Characterization of autochthonous lactic acid bacteria genus Lactococcus

Abstract

Lactic acid bacteria strains isolated from autochthonous cheeses were researched. In products such as these, where starters were not added fermentation occurs as a result of natural flora present in the surrounding environment. Thirty thermophilic, mesophilic and citrate+ LAB strains were isolated by selective medium (LM17 agar and LDC agar) from 5 samples of autochthonous cheeses. They were exposed to further analysis and identification. After examination by Gram test and catalase test, 12 strains of LAB, were selected for further analysis. On the basis of lactose fermentation and acid production in 1% reconstituted skim milk, 6 homofermentative strains were selected, that also had good acidogenic activity. Their proteolytic ability to hydrolyze B-casein was examined by SDS polyacrilamid electrophoresis, where these strains showed different proteolytic activity. Determination of these strains by API Rapid ID 32 Strep tests showed that 4 strains belong to the Lactococcus lactis ssp. tech's and 2 strains to the Lactococcus lactis ssp. lactis biovar. diacetylactis.

Rad je obuhvatio karakterizaciju bakterija mlečne kiseline izolovanih iz autohtonih sireva proizvedenih na tradicionalan način, bez dodavanja starter kultura. Iz 5 uzoraka sira izvršena je izolacija 30 termofilnih mezofilnih i cit-rat+ sojeva BMK na odgovarajućim selektivnim podlogama (LM17 agar i LDC agar). Od izdvojenih čistih kultura, nakon određivanja Gram reakcije i katalaza testa, izabrano je 12 sojeva za dalja ispitivanja. Na osnovu načina fermentacije laktoze (homo-heterofermentacija)i acidogene sposobnosti praćene u 1% rekonstituisanom obranom mleku u toku 24 sata, selekcionisano je 6 sojeva koji su pokazali homofermentativnu aktivnost i dobru acidogenu sposobnost. Za ove sojeve je ispitana proteolitička aktivnost u odnosu na β-kazein, pomoću SDS poliakrilamidne elektroforeze, koja je pokazala međusobne razlike u sposobnosti razgradnje β-kazeina. Na kraju je izvršena njihova identifikacija pomoću API Rapid ID 32 Strep testa za laktokoke, i utvrđeno je da 4 soja pripadaju vrsti Lactococcus lactis ssp. lactis, a dva soja vrsti Lactococcus lactis ssp. lactis biovar. diacetylactis.