Microbiology of Pale, Dark and Normal Pork

Abstract

Pale, soft, exudative (PSE), dark cutting, and normal colored pork were compared to determine differences in susceptibility to microbial growth. Chops were packaged and stored under simulated retail conditions. Color, marbling, pH, numbers of total aerobic mesophiles, psychrotrophs, proteolytic and lipolytic bacteria and fluorescent Pseudomonas and incidence of Salm&ella and coagulase positive Staphylococcus were recorded for pork chops as storage time progressed. Data were statistically analyzed. Differences in pH between PSE and normal chops, after aging, were significant, and dark chops had significantly higher pH values than normal chops. Development of microorganisms during storage was influenced by pH. Most rapid growth of organisms occurred on dark meat and slowest bacterial growth on PSE pork, although exudative conditions of the latter provided the highest expressible juice. pH of the meat also seemed to have a selective action on the microflora. Marbling of the meat did not influence growth of lipslytic bacteria. Relevance of various stages of processing as sources of contamination for the meat is discussed.

Freezing Effects on Quality, Bacteriology and Retail‐Case Life of Pork

“…Those results were obtained using longissimus dorsi (LD) muscle that had been previously frozen and thawed (F/ T). Although the results agreed with results reported for fresh pork (Rey et al, 1976), F/T treatment of meat has been observed to reduce bacterial populations (Sulzbacher, 1950; Ingram, 1956, 1960;Nassos et al, 1988), extend the lag before bacterial growth (Sulzbacher, 1952;Ingram, 1956, 1960;Rey et al, 1972;Lowry and Gill, 1985) and reduce bacterial growth rate (Sulzbacher, 1952). Despite reported effects of F/r on bacteria, the rate of spoilage development is generally agreed not to greatly differ in fresh or F/ T meat Ingram, 1956, 1960;Jeremiah, 1982;Jul, 1984;Lowry and Gill, 1985;Nassos et al, 1988).…”

“…Thus, for total psychrotrophs, pseudomonads, B. thermosphaca and enterics the bacterial lag phase was longest on PSE pork and shortest on DFD pork in comparison to N. Depending on the bacterium examined, lag phase was 1 to 2 days longer on PSE than DFD pork. Other researchers have also observed that muscle quality can effect duration of the bacterial lag phase (Rey et al, 1976;Newton and Gill, 1978). Few effects of pork muscle quality on the bacterial generation time were statistically significant.…”

“…Reports are published on effects of inherent differences in pork quality (PSE, N, DFD) on bacteriology (Rey et al, 1976;Greer and Murray, 1988), palatability (Merkel, 1971;Kemp et al, 1976;Jeremiah et al, 1990) and objective muscle quality measures (Van der Wal et al, 1988;Greer and Murray, 1988). Few studies, however, have been designed to evaluate effects of F/T' on pork of differing initial quality.…”

Dissolved carbon dioxide and oxygen concentrations in meat purge and relationship to microbial populations and shelf life

“…PSE has a low pH, around 5.3-5.6, compared to the normal pH range of 5.6-5.8 (Aberle et al, 2012;Fox, Wolfram, Kemp, & Langlois, 1980). Due to this low pH, there can be fewer microorganisms present compared to normal or DFD pork (Rey et al, 1976). For example, total microorganism load for 8 days at 37°C is log 8 CFU/g for normal pork but only log 4 CFU/g for PSE pork (Fox et al, 1980).…”

“…This increased pH is more favorable for microorganism growth because it is closer to a neutral pH. For example, DFD pork can reach log 5 CFU/cm 2 psychrotrophs while normal pork has log 4 CFU/cm 2 at 5°C for 9 days aerobically (Rey, Kraft, Toppel, Jr., & Hotchkiss, 1976). There is also a lower glycogen concentration in DFD meat because the animal was stressed before slaughter and used those reserves in the stress response.…”