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. (C) 2016 Elsevier Ltd. All rights reserved.