Role of protein oxidation in water-binding and hydration of meat

Juiciness and tenderness are the most important quality attributes of cooked meat and meat products. Juiciness is the manifestation of muscle retaining indigenous moisture and withholding extraneous water (injected or marinated) during processing and cooking, which is attributed to the myofibril lattices. Among the most important factors that affect water-binding (protein-water interaction) or water-holding (entrapment in interfilamental spaces or protein gel matrixes) by meat are the pH of meat, the presence of salt (ionic strength) and phosphate, and temperature. Our findings from a previous NRI project strongly suggest that protein oxidation may have a crucial role in regulating waterbinding in meat during normal processing and storage. The overall objective of the proposed study is to elucidate the morphological/structural changes in oxidatively stressed myofibrils and in their main constituting proteins, and to understand how such modifications contribute to waterbinding and hydration of meat. In the first experiment, we will expose muscle tissue and isolated myofibrils to hydroxyl radicals and oxidizing hemes at the concentration range expected to exist in commercial muscle foods during handling, storage or processing. We will then examine the dynamic ultrastructural changes in the myofibril architecture and interactions of main structural proteins that are involved, as well as hydration properties (with brine irrigation) of myofibrils and cooking yield of treated meat. A combination of several analytical tools will be used to elucidate the protein/myofibril structural changes (phase contrast; transmission electron microscopy with negative stain; atomic force microscopy). The biophysical measurements will be coupled with chemical analyses to elucidate the roles of specific proteins in meat hydration and water-binding under the oxidative conditions. Chemical analyses will focus on the changes and association of proteins, e.g., formation of protein carbonyls, myosin-myosin cross-linking (type and degree). In the second experiment, we will store fresh pork chops in a high-oxygen (80% O2/20% C02) atmosphere package for up to 21 days and monitor the above biophysical and chemical changes in muscle and myofibrils to elucidate the response of proteins in the in situ oxidative condition. The knowledge gained from this research will be valuable to the formulation of antioxidant ingredients and improvement of processing and packaging technologies for juicy and tender high-quality fresh and processed meats. The project addresses the following NRI research priority: "Basic mechanisms involved in the interaction of microand macromolecules in the food matrix in controlling structure, texture, stability, and flavor delivery infoods".