Influence of Growth Medium on Hydrogen Peroxide and Bacteriocin Production of Lactobacillus Strains

 The ability of lactic acid bacteria (LAB) to produce enough hydrogen peroxide (H2O2) without growing at refrigeration temperature should enable them to extend the shelf-life of some refrigerated foods without altering the acidity of the food (1). The synthesized H2O2 can inhibit the growth of psychrotrophic and pathogenic microorganisms at refrigeration temperature (2).

Lactobacillus delbrueckii subsp. lactis have been shown to produce higher amounts of H2O2 at low temperatures and to inhibit pathogens during refrigerated storage. This study indicated the potential use of Lactobacillus delbrueckii subsp. lactis as a biopreservative in other refrigerated foods. Hydrogen peroxide-producing Lactobacillus strains,  which were found to be  nhibitory to Bacillus, Proteus and Pseudomonas species, were isolated (3). The bactericidal effect of H2O2 has been attributed to its strong oxidizing effect on the bacterial cells and to the destruction of basic molecular structures of cell proteins. Therefore it is of a gaining importance to select and propagate lactobacilli with high inhibitory activity. Bacteriocins from LAB are proteinaceous compounds, which have inhibitory effect against closely related species and other Gram-positive bacteria. Several studies Z. ZALÁN et al.: Hydrogen Peroxide and Bacteriocin Production of Lactobacillus spp., Food Technol. Biotechnol. 43 (3) 219–225 (2005) 219 have been engaged in bacteriocins and their effect on Gram-positive bacteria (4–8). Bacteriocins form the pores in the membrane of sensitive cells and deplete the transmembrane potential and/or the pH gradient, resulting in the leakage of cellular materials (9,10). The inhibitory effect of bacteriocin is influenced by the phospholipid composition of the target strains and the pH of the environment (11). Several bacteriocins have effect against spoilage and pathogenic microorganisms, e.g. Listeria monocytogenes, Clostridium botulinum and Bacillus cereus (12,13). The bacteriocin producer strains can be used as natural food preservative starter cultures (14–16). Nowadays, interest has developed into biopreservatives because the customers wish to consume less artificial compounds. Natural bacteriocins may have good prospects in the preservation of food. Earlier we investigated some Lactobacillus strains in fermentation of vegetables (17) and these strains showed inhibitory effect not only against other lactobacilli, but also against certain yeasts (18). The present study was conducted to determine if MRS or TJ broth are suitable media for lactobacilli to accumulate H2O2 and whether the produced hydrogen peroxide can inhibit the growth of undesirable organisms, such as Listeria monocytogenes, Bacillus cereus and Escherichia coli. Moreover, we investigated the influence of media on the effectiveness of crude and concentrated bacteriocin suspensions from several Lactobacillus strains.

Zsolt Zalán*, Edina Németh, Ágnes Baráth and Anna Halász

Central Food Research Institute, Herman Otto str. 15, H–1022 Budapest, Hungary