Pre-rigor conditions in beef under varying temperature- and pH-falls studied with rigometer, NMR and NIR

Beef, M. longissimus dorsi (LD), were subjected to three different glycolytic rates during rigor (fast: pH 5.6, 4-5 h; medium: pH 5.6, 12 h; slow: pH 5.6, 20 h) combined with two chilling regimes (20 degrees C, 5 h; 12 degrees C, 5 h), in a 3*2 factorial experimental design with three replicates. Spectroscopic techniques, such as pulsed low-field nuclear magnetic resonance (NMR) and near infrared (NIR), were used together with pH, shortening (SH) and isometric tension (IT) measurements to characterise the meat during the development of rigor. Based mainly on interpretation of the NMR measurements it is demonstrated that meat with the fastest pH drop during rigor created larger extracellular volumes and cell membranes were destroyed, giving rise to a leakage of sarcoplasmic proteins at an earlier stage of the rigor process compared to meat subjected to a slower pH drop. The fast pH group yielded the most tender meat, measured as W-B shear values, at fully developed rigor, although shortening was among the highest for this group. The reason for the superior tenderness of the fast pH group is suggested to be caused by a quicker and a more substantial proteolytic breakdown for this type of meat compared to the more slowly glycolysing muscles. The multivariate studies of the spectroscopic data revealed a close relationship between the NMR measurements and pH. Indications of an inverse correlation between cooking loss and W-B values was observed. NIR spectroscopy revealed only little variation and no consequent relation to the physico-chemical parameters (C) 2000 Elsevier Science Ltd. All rights reserved.