Summary
The present report describes the results of three projects which have been largely conducted by Joanna Robertson as research projects within her DPI graduate program rotation at Meat Science UNE. The different projects are described in this report under the titles:The effect of processing conditions on beef quality
Development of an assay for post-mortem proteolysis
The effect of retail packaging method on meat quality traits
For project 1, objective meat quality traits (shear force, colour, water-holding capacity, sarcomere length, p.m. proteolysis) were determined on bovine M. longissimus lumborum et thoracis (striploin and cube roll; n = 189) and M. semimembranosus (topside; n = 144) samples aged for 5 or 26 days. These samples originated from an experiment conducted by John Thompson and Rod Polkinghorne at ACC (Brisbane), investigating the impact of cold-, and heat-shortening conditions and carcass hanging method on sensory beef quality. The objective meat quality traits determined in the present project corroborated the results of the sensory trials, in the sense that the cold-, and heat shortening conditions applied in this experiment did not significantly affect tenderness (shear force), muscle contraction (sarcomere length), or measures of post-mortem proteolysis. Tenderstretching, however, did result in an increase in sarcomere length and a reduction in shear force. Moreover, tenderstretching resulted in a significant improvement in water-holding capacity (thaw loss). These results indicate that tenderstretching is not only an effective way to improve meat tenderness, but can also have a significant impact on yield.
Within project 2 it was investigated whether potential indicators of post mortem proteolysis (ageing) in the soluble muscle fraction correlated with the improvement in tenderness (shear force) during ageing and well-established measures of post-mortem proteolysis (Myofibrillar Fragmentation Index (MFI) and quantification of desmin degradation after SDS-PAGE and Western blotting). For the purpose of this experiment striploins (n = 10) were divided into to 4 subsamples and allocated to ageing for 1, 7, 14 and 21 days. After the respective ageing periods, samples were analyzed for shear force and measures of post-mortem proteolysis. The amount of degradation products of titin in the soluble muscle fraction proved to be a useful measure of post mortem proteolysis. On the basis of this, a novel assay for p.m. proteolysis was developed which allows for a faster and more cost-effective quantification of the impact of ageing on p.m. proteolysis. As discussed, the principle that the ageing response can be assessed on indicators in the soluble muscle fraction, would lend itself to the development of assays suitable for screening of, for instance, purge/weep in vacuum packaged meat.
Project 3 addressed the issue whether retail packaging method (MAP [80% O2, 20% CO2] vs skinpack [Darfresh®]) affects sensory and objective meat quality traits. To this end, steaks from 1 day p.m. (n = 10) and 7 day p.m. (n = 10) striploins were MAP- and skin-packaged and stored under refrigeration for 7 days. After the storage period, steaks were sampled for sensory analysis and objective meat quality traits. MAP packaging resulted in an average 8 point decrease in MQ4 score and a 0.5 kgF increase in shear force. However, there was no significant effect of packaging method on indicators of post-mortem proteolysis. These results indicate that the decrease in MQ4 score is, at least partly, due to a physical effect of the packaging method on the muscle structure, other than inhibition of p.m. proteolysis. Results from other studies on this subject suggest that oxidative cross-linking of proteins may explain this effect, but thus far, quantitative data regarding this hypothesis are lacking. The results from this study indicate that retail packaging method represents a major factor affecting the sensory quality of beef, which at present, is not captured within the MSA grading system.
The major conclusions of these projects can be summarized as follows:
Tenderstretching of carcasses may result in a significant increase in water-holding capacity and therefore yield. Further research on the magnitude of this effect, may aid in the adoption of tenderstretching for reasons additional to its well-established beneficial effect on tenderness.
The impact of ageing on p.m. proteolysis of muscle proteins can be assessed on soluble muscle protein samples. This observation led to the development of a more cost-effective laboratory method to quantify p.m. proteolysis. Further development of this principle may allow for the development of at-line methods to assess the impact of ageing on p.m. proteolysis.
Retail packaging method (MAP vs skinpack) has a major effect on both sensory and objective meat quality traits. However, the effect of packaging method is currently not captured in the MSA grading system, and the physical mechanisms responsible for this effect are not fully understood and/or quantifiable.
