Genotype and age at slaughter influence the retail shelf-life of the loin and knuckle from sheep carcasses.

This study was conducted to determine the effect of genotype and age at slaughter (8, 14 and 22 months) on the retail display life of lamb chops [boneless loin (M. longissimus thoracis) and boneless leg steaks from the knuckle (M. rectus femoris)]. The genotypes represented were Poll Dorset Border Leicester Merino, Poll Dorset Merino, Merino Merino (M M) and Border Leicester Merino. The colour and retail shelf-life of lamb cuts were assessed objectively, using a HunterLab Miniscan, at 24 h postslaughter and at 0, 2 (midpoint of commercial retail display life) and 4 (endpoint of commercial retail display life) days for overwrapped product in a simulated retail display. M M had a higher ultimate pH (pHu) in the knuckle, but not the loin, at 8, 14 and 22 months of age relative to the other three genotypes. Generally, at 1 day postslaughter and over the 4 days of retail display, the loin from the M M genotype was lighter, less red and more brown with a lower oxymyoglobin:metmyoglobin (oxy:met) ratio, a faster time to discolouration and a higher percentage change in the oxy:met ratio during retail display. Conversely for the knuckle, the M M genotype was generally less brown (more red) and less yellow with a higher oxy:met ratio, a slower time to discolouration and a lower percentage change in the oxy:met ratio. There were few differences between the other genotypes in surface meat colour either at 1 day postslaughter or during retail display for either muscle. At 14 and 22 months of age, the loin was darker, redder and yellower with a higher oxy:met ratio relative to the previous age than meat from the 8- and 14-month-old sheep, respectively. In conclusion, the loin from Merinos was most susceptible to discolouration in retail display and thus would be least acceptable to the consumer. In spite of the higher pHu in the knuckle of the Merino genotype, the meat was less susceptible to discolouration during retail display compared with the other genotypes. [ABSTRACT FROM AUTHOR]