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Effect of Temperature on Molecular Properties of Post-Mortem Porcine Muscle^{1, 3,}

Iowa State University², Ames

Abstract

The structural and biochemical properties of porcine muscle strips and myofibrils were investigated immediately after death and after 8 hr. post-mortem at 2°, 16°, 25° and 37° C. Muscle strips shortened or developed isometric tension at all post-mortem storage temperatures, but shortening and isometric tension development were maximal at 2° or 37° and were minimal at 16°. Muscle strips at 2° showed a decline in isometric tension corresponding to a "resolution" of rigor mortis. Shortening or tension development at 2° occurred much sooner after death than shortening or tension development at the other temperatures, and results indicated that much of the shortening at the higher temperatures may be due to dehydration of the strips. Myofibrils prepared from muscle either immediately after death or 8 hr. post-mortem at any of the temperatures studied were in a relaxed state. It was suggested that sufficient ATP remained in the muscle after 8 hr. post-mortem, particularly at 2°, to cause relaxation of the myofibrils during homogenization in 1 mM EDTA. NTPase activity increased about 20–30% after 8 hr. post-mortem at 2°, 16° or 25°. Myofibrils prepared from muscle after 8 hr. post-mortem at 37° had almost no NTPase activity and did not exhibit syneresis. Some indirect evidence suggested that catheptic activity did not influence myofibrils up to post-mortem temperatures of 25° but did influence myofibrils at 37°. A hypothetical scheme involving hydrophobically stabilized myosin aggregates is presented to explain the loss of enzymic activity and contractile properties and the occurrence of pale, soft, exudative tissue during post-mortem storage at 37°.

¹ Journal Paper No.J-5594 of the Iowa Agricultural and Home Economics Experiment Station,Ames, Iowa. Project 1549,Supported in part by Public Health Service Research Grant GM 12,488. The authors gratefully acknowledge Joanne Main for her skilled technical assistance,Cedric Matsushima for assistance, in sample procurement, and Dean Henderson for help in myoffbril photography.

³ Abbreviations used throughout this paper are: ATP, adenosine triphosphate; ITP, inosine triphosphate; NTP, nucleoside triphosphate; Tris, tris-(hydroxymethyl)-aminomethane: EDTA, ethylenediaminetetraacetic acid; EGTA, 1,2-bis-(2 dicarboxymethylaminoethoxy)-athane; Pi, inorganic phosphate.

² Department of Animal Science.