Tribological and Rheological Properties of Lentil and Chickpea Proteins

Proteins can be efficiently used in different food systems; particularly in gels due to their functionality. Proteins may decrease oral lubrication and enhance mouthfeel. Rheology and tribology are effective tools that have been used to analyze the oral behavior of proteins. Chickpea and lentil proteins were investigated regarding their rheological and tribological properties to provide a more in-depth understanding of their effects on the sensory characteristics of food. For this purpose, protein isolates with 83 − 90% protein content were prepared from chickpeas and green, yellow, and red lentils. The net surface charge of the isolates varied between ⁓32.8 and ⁓-41.6 mV as a function of pH (3.0–9.0). The protein solutions were exposed to stress with polydimethylsiloxane (PDMS)-PDMS tribopairs with shear rates of 2, 5, 10, 20, and 30 Hz (range 0.6–20 mm/sec) and 1, 2, 5, 7 and 10 N values as load. No significant difference was observed in the friction coefficient of protein samples at different load values. On the other hand, the friction coefficient decreased with increasing speed. Red lentil and green lentil proteins exhibited a different trend compared to those of chickpea and yellow lentil proteins at higher speed measurements. In addition, mass (bulk) and interface dilatational (air/water/oil) rheology and surface tension values were investigated. Although the differences in viscosity values were mostly insignificant over the analyzed shear range, the chickpea protein showed relatively higher viscosity (1.6 mPa.s) compared to the other samples (1.4 mPa.s) at a shear rate of 4 s^-1. In terms of oil/water interface viscoelasticity, red lentil protein displayed the fastest crossover (3 h), followed by chickpea protein (4 h) whereas green lentil protein and yellow lentil protein exhibited a crossover only after 8 h. Moreover, the red lentil protein formed a stronger interfacial viscoelastic network and showed higher resistance to shear stress compared to the other samples; indicating better functional properties. Based on the functional properties assessed in this study, chickpea protein exhibits strong potential for use in alternative meat/emulsion/gel-based systems, due to its relatively higher viscosity and effective lubrication performance, which can enhance the mouthfeel and structural integrity. On the other hand, red lentil protein can be suggested as a natural emulsifier due to its rapid and robust interfacial network formation.