ELECTRICAL MEASUREMENT FOR DETECTING EARLY POSTMORTEM CHANGES IN PORCINE MUSCLE

Use of electrical measurements to detect quality defects in porcine mu scle in the early postmortem period was evaluated. Justification for u se of a tetrapolar, constant current electrode configuration instead o f bipolar electrodes was provided for measurements at low frequencies. Interrelationships among electrical properties, pH values, ATP declin e, temperature, time postmortem, and final water-holding capacity (WHC ) of porcine muscle were quantified using 25 hogs. Immediately after e xsanguination, a section of the left longissimus muscle (LM) excised t o obtain rigor shortening patterns complex impedance measurements over a 10-h period at 37 degrees C. Complex impedance measurements were ta ken using a tetrapolar electrode configuration at 1 kHz and .156 mA. A t 15, 45, and 90 min postmortem, pH, ATP/IMP absorbance (R), and condu ctivity measured by the Tecpro Pork Quality Meter(R) (PQM) were measur ed on the right side LM. At 24 h postmortem, WHC, pH, R, PQM, Hunter C olor Lab values, and subjective quality scores were evaluated on the l eft LM. The WHC measurements were used to group carcasses into normal (n = 17) and abnormal (n = 8) categories. Mean pH and R at 45 and 90 m in were different (P < .05) but pH at 24 h was not different between t he normal and abnormal groups. Onset and completion of rigor were more rapid in carcasses with low WHC (P < .05). The PQM values were greate r (P < .05) in the abnormal group at 90 min and 24 h postmortem. Excis ed muscle measurements of relative impedance (Z) and phase (theta*) s howed Z and theta* increased more rapidly within the first 15 min pos tmortem (P < .1) for samples with abnormal WHC. However, one PSE carca ss showed an immediate rapid decrease in Z and theta*. Results sugges t measurement of rate of change of impedance and phase angle before 90 min postmortem would be a better prediction of ultimate quality than absolute magnitude of impedance.