Effects of stress and high voltage electrical stimulation on tenderness oflamb m. longissimus

This study was conducted to investigate the reported effect of pre-slaughte r stress on meat tenderness independent from its effect on ultimate pH, and its interaction with electrical stimulation. From a group of 80 Coopworth lamb, 40 were stressed by subjecting the animals to a swim wash 3 h before slaughter and the use of dogs to assemble the animals to the access ramp of the abbatoir. Half of the carcasses of each group was electrically stimula ted within 30 min post mortem. Temperature and pH decline of the longissimu s was monitored and shear force of the cooked muscle was determined at 2 da ys post mortem and after 6 weeks vacuum storage at 1 degreesC. To investiga te an effect of stress independent of ultimate pH, 10 muscles with an ultim ate pH below 5.8 were selected from each group for detailed analysis. This analysis consisted of determination of calpastatin activity and sarcomere l ength, and immunoblotting of mu -calpain and calpain substrates. The stress treatment led to an increase in the number of muscles with an ultimate pH above 5.8 (32.5 vs 15%), and muscles with an ultimate pH above 5.8 were sig nificantly tougher than muscles with an ultimate pH below 5.8 at 2 days pos t mortem. Electrical stimulation improved tenderness at two days post morte m. This effect could be attributed to an effect on muscle contraction, but not on post mortem proteolysis of calpain substrates. A large variation in tenderness at 2 days post mortem was observed and this was not reduced by e lectrical stimulation. Six weeks of vacuum storage resulted in a 6 kgF drop in mean shear force and a uniformly tender product. Despite the fact that the stress treatment was similar to those in earlier studies, we failed to observe an effect of stress independent of ultimate pH on tenderness. The r eason for this is unclear, but differences in the response to stress betwee n breeds may be responsible. The results of the present study underscore th e importance of minimizing pre-slaughter stress and adequate post mortem st orage for meat quality. (C) 2000 Elsevier Science Ltd. All rights reserved.