of whole, and 15% in reduced fat organic milk through 2011. This popularity, coupled with the higher price commanded by organic milk (typically 25-100% more than non-organic), makes it a very attractive target for fraudsters.
While these substitutions invariably do not cause health problems, they still have a financial impact, with consumers not getting what they paid for and hard-working organic farmers losing business and having profit margins eroded. As such, tests to confirm the authenticity of the organic milk are important, not just for ongoing monitoring but also to act as deterrents.
Four of the major factors determining if milk may be labelled organic in the US are:
Many different techniques have been used to detect if there are traces of pesticides, antibiotics or even growth hormones in the milk or animal feed. Measuring if the cows have been fed a predominantly commercial feed diet, rather than fresh grass or silage, is more difficult.
Recent work has been looking at levels of minor acids in the milk. One such study used hippuric acid, which was suggested to be found in higher levels if more grass and silage were consumed by, in this case, goats. It was therefore decided to explore if this was also the case for cows, and if a much faster technique with less sample preparation, the DSA/TOF MS (direct sampling accessory connected to a time of flight mass spectrometer), could be used.
Three organic and three conventional milk samples were purchased from a local supermarket. All milk samples were subjected to the same preparation of a protein precipitation followed by spiking with a de-uterated internal standard analysis.
It was seen that, for conventional milk, for all three samples, the hippuric acid concentration was on average around 20mg/L. For two of the organic milk samples, the levels were higher as predicted at about 35mg/L. However, one had the same levels as the non-organic milk.
An explanation for this could be that this particular sample was the supermarket ‘home’ or generic brand and may not be organic. However, to support this theory, a wider study would be needed, ideally splitting a herd of cows into two groups, feeding one an organic diet over a year and one a conventional feed-based diet and measuring the hippuric acid levels in the resulting milk over time.
Robert Packer is food solutions development leader at biotechnology company PerkinElmer.
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