Date of Award
Doctor of Philosophy
Food Science and Technology
Ada Marie Campbell
Gracyce E. Goertz, Bernadine Meyer, John A. Dean
A simplified procedure for determination of myoglobin concentration in aqueous muscle extract was developed. The procedure was used in an investigation of possible interactions between phospholipids and bovine myoglobin, either isolated or as a component of sarcoplasmic proteins. Investigation of the possible interactions was carried out as follows. Solutions containing myoglobin or sarcoplasmic proteins and emulsions (phospholipid, sarcoplasmic protein-phospholipid, and myoglobin-phospholipid) were heated from 25°C to end point temperatures up to 77°C. The following measurements were made on all protein dispersions; (1) pH; (2) percent protein remaining dispersed; (3) myoglobin concentration; (4) available lysine, basic group and acidic group equivalents of dispersed and total protein; and (5) densitometric tracings of electrophoretic patterns of dispersed proteins. The following measurements were made on protein-containing emulsions: (1) quantities of free and bound lipid associated with dispersed, precipitated and total protein; (2) quantities of phospholipid classes (lysolecithin, sphingomyelin, lecithin, cephalin, ninhydrin-positive products) in the free and bound lipid; and (3) decomposition of phospholipids to water soluble phosphorus compounds. The following measurements were conducted only on phospholipid emulsions: (1) lipid concentration; (2) phospholipid classes; and (3) decomposition of phospholipids.
Interactions between phospholipids and myoglobin, either isolated or as a component of sarcoplasmic proteins, and between phospholipids and total sarcoplasmic proteins were found. The interactions between phospholipids and proteins in the sarcoplasmic extract involved mainly weak polar bonds but interaction between phospholipids and isolated myoglobin involved both polar and possibly non-polar bonds as well as either covalent or strong complex bonds between phospholipids and the basic groups, especially the ∈-NH2 of lysine in the myoglobin. These interactions formed phospholipid-protein complexes, altered the amount of protein precipitated by heat and caused the protein after being heating to be less stable to a higher pH (7.00) than if heated alone.
Densitometric tracings of the electrophoretic patterns of sarcoplasmic proteins showed the disappearance of certain proteins as a function of increasing end point temperature and showed differences in myoglobin concentrations in heated solutions and emulsions. Densitometric tracings of the electrophoretic pattern of myoglobin in dispersions with and without phospholipids indicated formation of a myoglobin-phospholipid complex that would not migrate in a gel at pH 8.1 until it was heated.
Heating the emulsions caused approximately 1 percent of the total phospholipids to decompose to water soluble phosphorus compounds in phospholipid emulsions and approximately 10 percent of the total phospholipids in sarcoplasmic protein emulsions to change ninhydrin-positive products tentatively identified as lysocephalin and a geometric isomer of cephalin. These quantities, respectively, were calculated from significant (P< 0.5) increases in water soluble phosphorus and in ninhydrin-positive products.
Heating the sarcoplasmic protein-phospholipid emulsions generally caused the following significant changes (P< 0.05): (1) a decrease in free lipid (and a decrease in quantities of lecithin and cephalin in that free lipid) associated with dispersed protein and (2) a decrease in the quantity of lecithin and an increase in the quantities of lysolecithin and ninhydrin-positive products in lipid bound to dispersed protein. Heating the myoglobin-phospholipid emulsions significantly (P< 0.05) affected the amount of lecithin in lipid bound to dispersed protein. Heating from 25 to 65°C caused an increase from 65 to 77°C, a decrease; the quantity at 77°C was significantly smaller than the quantity at 25°C. Heating the emulsions from 25°C to the first end point temperature caused the formation of a precipitate containing protein associated with free and bound lipid in which all phospholipid classes were represented.
When the protein of heated emulsions was separated into dispersed and precipitated protein and the bound and free lipids associated with dispersed or precipitated were separated into phospholipid classes, a partitioning of the phospholipids was found. Phospholipid classes were distributed differently between bound and free lipid associated with dispersed or precipitated protein. The partitioning occurred whether the emulsions contained total sarcoplasmic protein or myoglobin.
The color of cooked meat depends largely upon the nature and amount of myoglobin derivatives present. Therefore, interactions between phospholipids and myoglobin, such as those observed in this study, could affect directly the color of cooked meat.
Melton, Sharon Lynn, "Protein-Phospholipid Interactions in Heated Phospholipid Emulsions Containing Bovine Myoglobin or Sarcoplasmic Proteins. " PhD diss., University of Tennessee, 1973.