The Use of Enzyme-Linked Immunosorbent Assays to Detect Milk Residues in Thermally Processed Food Products
Document Type Article
A Thesis presented to the faculty of the graduate college at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science. Major: Food Science & Technology. Under the Supervision of Professor Steve L. Taylor. Lincoln, Nebraska. April, 2010. Copyright 2010 Melanie Downs.
This thesis is currently embargoed by request of its author. Authorized persons may access it at http://digitalcommons.unl.edu/embargotheses/1
Food allergic individuals manage their condition and prevent reactions by removing the offending food(s) from their diets. In order to insure consumers can effectively avoid specific foods when necessary, food labels must indicate the presence of several allergenic foods. The food industry uses enzyme-linked immunosorbent assays (ELISAs) to detect allergenic foods, including milk. Several commercial milk ELISAs are available, but these methods do not necessarily undergo validation with processed foods.
The first study presented herein aimed to evaluate the efficacy of three commercial ELISA kits detecting milk proteins in processed food products. A model food, pastry dough, was spiked with nonfat dry milk and processed as follows: boiled (100 °C for 2 min), baked (190 °C for 30 min), fried (190 °C for 2 min), or retorted (121 °C for 20 min). Samples were analyzed with three ELISA kits: Neogen Veratox® Total Milk, ELISA Systems β-lactoglobulin, and ELISA Systems Casein. The detection of milk residues depended on the type of processing applied to the food and the target analyte of the ELISA. The β-lactoglobulin assay had poor recoveries in all processed samples (2-9% of expected values). The kits targeting total milk and casein had better recoveries in boiled samples (43 and 58% respectively), but performed poorly in baked (9 and 21%) and fried samples (7 and 18%). Decreased detection, however, does not necessarily indicate lower allergenicity.
In light of the issues revealed by these experiments, an extraction solution was developed to improve the detection of milk residues in heated foods using commercial ELISA methods currently available on the market. The extraction additive solution (containing 2-mercaptoethanol and guanidine hydrochloride) successfully improved the detection of milk residues in baked and fried products analyzed with the total milk and casein kits. However, detection was not increased in samples analyzed with the β-lactoglobulin kit. The extraction additive solution developed in this study is a potential method for improving the detection of milk residues in thermally processed products.