Effect of Genotype, Age at Slaughter, Aging Temperature and Aging Duration on Meat Toughning of Beef Produced from Arsi, Borena, Harar and Cross of Holstein Friesian with Arsi Cattle Breeds

The study was conducted to evaluate the effect of genotype, age at slaughter, aging temperatu re and aging duration on meat toughning of beef produced from Arsi, Borena, Harar and cro ss of Holstein Friesian with Arsi cattle breeds. A total of 24 bulls from Arsi (6), Borana (6), Harar (6) and crossbreed of HF breeds (6) were used for this study. The bulls were stratified into two age groups 2 - 3 and 4 - 5 years. Temperature and pH were recorded at 45 min, 3, 6, 12 and 24 hours on semitendinosus muscle. Blood sample was collected to determine glucose and insulin level. Fat thickness was measured at p8 position by using mm. Meat samples from semitendinosus muscle collected to determine tenderness, water holding capacity and colour (L* , a * , b* ). The meat samples were packed in vacuum-seal and aged 6, 7 at room and 7, 14 and 21 days chilled room respectively. Instrumental tenderness was evaluated using Warner Bratzler Shear Force Device while Mini Scan EZ machine (model number - 4500L) used to determine color. The results of the study revealed that total heat toughening condition for carcass kept under room temperature post slaughter 24 hours was 12.5% while for carcass kept in chilling condition was 4.2%. The proportion of heat toughening for carcass kept under room temperature post slaughter 24 hours differ numerically between breed and ages with higher proportion for Arsi (8.3%) breed and lower proportion for Harar (0%) breed. Age group 2 - 3 year had exhibited no heat toughening while 4 - 5 year exhibited 12.5%. Chilling carcass minimized heat toughening to zero for all breeds except HF crossbreed (4.2%). The value of glucose, insulin and insulin resistance (IR) of the studied cattle breeds were significantly (p < 0.05) different between breeds. Age groups had affected the level of glucose with higher level of glucose for older group over the young one. Similarly, interaction of age and breed had influenced insulin resistance. Arsi and Harar cattle had relatively higher insulin and insulin resistance over Borena and HF crossbreed. Breed, age and temperature in which carcass were kept post slaughter 24 hrs significantly affected the Warner Bratzler Shear Force (WBSF) . Semitendinosus muscle from Borena and Harar bulls were tender than the muscle from Arsi and crossbreed of HF. Samples kept at chilling temperature were tender than beef kept at room temperature. Beef from younger bulls were tender than from older ones. WHC of meat samples kept at room temperature (62.83-73.2) post slaughter 24 hours were lower than samples kept at chilling room (69.2-73.33). In conclusion, keeping carcass in chilling environment post 24 hours and using younger bulls for meat improve eating quality of the beef by minimizing heat toughening condition. It was recommended that awareness need to be created for abattoir workers and butchers in Ethiopia on the importance of keeping carcass in chilled temperature post slaughter 24 hours to improve eating quality of beef. Further study is suggested to investigate the effect of chill temperature on microbial quality of beef