Sensitive ELISA and lateral flow immunoassay for the detection of walnut traces in processed food and working surfaces

Walnut represents one of the most allergenic nuts that can be found as a hidden allergen. In this study, sandwich ELISA and lateral flow immunoassay (LFIA), based on the determination of Jug r 1, were developed to detect walnut. Cross-reactivity was only found with Pecan nut among a panel of 88 food ingredients tested. ELISA and LFIA could detect 0.25 and 0.5 µg/g of walnut protein in complex food matrices spiked with walnut extract, respectively. Furthermore, walnut was detected in blended (chocolate) and model foods (ice cream and bread) added with ground walnut at levels of 0.5 and 1.5 protein µg/g by ELISA and LFIA, respectively. LFIA could also detect 0.1 μg of walnut protein in working surfaces. ELISA displayed acceptable precision and high recovery (71–97 %) and both tests were robust. This study showed that developed ELISA and LFIA are reliable tools to be applied in allergen control programs.