Dynamic rheological and structural characterization of fish gelatin – Gum arabic coacervate gels cross-linked by tannic acid

The propose of this study was to investigate the rheological and structural properties of fish gelatin (FG)–gum arabic (GA) complex coacervate gels treated with oxidized or non-oxidized tannic acid (OX-TA or NO-TA, respectively) at different concentrations ranged from 0.0 to 0.3% (v/v), using compositional, dynamic oscillatory rheological, and Fourier transform infrared (FTIR) analyses. The results revealed that the degree of NO-TA incorporation for cross-linking with FG via hydrogen bindings into the system was more pronounced than affinity of OX-TA for reaction through covalent bindings as evidenced by greater loss in volume fraction, moisture content, and biopolymer content values into the FG–GA coacervate phase. FTIR analysis showed addition of NO-TA led to more molecular disorder into the system, so that higher concentrations (0.2 and 0.3%) of the cross-linker disrupted electrostatic interactions through formation of stronger hydrogen bindings with proteins. Rheological results mentioned that addition and enhancement of (NO- or OX-) TA concentration improved gelling ability and mechanical properties of the FG–GA coacervate gels. However, frequency sweep test results implied that all the gels obtained can be classified as weak gels with shear-thinning behavior. Based on weak gel model, the gels obtained by treated FG–GA coacervates with NO-TA had more developed network structures and stronger intermolecular connectivities than those of obtained by the coacervates modified by OX-TA. The results of the current study provide basic knowledge necessary for the use of reinforced FG–GA complex coacervate gels in many useful applications, such as microencapsulation and hydrogel formation, in food and pharmaceutical industries.