30C-16 |
Stability of the globin moiety of porcine myoglobin to urea: reducibility of the denatured form |
L. ZHU and S. Brewer. Food Science and Human Nutrition, University of Illinois, 399 Bevier Hall, 905 S. Goodwin, Urbana, IL 61801 Enzymatic reduction of metmyoglobin is important in preserving the fresh red color in meat. The significance of the integrity of the globin moiety in the reduction of metmyoglobin is unclear. The objective of this study was to evaluate the effect of denaturation of the globin moiety on myoglobin's ability to undergo the reduction reaction at various pHs. Myoglobin was extracted from porcine hearts and converted to metmyoglobin with K3Fe(CN)6. 0.05 umol of metmyoglobin in phosphate or citrate buffer was incubated with 12 mmols of urea at 25°C for 30min to denature the globin. Following incubation, 0, 7.5, 15, 18.75, 22.5, 26.25, 30, 37.5, or 45 umols of Na2S2O4 was added. Absorbances at 555nm and 635nm were determined. The procedure was repeated from pH 5.0 to 7.0 at 0.2 unit intervals. The reducing potential of denatured metmyoglobin was compared to that of native. Increase in absorbance at 555nm (absorbance peak of deoxymyogloin) and/or decrease at 635nm (absorbance peak of metmyoglobin) during the reaction indicate that metmyoglobin reduction has occurred. The absorbance at 555nm after the reaction was 0.429 if the metmyoglobin was native. If the metmyoglobin was denatured before reduction, absorbance decreased to 0.368. Therefore, the reduction of urea-denatured metmyoglobin was less complete than that of native metmyoglobin. The reduction occurred to the least degree at pHs from 5.2 to 5.6 and to the greatest degree at pH 7.0 whether the metmyoglobin was native or denatured before reduction. Similar results were found when absorbance at 635nm was used to monitor the reduction of metmyoglobin. The mechanism causing pale, soft and exudative pork has not been fully elucidated. Results of the present study further the understanding of this mechanism. It will provide basic information that can allow development of efficient methods to reduce PSE occurrence and to remain fresh appeal longer.
Session 30C, Muscle Foods: Tenderness, Quality, Processing, Marination, Oxidation, and Shelf-Life
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