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 survival of five inoculated Listeria monocytogenes strains (DCS 31, DCS 184, AT3E, HT4E, and HR5E) was studied in dry fermented sausages prepared using two different starter cultures (starter A and B) with or without a protective Lactobacillus plantarum DDEN 2205 strain. L. monocytogenes was detected throughout ripening in every sausage sample in which the L. plantarum DDEN 2205 strain had not been used. The use of either starter A, with a high concentration of protective culture, or starter B, with a low concentration of protective culture, resulted in L. monocytogenes-negative sausages after 17 days of ripening. Differential survival was noted among the L. monocytogenes strains during fermentation. Strains AT3E and DCS 31 survived in sausages with protective cultures more often than did the other strains, whereas HT4E and HR5E were inhibited during ripening by all starter and protective cultures used. Protective cultures such as L. plantarum may be used as part of a hurdle strategy in dry sausage processing, but variations in susceptibility of different L. monocytogenes strains can create problems if other hurdles are not included.
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