Contaminants: novel methods for detection

30th April 2014

Posted By Paul Boughton

The AxION 2 TOF mass spectrometer can be used for rapid screening of adulteration of olive oil with soybean oil

Two new studies propose novel ways to identify pesticides in food and rogue vegetable oils in olive oil. Eugene McCarthy reports.

The latest application note from PerkinElmer demonstrates that its AxION direct sample analysis (DSA) system integrated with its AxION 2 time-of-flight (TOF) mass spectrometer can be used for rapid screening of olive oil adulterated with soybean oil.

Among edible oils, olive oil shows important characteristics due to its differentiated sensorial qualities (taste and flavour) and higher nutritional value. It is an important oil that is high in nutritional value due to its high content of antioxidants. Several health benefits, such as its ability to lower LDL cholesterol and its anti-inflammatory activity, associated with its consumption were initially observed among Mediterranean people.

However, olive oil is one of the most adulterated food products of the world due to its relatively low production costs and higher prices as compared to vegetable and seed oils.

Olive oil contains more oleic acid and less linoleic and linolenic acids than other vegetable and seed oils. Oleic acid is a monounsaturated fatty acid, whereas linoleic and linolenic acids are polyunsaturated fatty acids. The main fatty acids in olive oil are: oleic acid (65-85 per cents), linoleic acid (4-15 per cent), palmitic acid (7-16 per cent) and linolenic acid (0-1.5 per cent). The main fatty acids in soybean oil are: oleic acid (19-30 per cent), linoleic acid (48-58 per cent), palmitic acid (7-12 per cent) and linolenic acid (5-9 per cent). Therefore, the ratio of linoleic and linolenic acid to oleic acid in olive oil can be used as a way to detect its adulteration with soybean oil and other seed oils.

The addition of vegetable and seed oils of low commercial and nutritional value to olive oil results in frequent problems for regulatory agencies, oil suppliers and consumers.

A lot of scientific effort has been spent to develop rapid, reliable, cost effective analytical approach for measurement of adulteration of olive oils with other oils. In the past, methods employing gas chromatography/ mass spectrometry (GC/MS) and high performance liquid chromatography (HPLC) hyphenated to MS (HPLC/MS) have been implemented for this purpose. These methods are time consuming, expensive and require extensive sample preparation, method development and derivatisation.

In this work, PerkinElmer demonstrated that the AxION DSA system integrated with the AxION 2 TOF mass spectrometer can be used for rapid screening of adulteration of olive oil with soybean oil.

“The advantages of this method, compared to conventional techniques, are that no chromatography is required, the combination of direct sampling from the olive oil is done with minimal or no sample preparation and mass spectra results are generated in seconds,” says the company.

Meanwhile, a new application note from Thermo Fisher Scientific demonstrates how a novel online sample preparation technique could be used as an alternative to the QuEChERS (quick, easy, cheap, effective, rugged and safe) method for high throughput LC-MS/MS pesticide analysis in grapes, baby food and wheat flour.

European Regulation 396/2005 sets maximum residue levels of pesticides in different products of plant and animal origin. These regulations present a significant analytical challenge with respect to the low limits of quantification which are required for some specified food matrices such as baby food. Many gas chromatography (GC) and high pressure liquid chromatography (HPLC) methods have been developed for multi-residue determination of pesticides and are in widespread use – employing a variety of sample preparation and clean-up techniques.

In recent years the QuEChERS method has become widely adopted for handling fruit and vegetables. However, QuEChERS requires many manual sample manipulation steps, making it labour-intensive when large numbers of samples have to be analysed. It is therefore beneficial to consider options for automation of multi-residue methods, which can be cost-effective and can offer a high degree of reliability in recovery and repeatability. While the preliminary stages of homogenisation and solvent extraction of food matrices inevitably require manual intervention, once a crude extract has been obtained, the procedure is fully automated thereafter. This automated procedure is included in the method, which utilises turbulent flow chromatography with online liquid chromatography-mass spectrometry (LC-MS/MS).

Thermo’s multi-residue pesticide method can be applied to fruits, cereals and composite baby foods at limits of detection (LODs) in the range of 0.8–10.3 μg/kg which are below respective EU maximum residue limits (MRLs). The method has been validated for 48 pesticides from different classes, but can be readily extended to a larger number of residues.

Sample concentration, clean-up and analytical separation are carried out in a single run using an online coupled turbulent flow chromatography - Thermo Scientific’s Transcend TLX system powered by Thermo Scientific TurboFlow technology. TurboFlow technology enables very effective separation of matrix and target compounds – resulting in relatively clean sample extracts.

According to Thermo, using TurboFlow technology enables convenient, fast and cost-effective automated determination of selected pesticides, from polar to non-polar compound chemistry, in different matrix types.

Based on the short total run time and Transcend system with TurboFlow technology, 100 samples per day can be analysed under controlled sample preparation conditions. Method performance characteristics were established by in-house validation for baby food, grapes and wheat flour matrices.

“The method performance indicates it is suitable for routine use for regulatory purposes and can be readily extended to a larger and wider range of pesticide residues,” concludes the application note.

Screening for sulphonamides and Trifluralin

As an antimicrobial agent, sulphonamides are used in global food production to treat/prevent infections. However, serious health concerns exist over human consumption and the development of antibiotic resistance. As a result, many countries have banned or limited their use in animal production and set maximum residue limits (MRLs) for residues in food.

Randox Food Diagnostics meat & seafood manager, Joanne McKnight, said: “Standard products on the market are based on generic antibodies designed to detect a range of sulphonamides. However that compromises the performance of each individual compound. Both our Biochip Array Technology and ELISA products are based on specific antibodies for each individual sulphonamide so this reduces reliance on cross-reactivity and increases accuracy. Feedback from customers to date has been very positive, as investing in quality screening reduces false positives, and dramatically cuts associated costs with superfluous confirmatory testing.

The company has also developed an ELISA for the herbicide Trifluralin. While the World Health Organisation has classified the herbicide as unlikely to present an acute hazard in normal use, Japan, for example, closely inspects shrimp imports from Vietnam for its presence. Japan has warned that any detection of Trifluralin and it would immediately impose a 100 per cent inspection regime on shrimps. Randox developed its ELISA in response to this and limits of 0.17ppb can be achieved using a simple sample preparation. Forty samples can be prepared in less than three hours and assay time to results is 90 minutes.





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