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The effect of electrical stimulation on some parameters of postmortem avian muscle Sundeen, Garfield Byron


Four studies were conducted to assess the use of electrical shock on several parameters of avian muscle that contribute to its ultimate quality. In the preliminary study, the effect of preslaughter electric stunning on the tenderness of broilers processed and handled in a standard commercial manner was assessed. The tenderness of cooked breast muscle samples was evaluated by Kramer single blade shear force values. This evaluation indicated that samples from the electrically stunned birds were significantly more tender than those from the no stun controls (p<0.01). The effects of varying the duration, frequency and voltage of a post-exsanguination stimulatory current on the development of rigor mortis and the postmortem glycolytic rate were investigated in Study One. The pH of muscle homogenates at various postmortem sampling times was used as an index of glycolysis whereas rigor development was monitored by the isometric tension technique. Postmortem glycolysis in Biceps femoris and Pectoral is major samples was accelerated by electrical stimulation, as was the time course of rigor development. Pectoral is major samples from treated carcasses required significantly less time to develop maximum tension than control samples (p<0.05). Although Biceps femoris samples from stimulated carcasses also exhibited decreases in the time required to achieve maximum tension when compared to controls, these differences were not significant. Pectoral is maj or samples from carcasses treated with 70V for 2 minutes at either 40 or 80 pulses/s developed significantly lower tension than control samples (p<0.05). No significant differences due to the voltage or total number of pulses were observed for either the time required to achieve maximum tension or the maximum tension developed. The influence of electrical stimulation on the development of rigor was further examined in Study Two. Rigor development again was monitored by the isometric tension technique and changes in metabolite contents for both muscle types were determined by enzymatic analytical techniques. Electrical stimulation reduced the time required by Biceps femoris and Pectoral is major samples to reach maximum tension but this decrease was only significant for the latter (p<0.05). The amount of isometric tension developed by both muscle types was similarly reduced by electrical stimulation. The initial glycogen and ATP contents of both muscles were reduced by electrical stimulation, as were their ATP contents at subsequent sampling periods. Several correlations between the parameters of isometric tension and metabolite contents were noted and regression equations were developed to express the significant relationships. No significant differences due to electrical stimulation in the rate of isometric tension release were observed, but Pectoralis major samples from stimulated carcasses released their developed tension more rapidly than their respective Biceps femoris samples. In the final study, Study Three, the effect of electrical stimulation on muscle proteolytic activity was assessed by two analytical methods for TCA soluble material. In addition, changes in protein extractability, dispersibility and hydrophobicity were followed in control and treated samples during storage for one day at 2°C. Electrical stimulation significantly reduced the time required to reach maximum tension (p<0.05) and decreased the maximum tension achieved for Pectoralis major and Biceps femoris muscle samples. Pectoralis major samples from treated carcasses again released their developed tension faster than their respective Biceps femoris samples. When the muscle samples were analysed for nonprotein nitrogen, neither measure indicated a significant treatment effect. In a similar manner, neither extractable protein, protein dispersibility nor protein hydrophobicity were affected by electrical stimulation.

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