A novel ELISA test to detect soy in highly processed foods

Soy allergens detection is challenging when they are in trace amounts in foods, especially when foods are subjected to heat treatment, after which the target allergen maybe modified. Two ELISA formats, sandwich and indirect competitive, were developed using rabbit polyclonal antibodies against heat-denatured glycinin as the target protein. Sandwich format showed less cross-reactions and better sensitivity than the competitive format. The performance of both formats was tested using three model foods incurred with soy proteins. Results showed that the recovery decreased with the increase of heat treatment intensity applied to foods. Sandwich format could detect amounts of added soy isolate of 10 μg/g in sausage (pasteurized), 100 μg/g in bread (baked) and 1000 μg/g in pâté (sterilized); whereas competitive format only detected 2500 μg/g in sausage and 10000 μg/g in bread, and no glycinin was detected in pâté samples. A prototype of the sandwich ELISA was in-house validated giving acceptable results of precision and robustness. Recovery of model foods spiked with heat-denatured glycinin after processing ranged between 88 % and 149 %. In a survey of retail foods, the sandwich ELISA could differentiate most of the commercial foods with soy or derivatives declared or not in the ingredient list and could detect soy in highly processed foods.