The Effect of Chicken Skin Gelatin and Whey Protein

37 38 39 Physical, thermal and microstructural properties of whey protein isolate (WPI) and chicken 40 skin gelatin mixtures were investigated. This is a first study on the compatibility of an 41 unutilised gelatin source from chicken skin with a well-characterised food protein. The 42 physical-chemical and rheological properties of chicken skin gelatin alone, were reported in 43 our previous paper Sarbon, Badii & Howell, (2013). Preparation and characterisation of 44 chicken skin gelatin as an alternative to mammalian gelatin. Food Hydrocolloids 30, 143-151. 45 In the present study, small deformation rheology indicated that combinations of gelatin (3, 5 46 and 10 %) and 10 % whey protein (WPI) in distilled water resulted in high elastic modulus (G') 48 due to synergistic interaction. Frequency sweeps showed increased strength of networks in gels 49 containing higher concentrations of gelatin in WPI/gelatin mixtures. Gelatin gels were more 50 stable and stronger than 10 % (w/w)whey protein gels and did not exhibit frequency 51 dependence for G' and G", giving low tan δ (G"/G') values of <0.1. Large deformation gel 52 strength values of all samples increased significantly (p<0.05) with increasing gelatin 53 concentration and were greater at each concentration compared to gelatin alone. Differential 54 scanning calorimetry transition temperature (Tm) and enthalpy change (∆H) of gelatin and 55 whey protein mixed in the ratios 3:10, 5:10 and 10:10 (w/w) confirmed the reversibility of the 56 gelatin transition on heating to 90 oC and cooling to 10 o C and irreversible denaturation of 57 WPI on heating. The addition of 3, 5 or 10% gelatin to whey protein increased the Tm of whey 58 protein and decreased the Tm of gelatin. However, the presence of 10 % (w/w) WPI 59 significantly increased the ∆H values to 0.62, 1.34 and 2.20 J/g for 3, 5 and 10 % (w/w) gelatin 60 solutions respectively, indicating whey-gelatin interaction. Chicken skin gelatin gels exhibited 61 a fine network of uniform particles whereas whey protein gels comprised aggregates. 62 Differences in structure and molecular size led to phase separation of the mixed gels. The 63 above properties of an underutilized non-mammalian source of gelatin may lead to novel 64 applications in the food industry.