The effects of stem bromelain on the gelation behavior of kappa carrageenan under linear and nonlinear rheological regimes

Abstract

Carrageenans have shown a versatile and wide range of applications in the food and biomedical fields. To tune the rheological properties and improve the biological functions of carrageenan gels, the effect of stem bromelain (SBr) on the intermolecular interaction and rheological property of κ-carrageenan (κC) was investigated. The viscoelastic properties and gel network structure of pure SBr, κC, and SBr/κC mixtures were studied using dynamic rheology in the linear and nonlinear viscoelastic regimes. Different SBr/κC mixtures were prepared with varying final pH levels (pH 6.06, 6.95, and 8.08). The time series and frequency dependence of SBr/κC mixtures in the linear viscoelastic regime showed that the elastic modulus is (3–10 times) greater than the viscous modulus, indicating network structure formation. The temperature dependence of the viscoelastic moduli SBr/κC mixtures exhibited a significantly improved physical property than the pure SBr and κC, demonstrating synergistic relation between SBr and κC via enhanced electrostatic interaction. By increasing the pH level of the mixtures, a decrease in the shear moduli was observed attributed to the increasing repulsive interaction between SBr and κC. The observed nonlinear rheological responses suggest a transiently crosslinked network. Accordingly, with the gentle imposition of increasing stress levels, the nonlinear responses suggest that SBr/κC is a stress-mediated, highly entangled complex network with a pH-controlled dynamic viscoelastic property. Therefore, our results provide structural insights into the microscopic origins of the rheological behavior of SBr/κC mixtures as a basis for precise material design.