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Some biochemical and ultrastructural changes in intact and sarcoplasmic reduced, bovine Longissimus dorsi muscle strips inoculated with Pseudomonas fragi Yada, Rickey Yoshio


Intact bovine Longissimus dovsi muscle was subjected to a mild washing procedure in order to reduce the concentration of the sarcoplasmic fluid. Intact and washed muscle samples were inoculated with Pseudomonas fragi to evaluate the effect of a sarcoplasmic reduction on bacterial growth and subsequent spoilage during storage at 4°C for 12 days. Aseptic controls were stored under similar conditions. Alterations in the water-soluble, salt-soluble, urea-soluble and urea-insoluble protein fractions, as well as the total carbohydrate, pH and bacterial numbers, were monitored in both intact and washed inoculated muscle samples. Scanning and transmission electron microscopy were employed to monitor ultrastructural changes on the muscle surface as a consequence of the growth of P. fragi. Analysis of water-soluble components (non-protein nitrogen, water-soluble proteins and carbohydrates) indicated that the washing procedure effectively removed the majority of these components. Increases in the extractability of the water-soluble and salt-soluble protein fractions were observed in the intact inoculated muscle sample. Alterations in the SDS-gel electrophoretic pattern of the water-soluble, salt-soluble, urea-soluble and urea-insoluble proteins were evident. Total carbohydrate decreased as a result of growth of P. fragi. An increase in pH of the intact muscle occurred as bacterial numbers increased. Significantly (P < 0.01) higher growth rates were observed on the intact muscle tissue than the washed muscle tissue. Relatively little change in the non-protein nitrogen, water-soluble and salt-soluble protein content was observed in the washed inoculated muscle tissue. A slight decrease in total carbohydrate was seen. Minor changes in the SDS-gel electrophoretograms of the salt-soluble proteins were apparent. Little change in pH of the washed inoculated sample occurred due to the growth of P. fragi. Scanning electron micrographs indicated that surface degradation of both intact and washed inoculated muscle samples were apparent only in areas of localized colonization. Glycocalyx appeared to mediate not only cell to cell attachment, but also cell to muscle surface adhesion. Bacteria were observed growing between muscle fibers. Transmission electron micrographs of intact inoculated muscle tissue confirmed the mediation of glycocalyx in bacterial adhesion. Cellular evaginations were present on the surface of the bacteria. Autolysis was minimal in both intact and washed aseptic muscle controls.

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