Evaluation of Romer Labs’ AgraStrip Tree Nut Assays and a Multi-tree Nut Strip for Environmental Surface Testing

Introduction: Nut allergy affects roughly 1% of the U.S. population, with tree nuts and peanuts causing a higher percentage of life-threatening allergic reactions than other food allergens.  Because trace amounts of nuts still provoke allergic reactions, highly sensitive tree nut detection methods are a critical component of food allergen risk management.

Purpose: This study was undertaken to compare detection of tree nut residues on environmental surfaces, swabbed and tested by AgraStrip (AS) tree nut assays and a multi-tree nut strip.

Methods: Tris-buffered saline was used to make protein extracts of defatted and ground almond, cashew, pistachio, walnut, hazelnut and pecan, which were then analyzed by BCA assay for protein content.  Protein concentration was converted to whole allergen and used to calculate spikes at and near the stated limits of detection (LOD).  Tree nut extracts were spiked onto stainless steel coupons, dried, and tested according to the instructions in each kit.

Results: The multi-tree nut assay stated a LOD of 5-20 µg for all six tree nuts based on validation of tree nut extracts spiked onto a Teflon surface and swabbed.  This study showed that for stainless steel the multi-tree nut assay LOD’s were 15 µg for hazelnut, 20 µg for cashew and almond, 25 µg for pistachio and walnut, and 30 µg for pecan.  AS Cashew/Pistachio showed LOD of 1 µg for cashew and 2 µg for pistachio.  AS Walnut (cross-reacts with pecan) had a LOD of 5 µg for walnut and 200 µg for pecan.  AS Hazelnut had a LOD of 2 µg, while AS Almond had a LOD of 1 µg.

Significance: Single and dual tree nut strips demonstrated lower LOD’s than the multi-tree nut strip for 5 out of 6 tree nuts, showing them to be the more sensitive method for rapid detection of trace levels of tree nut residue.