| Value-added muscle food processing requires the incorporation of low-cost proteins to achieve desirable product quality. Yet, many of the nonmeat protein ingredients are either of low functionality (e.g., beef heart) or thermally incompatible with meat proteins (e.g., whey and soy proteins). The overall objective of the study was to investigate the feasibility of a microbial transglutaminase (MTGase™) as a cross-linking agent to: (1) improve the gelation properties of bovine cardiac myofibrillar proteins (BMP), (2) promote interaction between whey/soy proteins and chicken myofibrillar proteins (CMP), and (3) expand the functional properties of mixed muscle and structurally modified non-muscle proteins.; For BMP, the protein solution and paste (pH 6.0, 0.6 M NaCl) were incubated with 0.5% MTGase at 5 and 15°C up to 15 h. For CMP, MTGase-mediated protein cross-linking was examined under five processing conditions (pH 6.2–6.5): (1) ionic strength (0–0.6 M NaCl); (2) cation/chelating agent (5 mM CaCl2 or EDTA); (3) enzyme:substrate ratio (0.1% MTGase: 2–8 mg/mL protein); (4) CMP/WPI or SPI ratio (3:1, 1:1, and 1:3); and (5) preheating of WPI and SPI (80°C, 5–60 min). Treatments were incubated with 0.1% (w/v) MTGase at 5°C, and analyzed after reacting for up to 15 h. Electrophoresis, differential scanning calorimetry, and dynamic oscillatory testing for gelling properties were performed on both BMP and CMP samples, while emulsifying properties and rheology of the mixed protein emulsions were analyzed on CMP only.; MTGase-treatment in low-ionic-strength solution (μ 0) converted myosin heavy chain and actin in CMP into lower-molecular-weight polypeptides. The reaction was diminished by NaCl and completely reversed upon extended incubation. No visible CMP/WPI cross-linking was found in other processing conditions while soy β-conglycinin and glycinin had a greater reactivity with CMP. MTGase treatment enhanced elasticity of both BMP and mixed CMP/WPI and CMP/SPI protein gels due to formation of isopeptides. The mixed proteins had an increased emulsifying activity but reduced emulsion storage stability at both 0 and 0.6 M NaCl. The enzyme treatment also resulted in higher gel elasticity for all the emulsion gels.; Thus, by promoting intra- and intermolecular interactions, the microbial transglutaminase studied offers an excellent means for enhancing the functionality of beef heart and chicken muscle proteins. The presence of non-muscle proteins and ionic strength conditions have a major effect on the enzyme actions. |
