Validation of the R-Biopharm AG RIDASCREEN® Histamine (Enzymatic) Kit

Background: RIDASCREEN (R) Histamine (enzymatic) is an enzymatic test kit for quantification of histamine in fresh fish, canned fish, fish meal, cheese, and wine. Methods: Fish products are extracted with boiling water, while cheese is extracted with water, and the extract is treated with perchloric acid/potassium hydroxyde. Wine is extracted with the reagents of RIDA (R) Sample Decolorant kit to eliminate color pigments and interfering compounds. The enzymatic determination is based on histamine dehydrogenase, which catalyzes the oxidative deamidation of histamine in the presence of an electron carrier that converts a dye to a color product. The resulting color intensity is directly proportional to histamine concentration and is measured at 450 nm. The substrates are coated on the microtiter plate. Results: The linear range is from 1 to 20 mg/L in the extract. LOQs are 2 mg/kg for fresh fish, canned fish, and cheese, 1.4 mg/L in wine, and 10 mg/kg for fish meal. The linear range is from 5 to 100 mg/kg for fish products and cheese, 3.6 to 72 mg/L for wine, and 25 to 500 mg/kg for fish meal. Recovery and precision are very good for all matrices, and comparisons with HPLC reference methods revealed that the method also delivers true results for fish products and wine. Agmatine shows a low side activity of around 0.75% at 10 g/kg. Possible interfering substances are ascorbic acid (more than 250 mg/L in wine or 250 mg/kg in fish). A special sample preparation to deplete ascorbic acid from fresh fish is described.