Influence of Harvest Processes on Pork Loin and Ham Quality

Variation in fresh pork color, texture and water holding capacity continues to be a significant concern to the pork industry. If pork produced in the United States is to successfully compete in the global market, issues relating to product quality and uniformity must be addressed. Pork quality is influenced by many system “inputs”. These include genetics, nutrition, on-farm handling, transport, pre-slaughter handling, early postmortem processing, evisceration, chilling and fabrication (Meisinger, 1999). It is clear that genetics can have a profound effect on quality (Lonergan et al., 2001, Cameron et al., 1999). It is also clear that necessary handling and processing steps will either sustain or diminish the pork quality potential defined by the genetics and nutritional management of the pig. In essence, the pre-slaughter inputs (genetics, nutrition, transport and handling) set the stage for the response to the slaughter process (Sosnicki et al., 1998). Harvest and processing steps cannot improve quality defined by the pre-slaughter inputs. Rather, the harvest processes must be developed with the goal of maintaining quality.

 

Postmortem muscle metabolism has a significant role in determining pork texture, water binding capacity and tenderness. Postmortem production of lactic acid through glycolytic pathways can significantly alter pork quality. Variations in the rate (Piedrafita et al., 2001) or extent (LeRoy et al., 1990) of lactic acid production have been attributed to genetic factors such as the halothane gene or the RN gene. Products harvested from animals with these genetic conditions are likely to have very poor texture and water binding characteristics and do not perform well in fresh or further processed meat systems. Carcass handling early in the harvest process (most notably efficient removal of heat) can also have significant influence over pork quality. Many recommendations developed to maintain pork quality during the harvest process have focused on rapid processing and initiation of chilling (Honikel, 1999). It is also clear that other economic factors such as efficient utilization of processing employees, efficient removal of blood and effective removal of hair from the carcass must be considered. The current project has been designed to determine the consequence of changing the time of two key processing steps during harvest – exsanguination and scalding- on quality of fresh pork. Increasing “dwell time” prior to scalding may influence blood yield. Increasing scald time may decrease personnel needs in preparing the carcass for evisceration. This component of the pork processing chain is a vital link between producer inputs and final product quality. Information gained from this project will be used to allow processors to make informed decisions regarding early postmortem harvest procedures to produce high quality pork products as efficiently and consistently as possible.

 

The objectives of this trial were to identify the extent to which timing during the harvest process influences pork quality.

• Determine how holding time between exsanguination (dwell time) and scalding can influence pork color and water holding capacity.
• Determine the specific consequence of extending scalding time on pork color and water holding capacity.

 

Materials and Methods

 

Thirty-two crossbred (Duroc X Yorkshire) barrows and 32 (Duroc X Yorkshire) crossbred gilts were harvested at the ISU Meat Laboratory. 8 barrows and 8 gilts (average weight 113 kg) were slaughtered each week for a four-week period. A 2X2-treatment arrangement (16 pigs per treatment combination) was utilized. Carcasses were held for 5 or 10 minutes after sticking (dwell time) before entering the scald tank. Carcasses were placed in the scald tank for 5 or 8 minutes (water temperature of 60°C). Temperature and pH were measured on the inside ham muscle (semimembranosus) and loin muscle (longissimus) at 45 minutes, 2, 4, 6, and 24 hours postmortem. All carcasses were placed into the cooler at 50 minutes postmortem. This was done to avoid the effect of some carcasses in the short dwell time or scald time treatment groups entering the cooler earlier postmortem and to allow specific investigation of the influence of harvest treatments on pork quality.

 

Hams and loins were removed from the left side of the carcass at 24 hours postmortem. Two 2.5 cm chops for the last rib region of the loin were used to determine subjective scores of color (NPPC), firmness, wetness, and marbling. Drip loss and Hunter L*, a* and b* values were measured on longissimus chops from the center loin. The sirloin end of the loin was utilized to determine purge loss in a vacuum package for a 6-day storage period.

 

Hunter L, a, and b values were obtained on the semimembranosus and biceps femoris of the ham. Ultimate pH of the semimembranosus and biceps femoris from each carcass were recorded. Portions (approximately 1.5 kg) of the semimembranosus and biceps femoris were utilized to determine purge loss in a vacuum package for a 6-day storage period.

