Graduate Thesis Or Dissertation
 

Pressurization of prerigor beef muscle and its effect on the solubilization of myofibrillar proteins

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  • Investigations were conducted to evaluate some of the changes occurring in the myofibrillar proteins, particularly solubility properties, resulting from the hydrostatic pressurization (15,000 psi, 2-3 min, 40°C) of prerigor semitendinosus and longissimus dorsi beef muscles. Both pressurized muscles showed a sharp decline in pH (~0.9 unit) as the result of pressurization. Pressurized samples had an average pH of 5.9 as compared to 6.8 for the controls shortly after completion of the pressure treatment. Immediately after pressurization, the pressurized samples had higher Hunter Color "a" and "L" values than the controls indicating an increase in redness and brightness respectively. The water-holding capacity (WHC) of both muscles was influenced by pressurization. Myofibrils isolated from pressurized muscles showed an increase in WHC with increasing molar concentrations of KC1 in which they were suspended. In OM KC1, the WHC increased 29% while an increase of 46% was noted on pressurizing myofibrils suspended in 1.0M KC1. The dye-binding ability of myofibrillar proteins was affected by pressurization. Approximately 25% less protein was detected in the pressurized samples by the dye-binding method than by the biuret procedure. Extractibility of total myofibrillar proteins was reduced by pressurization. Pressurized semitendinosus and longissimus dorsi muscles yielded 39.6 and 34.4% less myofibrils respectively than their controls. When myofibrils isolated from non-pressurized muscles were pressurized and subsequently centrifuged, 35.7 and 36.8% more protein was solubilized in the supernatants of the semitendinosus and longissimus dorsi muscles respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and densitometric tracings of isolated reconstituted myofibrillar pellets from pressurized muscles showed myosin (heavy chain) to be 16.6% less than its control while larger losses of about 30% were observed for M-protein, C-protein, actin, troponin-T, and tropomyosin. Electrophoresis and densitometry of supernatants from isolated pressurized myofibrils indicated actin was most affected by pressurization at low ionic strength (μ<0.1) while myosin (heavy chain) was most affected at high ionic strength (μ≥0.5). Pressure-induced solubilization of actin at low ionic strength was about 48 milligrams percent while that of myosin was about 1 milligram percent. At high ionic strength, solubilization of myosin increased to 42 milligrams percent while actin was reduced to 23 milligrams percent.
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