Abstract
Selective thermal precipitation followed by a mechanical separation step is a well described method for fractionation of the main whey proteins, α-lactalbumin (α-la) and β-lactoglobulin (β-lg). By choosing appropriate environmental conditions the thermal precipitation of either α-la or β-lg can be induced. Whereas β-lg irreversibly aggregates, the precipitated α-la can be resolubilized by a subsequent adjustment of the solution’s pH and the ionic composition. This study reports on the analytical characterization of resolubilized α-la compared to its native counterpart as a reference in order to assess whether the resolubilized α-la can be considered close to ‘native’. Turbidity and quantification by RP-HPLC of the resolubilized α-la solutions were used as a measure of solubility in aqueous environment. RP-HPLC was also applied to determine the elution time as a measure for protein’s hydrophobicity. DSC measurement was performed to determine the denaturation peak temperature of resolubilized α-la. FTIR spectroscopy provided insights in the secondary structure. The refolding of α-la achieved best results using pH 8.0 and a 3-fold stoichiometric amount of Ca2+ per α-la molecule. The results showed that the mechanism of aggregation induced by gentle thermal treatment under acidic conditions with subsequent mechanical separation is reversible to a certain extent, however, the exact native conformation was not restored.
Highlights
Whey is a source of protein with excellent techno-functional properties and bioactive peptides
Of special interest is its property to carry different minerals, such as Mg2+, Mn2+, Na+, K+, and Ca2+, which is natively bound in the holo-state [4]. α-la is reported to enhance the regeneration of cells [5], to possess antimicrobial properties against a broad spectrum of bacteria, including antibiotic resistant strains [6,7], and to have antitumor properties in a complex with oleic acid [8,9]
The results of optical density at 550 nm (OD550) are shown in Figure 1a, the results of RD
Summary
Whey is a source of protein with excellent techno-functional properties and bioactive peptides. The key components, β-lactoglobulin (β-lg) and α-lactalbumin (α-la), make up for approximately 50% and 20% of the whey protein content, respectively. Due to their individual functional or physiological properties, the isolation in pure fraction is of increasing interest. The development of cost-efficient separation methods of the individual whey protein fractions has evolved as an important driver for innovation in dairy industry and food research. Α-la incorporates specific physiological and medical functionalities and a nutritional value that makes it an interesting candidate for the use as food additive or as a part of therapeutic concepts. Of special interest is its property to carry different minerals, such as Mg2+ , Mn2+ , Na+ , K+ , and Ca2+ , which is natively bound in the holo-state [4]. α-la is reported to enhance the regeneration of cells [5], to possess antimicrobial properties against a broad spectrum of bacteria, including antibiotic resistant strains [6,7], and to have antitumor properties in a complex with oleic acid [8,9]
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