β-Lactoglobulin and κ-Casein Disulphide Interactions after Controlled Addition of a Disulphide Reducing Agent

During the heating of milk (> 70°C), the free thiol group of unfolded βlactoglobulin (β-lg) can interact with the disulphide bonds of other milk proteins. This can lead to the formation of intermolecular disulphide bonds, especially between β-lg and κ-casein (κ-cn)1. The addition of low levels of a disulphide reducing agent will change the ratio of free thiol groups to disulphide bonds in milk proteins and therefore the interactions between the proteins. This study investigated the effect of adding low levels of a reducing agent (β-mercaptoethanol,β-ME) on the involvement of β-lg and κ-cn in disulphide bonding in unheated skim milk, heated skim milk and skim milk that was reduced before heating.