Adsorption kinetics and dilatational rheology of plant protein concentrates at the air- and oil-water interfaces

Adsorption kinetics and dilatational rheology of plant protein concentrates at the air- and oil-water interfaces were investigated at pH 7.0 in 100 mM NaCl. Three interfaces (air-water, triglyceride-water and terpene-water) and four protein concentrates (soy, pea, mung bean and rice) were examined. The dynamic interfacial properties were monitored by axisymmetric drop shape analysis. Kinetic modelling of the early and advanced stages of protein adsorption was carried out using the Ward-Tordai and Graham-Philips thermodynamic approaches. Construction of surface pressure master curves revealed a pseudo equilibrium plateau for legume proteins of ∼20, 12, and 22 mN/m at the air, triglyceride and terpene interfaces, respectively. In contrast, rice proteins have a lower capacity to increase the surface pressure at the oil interfaces (<15 mN/m). Data modelling revealed that diffusion is mostly independent of the protein composition, but protein rearrangement at the interfaces was faster at the oil than at the air interfaces. Dilatational rheological measurements revealed more elastic films at the air than at oil interfaces, with the dilatational storage modulus reaching values up to 37 mN/m. The least elastic films were formed at the terpene interfaces, with storage moduli being <25 mN/m for all isolates investigated. Lissajous plot construction revealed a strain-hardening behaviour of films upon compression and strain-softening on extension, the magnitude of which follows the order air > terpene > triglyceride. Overall, results show that botanical source and subphase composition are critical in selecting the optimum stabilisation strategy in multiphasic foods using plant proteins.