Heat-resistant spore-forming bacteria such as Bacillus and Clostridium can survive and grow in cooked potato products. This situation represents both a public health problem and an economic problem. The natural food preservative nisin is used in heat-treated foods to prevent the growth of such bacteria. A cocktail of Clostridium sporogenes and Clostridium tyrobutyricum spores was inoculated into cooked mashed potatoes, which were vacuum packed, pasteurized, and incubated at 8 and 25 degrees C. The shelf life of the mashed potatoes at 25 degrees C was extended by at least 58 days with the addition 6.25 microg of nisin per g. At 8 degrees C, in control samples not containing nisin, the natural contaminant Bacillus grew, but the inoculated Clostridium strains did not until the temperature was raised to 20 degrees C after 39 days. No bacterial growth occurred in nisin-containing samples. The shelf life of the mashed potatoes was extended by at least 30 days with 6.25 microg of nisin per g. In trials involving a cocktail of Bacillus cereus and Bacillus subtilis strains, 6.25 microg of nisin per g extended the shelf life of mashed potato samples that were not vacuum packed by at least 27 days at 8 degrees C. At 25 degrees C, 25 microg of nisin per g extended shelf life by a similar period. Shelf life extension was also observed at lower nisin levels. Microbiological analysis of the mashed potato ingredients showed that a high spore level was associated with the onion powder. It is emphasized that the preservative and the ingredients must be well mixed to ensure good nisin efficacy. Nisin remained at effective levels after pasteurization, and good retention was observed throughout the shelf life of the mashed potatoes.
Aims: To assess the antimicrobial efficacy of ascopyrone P (APP), a secondary metabolite formed by the fungi Anthracobia melaloma, Plicaria anthracina, Plic. leiocarpa and Peziza petersi belonging to the order Pezizales. Methods and Results:In vitro testing using a well diffusion procedure showed that APP at a high concentration (approximately 5%) inhibited the growth of Gram‐positive and Gram‐negative bacteria. Using an automated microbiology reader, growth curve analysis showed that 2000–4000 mg l−1 APP caused total or significant bacterial inhibition after incubation for 24 h at 30°C. Against certain yeast strains, 1000– 2000 mg l−1 APP enhanced growth, although at higher concentrations inhibition of some yeasts was observed. Clostridium and fungal strains were not sensitive to 2000 mg l−1 APP. No significant cidal effect was observed after 2 h against Listeria monocytogenes or Escherichia coli. Results were identical whether the APP samples tested had been produced enzymatically or chemically. Conclusions: At a level of 2000 mg l−1, APP demonstrated growth inhibitory activity against a broad range of bacteria, but not yeasts or moulds. Significance and Impact of the Study: A possible application for this novel natural antimicrobial is in food preservation, to control the growth of Gram‐negative and Gram‐positive bacteria in raw and cooked foods. Effective dosage levels would be 500–4000 mg kg−1, depending on food type. The efficacy, organoleptic and safety aspects of this compound in food still need to be assessed.
The last 25 years have witnessed a growing support for and recognition of the importance of nursing theory, both in education and practice. This paper seeks to explore this movement, and also the issues in theory development, study and application. Definitions of theory are reviewed, and linked to the purpose of theory and theory development in nursing. The origins and motivation for developing nursing theory are identified, and arguments for the use of theory in nursing are raised. Further questions from the discussion of these issues are identified, questions likely to provide continued debate and investigation within the profession for decades to come.
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