Beef tenderness evaluation using early post-mortem muscle nanostructure

Objective: Tenderness is believed to start immediately after slaughter, but there is little work that directly links tenderness to the muscle nanostructure early post-mortem. This study attempted early diagnosis of meat tenderness using muscle nanostructure at approximately 45 minutes and 24 hours post-slaughter. Methods: Carcass intrinsic factors (carcass mass, muscle pH, and temperature) were measured at 45 minutes and 24 hours post-slaughter on 52 A2-class beef carcasses from Bonsmara, Beefmaster, Hereford and Simbra steers. The muscle nanostructure (myofibril diameter [MYD], myofibril spacing [MYS], muscle fibre diameter [MFD], muscle fibre spacing [MFS], and sarcomere length [SL]) was also analysed at 45 mins and 24 hrs post-slaughter on 20 representative longissimus samples using a scanning electron microscope, while tenderness was measured using Warner Bratzler shear force (WBSF). Results: At 45 mins post-slaughter breed affected MYD and MYS while it also affected MFD and MFS at 24 hours. While pH 24 affected MYD and MYS; muscle Temp 45mins affected MYD, MFD, and MFS; and Temp 24hrs affected MYD; WBSF and SL were not affected by these factors. WBSF negatively correlated with pH 0 , MFD, and SL at 45 mins post-slaughter, while it positively correlated with MYD, MYS, MFS, warm carcass mass, and Temp 45mins . At 24 hours post-slaughter, WBSF had linear negative correlations with MYS, MFS, MFD, and SL, with WBSF decreasing as these muscle nanostructure components increased, thus enhancing tenderness. Meat tenderness was further enhanced by the muscle fibre bundle characteristics which include longer, visible, and finer muscle grain. Conclusion: Muscle tenderness is enhanced by muscle fibre bundle characteristics at approximately 24 hours post-slaughter. However, the myofibrillar structure at 45 mins post-slaughter can be a good predictor of the required ageing period for individual breeds to further enhance tenderness.