Analytica chimica acta (2012), 727, 47--53 DOI: 10.1016/j.aca.2012.03.034
The determination of alpha-lactalbumin in various dairy products attracts wide attention in multidiscipline fields because of its nutritional and biological functions. In the present study, we quantified the bovine alpha-lactalbumin in various infant formulas and whey protein concentrates using ultra-high performance liquid chromatography coupled to tandem mass spectrometer in multiple reaction monitoring mode. Bovine ?-lactalbumin was quantified by employing the synthetic internal standard based on the molar equivalent relationship among the internal standard, bovine alpha-lactalbumin and their signature peptides. This study especially focused on the recovery rates of the sample preparation procedure and robust quantification of total bovine alpha-lactalbumin in its native and thermally denatured form with a synthetic internal standard KILDKVGINNYWLAHKALCSE. The observed recovery rates of bovine ?-lactalbumin ranged from 95.8 to 100.6% and the reproducibility was excellent (RSD<6%) at different spiking levels. The limit of quantitation is 10 mg/100 g for infant formulas and whey protein concentrates. In order to validate the applicability of the method, 21 brands of infant formulas were analyzed. The acquired contents of bovine ?-lactalbumin were 0.67-1.84 g/100g in these infant formulas in agreement with their label claimed values. The experiment of heat treatment time showed that the loss of native ?-lactalbumin enhanced with an increasing intensity of heat treatment. Comparing with Ren"s previous method by analysis of only native bovine ?-lactalbumin, the present method at the peptide level proved to be highly suitable for measuring bovine ?-lactalbumin in infant formulas and whey protein concentrates, avoiding forgoing the thermally induced denatured ?-lactalbumin caused by the technological processing.