Proteolytic activity of Staphylococcus xylosus strains on pork myofibrillar and sarcoplasmic proteins and use of selected strains in the production of “Naples type” salami.

The aim of this study was to determine the proteolytic activities of Staphylococcus xylosus strains on sarcoplasmic and myofibrillar proteins in order to evaluate the suitability of selected strains as starter cultures in the processing of a dry fermented pork sausage. The proteolytic activity of 27 strains of Staphylococcus xylosus on sarcoplasmic and myofibrillar proteins was determined by agar plate method, o-phtaldialdehyde (OPA) spectrophotometric assay and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Four strains were selected for the formulation of six starter cultures to use in the production of `Naples type' salami. The proteolytic contribution of starters was determined by SDS-PAGE, comparing the protein pro®le of inoculated sausages with that of uninoculated sausages after 0, 15 and 33 days of ripening. The results showed that the proteolytic activity of some strains, determined by the agar plate method, were not confirmed by electrophoretic and spectrophotometric assays. In fact, of 24 strains of Staphylococcus xylosus able to hydrolyse muscle protein extracts on agar plate, only 12 strains were shown to change SDS-PAGE profile of pork proteins. The SDS-PAGE pro®le of sarcoplasmic proteins extracted from all sausages showed that the major changes were produced with starters S3, S4 and S5 after 15 days of ripening. Also myo®brillar proteins undergo major changes after 15 days of ripening and the protein pro®les showed the same pattern in all samples, except for the sausages produced with starter S4. The results of this work showed that the muscle protein extracts hydrolysis test is suitable for preliminary screening of Staphylococcus xylosus strains on the basis of their proteolytic activity. However, evaluation of muscle protein hydrolysis in a food model system could then be more appropriate for selecting micro-organisms for use as starter cultures for fermented sausages. The potential of the findings is discussed with reference to the formulation of starter cultures for the dry fermented sausages production.