The effects of temperature and ionic strength on the cross‐linking of myofibrillar protein isolate (MPI)/soy protein isolates (SPI) catalyzed by microbial transglutaminase (MTGase) were studied. The SPI treated with MTGase formed a substantial amount of cross‐linking at temperatures ≥50C. All the SPI constituents except the basic subunits (B) of glycinin were cross‐linked and formed polymers. For MPI/SPI mixtures heated with MTGase, the actin band was gradually reduced within the temperature range from 20 to 90C. The addition of KCl gradually reduced the protein band changes and the myosin heavy chain and actin bands became less noticeable detected by the sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The rheological results indicated that the treatment of MPI with MTGase significantly improved the elasticity of the MPI gels, irrespective of the incubation time. MTGase treatment significantly enhanced the gel properties of the mixed MPI/SPI protein gels. Practical Applications Myofibrillar proteins are the main contributors imparting textural attributes and functional properties to muscle foods. Defining the performance of myofibrillar proteins during heat‐induced gelation is beneficial in maintaining quality and developing processed meat products and processes. A better understanding of the gelation properties of protein (muscle and nonmuscle) in the presence or absence of microbial transglutaminase, would contribute to improving its industrial utilization and the quality of meat products.
Pale, soft, exudative (PSE)-like chicken breast is considered deteriorated raw material in the poultry meat industry that has inferior processing ability. The chemical and gelation properties of PSE-like chicken breast meat paste were studied. These pastes were prepared by the pH adjustment method and protein isolation using the isoelectric solubilization/precipitation (ISP) process from PSE-like chicken meat. The ISP-isolated samples were solubilized at pH 11.0 and recovered at pH 5.5 and 6.2. The ultimate pH of the ISP-isolated protein and meat paste was adjusted to 6.2 and 7.0. The ultimate pH in this article referred to the final pH of the extracted protein and meat paste. Higher reactive sulfhydryl content and surface hydrophobicity were found in the precipitation at pH 6.2 than at pH 5.5. However, various ultimate pH values showed no significant influence on the surface hydrophobicity. The hardness of gel, as measured by textural profile analysis, was improved using 6.2 as the precipitation pH compared with pH 5.5. The viscoelastic modulus (G΄) of gel pastes prior to the thermal gelation was higher with ISP treatment. However, lower G΄ was seen after thermal gelation compared with the control. Dynamic rheological measurement demonstrated a different gel-forming mechanism for protein precipitated at pH values of 5.5 and 6.2 compared with the meat paste. The cooking loss showed that the recovered protein failed to form a gel with good water-retention capacity unless the ultimate pH was adjusted to 7.0. Gels made from protein extracted by the ISP method had higher yellowness and lower redness values, probably due to protein denaturation. Precipitation at pH 6.2 formed a harder gel with lower water-retention ability than that at pH 5.5, and this result was possibly due to higher surface hydrophobicity and S-S bridge formation. Overall, network characteristics of ISP-treated protein gels were strongly dependent on precipitation pH and ultimate pH.
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