Abstract
Physical, thermal and microstructural properties of whey protein isolate (WPI) and chicken skin gelatin mixtures were investigated. This is a first study on the compatibility of an unutilised gelatin source from chicken skin with a well-characterised food protein. The physical-chemical and rheological properties of chicken skin gelatin alone, were reported in our previous paper Sarbon, Badii & Howell, (2013). Preparation and characterisation of chicken skin gelatin as an alternative to mammalian gelatin. Food Hydrocolloids 30, 143-151. In the present study, small deformation rheology indicated that combinations of gelatin (3, 5 and 10 %) and 10 % whey protein (WPI) in distilled water resulted in high elastic modulus (G') values of 1860, 23914 and 20145 Pa, respectively, compared with 120 Pa for 10% WPI alone, due to synergistic interaction. Frequency sweeps showed increased strength of networks in gels containing higher concentrations of gelatin in WPI/gelatin mixtures. Gelatin gels were more stable and stronger than 10 % (w/w)whey protein gels and did not exhibit frequency dependence for G' and G", giving low tan δ (G"/G') values of <0.1. Large deformation gel strength values of all samples increased significantly (p<0.05) with increasing gelatin concentration and were greater at each concentration compared to gelatin alone. Differential scanning calorimetry transition temperature (Tm) and enthalpy change (ΔH) of gelatin and whey protein mixed in the ratios 3:10, 5:10 and 10:10 (w/w) confirmed the reversibility of the gelatin transition on heating to 90 oC and cooling to 10 oC and irreversible denaturation of WPI on heating. The addition of 3, 5 or 10% gelatin to whey protein increased the Tm of whey protein and decreased the Tm of gelatin. However, the presence of 10 % (w/w) WPI significantly increased the ΔH values to 0.62, 1.34 and 2.20 J/g for 3, 5 and 10 % (w/w) gelatin solutions respectively, indicating whey-gelatin interaction. Chicken skin gelatin gels exhibited a fine network of uniform particles whereas whey protein gels comprised aggregates. Differences in structure and molecular size led to phase separation of the mixed gels. The above properties of an underutilized non-mammalian source of gelatin may lead to novel applications in the food industry.