The influence and interaction of breed and processing on pork tenderness

Intramuscular fat (IMF) and ultimate pH (pHµ̳) and processing factors, such as chilling-time and temperature, and storage time influence tenderness. However, the role of each of these factors and possible interactions between them has not been conclusively defined. The focus of this study was to determine the effects of pHµ̳, IMF, chilling conditions, and storage time on the tenderness of pork longissimus muscle. To obtain variation in IMF, Berkshire (B), Duroc (D) and Hampshire (H) boars were crossed with Yorkshire-Landrace sows. In 4 trials, a total of 176 pigs were used: 60 B, 62 H, 54 D. To obtain a range in pHµ̳, half of the pigs were fasted before slaughter. One side of each carcass was sent through a still-air, conventional chiller and the other side was sent through a blast-air, rapid chiller. At 24 h post mortem (PM), a 6-12th rib section of the loin was excised. The 10th rib section was used for pHµ̳, IMF, and sarcomere length (SL) analysis. The remaining section was divided into three parts, individually vacuum packaged, and stored at 0-4°C. At 2, 7 or 14 days PM, one part of each loin was cooked to an internal temperature of 70°C, and Warner-Bratzler shear force (WBS) was assessed. Myofibrillar protein fragmentation was analyzed with SDS-PAGE. The ratio of 30 kDa/actin and 30 kDa/α-tropomyosin was calculated. Irrespective of fasting and breed, chill method did not affect SL, WBS or pHµ̳. WBS decreased (P<0.05) from 4.89 kg at day 2, to 4.16 kg at day 7, to 3.52 kg at day 14. H pigs had a lower (P<0.05) WBS than the other breeds at day 2. This difference disappeared upon further storage. Based upon glycolytic potential, thirty of the H pigs were carriers of the RN-gene. When these pigs were excluded from the analysis, there was no difference in tenderness or tenderization between breeds. The RN carriers had a lower pH and WBS than any of the other breeds. The correlation (r) between IMF and WBS was -0.11 at day 2, -0.21 at day 7, and -0.19 at day 14. For D pigs, the relationship between IMF and WBS was linear; WBS decreased with increasing IMF levels. In H and B pigs, the relationship between IMF and WBS was not significant. For each breed, the relationship between pHµ̳ and WBS was different; in D pigs the relationship was quadratic (WBS decreased more rapidly as pHµ̳ increased), in H pigs it was linear (WBS increased as pHµ; increased) and in B pigs there was a trend (p=0.07) toward a linear negative relationship between WBS and pHµ̳. The 30 kDa/α-tropomyosin ratio increased with storage. The 30 kDa/actin ratio was higher in D than in B and H pigs, suggesting faster proteolysis in D pigs. It is concluded that irrespective of breed, blast chilling does not seem to have a negative effect on tenderness. The effect of pHµ̳ and IMF on WBS is breed dependent. Differences in proteolysis did not explain differences in tenderness or tenderization. Further research on tenderness and tenderization of pork is needed.