New types of antimicrobial compounds produced by Lactobacillus plantarum

New types of antimicrobial compounds were identified in the culture filtrate of Lactobacillus plantarum VTT E-78076. Activity was detected in the low molecular mass fraction separated by gel chromatography. This fraction totally inhibited the growth of the Gram‐negative test organism, Pantoea agglomerans (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 chromatographs and in antimicrobial tests. The active fraction included benzoic acid (CAS 65–85–0), 5-methyl-2,4-imidazolidinedione (CAS 616–03–5, methylhydantoin), tetrahydro-4-hydroxy-4-methyl-2H-pyran-2-one (CAS 674–26–0, mevalonolactone) and 3-(2-methylpropyl)-2,5-piperazinedione (CAS 5845–67–0, cyclo(glycyl-l-leucyl)). These compounds in concentrations of 10 ppm inhibited growth 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% lactic acid alone. The compounds were also active against Fusarium avenaceum (Gibberella avenacea) VTT D-80147. The inhibition was 10–15% by separate compounds in concentrations of 10 ppm and maximally 20% in combinations. Fungal growth was not inhibited by lactic acid. Inhibition by unfractionated Lact. plantarum culture filtrate was 37% and by the low molecular mass fraction, 27%.