The effect of pH decline rate on the meat and eating quality of beef carcasses

Abstract

Abstract. An experiment was undertaken to examine the effect of rapid pH fall at a high muscle temperature on meat and eating quality of two beef cuts (striploin and cube roll). From 115 beef steer carcasses of which the right side of each carcass was subjected to electrical stimulation, 25 carcasses which exhibited the largest difference in the rate of pH fall in the M. longissimus between sides were selected for subsequent sampling. All of the stimulated sides missed the 'ideal' pH/ temperature window (defined as temperature at pH 6 in the M. longissimus <35 C and >12 C) at the upper end, as did several of the non-stimulated sides. The mean temperature at pH 6 for stimulated sides from modelling was 40.9 versus 33.3 C for non-stimulated sides. Despite the significant effect of stimulation on pH decline there was no statistically significant impact on shear force or sensory traits of the M. longissimus, but there was a significant effect of aging on these traits. There was no effect of stimulation or pH decline on drip loss of the striploin. After 14 days of aging there was no effect of stimulation or ultimate pH on striploin purge, but there was a significant effect of pH decline. This was not, however, evident for purge of the cube roll aged for either 4 or 42 days. The redness of the cube rolls as reflected by a* values declined with days of display, with the decline more rapid for samples aged for 42 days compared with those aged for 4 days. For meat aged and displayed identically, the a* values were on average significantly lower for meat from non-stimulated carcasses, but apart from aging there was no effect on the wavelength ratio 630/580 nm, an indicator of the formation of metmyoglobin. There was also evidence that a rapid decline in pH increased the onset of lipid oxidation.

Muscle metabolism in sheep and cattle in relation to high rigor temperature – overview and perspective

“…The authors emphasised the fact that inefficient stimulation may lead to tougher meat and higher drip loss, probably through higher levels of protein denaturation as muscle spends more time in higher temperature zones during the course of rigor. Likewise, muscle of heavy carcasses that is not stimulated and chilled slowly pre-rigor will also be exposed to unfavourable conditions for a longer time, as also mentioned by Hopkins et al (2014). Despite this convincing argument, it is difficult to understand why Warner et al (2014c), supported by other studies (Devine et al 1999;Thompson 2001a, 2001b), reported a limited ageing potential for cuts above the MSA pH-temperature window.…”

“…At the latter point, high rigor temperature cuts reached their maximum tenderness level. In the study of Hopkins et al (2014), tenderness values of high rigor temperature cuts created by ES ran parallel to those of cuts that were within the pH-temperature window (non-stimulated carcasses, NES) from slaughter to 14 days, and differentiation after that was probably not likely to happen with ageing taking place at 0À1 C, although this was not confirmed. Furthermore, ES muscles recorded no initial advantage (1 day) as would have been expected (Thomson et al 2008;Kim et al 2012;Warner et al 2014a).…”

“…Of more importance to this discussion is the lack of consistent results with regard to tenderness when the MSA pH-temperature window is missed due to rapid pH decline and/or slow chilling rates. While Hopkins et al (2014) showed consistently similar sensory tenderness results for beef loin falling within or without the ideal MSA pH-temperature window, Warner et al (2014c), using the extensive consumer data of Watson et al (2008), reported initial preferences for high rigor temperature cuts, but these were soon outperformed in MQ4 scores by ones within the ideal pH-temperature window when ageing continued beyond 14 days. At the latter point, high rigor temperature cuts reached their maximum tenderness level.…”

“…The study did not indicate the reasons leading to a proportion of carcasses with high rigor temperatures, but it can be assumed that a combination of carcass weight, fatness, ES and chilling conditions would have been involved (Watson et al 2008). While some NES sides in the study of Hopkins et al (2014) were also exposed to high rigor temperature conditions, all stimulated sides missed the ideal window of pH 6 at a loin temperature <35 C. After the work of Rosenvold et al (2008) and Rosenvold and Wiklund 2011), a protecting effect of ES against denaturation of proteolytic enzymes and other proteins was proposed as a possible reason for the lack of negative effects of high rigor temperature conditions in the stimulated group. The reasoning behind this mechanism is that individual fibres go into rigor through their own time-course depending on initial glycogen level.…”

“…Hwang et al (2003) in their review on ES specifically refer to the problem of studying effects of rigor paths and conditions in situ as opposed to excised muscles that were restrained (or not) and held under specific controlled and/or constant conditions with regard to temperature (Rosenvold et al 2008;Thomson et al 2008;Kim et al 2012), a point stressed by Hopkins et al (2014). These conditions would differ from the steady temperature decline under conventional chilling conditions of intact carcasses.…”