Date of Award
Doctor of Philosophy
Food Science and Human Nutrition
Dennis G. Olson
Classical plate counting methods often understate the number of microorganisms when compared with counts made by direct microscopic examination or other methods. In addition, classical plate counting take days to obtain results because of the incubation time. The present study was undertaken to determine the possibility of developing a rapid method for bacterial enumeration based on the examination of muramic acid in pork and beef under both aerobic and anaerobic storage conditions. The muramic acid was measured by a technique in which lactic acid is released from muramic acid molecule followed by the reaction of the lactic acid with p-hydroxydiphenyl and CuSO[subscript]4;When comparing total bacterial numbers with amounts of muramic acid a correlation factor of 0.98 was found for pork stored under aerobic conditions. For pork stored under anaerobic conditions a correlation factor of 0.84 was found. No correlation was found in both beef treatments. On the average, the test predicts total bacterial counts but a single value is not overly reliable. In both pork and beef stored under vacuum-packaging conditions the amounts of muramic acid were twice as large as those found in both pork and beef stored under aerobic conditions. This could be explained by the fact that in vacuum-packaged meats a different bacterial flora predominates;In the second part of this study a rapid method for the evaluation of meat freshness based on the content of the amine cadaverine was developed. For the analysis of cadaverine the samples were derivatized with dabsyl chloride and plated on C18 TLC plates using ethanol:water:acetic acid (65:35:1) as solvent. After the plates were developed the cadaverine spots were measured on a Kontes scanner 800 densitometer equipped with a 425nm filter to measure visible yellow spots. The method can replace the microbiological methods which require at least 48 hours of incubation time and which are also too lengthy and expensive for meat processing firms. In addition the test developed only takes about two hours to complete. In the present study, meat freshness as assayed by the content of cadaverine versus total bacterial numbers throughout aerobic chilled storage of commercial pork, beef, and turkey was studied. In pork loins we found a correlation factor of 0.95 for cadaverine and total bacterial counts. Cadaverine levels ranged from about 60 ug/cm[superscript]2 to about 280 ug/cm[superscript]2. On the other samples we found excellent correlation between cadaverine and total counts on both beef rounds and beef loins (0.95). Our lowest correlation was found on turkey breast meat (0.87). These results suggest that cadaverine has an excellent potential as a quality indicator not only in pork but also in beef and turkey.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Carlos Ivan Lebron
Lebron, Carlos Ivan, "Rapid method for detection of muramic acid and cadaverine as indicators of microbial load on fresh meats " (1992). Retrospective Theses and Dissertations. 10293.