Probing the improved heat stabilizing capacity of dry heat conjugated whey protein in oil-in-water emulsions: A microrheological study

Abstract

Dry heat conjugation of whey protein has been shown before to improve its heat stabilizing properties when applied as an emulsifier. However, the range of feasible heating conditions of these conjugates has not yet been evaluated. Microrheology, a non-destructive method, was utilized in this study to determine the acceptable heating range for whey protein stabilized-emulsions. Practically, oil-in-water emulsions stabilized by whey protein-lactose conjugates were subjected to either an in-situ thermal treatment, including a heating-cooling cycle, or to an isothermal period. The observed microstructural rearrangements were also confirmed by examining the bulk emulsion behavior through oscillatory rheology.The obtained results indicated that microrheology could unravel the range of heating temperatures and durations for emulsions stabilized by whey protein concentrate (WPC) that was dry heated for 8 and 48 h as compared to the native WPC. The improved heat stability was a result of the conjugates’ ability to prevent the formation of an oil droplet network. Consequently, the conjugated WPC-stabilized emulsions remained mainly viscous with a low elasticity index (EI) and macroscopic viscosity index (MVI) during heating. Furthermore, the microrheology findings were found to be largely in line with bulk rheological properties: both methods indicated a comparable temperature for the onset of network formation upon applying a temperature sweep. The insights from this study may help to stimulate the industrial application of whey protein-sugar conjugates as heat stable natural emulsifiers.