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Structure-functionality impact of heat treatment on the interfacial adsorption of whey proteins at millisecond time
Boxin Deng1, Inge Roelofs1, Amarins Post1
1Wageningen University, Department of Agrotechnology & Food Sciences, Laboratory of Food Process Engineering Group, Bornse Weilanden 9, 6708, WG, Wageningen, The Netherlands.
Hypothesis:
Proteins are usually used in food emulsions and foams due to their nutritional values and functionality. Heat treatment may induce changes in protein functionality, for instance its ability to physically stabilize emulsion droplets during emulsification at droplet formation time scales. We hypothesized that the interfacial adsorption of proteins largely determines the emulsion stability during emulsification, and that it is affected by protein structure, which in turn is sensitive to temperature.
Experiments:
Whey protein solutions were pre- or real-time heated for various combinations of temperature and time. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), and Fourier-transform infrared spectroscopy (FTIR) were performed to characterize the structural changes in proteins after the heating and cooling treatment received. A microfluidic tensiometer was used to link dynamic interfacial tension reduction at (sub)millisecond time scales to these structural changes.
Findings:
Depending on the heating conditions, we found structural changes at the level of individual protein molecules, as well as protein aggregation taking place. Firstly, when using real-time heating, the interfacial tension decreased faster with increasing temperature due to enhanced mass transfer, and even to moderate changes (unfolding) in protein structure. The time needed to lower the interfacial tension by 1 mN/m reduced from about 22 to 2.5 ms as the temperature increased from 20 to 70 °C. Additionally, high (pre- and real-time) heating temperatures and long heating times may facilitate protein aggregation in the continuous phase. These aggregates may diffuse and adsorb slower, but exhibit improved interfacial interactions at (sub)second time scales. These insights strengthen our understanding of the correlation between protein structure and heating-related protein functionality at time scales that closely resemble those encountered in large scale emulsion production, which connects emulsion formulation with process design.
