Graduate Thesis Or Dissertation
 

The effect of prerigor electrical stimulation pH decline, protein solubility and water holding capacity in beef muscles

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  • This study was designed to investigate the rate of pH decline, changes in protein solubility and in the water-holding capacity (WHC) of beef muscles subjected to pre-rigor electrical stimulation. Samples for the experiment were obtained from animals slaughtered at the Meat Science Laboratory, Oregon State University. Nine good quality steers were slaughtered, split longitudinally into sides and the left sides were electrically stimulated for 1 min (600 volts, 7 amps, 60 cycles per sec) within 30-40 min postmortem. Samples were removed from the semitendinosus (ST) and longissimus dorsi (LD) muscles of each side for the appropriate analyses at 1-, 2-, 4- and 24-hr postmortem intervals. Immediately following electrical stimulation, pH of the treated samples of both muscles was significantly lower (P < 0.01) than their respective controls. Similar differences were also noted at 2 and 4 hr postmortem. At 24 hr postmortem, the pH of the stimulated and control samples of ST muscle were essentially equal, whereas the pH of the stimulated LD muscles was significantly lower (P < 0.05) than the controls. WHC measurements revealed that electrical stimulation had no effect on the treated samples of ST muscles. The stimulated LD muscles had significantly lower (_P < 0.05). WHC values than the controls during the first 2 hr postmortem. However, the differences were not significant at 4 and 24 hr postmortem. Initially, the solubility values of the sarcoplasmic porteins of the stimulated samples of both muscles were significantly higher (P < 0.05) than their controls. At 24 hr postmortem, sarcoplasmic protein solubility values were equal for both the stimulated and control samples of the ST muscles, whereas those of the stimulated LD muscles were significantly lower (P < 0.1) than the controls. The solubility values of the myofibrillar proteins of the stimulated samples of both the ST and LD muscles were significantly (P < Q.05) lower than the controls at 1 and 2 hr postmortem. At 4 and 24 hr postmortem, solubility of the myofibrillar proteins of the stimulated ST muscles had increased but not significantly. At 24 hr postmortem, myofibrillar protein solubility values of the stimulated LD muscle samples were significantly (P < 0.1) higher than the controls. Solubility values of the salt-soluble proteins were lower in the stimulated samples than in the controls of both muscles during the 24 hr postmortem test period. At 4 and 24 hr postmortem, solubilities of the stimulated ST and LD muscles samples were significantly less, P < 0.05 and P < 0.01, than their respective controls. Data of this study show that electrical stimulation of beef muscles results in an accelerated rate of pH decline and a substantial reduction in the solubility of the myofibrillar proteins during the first 2 hr postmortem. During this interval, however, the WHC and the solubility of the salt-soluble proteins of the stimulated muscles are at higher levels than at later postmortem times. In fact, solubility of the salt-souble proteins of the stimulated muscles was markedly reduced at the 4 and 24 hr sampling times. These data suggest that if electrically stimulated beef is to be used in the production of processed meat products it should be utilized within 1 to 2 hr post stimulation when the WHC and the solubility of the salt-soluble proteins are at their peak levels.
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