Antimicrobial activity ofLactobacillus rhamnosusagainstPseudomonas fluorescensandPseudomonas putidafrom raw milk

This work aimed to assess the inhibitory effect of Lactobacillus rhamnosus against different populations of Pseudomonas fluorescens and Pseudomonas putida, isolated from refrigerated raw milk and the compounds responsible for inhibitory effects over storage time. An initial population of 4 log cfu/ml (50 ml) of L. rhamnosus (working culture) was added to 150 ml of reconstituted powder milk (12%) with P. fluorescens and P. putida, with an initial concentration of 2, 4, and 6 log cfu/ml. After activating at 21°C/72 hr, 200 ml of inoculum was stored at 10°C/48 hr. L. rhamnosus inhibited the growth of P. fluorescens and P. putida for all populations analyzed after inoculation (0 hr), 24, and 48 hr. The inhibitory compounds were organic acids. The average diameter measurement of inhibition zones for P. fluorescens was 1.9 cm and for P. putida was 1.6 cm. Practical applications This study demonstrated the antibacterial activity of L. rhamnosus against P. fluorescens and P. putida, both of the species isolated from the milk microbiota found in the environment of milk-processing facilities. Although these findings need further validation on an industrial scale, it was demonstrated that L. rhamnosus can contribute for the improvement of raw milk quality.