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Mass spectrometry applied
Author: CAF - by dr Marietjie Stander, Malcolm Taylor and Erick van Schalkwyk
Published: 12/09/2018

In today’s well-informed society people are more aware of what they consume and would like to be sure that the contents of a product correspond to its label. The food industry, like most industries suffers from the odd criminal mind that would put self-gain and the highest possible profits above the quality of their products and the well-being of their consumers. 

Over the past 14 years the Mass Spectrometry Unit at CAF has been involved in the testing of products as a result of a number of food/ notorious beverage scandals in 2007/2008 when 6 Chinese babies died and 296 000 fell ill after drinking melamine-tainted infant formula. Melamine is an industrial chemical which is used to produce kitchen ware and table tops. Melamine (C3H6N6) has a high nitrogen content. The industry standard method to determine protein content is to measure the nitrogen content of a sample, which makes melamine adulteration an easy and inexpensive way to artificially increase the apparent protein content of products.

Melamine was also added to gluten meal that was exported world-wide including South Africa, where it was used in pet food. A method developed for Prof Cruywagen at the Department of Meat Science, University of Stellenbosch, was used to test for melamine in hundreds of pet food products and milk formula at our laboratory. The method was later transferred to commercial labs and is still used weekly to test raw materials used in the manufacturing of pet food as well as in milk products.

The same method was used by Cruywagen et al 1,2 to show that when melamine is used as fertilizer, it passes through the food chain into grass and will end up in meat, milk and eggs.

Beverages like fruit juice, wine and spirits also fell prey to foul play in Europe and the East over the past decade.

In 2011 di(2-ethylhexyl) phthalate (DEHP) was found in food and drinks in Taiwan after it was added as a clouding agent which affected 900 products sold by 40 000 retailers.

Phthalates are added to plastics, primarily polyvinyl chloride (PVC) as plasticizers to increase their flexibility and transparency. They are anti-androgens and have various other adverse health effects resulting in their banning in a large number of products including childrens toys and erasers.

Diet is believed to be the main source of phthalates in our bodies, with fatty foods like milk, butter and meat the major source and not water bottles like many people believe. Many studies have been conducted at our laboratory to test for phthalates, for many different clients.

It includes the testing of baby bottles, water bottles, printed paper and soft plastic toys for plasticizers including phthalates and bisphenol A.

The GC-MS laboratory has implemented a very sensitive method to test for phthalates in wine and spirits to ensure that products were not contaminated when pumping them through pipes that may contain phthalates.

The LC-MS laboratory has developed a number of tests to ensure that beverages are not contaminated by preservatives like natamycin, sorbic acid, citric acid and benzoic acid, colorants and artificial sweeteners. Additionally, wine is tested for traces of Ochratoxin A, a harmful secondary metabolite of fungi growing on grapes. Fruit juice and honey are also prone to adulteration where cheap adulterated imported products is a serious threat to our own industries.

Adulteration of fruit juice can have many forms including the substitution of higher value fruits with inexpensive fruits, the addition of sugar and water to stretch the volumes and the addition of artificial sweeteners. We have developed a fast screening method for fruit juice testing that screen for a number of preservatives, colorants and artificial sweeteners and at the same time tests for marker compounds for certain fruits and test for the ratio of sugars and oligosaccharides.

Grapes for example contains roughly equal amounts of fructose and glucose and only trace amounts of sucrose. High amounts of tartaric acid are a marker for grape juice. Apples and pears contain sorbitol that is not present in grapes, whilst certain amino acids are more prevalent in apple juice.

The accidental or fraudulent mixing of animal products or by-products from different species is also an important concern for consumers with health or ethical concerns. Gelatin, for example, is produced by the hydrolysis of collagen, which is extracted from materials such as bones and hides of pigs and cows obtained from abattoirs, and is used as a gelling and thickening agent in a variety of food products including meat, confectionery products and water-based desserts. It is also widely used in nutriceuticals and the pharmaceutical industry.

Nearly 80% of gelatin manufactured worldwide is produced from pork by-products. In Islamic countries, however, consumption of porcine products is forbidden so alternative products such as agar agar, carrageenan and vegetable gums are often used as gelatin substitutes to avoid the health and ethical concern associated with gelatin.

However, cross-contamination between different pro­ducts can occur since they are often produced in the same processing facility. It is important therefore to be able to test for either the presence of gelatin in vegetarian products, or to distinguish between porcine and bovine gelatins in Halal products.

Gelatin has a characteristic amino acid sequence, namely a repeating G-X-Y sequence, where G is glycine, X and Y are proline and hydroxyproline. Acid hydrolysis of the collagen peptides making up the gelatin leads to the presence of glycine (Gln), hydroxyproline (OHPro) and proline (Pro) amino acid residues in the acid hydrolysate. In the LC-MS laboratory at CAF, these amino acids are first derivatized and then analysed using ultra-performance liquid chromatography using UV detection.

Nutritional supplements are widely used by consumers to improve their health and general well-being, and by athletes to give them an edge in performance over their competitors. Due to the high stakes in international sport, athletes are constantly being driven to perform.

This has led to a booming global industry, worth 1 billion Euro in Germany in 2002 and US$16.7 billion in the USA in 2000. Competition amongst manufacturers for this lucrative market has led to the addition of banned performance-enhancing substances into various nutritional supplements.

An International Olympic Committee study in 2002 found 94 out of 634 (14.8%) supplements contained one or several prohormones not mentioned on the label. These prohormones are metabolized by the body into the active drug, often a banned anabolic steroid, resulting in a positive drug test with serious consequences for the athlete.

The LC-MS laboratory of CAF, together with Prof. Kathy Myburgh of the Muscle Research Group, Department of Physiology, University of Stellenbosch, has developed an untargeted screening method for banned stimulants and steroids using the Synapt G2 High-Resolution Mass Spectrometer (Waters, Milford, USA). This allows supplement samples to be screened to check that their contents correspond to their labels, and also to check for the presence of 45 compounds against a set of calibration standards.

Mass spectrometry is well suited to its emerging role in the new science of Foodomics and it is expected that the Mass Spectrometry Unit of CAF will play an increasing role in years to come, in ensuring the quality and safety of the products used by South Africa’s population.

Please note: graphs and references in this article can be seen in the CAF Annual Report 2017-2018 (click here to view)