Characterization of the Enterobacteriaceae isolated from an artisanal Italian ewe's cheese (Pecorino Abruzzese)

To evaluate some physiological characteristics of the Enterobacteriaceae isolated from Pecorino cheese. The production of organic acids, secondary volatile compounds, biogenic amines (BA) and the lipolytic and proteolytic activities of Citrobacter braakii, Enterobacter sakazakii, Escherichia coli, Kluyvera spp., Salmonella enterica ssp. arizonae and Serratia odorifera strains were determined in skim milk after 48 h of fermentation at 30°C. The proteolytic activity observed only in Ser. odorifera and Kluyvera spp. was confirmed by the peptide profiles of the pH 4·6-insoluble fraction using RP-HPLC; however, the lipase activity was evidenced in all the isolates of E. coli, Kluyvera spp. and Salm. enterica ssp. arizonae. During fermentation, all the strains utilized citric acid and produced significant quantities of putrescine followed by histamine, spermine and spermidine as well as acetic and lactic acid. Moreover, the major volatile compounds produced were ethanol, 2,3-butanedione, 3-hydroxy-2-butanone, 2-heptanone and acetone. The Enterobacteriaceae of dairy origin possess many metabolic activities that could affect the sensory quality of the cheese in which they grow during ripening. The important physiological characteristics possessed by Enterobacteriaceae confirm the complexity of the microbiota of Pecorino Abruzzese cheese, which influences the typical sensory properties of this product.