What's really in your milk?

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  • Published: Jun 15, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: HPLC
thumbnail image: What's really in your milk?

The dangers of diluted milk

Milk is a major source of nutrition worldwide as it contains protein, lactose sugars, vitamins and minerals. More than 6 billion people consume milk and milk products, produced by over 270 million dairy cows, which together make over 700 million tonnes of milk a year.

For many of us, milk is our first source of nutrition and an important part of our diet throughout our lives. Indeed, milk is a major source of nutrition worldwide as it contains protein, lactose sugars, vitamins and minerals. More than 6 billion people consume milk and milk products, produced by over 270 million dairy cows, which together make over 700 million tonnes of milk a year.

As well as milk itself, milk-derived products, such as powders and concentrates, are traded globally for the manufacturing of a range of products, including baby formula, chocolate, and baked goods. Owing to its nutritional value, powdered milk is also a common component of aid supplies as it is non-perishable, easy to transport and doesn't require refrigeration.

However, the high demand for milk products has motivated malicious efforts to tamper with them to make them more profitable, most notably by increasing perceived protein content by adding nitrogen-rich compounds (thereby allowing dilution). This issue became globally recognised in 2008 when Chinese baby food was contaminated with melamine – white crystals that are rich in nitrogen – resulting in the illness of thousands of children and several fatalities.

So history doesn't repeat itself, it is important to be able to rapidly and accurately screen milk for tainted ingredients. Using a list of criteria, such as the physical and sensory properties of compounds, some countries have developed a list of potential adulterants. However, lists are only in useful in conjunction with an analytical technique able to detect them. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) is the current technique of choice, but it is pricy and can be difficult to use.

Two-pronged trials

In a paper published in Rapid Communications in Mass Spectrometry, researchers from Advion – experts in mass spectrometry – and Abbott Nutrition – a medical nutrition company that creates several milk-based products – came together to develop a simpler and cheaper alternative.

Their method uses hydrophilic interaction chromatography (HILIC) alongside a compact mass spectrometer. The method can detect a range of potential milk adulterants, including melamine and five other nitrogen-rich compounds: cyromazine (an insecticide related to melamine); ammeline (an acid produced by melamine breakdown) and its hydrolysis product ammeline; amidinourea (a urea based compound containing four nitrogen atoms) and cyanuric acid (an industrial compound used in bleaches, disinfectants and herbicides) – none of which you’d want to find in your milk (or milk products).

They tested the method on three products – whole milk powder, non-fat milk powder, and whey protein concentrate (the cheapest and most common form of whey protein, often used by bodybuilders). These samples represent the chemical diversity of milk products (whole milk powder is around 25% protein while whey protein concentrates are over 80% protein) and were chosen to really put the method to the test.

The researchers developed a two-pronged sample extraction procedure based on dilute-and-shoot and solid-phase extraction (SPE). The SPE-based method of sample preparation showed greater precision and accuracy across all samples, which suggests dilute and shoot analysis is perhaps more suited to rapid, semi-quantitative screening analysis than comprehensive quantitative analysis.

Screening at the front line

To validate the method, they spiked samples of each powder with target analyte standard solutions of specific concentrations. The data were evaluated for the presence or absence of each target analyte against the spiking scheme. The analysis showed that all 36 spiked compounds were correctly detected with no false positives or negatives, proving that the method is reliable. The validated method was then used to screen the commercial ingredients, fortunately not detecting any of the analytes.

The simple method, using a ‘dilute-and-analyse’ sample preparation scheme, can rapidly detect six different contaminants, while the SPE-based approach can more sensitively detect melamine. Both are accurate and precise and were able to accurately detect contamination in three popular milk-derived ingredients. What’s more, the analysis scheme is simple and easy to implement, enabling high throughput screening. This method could therefore be used on the frontline – for example, in manufacturing plants – to rapidly screen milk for dangerous contaminants.

Related Links

Rapid Commun. Mass Spectrom., 2016. Draher et al., Determination of emerging nitrogenous economic adulterants in milk proteins by high-performance liquid chromatography/compact mass spectrometry.

FAO: Status and Prospects for Smallholder Milk Production, A Global Perspective

World Dairy Cow Numbers

FAO: Food Outlook, Global Market Analysis

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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