 

Results

 

The total blood collected accounted for 3.59% of the live weight. Of the blood that was collected, 89.66% was collected in the first minute, and 7.91% was collected in the second minute (Figure 1). In other words, 97.57% of the total amount of blood collected was obtained in the first two minutes after sticking. These data are consistent with the results reported by Warris (1984). Very little blood was collected after two minutes, which provides evidence that processing facilities can decrease dwell time prior to scalding. Decreasing this time would allow for carcasses to enter the cooler at an earlier time postmortem, which may improve overall pork quality.

 

Our primary objective was to determine the impact of early postmortem processing traits on overall pork quality. Analysis was conducted with scald time, dwell time, harvest date, and sex of the animal as the independent variables. The longer scald time tended to result in a lower loin pH 45 minutes (P = 0.058) and two hours postmortem (P=0.09; Table 2). We observed lower temperatures at 2 hours postmortem in the semimembranosus muscles of carcasses in the shorter dwell time and scald time treatment groups (Table 3). These observations suggest that altering the harvest procedure has the potential to alter pH and temperature in the early postmortem period. Scald time had a significant effect (P < 0.005) on the 24-hour pH of the biceps femoris (Table 4).   Although the harvest treatments appeared to minimally influence pH and temperature decline early postmortem, treatment effects on pork quality measures were not consistently observed. Scald time had a significant effect (P < 0.005) on the a* value in the longissimus (Table 6). Dwell time had a significant effect (P < 0.005) on the b* value in the semimembranosus (Table 6). Dwell time had a significant effect (P < 0.005) on the a* and b* values in the biceps femoris (Table 6). No treatment differences were noted in purge loss (Table 7).   [caption id="attachment_9150" align="alignleft" width="300"] Figure 1. Cumulative blood loss during exsanguination[/caption]
It is necessary to develop harvest procedures that maintain the quality defined by pre- slaughter inputs. This report demonstrates that duration of the dwell time and the scald time has the potential to influence pork quality. It is expected that an abbreviated dwell time and/or scald time would decrease the amount of time necessary to reach the cooler. The impact of decreasing the processing time in combination with earlier chilling on pork color and water holding capacity remains to be defined.

 

References

 

Cameron, N. D., G. R. Nute, S. N. Brown, M. Enser, and J. D. Wood. 1999. Meat quality of Large White pig genotypes selected for components of efficient lean growth rate. Animal Science 68:115-127.
 
Honikel, K. Influence of Chilling of Pork Carcasses on Physical Quality Traits. November 2, 1999. NPPC Chilling Workshop.
 
LeRoy, P, J. Naveau, J. M. Elsen and P. Sellier. 1990. Evidence for a new major gene influencing meat quality traits. Genet. Res. Camb. 55:33-39.
 
Lonergan, S. M., E. Huff-Lonergan, L. J. Rowe, D. L. Kuhlers, and S. B. Jungst. 2001. Selection for lean growth efficiency in Duroc pigs: Influence on pork quality. J. Anim. Sci. 79:2075- 2085.
 
Meisinger, D. 1999. A system or assuring pork quality. NPPC. Des Moines, IA.
 
Piedrafita, J., L. L. Christian, and S. M. Lonergan. 2001. Fatty acid profiles in three stress genotypes of swine and relationships with performance, carcass and meat quality traits. Meat Sci. 57: 71-77.
 
Sosnicki, A.A., E. R. Wilson, E. B. Sheiss, and A. deVries. 1998. Is there a cost effective way to produce high quality pork? Proc. Recip. Meat Conf. 51:19-27.
 
Warris, P.D. 1984. Exsanguination of animals at slaughter and the residual blood content of meat. The Veterinary Record. 115:292-295

 

Table 1. Loin temperature decline means for scald and dwell time treatments.

 

Table 2. Loin pH means for scald and dwell time treatments.

 

Table 3. Semimembranosus temperature decline means for scald and dwell time treatments.

*Semimembranosus, **Biceps Femoris

 

Table 4. Semimembranosus pH means for scald and dwell time treatments

*Semimembranosus, **Biceps Femoris

 

Table 5. Summary of treatment means for loin quality traits.

^a1=pale, 6= dark ^b1= soft, 3 = firm ^c1= watery, 3= dry ^dMarbling score is a prediction of the percent lipid.

 

Table 6. Influence of harvest treatments on longissimus dorsi (LD), semimembranosus (SM) and biceps femoris (BF) Hunter L*, a* and b* values.

 

Table 7. Influence of harvest treatments on purge (%) in sirloin, semimembranosus (SM) and biceps femoris (BF) roasts.