title: Characterisation of the Thermostable Protease AprX in Strains ofPseudomonas Fluorescensand Impact on the Shelf-life of Dairy Products: Preliminary Results.
abstract: Bacterial proteases are involved in food spoilage and shelf-life reduction. Among the bacterial proteases, a predominant role in spoilage of dairy products seems to be played by the thermostable metallo-protease AprX, which is produced by various strains ofPseudomonas fluorescens. Differences in AprX enzyme activity among different strains were highlighted, but the most proteolytic strains were not identified. In this study, the presence of theaprXgene was evaluated in 69 strains isolated from food matrices and 18 reference strains belonging to theP. fluorescensgroup, which had been previously typed by the multi locus sequence typing method. Subsequently, a subset of reference strains was inoculated in ultra-high temperature milk, and the expression of theaprXgene was evaluated at 22 and 6°C. On the same milk samples, the proteolytic activity was then evaluated through Azocasein and trinitrobenzenesulfonic acid solution assays. Finally, to assess the applicability of the former assay directly on dairy products the proteolityc activity was tested on industrialricottasamples using the Azocasein assay. These results demonstrate the spread ofaprXgene in most strains tested and the applicability of Azocasein assay to monitor the proteolytic activity in dairy products.
authors.affiliation: Department of Comparative Biomedicine and Food Science, University of Padua , Legnaro (PD), Italy.
authors.forename: Nadia Andrea
authors.initials: NA
authors.lastname: Andreani
authors.affiliation: Department of Comparative Biomedicine and Food Science, University of Padua , Legnaro (PD), Italy.
authors.forename: Lisa
authors.initials: L
authors.lastname: Carraro
authors.affiliation: Department of Comparative Biomedicine and Food Science, University of Padua , Legnaro (PD), Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Fasolato
authors.affiliation: Department of Comparative Biomedicine and Food Science, University of Padua , Legnaro (PD), Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Balzan
authors.affiliation: Institute for Experimental Veterinary Medicine of Venezie , Legnaro (PD), Italy.
authors.forename: Rosaria
authors.initials: R
authors.lastname: Lucchini
authors.affiliation: Department of Comparative Biomedicine and Food Science, University of Padua , Legnaro (PD), Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Novelli
authors.affiliation: Department of Comparative Biomedicine and Food Science, University of Padua , Legnaro (PD), Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Cardazzo
keywords: AprX; Dairy products; Pseudomonas fluorescens; Spoilage