Screening of biogenic amines production by bacteria isolated from "pecorino" cheese

Biogenic amines (BA) are naturally present in many foods and beverages, especially fermented ones. Due to their toxicity, high levels of BAs in food can be a health risk. In cheese the most abundant amine is tyramine (TYR) which is the main cause of the so-called “cheese reaction”. BAs presence in food is mainly caused by aminoacids decarboxylating bacteria. Aim of the study is toevaluate BAs in vitro production by bacteria isolated from a medium-ripened “pecorino” cheese.Materials and Methods: 72 strains of potential BAs producers (Enterococci (Ec), Enterobacteriaceae (Eb) and mesophilic lactobacilli (Lb)) were isolated during the cheesemaking and the ripening phases of a “pecorino” cheese, manufactured in a dairy factory in Tuscany. Ec (34) and Lb (28) were identified by PCR [1,2,3,4], Eb (10) were identified by API 20E kit (Biomérieux). After 72h incubation in a decarboxylase broth added with 1% w/v of the precursor aminoacids, the production of 7 BAs (triptamine, 2-phenylethylamine (2PHE), putrescine (PUT), cadaverine (CAD), histamine, TYR, spermidine, spermine) was quantified on the acid extract of the cultural medium by HPLC analysis as described in a previous study [5]. All the strain tested produced BAs although in varying degrees. Overall our data on BAs production by the different microbial groups agree with previous studies [6,7,8,9]. Eb were confirmed as good PUT and CAD producers, both for number of decarboxylating strains (100% and 90% respectively) and for BAs concentrations (on average 341 and 785 µg/ml, respectively). All Ec strains produced TYR, with very high mean amounts (1608µg/ml), and many of them gave not negligible 2PHE, PUT and CAD production (on average 184, 121 and 146 µg/ml, respectively). These data agree with Ladero et al. [10] hypothesis that TYR production is genomic trait of E. faecium and E. faecalis species. On the other hand the same Authors speculated that PUT is a genomic trait of E. faecalis, while in our study 50% of the tested strains of this species showed no detectable PUT production. Indeed, other Authors reported PUT-negative strains of E. faecalis [6,9,11]. Strains that produce high amounts of BAs, although with a low prevalence, when growing to high cell counts can substantially contribute to BAs formation [9]. In view of this, it is noteworthy that, although our data confirm that Lb are overall not good BA producers, few Lb strains, isolated from pasteurized milk cheeses, produced very high amounts of TYR (810, 1766 and 1959 µg/ml). BA presence in cheeses is not solely associated with undesired bacterial groups (Eb, Ec), but technologically useful microorganisms, like Lb, could play a role in TYR accumulation in ripened cheeses, especially considering the high Lb loads reached and maintained throughout the ripening period.