title: Electrical measurement for detecting early postmortem changes in porcine muscle.
abstract: Use of electrical measurements to detect quality defects in porcine muscle in the early postmortem period was evaluated. Justification for use of a tetrapolar, constant current electrode configuration instead of bipolar electrodes was provided for measurements at low frequencies. Interrelationships among electrical properties, pH values, ATP decline, temperature, time postmortem, and final water-holding capacity (WHC) of porcine muscle were quantified using 25 hogs. Immediately after exsanguination, a section of the left longissimus muscle (LM) was excised to obtain rigor shortening patterns and complex impedance measurements over a 10-h period at 37 degrees C. Complex impedance measurements were taken using a tetrapolar electrode configuration at 1 kHz and .156 mA. At 15, 45, and 90 min postmortem, pH, ATP/IMP absorbance (R), and conductivity measured by the Tecpro Pork Quality Meter (PQM) were measured on the right side LM. At 24 h postmortem, WHC, pH, R, PQM, Hunter Color Lab values, and subjective quality scores were evaluated on the left 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 min were different (P < .05) but pH at 24 h was not different between the normal and abnormal groups. Onset and completion of rigor were more rapid in carcasses with low WHC (P < .05). The PQM values were greater (P < .05) in the abnormal group at 90 min and 24 h postmortem. Excised muscle measurements of relative impedance (Z*) and phase (theta*) showed Z* and theta* increased more rapidly within the first 15 min postmortem (P < .1) for samples with abnormal WHC. However, one PSE carcass showed an immediate rapid decrease in Z* and theta*. Results suggest 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.
authors.affiliation: Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Whitman
authors.forename: J C
authors.initials: JC
authors.lastname: Forrest
authors.forename: M T
authors.initials: MT
authors.lastname: Morgan
authors.forename: M R
authors.initials: MR
authors.lastname: Okos
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D001823:Body Composition / Q000502:physiology*; D001834:Body Water; D017097:Electric Impedance; D004566:Electrodes; D005524:Food Technology / Q000379:methods; D006863:Hydrogen-Ion Concentration; D008460:Meat / Q000592:standards; D018482:Muscle, Skeletal / Q000737:chemistry / Q000502:physiology*; D011180:Postmortem Changes; D013552:Swine / Q000502:physiology*
chemical_list: D000255:Adenosine Triphosphate