The words 'needle' and 'haystack' spring to mind when discussing pesticide testing. Over 700 pesticides are regulated worldwide; there are probably an additional 300 or so in circulation and new pesticides are emerging all the time. On top of this, food manufacturers have to contend with continued lowering of acceptable residue limits and pressure to accelerate test result turnaround and product release. These pressures are also the drivers behind developments in testing and analysis technology.
"We are looking at speeding up analysis from sample preparation to reporting," says Denise Ibens, worldwide food marketing manager for Agilent Technologies. "Because of the increased regulatory burden, and the global nature of the food industry, the number of tests is increasing all the time and there is a requirement to be able to do them faster and for closer to process testing."
She says liquid chromatography (LC) triple quadrupole mass spectrometry (MS) delivers on some of these counts, providing high sensitivity for complex matrices and requiring minimal sample preparation. This technique works by reducing the chemical background or 'noise', so the user can obtain a reliable measurement in 'dirtier' matrices than with a single quadrupole.
She cites the example of soy sauce: "If you tried to measure pesticides using a single quadrupole mass spectrometer, the chemical noise from the matrix would overwhelm the detector and prevent quantitative measurement without extensive sample clean-up."
For labs or manufacturers wanting to screen for large numbers of compounds, Agilent is working on a two-stage process which involves using a LC time-of-flight mass spectrometer to quickly screen for pesticides. Only in the event of a positive result will the secondary test - triple quadrupole MS - be necessary. "This reduces the cost of tests involving large numbers of compounds," says Ibens.
Web enabled reporting
Bodycote LawLabs says it has doubled up on gas and liquid chromatography triple quadrupole mass spectrometers dedicated to pesticide testing to keep up with demand.
"We have also enhanced the functionality of web enabled reporting, so that results can be rapidly communicated to customers when and where they need them," says Liz Paterson, sales and marketing director with Bodycote LawLabs. "We can now offer a 24h turnaround."
Around 240 pesticides are targeted via a single test, which uses a cryogenic sample extraction method to overcome the issues associated with testing in different matrices - it is robust across the whole range of food types.
Restek, meanwhile, has developed gas spectrometry (GS) columns specifically for analysis of organophosphorus pesticides. Called Rtx-OPPesticides (see picture above) and Rtx-OPPesticides2, these application-specific columns were created by computer modelling and are capable of separating 55 organophosphorus pesticides. "Separation is improved, and analysis time is significantly reduced compared to other columns," says Restek innovations chemist Julie Kowalski.
The extended upper temperature limit of these phases (330°C) allows analysts to bake out high molecular weight contamination typically associated with pesticide samples, says Restek. Narrow bore columns produce very narrow peaks, allowing analysts to take advantage of fast scanning mass spectrometers - it is possible to analyse and confirm 20 pesticides in eight minutes, says Restek.
The impetus to reduce time taken to obtain test results, however, applies to food analysis methods across the board.
Allergen and authenticity testing
Tepnel claims to have brought allergen testing on to the factory floor for the first time with its new Rapid 3-D Tests. Sample preparation and testing take under 10 minutes and real-time results are viewed via a hand-held device which confirms the method has been performed successfully and differentiates low and high levels of detection.
Another area where Tepnel says major inroads have been made is in authenticity testing. The Food Standards Agency has been leading the battle against food fraud, funding the development of a battery of DNA tests for checking the authenticity of foods, from basmati rice to durum wheat pasta.
The most recent success story has been the development by Campden and Chorleywood Food Research Association (CCFRA) of a database with DNA profiles for 50 species of fish, thanks to DNA fragment profiling and lab-on-a-chip technology. Using the polymerase chain reaction (PCR) technique, target strands of DNA are multiplied many times in an automated system to produce sufficient quantities of DNA. A chip-based capillary electrophoresis system (the Agilent 2100 bioanalyser) is then used for analysis.
