PubMed | Institute of Chemistry and Physics
Type: Journal Article | Journal: Meat science | Year: 2011
At sufficient ATP concentration and temperatures below about 15C, pre-rigor beef muscles (neck muscles) contract; this phenomenon is known as cold shortening. There is also a contracture at higher temperatures occurring just before rigor onset which is called rigor shortening. While rigor shortening starts in neck muscles at pH around 63-60 and at about 2 Mol ATP/g muscle, cold shortening can begin at pH around 70 and the full ATP concentration (4 Mol ATP/g) in the muscle. Shortening can take place as long as there is no irreversible formation of the actomyosin complex in the muscle, i.e. before rigor onset occurs, which can be measured by intermittent loading of the muscle. The degree of extensibility which follows starts to decrease at the moment of rigor onset. This irreversible loss of extensibility at temperatures between the freezing point (-1C) and physiological temperatures (38C) starts at various pH values and ATP concentrations in the muscle. At 38C the rigor onset occurs at pH 625 and about 2 Mol ATP/g muscle, dropping at 15C to pH 575 and 1 Mol ATP/g muscle. At 0C, as at all temperatures below 10C, the loss of extensibility at medium loads (about 250 g/cm(2)) begins shortly after cold shortening. This loss of extensibility is reversible by increasing the load or raising the temperature. The irreversible loss, or rigor onset, however, occurs at 0C with pH of 61-62 and 18-20 Mol ATP/g muscle. Thus, the onset of rigor is influenced by more than one factor. Temperature, pH and ATP concentration each play a rle. Maximum loss of extensibility or completion of rigor is reached between 10C and 38C at pH 55-56 and less than 05 Mol ATP/g muscle. At 0C the completion of rigor takes place at pH 60, but still at 05 Mol ATP/g muscle. The latter fact shows that the completion of rigor is solely dependent on the ATP concentration in the muscle; nevertheless, the pH of rigor completion is higher in the extreme cold shortening range. This is apparently due to a different pH/ATP relationship in muscles at low temperatures. The results are discussed in terms of changes in the concentration of Ca(2+) ions and ATP. The results are of particular interest for the handling of hot-boned meat; that is, for both the cooling of pre-rigor muscle and the use of hot-boned meat for processing.