Sophisticated analysis techniques such as gas and liquid chromatography are becoming an increasingly important tool in ongoing efforts to ensure food quality and detect contamination. So, what have been the most recent developments in the use of liquid and gas chromatography techniques to analyse food products? And how exactly are such techniques used in the laboratory setting?
Unknown chemicals
One interesting recent development was a Danish project that used liquid chromatography to estimate the levels of unknown chemicals in complex food mixtures. As Eelco Nicolaas Pieke, PhD student at the Research Group for Analytical Food Chemistry – National Food Institute at the Technical University of Denmark, explains, many of the samples the team obtain from food materials or food contact materials are fairly complex and contain ‘a large number of chemical substances of often undetermined origin.’
“For many of these chemicals, we don’t even know their chemical structure. Most of the currently employed analytical techniques are quite incapable of dealing with chemical analytes when a lack of information is present. Especially nowadays we are capable of detecting more analytes and at lower levels, so we often don’t know beforehand what we are looking for,” he says.
To alleviate the difficulty in estimating the levels of these ‘unknowns’ Pieke reveals that team devised a semi-quantitative method that is capable of quantifying any analyte in a sample without the need for identification or standard-matching. Although he admits the new method is slightly less accurate, largely because semi-quantification has an inherently larger error of prediction, Pieke stresses that it ‘permits the investigation of the concentration of any number of analytes in a complex sample, given that the prediction has a lesser certainty than traditional methods.’
“However, as traditional methods often simply don’t work, or need significant work to be made to work on complex samples, this may be a much-needed alternative to take a first look at samples without digging too deep,” he says.
In terms of technology, Pieke says that the new method uses a mixed Agilent 1260/1290 Infinity liquid chromatography (LC) system combined with an Agilent 6550 Q-TOF (quadrupole time-of-flight) mass spectrometer (MS). To couple the LC with the Q-TOF, the team also used an Agilent Jet Stream (AJS) electrospray ionisation interface (ESI) - and relied on a number of software tools to data-mine the results.
Broadly speaking, Pieke believes that liquid chromatography is a ‘very powerful tool’ for food and food-related analysis, and enables a ‘really good coverage’ for the chemicals that are typically found in samples.
“It also has a fairly good tolerance for samples that are not optimally pre-treated and works extremely well with liquid extractions using polar solvents, which seems to be a trend.”
Contaminant analysis
Elsewhere, Dr Niels Martha, laboratory manager at TLR International Laboratories, observes that the scope of contaminant analysis in food products is still expanding, especially in the field of pesticide analysis, where he says more specialised methods using Single Residue Methods (SRM) are being developed ‘in order to be able to cope with difficult analytes and analyte-matrix combinations.’
“We primarily use triple quadrupole instruments, but are also implementing high-resolution approaches for contaminant determinations. The advantage of using liquid and gas chromatography technology for food analysis is that it is fast, sensitive and rugged,” he says.
“Most of the new development is related to expanding our contamination scope. LC-MS/MS is not new to us but investment in new sensitive equipment has broadened the playing field and we are going to explore this in the forthcoming years,” he adds.
Versatility
Meanwhile, in September 2017, olive oil company Pompeian opened a new Quality Control and Research & Development Centre at its headquarters in Baltimore, USA. According to Luisito Cercaci, vice president of Quality and Research & Development at Pompeian, the centre carries out a full range of tests related to the quality and purity of extra virgin olive oil, as well as many other analytical tests related to other types of product such as vegetable oils and vinegars.
The main scope of these tests is to evaluate the quality of raw materials and finished goods by checking variables such as free fatty-acid levels, fatty-acid composition and contaminants, as well to investigate the state of conservation of the oil by measuring primary and secondary oxidation parameters such as peroxide value and UV absorptions, type and amount of partial glycerides, chlorophylls and metabolites. According to Cercaci, the team mostly uses liquid or solid phase extraction for preparation and purification purposes, depending on the type and quantity of analytes needing to be checked – and uses thin layer chromatography to comply with the standards laid down by international authorities such as the International Olive Council (IOC).
“We mainly use reverse-phase HPLC with both isocratic or gradient eluents to analyse the triglyceride composition of our oils, as well as polar components or metabolites of pigments and refractive index and UV-Vis detectors,” he says.
“Capillary gas-chromatography is another type of separation technique commonly used in our lab, since most of the major and minor components of olive oil are identified and quantified by that. We commonly use polar, mid-polar and non-polar capillary GC stationary phases, with length ranging from 4m to 100m, with split, PTV or on-column injection techniques, equipped with FID or MS detectors when required,” he adds.
Looking ahead, Cercaci expects that the centre will continue to use both liquid and gas chromatography techniques for both ‘daily needs and future research’ - particularly since both technologies offer the ‘versatility and sensitivity’ needed as a result of the complexity of the matrix analysed. Specifically, the team is now looking to automate its purification procedures in an effort to respond to growing company needs, as well as to
be able to ‘provide results in a faster way and increase the number of samples tested in the lab.’
Crisp flavours
Back in the UK, Deepa Agarwal, Research Fellow in the School of Biosciences at the University of Nottingham, has recently worked on a research project at Pipers Crisps, to increase what she describes as ‘fundamental understanding of different flavour profiles of crisp flavours’ – as well as to ‘enhance the flavour perception and stability during shelf life’ and use the knowledge gained to develop new flavours for the company.
Throughout the project, Agarwal used headspace gas chromatography-mass spectrometry (SPME) with an ISQ single quadrupole mass spectrometer, paired with Trace 1,300 GC and equipped with a ZB-Waz column, and a TriPlus RSH autosampler from Thermo-Fisher Scientific. She also used a fused silica fibre coated with a 50/30µm layer of divinylbenzene–carboxen–polydimethylsiloxane to sample analytes from the headspace and processed the peak area with Xcalibur software.
In Agarwal’s experience, GC-MS enables a ‘quick and easy form of aroma analysis of food products’ and ‘really helps in monitoring the impact of process conditions and ageing process on the volatiles associated with oxidations, or degradation in the product.’
“Importantly, it’s a less time consuming technique compared to sensory analysis, where you need either highly trained sensory panels or loads of consumer panels. However, the correlations between the sensory analysis and GC-MS profiling cannot be discounted, and combined analysis is a powerful skill to tackle various challenges in the food industry,” she says.
“In the university’s flavour lab, we have been using both GC-MS and LC-MS for various food applications such as crisps, coffee, cheese and biscuits. I believe this is a very versatile technique that can be employed for any food application, as long as one can develop methods appropriate to the product and the targets and requirement of the project,” she adds.
