Detection of Moulds in Food by Latex Agglutination: A Collaborative Study

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Abstract
The latex agglutination assay for detection of Aspergillus and Penicillium species in food products was tested by nine different laboratories. The test is a slide agglutination test which uses latex particles sensitized with immunoglobulins specific for extracellular polysaccharides (EPS) produced by species of Aspergillus and Penicillium. False positive results are recognized by use of sensitized latex particles, to which synthesized haptens have been added. These haptens, with an identical structure of the epitopes present on the EPS, specifically block the immunoglobulins present on the latex particles. False negative results are recognized by addition of EPS to test samples. Besides the latex agglutination assay, the collaborative laboratories used their own methods for detection of moulds in the food products. Eight of the nine laboratories applied the colony counting method for enumeration of moulds and in total seven different media were used. Using purified EPS, eight laboratories were able to detect a quantity ranging from 5–15 ng/ml. Of the different foods tested cereals, animal feed and spices showed fair correlation between mould colony count and latex agglutination titre. For other products, such as different fruit juices, a correlation was not observed. Of the different foods tested by the participating laboratories, walnuts gave clearly false positive results. The results of the collaborative study have shown that the latex agglutination is a rapid, simple and reliable quantitive method for detection of Penicillium and Aspergillus in cereals, spices and animal feeds.