Dynamic rheology and endothermic transitions of proteins recovered from chicken-meat processing by-products using isoelectric solubilization/precipitation and addition of TiO₂

Chicken-meat processing generates large quantities of by-products (backs, necks, etc.). Dark chicken-meat processing by-products present the lowest value and greatest challenge. Therefore, recovery of functional proteins from this source for inclusion in food products resembling those from light chicken-meat presents the greatest value addition and opportunity. Novel isoelectric solubilization/precipitation (ISP) was applied to model, dark chicken-meat processing by-products (skin-on bone-in chicken drumsticks) to recover muscle proteins. Thermal denaturation (endothermic transitions), gelation (elasticity, G′), and fundamental texture properties (shear stress and strain at mechanical fracture) of the ISP-recovered proteins were determined with differential scanning calorimetry (DSC), dynamic rheometer, and torsion test, respectively; and compared to boneless skinless chicken breast. Endothermic transition of myosin was not detected only when TiO₂ was not added, while the ISP-recovered proteins with TiO₂ showed small myosin peak and large actin peak. However, the level of TiO₂ addition did not affect thermal transition/denaturation of the ISP-recovered proteins. The ISP-recovered proteins had a greater transition for actin compared to chicken breast, suggesting that ISP predisposes this protein to thermal denaturation. Similar to endothermic transitions, elasticity (G′) generally increased when TiO₂ was added to the ISP-recovered proteins. Gels made of chicken breast had the highest (P < 0.05) shear stress (i.e., gel strength), but gels made of the ISP-recovered chicken proteins had greater (P < 0.05) shear strain (i.e., gel cohesiveness). Addition of TiO₂ to the ISP-recovered proteins resulted in increased (P < 0.05) gel strength. Based on the present study, addition of TiO₂ is suggested for the development of restructured food products based on proteins recovered from dark chicken-meat processing by-products using ISP. Although the results of this study point towards a novel food product, further studies are recommended.