Certain chemical, physical, and histochemical characteristics of three quality levels of Porcine Longissiumus

This study was conducted in two phases. In phase I, muscle pH, muscle color (subjective and objective), percentage of fiber types, number of giant fibers, and muscle fiber waviness were studied in three quality levels of porcine longissimus. Thirty-six loins were purchased at a local packing plant after a 20 hour postmortem chill, and placed into quality levels according to the muscle pH. Loins were classified as pale, soft and exudative (PSE) if the pH was below 5.30, normal if the pH was between 5.30 and 5.70, and dark, firm and dry (DFD) if the pH was above 5.70. Of the 36 loins tested, 14 did not demonstrate typical fiber distribution or show reciprocal enzymatic activity between the oxidative and phosphatase enzyme stains. Subjective color score differed (P < .01) between the enzymatically normal and abnormal groups. The PSE group was lighter (P < .01) than the DFD group in subjective color. The only variance in measured objective color was due to the difference in lightness between quality levels. There was no visual difference in the chromaticity among quality level. Therefore, the differences perceived in the subjective color determination were the result of variation in lightness. The percentage of muscle fibers types was not affected by quality levels, but a greater number (P < .05) of giant fibers was found in the DFD group. The loins with abnormal enzymatic activity had a higher (P < .01) percentage of fibers that did not show reciprocal enzymatic activity. Waviness of muscle fibers was found to be nonsignificant among quality levels. In phase II, the longissimus of nine pork carcasses was sampled at 45 minutes, 90 minutes, six hours and 20 hours postmortem. Muscle pH and temperature, percentage of fiber types, and number of giant fibers were recorded for each time period. Muscle color was measured objectively and subjectively at 20 hours postmortem. Five of the nine carcasses had abnormal enzymatic activity at each sampling time postmortem, three were normal at each sampling time, and one showed abnormal enzymatic activity only at 20 hours postmortem. The percentage of fiber types did not significantly change with time postmortem, but was different (P < .01) among carcasses sampled.