Purification and physicochemical characterization of ovine beta-lactoglobulin and alpha-lactalbumin.

Abstract

Ovine whey proteins were fractionated and studied by using different analytical techniques. Anion-exchange chromatography and reversed-phase high-performance liquid chromatography (HPLC) showed the presence of two fractions of beta-lactoglobulin but only one of alpha-lactalbumin. Gel permeation and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis allowed the calculation of the apparent molecular mass of each component, while HPLC coupled to electrospray ionisation-mass spectrometry (ESI-MS) technique, giving the exact molecular masses, demonstrated the presence of two variants A and B of ovine beta-lactoglobulin. Amino acid compositions of the two variants of beta-lactoglobulin differed only in their His and Tyr contents. Circular dichroism spectroscopy profiles showed pH conformation changes of each component. The thermograms of the different whey protein components showed a higher heat resistance of beta-lactoglobulin A compared to beta-lactoglobulin B at pH 2, and indicated high instability of ovine alpha-lactalbumin at this pH.