The incidence of pale soft exudative pork in entire male pigs from an Australian herd

Pale, soft, exudative (PSE) pork is caused by protein denaturation resulting from high temperature and low pH conditions occurring in the early post-mortem period. This changes the light reflectance and water binding characteristics of meat. However, the description of PSE varies within the literature and the Australian Pork industry has no definition for PSE pork. Since the removal of the halothane gene from the Australian herd (Channon and Warner 2011), the incidence of PSE pork may have been underestimated, with no studies conducted to determine the prevalence of PSE pork as it is no longer seen as an issue. However, factors other than the halothane gene are known to lead to the temperature and pH conditions required to cause PSE (Scheffler and Gerrard 2007). The objective of this study was to present data for the incidence of PSE, based on published PSE classifications, in an audit of carcasses from an Australian pork farm.

Data from 198 randomly selected entire male, Large White × Landrace carcasses, sourced from one farm, were collected over 6 days in an Australian abattoir. The pH of the Musculus longissimis dorsi was measured at 0.75, 3 and 72 h post-mortem. A 50 g sample of the M. longissimus dorsi was collected at 72 h post-mortem to measure colour values for lightness (L*) and was then subsequently used to measure drip loss over a 24 h period. Five published PSE definitions of varying parameters were selected to test the incidence of PSE pork in the samples collected (Table 1). The carcasses that fell outside these thresholds were considered PSE and are presented as a proportion of the consignment (%). The prevalence of PSE was highly variable depending on which thresholds were used. Only six carcasses in total (3%) had an L* value of greater than 60, to be considered PSE in Category 1 (Warriss and Brown 1995). Although paleness is an attribute of PSE, the colour of fresh meat is not associated with eating quality and is a consumer preference, thus colour alone should not be used to determine PSE. Of the 198 carcasses sampled, 63.6% would be considered PSE based on Category 2 (Warner et al. 1997) for L* and drip loss percentage. The fact that almost two-thirds of all carcasses had a drip loss over 5% highlights that water holding capacity can increase without L* increasing to high levels. Determination of PSE using an ultimate pH threshold of pH 5.5 (Category 3; Gajana et al. 2013) resulted in 68% of carcasses being classified as PSE. However, ultimate pH is independent of the rate of pH decline, so can be low without causing protein denaturation (Scheffler and Gerrard 2007), therefore ultimate pH alone is a poor indicator of PSE. Categories 4 (Bee et al. 2007) and 5 (Offer 1991) take into account rate of pH decline hence are a more accurate presentation of circumstances in post-mortem muscle that cause PSE. Although the rates described are lower than Categories 2 and 3, high rates still existed with 28.3 and 39.4% respectively, highlighting a likely issue with PSE in Australian pork when 4 of the 5 published thresholds are applied.

Table 1.  The incidence (%) of PSE in 198 carcasses based on five published definitions for PSE

The Australian pork industry must consider the development of an industry standard for describing PSE pork. The current data presents a high incidence of PSE across most definitions; thus, PSE could explain some eating quality variation in Australian pork.