Milk is an incredibly versatile beverage if you think about it. Enjoy it chilled, flavored or as hot drink containing cocoa or chocolate. Milk is not only a delicious drink, but it is a nutritious and complete food containing a good balance of carbohydrates, fat, protein and nutrients.
Milk is also the raw material for cream, butter, yoghurt, cheese, ice cream, etc. And it is widely used in cooking and by the food industry in processed foods. But let us talk milk analysis in this blog post and specifically the potential food safety issues.
Milk Requires a High Level of Food Safety Protection
Milk consumption ranges widely, from as high as an amazing 360 L per capita in Scandinavia to less than 20 L per capita in Asia. With high consumption by infants and children, milk is a priority foodstuff in terms of ensuring it is free from residues and contaminants. Of particular concern for some time has been to ensure that milk does not contain detectable residues of veterinary medicines used for treatment of cows for various ailments. There are strict rules in the European Union and in the USA governing the approval for veterinary drugs, and these regulations not only limit what drugs can be used, but also impose withdrawal periods between the time of treatment and collection and sale of milk. Nevertheless, through carelessness or even deliberately driven by strong economic motivation, these rules are sometimes ignored necessitating routine testing by regulatory authorities. It can be seen that the level of scientific interest in monitoring veterinary drug residues in animal products remains high as demonstrated by the recent success of Euroresidues VIII held in May 2016 where more than 26 scientific talks and over 200 posters were presented. Many of these presentations covered new or improved methods for drug residues and their validation.
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How can we monitor milk for drug residues?
Screening of milk for drug residues such as antibiotics can be carried out by inhibition assays or immunochemical methods, but positive results still need to be confirmed and these screening assays are generally limited in scope to a single class of veterinary drugs. Without any prior knowledge of what residues might be present in milk, the aspiration of authorities is to have access to sensitive and comprehensive testing for all possibilities. The attraction of a method recently published by Jian Wang and co-workers in J Agric. Food Chem, is that 11 classes of veterinary drugs comprising a total of 105 residues can be simultaneously monitored. Their multi-class method covers endectocides, fluoroquinolones, ionophores, macrolides, nitroimidazole, NSAIDs, β-lactams, penicillins, phenicols, sulfonamides, and tetracyclines. A method in the publication by Kaufmann et al compares and optimizes SOSLE together with the more familiar QuEChERS as approaches to sample extraction and cleanup. SOSLE stands for Salting-Out Supported Liquid Extraction. The process entails precipitation of milk proteins using an extraction buffer (oxalic acid and EDTA, pH 3); acetonitrile, a salting-out acetonitrile/water phase separation using ammonium sulfate: and then solid-phase extraction (SPE) using polymeric reversed-phase sorbent cartridges. QuEChERS together with three variations of SOSLE were compared in terms of recoveries and other performance parameters, concluding that a variation of SOSLE was the best option. After SOSLE extraction and cleanup, milk extracts were analyzed by UHPLC-Q-Orbitrap™ mass spectrometry. This method was not only very sensitive, but operating at a mass resolution of 70,000 FWHM at m/z 200 provided a high confidence in correct identification from full scanned spectra. If the targeted compound was detected within the 10 ppm mass error window and achieved a designated intensity threshold, the precursor ions in an inclusion list were then isolated by the quadrupole, and sent to the HCD collision cell for fragmentation via the C-trap. Analysis by UHPLC/ESI Q-Orbitrap™ provided a measured mass accuracy <5 ppm and a retention time tolerance within ±0.2 min. Full MS/dd-MS2 was able to obtain product-ion spectra that included both precursor and product ions with accurate masses. Overall, UHPLC Q-Orbitrap™ was demonstrated to be a practical tool for the analysis of a large number of veterinary drug residues in milk with a single extraction and in a 14 min analytical runtime.
Meeting Future Regulatory Demands for Monitoring Foodstuffs
This blog post has highlighted how state-of-the-art instrumental techniques are being applied to screening of milk for drug residues and the increasing reliance on Orbitrap™ high resolution mass spectrometry. However, it is not only in veterinary drug residue monitoring that this trend can be seen. A recent issue of Food Additives & Contaminants was dedicated exclusively to applications of Orbitrap™ high resolution mass spectrometry in food safety and authenticity and is certainly worth a read. Pesticide residues, mycotoxins, allergens, illegal food dyes, adulteration of animal products and dietary supplements are all areas where high resolution mass spectrometry can be seen to be making an important contribution to food safety and authenticity.
Interested in learning more about milk analysis, check out the dedicated pages by clicking here.