Abstract
The objective of this study was to evaluate the effect of timing of electrical stimulation on free calcium concentration, calpain-2 activity, Warner-Bratzler shear force (WBSF), and consumer sensory analysis. Twenty-three beef steers were harvested and stimulated (S) using extra-low voltage or not stimulated (NS), at exsanguination and/or 1 h postmortem, resulting in 4 different stimulation treatments: NS-NS, NS-S, S-NS, or S-S. Samples were removed from the longissimus lumborum (LL) and semimembranosus (SM) for free calcium and calpain-2 analysis on days 1, 4, and 14 postmortem. WBSF and sensory analysis steaks were removed on day 4 and frozen (4 d) or aged to 14 d postmortem. Data were analyzed using the mixed model or generalized linear mixed model procedure of SAS (SAS Institute, Inc., Cary, NC), with significance determined at P < 0.05. There was a tendency for an aging-period-by-stimulation-treatment interaction for LL free calcium concentration (P = 0.05), and there was a significant difference between aging periods (P < 0.01). No difference was observed in free calcium concentration in the SM between stimulation treatments (P = 0.44); aging, however, significantly increased SM free calcium concentration (P < 0.01). Stimulation did not impact native calpain-2 activity in the LL (P = 0.71) or SM (P = 0.89). Stimulation treatment did not improve tenderness values for WBSF analysis for the LL (P = 0.69) or SM (P = 0.61) or consumer sensory analysis in the LL (P = 0.56) or SM (P = 0.36). A longer aging period tended to increase calpain-2 activity in the SM (P = 0.08), improve WBSF in the LL (P = 0.09), and significantly improve consumer tenderness scores in the SM (P < 0.01). In conclusion, the timing of electrical stimulation utilized in the current study tended to influence free calcium concentration in the LL but did not influence calpain-2 activity or beef tenderness. Aging, however, improved tenderness.
Highlights
Consumers have consistently reported that tenderness is the most important quality trait they consider when consuming beef (Koohmaraie and Gesink, 2006)
Significant differences were not seen between stimulation treatments on day 4 final pH in the longissimus lumborum (LL) (P = 0.06; Table 1) or SM (P = 0.47; Table 1)
There was a trend for an interaction between aging period and stimulation treatment for LL free calcium concentration (P = 0.05; Table 2)
Summary
Consumers have consistently reported that tenderness is the most important quality trait they consider when consuming beef (Koohmaraie and Gesink, 2006). It is believed that proteases play a major role in the tenderization phase and determine the overall level of postmortem myofibrillar protein breakdown, including desmin, C-protein, tropomyosin, troponin T, troponin I, titin, nebulin, vimentin, gelsolin, vinculin, and α-actinin (Goll et al, 1991; Huang and Forsberg, 1998). Fragmentation of these proteins disrupts sarcomere integrity and influences postmortem tenderization. Because of the role calpains play in improving product acceptability, it is necessary to research interventions that could be used to improve calpain activity, and tenderness
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