EXTRACT RELEASE VOLUME (ERV) RESPONSES WITH ASEPTIC AND INOCULATED PORK

SUMMARY– The extract-release volume (ERV) phenomenon, previously reported as a reliable rapid indicator of bacterial spoilage in meat, was observed for pork muscle obtained aseptically and for that inoculated with pure and mixed cultures of bacteria over a 20-day storage period at 2° and 10°C. ERV values obtained using pork longissimus dorsi muscle were found to be inversely related to bacterial numbers regardless of population type (homogeneous or heterogeneous) of the microorganisms. The correlations between ERV and bacterial numbers did not denote reliable prediction of the bacteriological quality of pork by ERV. Under conditions of mixed culture sample contamination the correlation between ERV and bacterial numbers was much higher than for pure culture sample contamination with psychrophilic, anaerobic, or acid-producing bacteria. Minor initial differences in ERV between control (aseptic) and inoculated samples indicated that ERV responded to growth of the bacteria rather than to their presence per se. Differences in ERV that were attributable to sample source (animal differences) by analysis of variance test indicated there was a wide range of hydration capacities in pork longissimus dorsi muscle samples. This disparity minimized the significance of the influence of bacterial growth on the ERV response for practical applications. Contrary to the usual ERV response observed with meat spoiled under refrigerator conditions, ERV was found to increase with storage time and bacterial growth when pork was contaminated with a putrefactive anaerobe (Clostridium perfringens) and stored at 35°C. Though pH appeared to influence the magnitude of the changes observed in ERV, decreases in ERV with bacterial growth or storage time could not be explained solely as a pH effect.