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Matrix and food processing induced changes in the accuracy of different commercial milk ELISA kits
Milk proteins are common functional food ingredients but major milk proteins are also allergens. Commercial milk ELISAs are widely used to detect milk residues in foods. However, these milk kits have not been well validated for their performance with processed food matrices. Thus, the recovery of spiked amounts of non-fat dry milk (NFDM) before and after processing from two different matrices was compared using 9 different milk ELISA kits. The first matrix was wheat pastry squares spiked with NFDM which then underwent thermal (boiling, baking, frying, retorting, microwaving, radiofrequency) and non-thermal (high-pressure, acidification) processing. Initially from the unprocessed pastry squares, excellent recoveries were obtained with the β-lactoglobulin kits, while recoveries were not nearly as good (average of 40% of the spiked amounts) for the total milk and casein kits. The results suggest that interactions are occurring between matrix components and milk proteins after addition of water. With the pastry matrix, thermal treatments resulted in even further reduced recovery, with baking completely eliminating the detection of milk proteins for many kits. Among non-thermal treatments, acidification resulted in an extremely reduced recovery of milk proteins. The effects of processing treatments on milk protein extraction and recovery were also concentration dependent. The findings suggest that attempts to use commercial milk ELISA kits to detect low levels of milk residue from complex food matrices may not be reliable in many circumstances. Recoveries were much better (80% or more with most ELISAs) from a model liquid matrix following various thermal and non-thermal treatments. Differences encountered were dependent upon kit and milk protein concentration. Therefore, selection of the most appropriate kit should be approached carefully to ascertain the ELISA that works best with a particular processing method and matrix. Attempts to improve milk protein recovery with new extraction buffers or enzyme treatment were not advantageous. Thus, especially for solid food matrices, the development of improved ELISAs is needed for more reliable detection of low-level milk residues.
Bly, Brigitta, "Matrix and food processing induced changes in the accuracy of different commercial milk ELISA kits" (2014). ETD collection for University of Nebraska - Lincoln. AAI3618182.