Modification of extruded chicken collagen films by addition of co-gelling protein and sodium chloride

The properties of extruded chicken collagen sausage casings can be tailored by the addition of sodium chloride (NaCl) or proteins prior to extrusion in order to gain films with modified mechanical properties. In this study, 4% (w/w) chicken skin collagen and telopeptide-poor collagen from bovine hide were modified by the addition of 0.05 mol/kg NaCl and/or partial substitution of collagen by soy protein isolate, at 1.25% (w/w). The collagen formulations were extruded to films and characterized in terms of their microstructure (light microscopy and scanning electron microscopy) and rheological properties (storage and loss modulus and phase angle). Moreover, the tensile strength and film thickness were examined. The addition of NaCl to the gel allowed for telopeptide-poor and chicken collagen films with high tensile strengths and elasticities to be formed. In contrast, a substitution of collagens with soy proteins decreased gel and film strengths. The soy protein induced weakening of collagen networks could be compensated by again adding NaCl leading to more homogeneous gels yielding films with higher storage moduli upon extrusion. The compensating effect of NaCl was more pronounced for chicken skin than for telopeptide-poor collagen in the film state suggesting differences in molecular interactions and network formation between the two different collagen types. Overall, the modulation of chicken collagen interactions by NaCl and soy protein addition enables the production of functional chicken collagen films, in turn providing the food and pharmaceutical industry with a viable alternative to the increasingly scarce beef collagen.