New types of antimicrobial compounds produced by Lactobacillus plantarum

New types of antimicrobial compounds mere identified in the culture filtrat e of Lactobacillus plantarum VTT E-78076. Activity was detected in the low molecular mass fraction separated by gel chromatography. This fraction tota lly inhibited the growth of the Gram-negative test organism, Pantoea agglom erans (Enterobacter agglomerans) VTT E-90396. Characteristic compounds from this fraction were identified by GC/MS-analysis and the identification was confirmed using pure commercial reference compounds in identical chromatog raphs and in antimicrobial tests. The active fraction included benzoic acid (CAS 65-85-0), 5-methyl-2,4-imidazolidinedione (CAS 616-03-5, methylhydant oin), tetrahydro-4-hydroxy-4-methyl-2H-pyran-2-one (CAS 674-26-0, mevalonol actone) and 3-(2-methylpropyl)-2,5-piperazinedione (CAS 5845-67-0, cyclo(gl ycyl-L-leucyl)). These compounds in concentrations of 10 ppm inhibited grow th of the test organism by 10-15% when acting separately, but 100% when all were applied together with 1% lactic acid. The inhibition was 40% by 1% la ctic acid alone. The compounds were also active against Fusarium avenaceum (Gibberella avenacea) VTT D-80147. The inhibition was 10-15% by separate co mpounds in concentrations of 10 ppm and maximally 20% in combinations. Fung al growth was not inhibited by lactic acid. Inhibition by unfractionated La ct. plantarum culture filtrate was 37% and by the low molecular mass fracti on, 27%.