The effect of homogenization and heat treatment on gelation of whey proteins in emulsions

The effect of multiple high-pressure homogenization (HPH) pre-processing, oil content (3.2% or 30% w/v) and salt presence (0.1 M NaCl) on the heat-induced gel structure in oil-in-water emulsions stabilized by whey protein concentrate (WPC) was monitored by temperature sweep tests using both oscillatory rheology and multi-speckle diffusing wave spectroscopy (MSDWS). In addition, viscosity and flow parameters, thixotropy and storage stability were assessed for HPH- and heat-treated emulsions. The high-fat emulsion pre-processed by one HPH pass as well as low and high-fat emulsions with NaCl, pre-processed by both one or three HPH passes, formed a strong gel by heating. Heating of low-fat emulsions resulted in denaturation and aggregation of protein molecules, either present in the aqueous phase or adsorbed at the oil–water interface, and subsequent formation of a weak gel structure. The high-fat emulsion after intensive emulsification by three HPH passes was resistant to creating a protein spatial network by heating. The gel point temperature obtained from oscillatory rheology tests was close to the end point temperature of protein denaturation obtained from MSDWS tests for all types of emulsions tested in this study. •Droplet size can be lowered by multiple high-pressure homogenization (HPH) of whey protein (WP) stabilized emulsion.•Multiple HPH can also improve droplet size uniformity.•Rheology and stability of heat-treated WP emulsion can be altered by the number of pre-HPH passes.•Heat-induced WP gelation in emulsion can be altered by the number of pre-HPH passes.•Multi-speckle diffusing wave spectroscopy allows to characterize heat-induced WP denaturation/gelation in emulsion.