Analysis of α-lactalbumin, β-lactoglobulin A and B in whey protein powder, colostrum, raw milk, and infant formula by CE and LC

Two analytical methods, capillary electrophoresis (CE) with UV detection and high-performance liquid chromatography (HPLC) with photodiode array detection, were developed for the determination of alpha-lactalbumin (alpha-Lac), beta-lactoglobulin A (beta-Lg A), and beta-lactoglobulin B (beta-Lg B) in whey protein powder, colostrum, raw milk, and infant formula. The CE analysis was performed in a bare fused silica capillary (57 cm x 50 mu m, effective length 50 cm) with a separation buffer consisting of 0.5 mol L-1 boric acid, 0.025 mol L-1 hydroxypropyl-beta-cyclodextrin, and 0.8 g L-1 poly(ethylene oxide) 4,000,000 at pH 9.10. The HPLC analysis was performed on a CAPCELL PAK C-8 SG 300 (200 x 4.6 mm, 5-mu m particles) column with a gradient mobile phase mixture consisting of acetonitrile and water containing trifluoroacetic acid. The CE method is suitable for the simultaneous determination of alpha-Lac, beta-Lg A, and beta-Lg B in whey powder, colostrum, and raw bovine milk, whereas the HPLC method can only be used for quantitative assays of beta-Lg A and beta-Lg B due to the co-elution of lactoferrin with alpha-Lac. Recoveries for both methods over the concentration range were between 90.7% and 116.8%. Whey protein powder had the highest content of the above three proteins. The contents of alpha-Lac in infant formula increased with the raise of age stage. Infant formula with the same age stage but different brands and countries had significant differences in the content of alpha-Lac.