Surface adsorption and lubrication properties of plant and dairy proteins: A comparative study

Abstract

The aim of this work was to compare the surface adsorption and lubrication properties of plant and dairy proteins. Whey protein isolate (WPI) and pea protein isolate (PPI) were chosen as model animal and plant proteins, respectively, and various protein concentrations (0.1–100 mg/mL) were studied with/without heat treatment (90 °C/60 min). Quartz crystal microbalance with dissipation monitoring (QCM-D) experiments were performed on hydrophilic (gold) and hydrophobic polydimethylsiloxane (PDMS) sensors, with or without a mucin coating, latter was used to mimic the oral surface. Soft tribology using PDMS tribopairs in addition to wettability measurements, physicochemical characterization (size, charge, solubility) and gel electrophoresis were performed. Soluble fractions of PPI adsorbed to significantly larger extent on PDMS surfaces, forming more viscous films as compared to WPI regardless of heat treatment. Introducing a mucin coating on a PDMS surface led to a decrease in binding of the subsequent dietary protein layers, with PPI still adsorbing to a larger extent than WPI. Such large hydrated mass of PPI resulted in superior lubrication performance at lower protein concentration (≤10 mg/mL) as compared to WPI. However, at 100 mg/mL, WPI was a better lubricant than PPI, with the former showing the onset of elastohydrodynamic lubrication. Enhanced lubricity upon heat treatment was attributed to the increase in apparent viscosity. Fundamental insights from this study reveal that pea protein at higher concentrations demonstrates inferior lubricity than whey protein and could result in unpleasant mouthfeel, and thus may inform future replacement strategies when designing sustainable food products.

Oral tribology, adsorption and rheology of alternative food proteins

“…(Chen & Stokes, 2012;Kokini, Kadane, & Cussler, 1977;Pradal & Stokes, 2016;Prakash, Tan, & Chen, 2013;Sarkar & Krop, 2019). Although biopolymers in general have attracted significant research attention for tribological analysis, systematic tribological characterization of proteins is fairly limited in literature to date (Chojnicka, de Jong, de Kruif, & Visschers, 2008;Kew, Holmes, Stieger, & Sarkar, 2020;Zembyla, et al, 2021).…”

Protein–saliva interactions: a systematic review

“…61 It is noteworthy that there has not been a single study performed to investigate the interaction of plant protein with saliva within the search date of this systematic review. A recent study on the interaction of pea proteins with BSM ( published outside the inclusion dates) 62 shows that the adsorption capacity of pea protein to a hydrophobic surface is reduced in the presence of BSM due to electrostatic repulsion between pea protein and BSM. Nevertheless, the extent and kinetics of adsorption of pea protein has been found to be significantly higher than WPI on BSM-coated surfaces.…”

“…This suggests pea protein might give rise to astringency perception due to more binding to BSM-coated surface compared to that of WPI, however no sensory evaluation was conducted in this study. 62 Thus, understanding the interaction of pea protein with saliva…”

“…From this, it was shown that heat treatment increased viscosity of both pea protein and whey protein isolate solutions. This in turn reduced friction in mixed and elastohydrodynamic lubrication regimes but the boundary regime (where astringency is thought to arise) was unaffected 62 . Furthermore, pea protein isolate was not affected by heat treatment whereas WPI had significant structural changes.…”

“…Furthermore, pea protein isolate was not affected by heat treatment whereas WPI had significant structural changes. 62 In general heat treatment of milk is a critical process used by the dairy industry. It is used to prolong stability and enhance quality through lowering microbial load or manipulating functionality of dairy proteins and strengthening the organoleptic properties.…”