ELISA kit for casein determination: interlaboratory study.

An interlaboratory study was performed in eight laboratories to validate an ELISA method developed for quantitative determination of casein in foods. The ELISA kit used is based on rabbit polyclonal antibodies. The kit is quite specific; no false-positive results or cross-reactivities were obtained for a broad range of food matrixes with zero content of milk proteins. All participants in the study received the casein kit, which included a standard operating procedure, a list of the samples, the samples, and a protocol for recording test results. The study included nine food samples: wheat flour, buckwheat flour, instant potato purée with milk, instant coffee with sugar and cream, a mixture for fancy bread, salami, liver paté, chocolate muesli with nuts, and a mixture for gluten-free bread. Three food samples with zero content of milk proteins showed a casein content lower than the lowest casein standard (1.0 mg CAS/kg) in most laboratories and measurements (64%). In 98% of the cases, the casein content was lower than the estimated LOQ. Two food samples with no dairy ingredient declared on the ingredient list contained casein levels higher than the second casein standard (3.0 mg CAS/kg) and the third standard (10.0 mg CAS/kg), respectively. Four food samples containing milk as an ingredient tested positive, and three showed casein contents higher than the highest standard (30.0 mg CAS/kg). The statistical tests (Cochran, Dixon) and analysis of variance were used for evaluation of the interlaboratory study results. Repeatability and reproducibility limits as well as LOQ (1.8 mg CAS/kg) and LOD (0.5 mg CAS/kg) for the kit were calculated from the results of the interlaboratory study.

Enzyme-linked immunosorbent assay kit for beta-lactoglobulin determination: interlaboratory study.

An interlaboratory study was performed in six laboratories to prove the validation of the ELISA method developed for quantitative determination of beta-lactoglobulin (BLG) in foods. The ELISA kit used for this study is based on rabbit polyclonal antibody. In-house validation of the kit did not produce false-positive results or cross-reactivity in a broad range of food matrixes containing no milk proteins. All participants obtained the BLG kit with a standard operational procedure, the list of the samples, samples, and a protocol for recording test results. The study included 14 food samples (extruded breakfast cereals, bread, two soy desserts, butter, chicken ham, chicken meat, wheat flour, long grain rice, jelly, two whey drinks, crackers, and bitter chocolate) and six spiked samples (two rice, two wheat flour, and two chicken meat). Nine samples of food matrixes containing no milk proteins showed BLG content lower than the first standard (0.15 mg/kg). Two samples of food matrixes with no milk proteins revealed BLG content higher than standard 3 (1.5 mg/100 g) and standard 4 (5.0 mg/100 g). Three food samples containing milk were tested as positive, and all spiked samples were evaluated as positive. The statistical tests (Cochran, Dixon, and Mandel) and analysis of variance were used to evaluate the interlaboratory study results. Repeatability and reproducibility limits, as well as LOQ (0.22 mg BLG/kg) and LOD (0.07 mg BLG/kg), for the kit were calculated.

Gluten determination by gliadin enzyme-linked immunosorbent assay kit: interlaboratory study.

An interlaboratory study with 10 participants was performed to obtain validation and performance data for an enzyme-linked immunosorbent assay (ELISA) kit developed for quantitative gluten determination in foods. The ELISA kit used for this study is based on 2 monoclonal and 1 polyclonal antibody developed by Immunotech, a Beckman Coulter Co. This kit did not show any false positive results or cross-reactivity with oat, rice, maize, and buckwheat. The gliadin standard from the Working Group on Prolamin Analysis and Toxicity was included in the kit as reference material for calibration. All participants obtained a gliadin ELISA kit with Standard Operational Procedure and a form for recording test results. The study included 13 samples labeled as "gluten-free" and 2 samples spiked by wheat flour. Seven samples had gliadin content below the limit of quantitation (LOQ) of the method, and 1 sample exceeded the highest calibration level. Gliadin content in the range from 10 to 157 mg/kg (1st day) and from 11 to 183 mg/kg (2nd day) was found in 7 samples (including 2 spiked samples). Results of these samples were used for further statistical analysis and evaluation. The Cochran, Dixon, and Mandel statistical tests were applied for detection of outliers. The LOQ of the kit was estimated.