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X-Ray Diffraction Measurements of Myofilament Lattice Spacing and Optical Measurements of Reflectance and Sarcomere Length in Commercial Pork Loins¹

University of Guelph, Guelph, Ontario, Canada N1G 2W1

Abstract

Ten pork carcasses were taken 24 h postmortem from a commercial abattoir and were ranked in a range from mild pale, soft, exudative (PSE) pork to mild dark, firm, dry (DFD) pork. Measurements were made on intact samples of muscle: reflectance spectra by fiber optics, the lateral separation of myofilaments by x-ray diffraction and sarcomere length by diffraction of laser light. The separation of myofilaments ranged from 39.3 nm at sarcomere length 2.00 µm (mild PSE) to 45.6 nm at sarcomere length 1.49 µm (mild DFD). With nonparametric analysis, the rank order for PSE-DFD was correlated with the rank order for 400/700 nm reflectance (r = .72, P < .01, n = 10), with the rank order for filament spacing (either r = .78, P < .005, n = 10 for all samples or r = .93, P < .005, n = 8, excluding diffraction patterns similar to those of prerigor muscle) and with the rank order for sarcomere length (r = –.90, P < .005, n = 10). Thus, PSE pork had greater red reflectance, more closely placed myofilaments and longer sarcomeres than DFD pork. With parametric analysis, filament separation was correlated with 400/700 nm reflectance (r = .79, P < .025) and with sarcomere length (r = –.74,P < .025). The occurrence of diffraction patterns like those of prerigor muscle tended (r = .48, P < .005) to be more common in PSE than in DFD pork. Disruption of cross-bridges between thick and thin filaments might have allowed sarcomeres to lengthen as they were prepared for examination by x-ray diffraction.

¹ Research supported by the Natural Sciences and Engineering Research Council of Canada and by the Ontario Ministry of Agriculture and Food.

² Biophysics Interdepartmental Group, Dept. of Physics.

³ Dept. of Food Sci. and Dept. of Anim. and Poul. Sci.