3 samples from 3 different batches were purchased from 12 outlets in the Bath & North East Somerset area in-line with the sampling protocol in Appendix I and then sent for analysis at Worcestershire Scientific Services laboratory. Each sample was then tested for the presence of peanut, almond, hazelnut and walnut.
The presence of each species of nut protein was determined using a standard sandwich enzyme immunoassay procedure.
The samples were homogenised, and a test portion was quantitatively extracted into a buffer solution. An aliquot of the extract is exposed to specific antibodies coated onto the sidewalls of a test well. Any target nut protein present will conjugate to the antibody, and become bound. Other components are then removed by washing, and a second antibody conjugate is added forming an antibody – conjugate (protein) – antibody – complex (the 'sandwich'). Further reagents are added resulting in colour formation within the well, the intensity of which can be measured and is directly proportional to the amount of the target nut protein present in the sample. Quantification is achieved by comparison with standards of known concentrations. Limit of detection is typically 2.5mg/kg (ppm).