Use of sandwich IgG ELISA for the detection and quantification of adulteration of milk and soft cheese

The aim of this work was to develop an assay capable of detecting adulteration of soft goat, sheep and buffalo milk cheese with bovine milk from cheaper sources. A previously developed indirect competitive ELISA had a lower sensitivity when applied to cheese, compared with milk. A sandwich ELISA was developed utilising the same monoclonal antibody in combination with a polyclonal goat anti-bovine IgG antibody. Once optimised, the ELISA was found to be highly specific. Detection limits in milk were 0.001% cows’ milk adulteration of sheep or buffalo milk, and 0.01% cows’ milk adulteration of goat milk. Detection limits in soft cheese were 0.001% in goat cheese and 0.01% in sheep or buffalo cheese. The assay was highly reproducible with both intra- and inter-assay coefficient of variation <10%. The ELISA performance makes it suitable for development as a kit for use in routine surveillance of milk and soft cheese.