Interactions of milk proteins during heat and high hydrostatic pressure treatments — A Review

Pressure treatment of β-lactoglobulin (β-LG), whey protein concentrate (WPC), whey protein isolate and skim milk has been explored by many groups using a wide range of techniques. In general terms, heat treatment and pressure treatment have similar effects: denaturing and aggregating the whey proteins and diminishing the number of viable microorganisms. However, there are significant differences between the effects of the two treatments on protein unfolding and the subsequent thiol-catalysed disulfide-bond interchanges that lead to different structures and product characteristics. Application of a range of techniques has given insight into the subtle differences between the pathways from native proteins to the final product mix. This review covers some of the techniques used and their strengths, and the probable pathways from native protein to the final products. β-LG is one of the most pressure-sensitive proteins and α-lactalbumin (α-LA) is one of the most pressure resistant. In a heated WPC system, bovine serum albumin is very sensitive and β-LG is more resistant. In a heated milk system, β-LG reacts with κ-casein (κ-CN) and not with α_S2-CN, but, in pressure-treated milk, β-LG forms adducts with either κ-CN or α_S2-CN. In both treatments, the role of β-LG is central to the ongoing reactions, involving α-LA and κ-CN in heated systems but involving κ-CN, α_S2-CN and α-LA in pressurized systems.Industrial relevanceHigh hydrostatic pressure (HHP) processing, as opposed to heat treatment, has received much attention recently as a means of processing milk proteins. This review examines the differences in the denaturation pathways that give rise to different final products.