Lactic acid bacteria (LAB) can be isolated from different sources such as milk and cheese, and the lipolytic, proteolytic and glycolytic enzymes of LAB are important in cheese preservation and in flavour production. Moreover, LAB produce several antimicrobial compounds which make these bacteria interesting for food biopreservation. These characteristics stimulate the search of new strains with technological potential. From 156 milk and cheese samples from cow, buffalo and goat, 815 isolates were obtained on selective agars for LAB. Pure cultures were evaluated for antimicrobial activities by agar antagonism tests and for proteolytic activity on milk proteins by cultivation on agar plates. The most proteolytic isolates were also tested by cultivation in skim milk followed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the fermented milk. Among the 815 tested isolates, three of them identified asStreptococcus uberis(strains FT86, FT126 and FT190) were bacteriocin producers, whereas four other ones identified asWeissella confusaFT424,W. hellenicaFT476,Leuconostoc citreumFT671 andLactobacillus plantarumFT723 showed high antifungal activity in preliminary assays. Complementary analyses showed that the most antifungal strain wasL. plantarumFT723 that inhibitedPenicillium expansumin modified MRS agar (De Man, Rogosa, Sharpe, without acetate) and fermented milk model, however no inhibition was observed againstYarrowia lipolytica. The proteolytic capacities of three highly proteolytic isolates identified asEnterococcus faecalis(strains FT132 and FT522) andLactobacillus paracaseiFT700 were confirmed by SDS–PAGE, as visualized by the digestion of caseins and whey proteins (β-lactoglobulin and α-lactalbumin). These results suggest potential applications of these isolates or their activities (proteolytic activity or production of antimicrobials) in dairy foods production.
Effects of ultrasound on the fermentation profile of fermented milk products incorporated with lactic acid bacteria
