Effect of Cocultivation on Lactobacillus plantarum Strains Growth and Antagonistic Activity

Abstract

The use of bacterial starters for the production of fermented foods has several advantages over traditional spontaneous fermentation, as it provides a rapid and controlled decrease of pH, improves the microbiological quality of the product, and prolongs the shelf-life. Fermented foods are typically produced using mixed cultures of lactic acid bacteria (LAB) due to the synergism between their constituent bacterial cultures. So, the compatibility of the LAB strains decides the efficacy of a multi-strain starter. The purpose of this study was to investigate the effect of the cocultivation of Lactobacillus plantarum strains on the growth, acidification, and antagonistic activity to determine suitable strain combinations for fermented vegetable production. Methods. The effect of cocultivation on growth characteristics of four L. plantarum strains was determined in MRS medium and cabbage-based medium with 2.5% NaCl. After 8 h of cultivation at 30°C and 37°C, the number of viable cells (CFU/ml) and the pH of the medium were determined. The antagonistic activity of monocultures of L. plantarum and their six compositions against opportunistic pathogenic microorganisms was determined by the method of delayed antagonism. Results. During growth in MRS broth at 30°C cocultivation of L. plantarum 47SM with L. plantarum 691T or L. plantarum 1047K strains led to enhanced rates of growth compared to the monocultures, suggesting some degree of symbiosis between these strains. Viable cell counts of L. plantarum 47SM, 1047K and 691T strains and ΔpH values of L. plantarum 952K, 1047K, and 691T strains were higher after 8 h growth in the cabbage-based medium at 30°C compared to MRS broth. Despite the intensive growth of L. plantarum monocultures in cabbage-based medium, a significant decrease of viable cell counts and ΔpH values during cocultivation at 30°C were found. Cocultivation did not affect the average size of the growth inhibition zones of most of the indicator strains used. However, growth inhibition zones of Shigella flexneri, Escherichia coli, and Proteus vulgaris decreased in some L. plantarum mixed cultures compared to monocultures. Thus, the growth inhibition zones of E. coli and S. flexneri by mixed culture L. plantarum 47 SM+1047K were significantly smaller compared to the growth inhibition zones of L. plantarum monocultures. Conclusions. Thus, based on the data obtained in present work, we can assume that some of these L. plantarum strains used in the work may be bactericinogenic. Although the four L. plantarum strains studied are compatible when cocultivated in a standard rich MRS medium, the results of cocultivation in a cabbage-based medium with 2.5% NaCl does not allow to recommend the use of these L. plantarum strains simultaneously in the starter for vegetable fermentation. Further investigation of bacteriocinogenic properties and mechanisms of growth inhibition under cocultivation in vegetable-like conditions are needed, which will allow combining of some of these L. plantarum strains with LAB strains of other species or genera to create multi-starters for vegetable fermentation.