A practical means to accelerate beef ageing and sustain acceptable eating quality and safety: Chilled storage temperature manipulation

This thesis reports the effects of different combinations of storage temperatures and times (temperature-time combinations; TTCs) on beef safety, shelf life and eating quality. In Australia, beef is currently aged for 14 days at 0 °C to allow meat to develop an acceptable eating quality to consumers. It was hypothesised that one or more combinations of higher temperatures and shorter times accelerate this ageing process while maintaining acceptable tenderness, but with varying effects on the microbiological safety, shelf life, organoleptic traits and volatile organic profile of the beef.
A total of 40 grass-fed beef M. longissimus lumborum (LL) were selected at random from a collaborating abattoir, divided into 8 different portions, vacuum packaged and allocated to one of 72 unique TTCs, which included temperatures of ~ 3, 5 or 7 °C and ageing times of 6, 8, 10 or 12 days, with some samples undergoing temperature changes at 4, 6, 8 or 10 days. Controls were aged for 14 days at approximately 1 °C. At the conclusion of the designated ageing period, samples were removed from vacuum and sectioned further and frozen for analysis, the exceptions being one unfrozen section placed under simulated retail display conditions for 72 hours for the measurement of colour stability and an unfrozen core analysed for fresh meat drip loss determination. To determine microbial loading, samples were sent to a commercial laboratory for analysis, and instrumental tenderness was measured as shear force. Particle size analysis and sarcomere length were also measured in an attempt to understand tenderness differences. Consumer sensory evaluation was undertaken, followed by determination of the volatile organic compound profile to support the consumer sensory evaluation results.
The results indicated that TTCs did accelerate the rate of ageing, with most TTCs exhibiting tenderness values comparable to the controls. Safety thresholds were not compromised by the application of TTCs, however an increase of microbial growth was observed under higher storage temperatures and over longer ageing periods, as expected. Instrumental colour stability values remained acceptable over the display period, confirming that shelf life was not affected by the application of TTCs. Consumer sensory evaluation indicated that consumers were unable to discriminate between TTCs and controls, with many consumers preferring samples aged under TTCs to the controls. Volatile organic compound profile was not altered by the application of TTCs, supporting the sensory results for flavour and aroma.
From these results, it was evident that alternative TTCs may offer a practical method of accelerating the ageing rate of beef while still ensuring safety, eating quality, shelf life and consumer acceptability. Some specific TTCs were recommended based on the eating quality and VOC results, including BBB (8 days at 5 °) due to its temperature lying within a safe range, and lack of temperature change in the ageing period, and BA (4 days at 5 °C followed by 2 days at 3 °C) and CC (6 days at 7 °C), as these TTCs exhibited an acceptable flavour profile, coupled with high consumer acceptability. Nonetheless, further research is required to confirm the results presented in this thesis, as well as research undertaken into the oxidation and nutrition status of beef after the application of TTCs to confirm the overall practicality of this alternative method of ageing beef.