Association of caseins with 13-lactoglobulin influenced by temperature and calcium ions: A multi-parameter analysis

Aggregation of the major whey protein in bovine milk, 13-lactoglobulin (13-Lg) is strongly influenced by associ-ation with caseins (CNs). Here, by using combined differential scanning fluorimetry and dynamic light scattering, the conformational stability and aggregation propensity of 13-Lg and three types of CNs (a, beta and kappa CNs) as well as their mixture have been systematically evaluated at different temperatures and Ca2+ concentrations in a multi -parametric approach. While 13-Lg was affected significantly through denaturation and resulting aggregation by heat treatment with little dependency on Ca2+, aCN and 13CN were influenced considerably by Ca2+. Through modifying the aggregation of 13-Lg, CNs showed a different chaperone-like activity among the three types which were markedly dependent on the temperature and Ca2+ concentration. The presence of CNs resulted in smaller mixed aggregates compared to pure 13-Lg aggregates, mainly through interaction of CNs with unfolded 13-Lg and also by influencing the process of 13-Lg unfolding. This was further confirmed by small angle X-ray scattering and isothermal titration calorimetry indicating that Ca2+ enhanced the interaction between 13-Lg and CNs. Our experimental approach sheds light on molecular understanding of CN-13-Lg interactions and provides insight into how micro-structural assembly of milk proteins can be modulated to enable different functionalities in milk -based products.

Automated summary

In this study, the conformational stability and aggregation propensity of 13-lactoglobulin (13-Lg) and three types of caseins (CNs) were systematically evaluated. The results showed that 13-Lg was affected by heat treatment, while a-CN and 13-CN were influenced by Ca2+. The presence of CNs resulted in smaller mixed aggregates compared to pure 13-Lg aggregates. The study provides insight into how micro-structural assembly of milk proteins can be modulated to enable different functionalities in milk-based products.