Screening for prebiotic activity
Just as consumers of Atlantic cod or Aberdeen Angus beef want to be sure they are getting what they pay for, so shoppers who pay a premium for functional foods want to know they're getting a health benefit in return.
"We're seeing growing demand in testing for the potential prebiotic functionality of a variety of different ingredients," says Dr Evangelia Komitopoulou, bioscience and microbiology research business manager at Leatherhead Food International (LFI).
Effective prebiotics must not be digested or absorbed by the body, rather, they must pass through to the colon where they are fermented by positive bacteria.
A preliminary screening to identify prebiotic activity would measure stability and evaluate gut activity. The stability of the prebiotic when exposed to gastric fluid and small gut enzymes can be assessed by monitoring changes in molecular structure using high performance size exclusion chromatography and the elution profiles produced.
Potential prebiotic activity can be evaluated using batch culture fermentation. Results are compared with those obtained from the same systems in the absence of the ingredient. Analysis of predominant microflora components, short chain fatty acid generation and gas generation through fermentation can then be carried out.
An important aspect of prebiotic screening is to reliably discriminate changes in the gut flora in response to the prebiotics, says Komitopoulou. Traditional mixed culture methods have fundamental problems of subjectivity, poor selectivity in nature and the lack of recovery of non-culturable diversity. However, the advent of a range of molecular techniques has remedied this situation.
Besides testing for prebiotic activity, LFI's Komitopoulou says food manufacturers would like to be able to detect, identify and enumerate probiotic bacteria in a variety of different probiotic dairy products.
"In order to do this, methods that can distinguish between the target probiotic and the background lactic acid bacteria contained within those products need to be developed," she explains. "Using currently available conventional methods that rely on the use of selective media, it is not always possible to distinguish between starter cultures and probiotic organisms." FM
KEY CONTACTS
- Agilent Technologies 0131 331 1000
- Bodycote LawLabs 0121 251 4000
- CCFRA 01386 842 000
- CSL 01904 462 000
- Leatherhead Food International 01372 376 761
- Restek 01494 563377
- Tepnel 01244 280202
What about the Need for nano particle testing?
As nanomaterials start to find their way into food and beverage products and packing, the very properties that make engineered nano particles (ENPs) attractive in these applications could also render them emerging contaminants.
At present, the use of ENPs in food and beverage applications is unregulated and there are massive gaps in knowledge of their potential toxicity and impact on human health and the environment.
Karen Tiede, a PhD student from the University of York, is carrying out doctoral research on placement at the Central Science Laboratory (CSL). She discussed her research on the development of analytical methods to test the behaviour and toxicity of ENPs at the 3rd International Symposium on Recent Advances in Food Analysis in Prague last November.
"My aim is to increase knowledge of these particles, because no-one knows whether we actually have a problem with them," she says. "They could be perfectly safe, but we need to develop appropriate analytical procedures to assess if potential problems exist."
The limitations of existing testing methods are that they are destructive, bring about sample alteration, require high spatial resolution, fail to differentiate between natural and engineered nano particles and generally do not size the particles. ENPs should, she says, be analysed in the medium in which humans and the environment are exposed to them. Analytical techniques should therefore enable in situ characterisation in food and beverages, separate a wide range of particle sizes, deal with heterogeneous samples and minimise sample alteration.
Tiede has been working on several new analytical approaches, including electron microscopy in liquid, hydrodynamic chromatography (HDC) and inductively coupled plasma mass spectrometry (ICP-MS).
"Usually, you have to prepare a dried sample for electron microscopy because it takes place in a vacuum chamber, which precludes the use of liquid samples," she says. "However, I have been using QuantomiX capsules (WetSEM), which allow imaging of liquid samples - giving better insight of nanoparticle agglomeration in complex media."
The HDC coupled with ICP-MS allows a complex sample containing different sized particles to be analysed. "First, particles are separated via HDC, then they go directly into ICP-MS, which gives the chemical composition of the size fraction," she says.
A paper outlining the findings of the research will be published in early 2008.