17 May 2005: This product may contain nuts

European researchers have developed fast enzyme-linked immunosorbent assays that will help food producers and consumer protection agencies identify traces of peanuts and hazelnuts in foods.

Nut allergies are an increasingly recognised problem, especially in children, where reactions can be so severe that small traces are sufficient to kill. The problem is exacerbated by the use of nuts in many foods, including ice cream, chocolate and biscuits.

The only defence is avoidance, so food labelling is critical. However, even in factories, shared utensils and the use of common production lines contribute to cross contamination of food products.

The major nut allergens are proteins, but current immunoassays for nut proteins can take several hours to complete. Michael Weller from the Technical University of Munich, Germany and colleagues from the UK, Austria and the Netherlands designed a new sandwich-type immunoassay that takes only 30 minutes. Mouse monoclonal antibodies were used to capture the proteins, and enzyme-labelled rabbit monoclonal antibodies were used for detection, with a colorimetric reaction.

The cross reactivities against 19 other seeds and nuts were negligible and the limits of detection were all in the low parts-per-million range. This is sufficient for allergic patients, but sensitivity could be increased by up to tenfold by raising the incubation times of the sampling and detection stages, says Weller.

In the analysis of commercial foods, all products labelled as possibly containing hazelnuts did so, whereas all those possibly containing peanuts were negative, presumably because the concentrations were below the detection limit or the manufacturers were playing safe.

Most products without peanut or hazelnut on the label were confirmed as negative, but a few did contain traces in the low parts-per-million range, and one milk chocolate contained 0.6 per cent hazelnut. For an allergy sufferer, this could be a dangerous level and reinforces the value of product testing before release from the factory.

Steve Down