The influence of ultimate pH and intramuscular fat content on pork tenderness and tenderization

Abstract

Intramuscular fat (IMF) and ultimate pH (pHu) influence tenderness, but their roles have not been conclusively determined. Length of storage also affects tenderness and may interact with IMF and pHu. We evaluated the effects of pHu, IMF, and storage time on the tenderness of pork longissimus muscle and determined whether the contribution of the various factors was dependent on genetic line. To obtain variation in IMF, Berkshire (B), Duroc (D) and Hampshire (H) boars were crossed with Yorkshire-Landrace sows. In four trials, a total of 176 pigs were used. To obtain a range in pHu, half of the pigs were deprived of feed before slaughter. Warner-Bratzler shear force (WBS) of each loin was assessed after 2, 7, and 14 d of storage at 0 to 2 degrees C. Warner-Bratzler shear force decreased (P < 0.05) from 4.89 kg at d 2 to 4.16 kg at d 7 to 3.52 kg at d 14. The H pork (n = 62) had a lower (P < 0.05) WBS than the other pork at d 2. After 7 d of storage, this difference had disappeared. Based on glycolytic potential, 30 of the H pigs were carriers of the Rendement Napole (RN) gene. When these pigs were excluded from the analysis, there was no difference in tenderness or tenderization of H, D, and B pork. The correlation between IMF and WBS was -0.11 at d 2, -0.21 at d 7, and -0.19 at d 14. In D pork, the relationship between IMF and WBS was linear, and IMF accounted for 47% of the differences in WBS. In H and B pork, the relationship between IMF and WBS was not significant. For each cross, the relationship between pHu and WBS was different; in D pork it was quadratic, in H pork WBS increased linearly, and in B pork there was no significant relationship between WBS and pHu. The 30 kDa/actin ratio, a measure of myofibrillar degradation, increased (P < 0.05) during storage. Differences in 30 kDa/actin ratio did not explain differences in pork tenderness or tenderization. Further research on determinants and mechanisms of pork tenderness and pork tenderization is needed before production of consistently tender pork will be possible.