Modeling the aminogenic potential of Enterococcus faecalis EF37 in dry fermented sausages through chemical and molecular approaches.
ABSTRACT Amino acid decarboxylase activity of the Enterococcus faecalis strain EF37 was monitored during fermentation and ripening of a traditional dry fermented sausage from Northern Italy (Salame Veronese) by means of microbiological, chemical, and molecular approaches in relation to three technological factors: fermentation temperature, sodium chloride concentration, and amount of glucose added to the meat mixture. Besides the analytical determination of tyramine and phenylethylamine accumulation and the counts of enterococci, the presence and quantification of the tyrosine decarboxylase gene (tdc) and its mRNA transcript were also investigated by using real-time PCR. According to the mathematical models obtained, all of the three factors studied were statistically significant and microbiologically relevant for the early development of enterococci, although the fermentation temperature had a more relevant influence on the enterococcal viable cells of the ripened product. Sodium chloride concentration was the most determinant factor of the final tyramine and 2-phenylethylamine accumulation and also of the levels of tdc present in the final product. In contrast, an effect of glucose concentration on tdc expression was observed in the last period of ripening. Moreover, increasing amounts of sodium chloride and decreasing fermentation temperature resulted in a reduced tdc expression. This is the first time that bacterial tyrosine decarboxylase potential is directly examined through a molecular approach in a fermented meat. The quantification of tdc and its transcript can help to elucidate the critical steps and factors during food manufacturing at which bacterial aminogenesis is possible, thus allowing researchers to propose technological measures to control decarboxylase activities.
[show abstract] [hide abstract]
ABSTRACT: The genus Enterococcus is the most controversial group of lactic acid bacteria. Studies on the microbiota of many traditional cheeses in the Mediterranean countries have indicated that enterococci play an important role in the ripening of these cheeses, probably through proteolysis, lipolysis, and citrate breakdown, hence contributing to their typical taste and flavour. Enterococci are also present in other fermented foods, such as sausages and olives. However, their role in these products has not been fully elucidated. Furthermore, the production of bacteriocins by enterococci is well documented. Moreover, enterococci are nowadays used as probiotics. At the same time, however, enterococci have been associated with a number of human infections. Several virulence factors have been described and the number of vancomycin-resistant enterococci is increasing. The controversial nature of enterococci has prompted an enormous increase in scientific papers and reviews in recent years, where researchers have been divided into two groups, namely pro and contra enterococci. To the authors' impression, the negative traits have been focused on very extensively. The aim of the present review is to give a balanced overview of both beneficial and virulence features of this divisive group of microorganisms, because it is only acquaintance with both sides that may allow their safe exploitation as starter cultures or co-cultures.International Journal of Food Microbiology 02/2006; 106(1):1-24. · 3.33 Impact Factor