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Modeling the Aminogenic Potential of Enterococcus faecalis EF37 in Dry Fermented Sausages through Chemical and Molecular Approaches

Dipartimento di Scienze degli Alimenti, Università degli Studi di Bologna, Piazza Goidanich 60, 47023 Cesena, Italy,¹ Institute for Food and Agricultural Research and Technology, Food Technology, Finca Camps i Armet, 17121 Monells, Spain,² Dipartimento di Scienze degli Alimenti, Università degli Studi di Teramo, Via C.R. Lerici 1, 64023 Mosciano Stazione, Teramo, Italy,³ Dipartimento di Scienze, Tecnologie e Mercati della Vite e del Vino, Università degli Studi di Verona, Via della Pieve 70, 37029 San Floriano, Verona, Italy⁴

Received 5 October 2007/ Accepted 10 February 2008

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.

Published ahead of print on 22 February 2008.