The effect of growth rate and ultimate pH on meat quality of lambs

Entire male Romney lambs (n = 60) were grown slowly (67 g/day) and slaughtered at 14 months of age at an anticipated carcass weight of 18 kg. Another group of ram lambs (n = 15) from the same genetic background (born 7 months later) were grown rapidly (162 g/day) for 7 months and slaughtered at the same time and at a similar carcass weight. Preslaughter shearing (20 days prior to slaughter) and swim washing (3 times) were variously imposed upon the 14-month old lambs to give them a graded preslaughter stress. The lambs were head-only electrically stunned and slaughtered. Dressed carcasses were electrically stimulated at 20 min post mortem for 90 s at 14·3 pulses/s, 1·8-2 A and 1130 V peak, then held at 12°C for 2 h and frozen so that the deep leg reached -4°C in 12 h. The ultimate pH was measured for the longissimus dorsi, and loin samples were assessed by tenderometer and a sensory panel. The groups with the greatest stresses imposed had the highest ultimate pH. The most tender meat came either from carcasses with an ultimate high pH greater than 6·3 or from young lambs with an ultimate pH from 5·5-5·7. While 7-month old lambs were slightly more tender than the 14-month old lambs of iso pH, the 14-month old lambs of high pH were the most tender. This suggests that age-related connective tissue effects were minimal for the loin. The shear force values and taste panel tenderness scores were linearly related. When the shear force and panellists' tenderness scores were expressed in relation to ultimate pH, there was a decreased acceptance of meat with a moderate ultimate pH between 5·8 and 6·0. Panel texture assessments showed a less clearly defined, but statistically significant decrease in acceptance at pH 5·8-6·0. Other sensory attributes of flavour, juiciness and aroma were uniform across the whole ultimate pH spectrum.