Rheological characterization of protein solutions under pressure, shear, temperature and interactions

Jerish Joyner Janahar
Graduate (PhD)
Dr. V. M. Balasubramaniam
Food Science and Technology

Health-conscious consumers interest in protein beverages creates opportunities to introduce variety of plant and dairy based beverages. To preserve health-promoting properties of such beverages, researchers investigate various continuous minimal processing technologies including a high pressure based method called Ultra Shear Technology (UST). For development and optimization of such continuous methods, it is important to understand the rheological characteristics of protein solutions as influenced by processing parameters. In this research, the impact of pressure, shear, temperature, and interactions during UST on flow behavior of selected protein solutions was investigated.
Research methods
Milk was added with pea protein to prepare solutions with different protein concentrations. Experiments were conducted at 400MPa for two temperatures (40 and 70°C) using custom-fabricated UST laboratory tester (PBI, USA). To study effect of pressure-only, batch high pressure processing(HPP) was performed at 400MPa, 25±2°C for 0 min(come-up time). The contribution of temperature was determined by thermal treatment at 70°C for 0 min. Untreated samples served as control. Discovery HR3 hybrid rheometer(TA instruments, USA) was used to determine viscoelastic properties by strain sweep and frequency sweep, and shear viscosity by steady flow sweep. To characterize the rheological behavior, common models viz., Newtonian, Power law, Bingham, and Casson were used. Treatments and analyses were triplicated and statistical analyses were done by ANOVA. The best model was selected based on higher correlation coefficient(R) and simplicity.
The control, HPP and thermal treated high protein solutions were shear-thickening(n1). Low protein solutions under different treatments were pseudoplastic(n1). For all samples, the viscoelastic properties G' and G" increased with frequency; their magnitudes varied by protein concentration and treatments. For high protein samples, 40 and 70°C UST resulted in higher viscosity than other samples. Further, tan was independent of frequency for longer range indicating solid-like behavior of these samples, likely due to non-covalent interactions between chemical components promoted by UST.
Different combination of pressure-thermal and shear intensities differently altered the rheological characteristics of solutions through complex molecular interactions of proteins. The knowledge gained from this study serve as guidelines in designing UST equipment and formulating novel protein beverages.