Meat tenderness is an important meat quality trait. The variation in meat tenderness has a negative effect on consumer's perceptions and thus will impact on repeat purchasing decisions. Meat tenderness is known to be affected by many factors such as muscle fibre shortening, post-mortem proteolysis and collagen content.

Experiment 1 (Chapter 3) focused on using the aforementioned factors to explain the amount of variation in tenderness in the longissimus muscle of 3 different ageing time periods. It was found that measures of post-mortem proteolysis combined with collagen content and sarcomere length (measure of muscle fibre shortening) explained just under 40% of the variation in shear force tenderness of the longissimus muscle. Particle size analysis accounted for 32% of the explainable variation across the different aging periods. It was concluded that to improve the tenderness of lamb longissimus, methods need to focus on improving the extent of post-mortem proteolysis.

Experiment 2's (Chapter 4) main aim was to identify if there was variation between shear force tenderness between different laboratories. 26 longissimus samples were collected and aged for 2 alternate aging periods. Each laboratory used different cooking methods and machine settings. Strong correlations were observed for the data from each laboratory (r = 0.79). It was concluded that provided there were sufficient replications performed across other sources of variation, the two laboratories will rank shear force samples the same.

Experiment 3 (Chapter 5) utilised three different ovine muscles (longissimus, biceps femoris and semimembranosus) with the aforementioned traits and the inclusion of IMF (intramuscular fat) to identify the variation in both sensory (longissimus and semimembranosus) and shear force (all three muscles) tenderness. It was found that for the longissimus shear force samples that IMF, sarcomere length and desmin degradation were the significant factors. However, sensory tenderness for the longissimus had IMF, ultimate pH and gender as the significant factors. For the semimembranosus, desmin degradation was the best predictor for both sensory and shear force tenderness. The biceps femoris utilised soluble collagen and animal age for shear force samples. It was concluded that different factors impact on tenderness across different muscles and no one prediction model applied effectively across all muscles.

Based on the results of these experiments, no one model will be effective in predicting the explainable variation in tenderness in different muscles. Further research is warranted to identify how different muscles are influenced by these aforementioned traits. The suggested project would encompass 12 different muscles from different positions on the carcase to identify how carcases respond to muscle shortening, aging and collagen content. This will allow processors to adapt new methods to allow for the production of more tender lamb.

Meat tenderness is known to be affected by sarcomere length (SL), proteolysis and collagen content (CC). Sixty lambs were slaughtered and the Longissimus muscle was sampled. Samples for shear force (SF), SL, proteolysis indicators (desmin degradation, particle size: PS) and CC were taken after the allotted ageing periods (1, 7, and 14 days). PS, explained a large part of the variation in shear force (approximately 34%) when modelled across ageing periods. Other factors (CC, SL) combined with proteolysis indicators (PS, desmin degradation) explained just under 40% of the variation in shear force. Within ageing periods SL explained a small, but significant, part of the variation in shear force after 14 days of ageing (8%) and at day 1 of ageing desmin degradation explained 17% of the variation in shear force. Methods to improve the tenderness of lamb longissimus muscle should focus on increasing the extent of post-mortem proteolysis, when processing conditions are sufficient to prevent muscle fibre shortening.

Context. The texture of beef is highly important for the eating experience, and there is a continued interest in understanding the biochemical basis for the variation in texture between cattle and their meat cuts in order to improve and minimise variation in tenderness due to production and processing factors.

Aims. The present study aimed to investigate the impact of characteristics of meat on Warner-Bratzler shear-force (WBSF) as an indicator of texture of beef as affected by breed type, age/feeding phase, and muscle.

Methods. Seventy-five steers of three breed types (Angus, Hereford and Wagyu x Angus) were slaughtered after weaning 6 months old (n = 15), after backgrounding 17 months old (n = 30) and after feedlotting 25 months old (n = 30). At slaughter three muscles (M. supraspinatus, M. semitendinosus and M. longissimus lumborum) were sampled from each steer, and pH, intramuscular fat and collagen content, sarcomere length, and proteolysis (desmin degradation) were measured and used to explain the variation in WBSF after 7 and 14 days of aging.

Key results. Meat from Hereford and Angus steers had higher WBSF after 7 days of aging compared with Wagyu x Angus steers, but after 14 days of aging there was only a difference between Hereford and Wagyu x Angus in the M. supraspinatus and M. semitendinosus. The WBSF of the young weaned steers and steers slaughtered after backgrounding were dependent on the degree of proteolysis in the muscles, whereas for steers slaughtered after feedlotting the content of collagen was more important for the WBSF. The amount of intramuscular fat had a significant impact on the differences in WBSF within the specific muscle studied. In contrast to the general dogma that WBSF increase with age, WBSF decreased in M. semitendinosus and M. longissimus lumborum from the weaned 6-month-old steers to the 25-month-old steers finished in feed-lot, whereas in M. supraspinatus the older feed-lot finished steers had a higher WBSF.

Conclusion. The factors contributing to the Warner-Bratzler shear force of beef depends on the age/feeding phase of the animal and the muscle and less on the breed type. Implications. Optimisation of texture in beef through breeding and production should address different traits dependent on the age/feeding phase of the slaughter animal.

Implications. Optimisation of texture in beef through breeding and production should address different traits dependent on the age/feeding phase of the slaughter animal.

The longissimus, (n = 118) (LL), semimembranosus (n = 104) (SM) and biceps femoris (n = 134) (BF) muscles were collected from lamb and sheep carcases and aged for 5 days (LL and SM) and 14 days (BF) to study the impact of muscle characteristics on tenderness as assessed by shear force (SF) and sensory evaluation. The impact of gender, animal age, collagen content, sarcomere length (SL), desmin degradation, ultimate pH and intramuscular fat (IMF) on tenderness was examined. The main factors which influenced SF of the LL were IMF, SL and desmin degradation, but for sensory tenderness, IMF, ultimate pH and gender were the main factors. The SF and sensory tenderness of the SM was best predicted by the degree of desmin degradation. For the BF-soluble collagen and animal age both influenced SF. Different factors affect tenderness across muscles and not one prediction model applied across all muscles equally well.