Techniques - Microscopy

Microscopy is probably the oldest method for food analysis and determining authenticity.  Food authenticity applications date back to the mid-19^th century.  Classical microscopes use visible light.  Scanning Electron Microscopes (SEM) produces images of a sample by scanning the surface with a focused beam of electrons, producing various signals that contain information about the surface topography and composition of the sample. An SEM can produce magnified images of features at the nanometer scale.

Detecting Recovered Meat (MRM or DSM) in Meat Products

Microscopic examination after sectioning and staining can distinguish between the meat structure of mince compared to meat produced by machines which remove meat from the bone after hand deboning ("recovered meat"). Such recovered meat has a different sinew structure.  Recovered meat may be either:

• Mechanically Recovered Meat (MRM).  Very high pressures (over 200 bar) are generated by a piston, which causes the meat to flow off the bone in a puree.
• Desinewed Meat (DSM).  This is a gentler process. The bones are fed into a filling chamber, from where the main ram transports them to the pressing chamber. Gentle pressure causes the bones to rub the meat off one other and allows it to pass through filter perforation. The bones are retained inside the filter and discharged at the end of the cycle. The meat is then fed through pipes into a belt separator to remove sinew and cartilage.  There are other machines using an auger rather than a piston to produce a similar meat preparation.

The difference is shown in the figure below.  Sections were stained with toluidine blue and compared against the minced control, which shows muscle bundles with some disruption of the muscle structure. The Beehive and DMM50 machines produce DSM, which shows some muscle bundles but more muscle disruption. The MPD 60 and Lima machines are high pressure machines producing MRM, which show total disruption of the muscle fibre structure and only dispersed protein.

Image - Crown Copyright

Note that, despite the fact that DSM has muscle structure, which manifests itself as fine mince and therefore should normally be considered as a meat preparation, the ECJ ruled that it should be classed as MRM/MSM and be labelled as such i.e. not counting towards the meat content.

Botanic Origin of Honey (Melissopalynology)

Melissopalynology is the study of pollen. By examining the pollen in honey, it is possible to confirm floral origin and possibly geographic origin. It is challenging to confirm geographic origin from the pollen, because many species of plants are widespread in continental areas. More often it is possible to note that pollen is present from plants in the honey, which do not occur in a declared geographic origin on the label, and hence the honey could not have originated from that country.

If honey is labelled with its floral origin, then although the pollen from that named botanical origin may predominate, bees will also collect from other plants so that the image will show several or many types of pollen.

Microscopes are relatively cheap and portable, and require no specialist laboratory environment or services.  In principle, it is a highly accessible technique which can be performed anywhere in the world.

For Mechanically Recovered Meat detection, microscopic examination can only be done on the raw materials and cannot be used on final products.

Pollen analysis is reliant on specialist training and experience of the microscopist, to recognise which plant the pollen originates from. It takes practical experience to be able to recognise when the image of pollen indicates that the honey comes predominantly from the named botanical source.

Results interpretation can be subjective, and is highly reliant on the experience of the microscopist.  Experienced microscopists are in short supply.  When looking for accredited providers, in the case of microscopy, it is the expert who is personally accredited (for "Opinions and Interpretations") rather than the "method".