Characterization of Lactobacillus strains as functional starter cultures for the production of fermented Istrian sausage

Da bi se neki mikroorganizam mogao primijeniti kao funkcionalna starter kultura potrebno je prvenstveno provesti ispravnu taksonomsku identifikaciju. U ovom radu su stoga pomoću klasičnih mikrobioloških metoda i analizom fermentacijskih profila šećera, odabrani predstavnici bakterija iz roda Lactobacillus. Odabrani sojevi su identificirani pomoću PCR metode primjenom specifičnih početnica za determinaciju roda bakterija mliječne kiseline (BMK). Nakon ispravne taksonomske identifikacije potrebno je ispitati funkcionalne i tehnološke kriterije za starter kulture. Prilikom industrijske proizvodnje različitih fermentiranih proizvoda, starter kulture su često izložene različitim nepovoljnim uvjetima specifičnim za tehnološki proces proizvodnje, poput visokih koncentracija soli, promjena pH vrijednosti i temperature, te nedostupnosti kisika. Stoga je ispitan rast odabranih laktobacila pri različitim koncentracijama NaCl (1,6 %, 5 %, 10% i 15 %) u tekućoj MRS podlozi i različitim pH vrijednostima. Neophodno je provjeriti i sigurnost odabranih funkcionalnih starter kultura s aspekta širenja antibiotičke rezistencije, zbog čega je testirana osjetljivost sojeva na različite grupe antibiotika. Kao važno funkcionalno svojstvo, ispitano je antibakterijsko djelovanje odabranih laktobacila prema bakterijama, učestalim kontaminantima, prisutnim u hrani. Na temelju selekcijskih kriterija za funkcionalne starter kulture, od 50 autohtonih izolata BMK roda Lactobacillus, odabrani su sojevi Lb. fermentum 10, Lb. brevis 19, Lb. fermentum 23 i Lb. curvatus 30 kao potencijalne funkcionalne starter kulture za proizvodnju fermentiranih istarskih kobasica.In order to be applied as a functional starter culture, certain microorganism needs to be properly identified at the strain level. Therefore in this study, the representatives of Lactobacillus strains were selected by aid of classical microbiological methods and analysis of fermentation sugar profiles. The selected strains were identified with PCR method with specific primers relevant for the determination of species of lactic acid bacteria (LAB). Following the correct taxonomy identification, it is necessary to examine the functional and technological criteria for the selection of the functional starter cultures. During the industrial production of different fermented products, starter cultures are often exposed to various stress conditions which are specific for the technological production, such as the high salt concentrations, changes in pH values and temperature, unavailability of oxygen. Thus, it is important to examine how the selected strains survive in these conditions. So, the growth of the selected lactobacilli was tested at different NaCl concentrations (1,6 %, 5 %, 10% and 15 %) added to MRS broth medium, and with adjusted different pH values. It is also essential to confirm the safety of the selected functional starter cultures in the terms of their capacity to spread antibiotic resistance. Hence, the strain susceptibility to different groups of antibiotics was examined as well. As an important functional property, antibacterial activity of lactobacilli against frequent bacterial food contaminants was examined. According to the selection criteria for functional starter cultures, the strains of Lb. fermentum10, Lb. brevis 19, Lb. fermentum 23 and Lb. curvatus 30, out of 50 autochthonous isolates of Lactobacillus genus were selected as potential functional starter cultures for the production of fermented Istrian sausage