Impact of post mortem aging of pork on changes in the isoelectric point of the proteins and tenderness

Abstract

The aim of the study was to evaluate the post mortem proteolysis of centrifugal drip protein derived from pork. The varied course of the process of meat tenderization in muscles using the isoelectric focusing (IEF) technique was observed. The experimental material was the longissimus lumborum et thoracis muscle excised from 24 pigs of known origin, breeding and rearing conditions. Meat of normal quality (RFN) was examined in this study. On the basis of shear force values, the experimental muscles were divided into 4 groups of different courses of tenderization: A – meat remaining tough during the entire 6-day period of post-slaughter changes; B – meat characterized by a typical tenderization process, i.e. tough 48 h after slaughter and tender after 6 days of storage; C – tender or relatively tender meat on both dates of examination; D – meat which was the toughest 48 hours after slaughter and the most tender 144 hours after slaughter. Proteins for electrophoretic analysis on the agarose gel of the centrifugal drip fraction were submitted after 48 h and 144 h post mortem. The separation of the proteins was performed in a horizontal layout, using an FBE-3000 apparatus and an ECPS power pack (Pharmacia). On every path of the proteins separation, four ranges of pH value were evaluated, namely: 4.0 ÷ 6.0 pI, 6.1 ÷ 7.2 pI, 7.3 ÷ 7.7 pI and > 7.7 pI. Meat tenderness on the second day after slaughter was influenced by proteins, in which their pI was in the range of 6.1÷ 7.2 and 4.0 ÷ 6.0. From the evaluation which was carried out in the immunoblotting analysis of proteins using troponin T (9D) antibodies it was demonstrated that 48 h after slaughtering the most intense reactions were observed in the range of pI of 5.5 ÷ 5.9, which is the pH range corresponding to the isoelectric point of troponin T. However, after 144 h post mortem the most intense reaction was demonstrated in the range of pI of 6.1÷ 7.7. This indicates the breakdown of troponin T and an increase of the number of degradation products of this protein occurring while the meat tenderization process progresses. The degradation products of troponin T identified by IEF can be an indicator of meat tenderization.