The impact of genetic variation on the functional properties of β-lactoglobulin

β-lactoglobulin (β-lg) is the most abundant whey protein in milk. There are two main phenotypes of β-lg, namely the AA and BB phenotypes, which differ in their amino acid sequence at position 64 and 118, whereby aspartic acid (AA phenotype) is replaced with glycine (BB phenotype) and alanine (AA phenotype) is replaced with valine (BB phenotype), respectively. In this study, whey protein isolate (WPI) powders were studied containing exclusively the AA or BB phenotypes of β-lg. Analysis of the secondary structure of the AA and BB phenotypes by FTIR indicated that the level of beta sheets was higher in the BBcompared to the AA phenotype. Differential scanning calorimetry (DSC) analysis indicated that the A and BB phenotypes had thermal denaturation onset temperatures (T_{d onset}) of 72.01 and 75.58 °C, and peak denaturation temperatures (T_d) of 74.50 and 78.39 °C, respectively. The difference in T_{d onset} and T_d are possibly linked to the differences in the proportion of beta sheets between the phenotypes. Analysis of the heat induced gelation properties demonstrated that, in the pH range of 6.6–7.2, the BB phenotype of β-lg produced stronger gels than the AA phenotype, as evidenced by higher storage modulus values. This was possibly due to increased electrostatic repulsion between the protein molecules caused by the additional charged amino acid in the AA phenotype of β-lg. These findings could be of importance to processors who manufacture whey products, as the difference in thermal behaviour between the AA and BB phenotypes could impact fouling during processing and susbsequent functionality in finished products.