Postmortem changes in protein composition up to 24 h in bovine longissimus thoracis muscle were investigated by two-dimensional gel electrophoresis and MALDI-TOF MS/MS. A total of 47 spots were significantly changed the first 24 h postmortem. The 39 identified proteins can be divided into five groups: metabolic enzymes, defense and stress proteins, structural proteins, proteolytic enzymes, and unclassified proteins. The identified metabolic enzymes are all associated with ATP-generating pathways, either the glycolytic pathway or energy metabolism. In addition, several defense and stress proteins were changed in abundance in this study. These findings contribute to a better understanding of the biochemical processes during postmortem storage of meat.

Cereal Chem. 80(5):587-595The rheological properties of dough and gluten are important for enduse quality of flour but there is a lack of knowledge of the relationships between fundamental and empirical tests and how they relate to flour composition and gluten quality. Dough and gluten from six breadmaking wheat qualities were subjected to a range of rheological tests. Fundamental (small-deformation) rheological characterizations (dynamic oscillatory shear and creep recovery) were performed on gluten to avoid the nonlinear influence of the starch component, whereas large deformation tests were conducted on both dough and gluten. A number of variables from the various curves were considered and subjected to a principal component analysis (PCA) to get an overview of relationships between the various variables. The first component represented variability in protein quality, associated with elasticity and tenacity in large deformation (large positive loadings for resistance to extension and initial slope of dough and gluten extension curves recorded by the SMS/Kieffer dough and gluten extensibility rig, and the tenacity and strain hardening index of dough measured by the Dobraszczyk/Roberts dough inflation system), the elastic character of the hydrated gluten proteins (large positive loading for elastic modulus [G], large negative loadings for tan d and steady state compliance [J e 0 ]), the presence of high molecular weight glutenin subunits (HMW-GS) 5+10 vs. 2+12, and a size distribution of glutenin polymers shifted toward the high-end range. The second principal component was associated with flour protein content. Certain rheological data were influenced by protein content in addition to protein quality (area under dough extension curves and dough inflation curves [W]). The approach made it possible to bridge the gap between fundamental rheological properties, empirical measurements of physical properties, protein composition, and size distribution. The interpretation of this study gave indications of the molecular basis for differences in breadmaking performance.

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Changes in the insoluble protein fraction of bovine longissimus thoracis muscle from eight Norwegian Red (NRF) dual-purpose young bulls during the first 48 h postmortem were investigated by two-dimensional gel electrophoresis (2DE) and matrix-assisted laser desorption ionization-time of flight tandem mass spectrometry (MALDI-TOF MS/MS). Significant changes were observed in a total of 35 proteins, and of those, 26 were identified and divided into three different groups: metabolic enzymes, cellular defense/stress proteins, and structural proteins, according to their predicted function. The majority of the metabolic enzymes identified are involved in the energy metabolism of the cell, while the cellular defense/stress proteins can be related to regulation and stabilization of the myofibrillar proteins. Both easily soluble proteins as well as structural proteins were identified in the insoluble protein fraction. We have studied the changes in solubility during postmortem storage by comparing the postmortem changes in protein composition between the soluble and insoluble protein fractions. We have identified two metabolic enzymes (2,3-bisphosphoglycerat mutase and NADH dehydrogenase) and one protein involved in the stress responses/apoptosis of the cell (Hsp70) that have not been identified previously in the insoluble protein fraction. The occurrence of these easily soluble proteins in the insoluble protein fraction could be due to precipitation or aggregation, thereby going from a soluble to an insoluble state.