Mechanically recovered meat: how it differs from other types of meat
Mechanically recovered meat (MRM) is obtained by removing residual raw meat from animal bones after the main flesh has been removed from the bones with a knife. It is produced by forcing the bones at high pressure though machines such as sieves to detach the meat, which emerges as a smooth paste.
The EU has declared that MRM is not "meat", partly due to consumer concerns about its safety, but it can still be used in food products such as economy burgers, sausages, meat pies and nuggets. Ideally, products containing MRM should be correctly labelled, to distinguish them from foods containing "real" meat.
Desinewed meat is prepared under lower pressure than MRM and is more meat-like, falling within the EU definition of meat. It does not require separate labelling, and neither does hand-deboned meat.
Nowadays, the MRM is limited to chicken and pork, since beef was banned due to the potential of BSE, but the task of differentiating MRM from other types of meat remains difficult. There are natural variations between animals and species to consider, as well as the different types of conditions encountered in MRM production which might have an influence on the final food product.
The metabolomics of MRM: GC/MS detects a range of compound classes
One team of scientists in the UK has adopted a metabolomics approach to MRM differentiation, with the aim of exposing meat products that have been adulterated with MRM. Peter Bramley, Izabella Surowiec, Paul Fraser, Raj Patel and John Halket from Royal Holloway University of London, Egham, were encouraged by the success of metabolomics for biomarker detection in a range of settings, including disease differentiation, drug toxicity and phytochemicals.
In a pilot study, they had derived the best conditions for extracting the highest number of compounds from MRM and hand-deboned meat, which they applied in this extended study. Desinewed meat, hand-deboned meat and MRM were each homogenised and extracted with a solution of methanol-water (9:1, v/v), which yielded fatty acids, sugars, amino acids and small organic acids.
Only one extraction step was required, with further steps producing very low additional amounts of compounds and the procedure was fast with average intra- and inter-day reproducibilities of 22 and 31%, respectively.
The extract was derivatised to produce methoxime-trimethylsilyl derivatives of the polar metabolites to make them amenable to GC/MS analysis by electron ionisation.
A total of 80 compounds were selected from the total ion current chromatograms and identified by database matching from the retention times and mass spectra. The compounds were quantified using the retention times for unequivocal peak detection.
A principal components analysis achieved relatively clear separation for pork samples using the first two components, classifying the three types of meat, but the separation for chicken samples was not as well defined.
Better results were obtained using an orthogonal partial least squares discriminant analysis (OPLS-DA), which allows the introduction of classes into the model. All three types of meat were correctly grouped for both pork and chicken. In addition, the model was able to predict the correct classification of other meat samples.
The OPLS-DA model was then used to analyse pork sausages from a local shop. They were classified correctly as hand-deboned meat, in agreement with their labelling.
The actual compounds responsible for the differentiation, identified from their mass spectral data, included fatty acids (such as linoleic and oleic acid), cholesterol, amino acids (pyroglutamic acid, N-acetylglutamic acid) and sugars (threonic acid, glyceric acid). Most of them were fat-related metabolites. These metabolites could not be used individually for meat differentiation but worked together for multivariate sample classification.
So, metabolomics analysis by GC/MS with multivariate analysis was able to classify MRM, desinewed meat and hand-deboned meat. The research team suggested that the work could be broadened to seek out MRM markers within lipids, which would require a different mode of sample extraction. It could also be extended to include other meats apart from pork and chicken.
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