A novel ultra-high performance liquid chromatography method for the rapid determination of beta-lactoglobulin as heat load indicator in commercial milk samples

摘要

The level of undenatured acid-soluble beta-lactoglobulin can be used as an indicator to assess the heat load applied to liquid milk, thus further allowing the discrimination between milk originating from different thermal production processes. In this work, a new UHPLC method for the rapid determination of bovine beta-lactoglobulin in 1.8 min only (total runtime 3 min) is presented using simple UV detection at 205 nm. Separation selectivity for possibly co-eluting other major whey proteins (bovine serum albumin, lactoferrin, alpha-lactalbumin, immunoglobulin G) was verified, and the method validated for the analysis of liquid milk samples regarding linearity (20-560 mu g/mL, R-2 >0.99), instrumentation precision (RSDs <2.8%), limits of detection and quantification (7 and 23 mg/L milk), repeatability of sample work-up (RSDs <= 2.6%) and method recovery (103%). In total, 71 commercial liquid milk samples produced using different preservation techniques (e.g., thermal or mechanical treatment), hence featuring different applied heat loads, were profiled for their intrinsic undenatured acid-soluble beta-lactoglobulin levels. As expected, pasteurized milk showed the highest concentrations clearly above 3000 mg/L due to pasteurization being the mildest thermal treatment, while in contrast, ultra-high temperature heated milk featured the lowest amounts (<200 mg/L). For extended shelf life (ESL) milk, quite diverse levels were determined ranging from similar to 100 up to 4000 mg/L, thus clearly illustrating variable applied heat loads and impacts on the "nativeness" of milk essentially due to the fact that the production technologies used for ESL milk may differ significantly, and are currently not regulated in the EU. (c) 2015 Elsevier B.V. All rights reserved.