Incorporating chitin nanocrystal yields stronger soy protein gel: Insights into linear and nonlinear rheological behaviors by oscillatory shear tests

Abstract

Chitin nanocrystals (ChNs) were successfully fabricated from shrimp and their effects on the microstructure and gelling properties of glucono-δ-lactone-induced soy protein isolate (SPI) were investigated. Firstly, transmission electron microscopy (TEM) showed that the average length and width of ChNs were 208.8 nm and 19.2 nm, respectively. The zeta potentials of ChNs changed from +38.6 mV at pH 3.0 to +16.4 mV at pH 8.0. Subsequently, the gel strength, water holding capacity (WHC) and viscoelasticity of the composite gels were improved by increasing the ChNs concentration from 0 to 1.0% (w/v). Based on low field nuclear magnetic resonance (LF-NMR) analysis, the decrease in PT 22 and increase in PT 21 indicated that the improvement of WHC was associated with the transformation of free water into immobilized water. Scanning electron microscopy (SEM) showed that the incorporation of ChNs promoted the formation of a denser and more homogenous gel network. All composite gels showed high frequency dependence and a typical Type I (strain thinning) network behavior. The increase in both elastic and viscous moduli further showed the improvement in the microstructure of composite gels, which was induced by the addition of ChNs. The Sequence of Physical Processes (SPP) analysis provided a detailed deformation history of gel microstructure by the evolution of the instantaneous storage (G′t) and loss moduli (G″ t ). In this method, gel samples experienced various degrees of microstructural rearrangements at small amplitude oscillatory shear (SAOS) region (γ = 0.64%) and large amplitude oscillatory shear (LAOS) region (γ = 100%). • Formation of stronger SPI gels through incorporation of ChNs. • ChNs increased the gel strength, WHC and viscoelasticity of SPI gels. • ChNs provided a denser and more uniform microstructure for SPI gels. • All gels showed high frequency dependence and type I behavior. • The gel microstructure showed stepwise changes during large deformation.