. 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%.

Fungal infection of barley and malt, particularly by strains of the genus Fusarium, is known to be a direct cause of beer gushing. We have shown previously that small fungal proteins, hydrophobins, isolated from strains of the genera Fusarium, Nigrospora and Trichoderma act as gushing factors in beer. A hydrophobin concentration as low as 0.003 ppm was sufficient to induce gushing. The gushing-inducing abilities of the isolated hydrophobins varied probably due to their structural differences. The hydrophobins did not affect beer foam stability. A correlation was observed between the hydrophobin level analyzed by the hydrophobin ELISA developed and the gushing potential of malt. The risk of gushing was found to increase with hydrophobin concentrations above 250 µg/g malt. The levels of hydrophobin and the Fusarium mycotoxin deoxynivalenol (DON) in malts were not correlated which indicated that the formation of those two fungal metabolites may not be linked. Furthermore, we did not observe a correlation between the DON content and the gushing potential of the malt studied. Our observations suggest that the accuracy of predicting gushing could be improved by measuring the amount of the actual gushing factors, hydrophobins, in barley or malt.

Aims: The Lactobacillus plantarum strains VTT E-78076 (E76) and VTT E-79098 (E98) were studied for their antifungal potential against Fusarium species. Methods and Results: In vitro screening with automated turbidometry as well as direct and indirect impedimetric methods clearly showed Lact. plantarum cell-free extracts to be effective against Fusarium species including Fusarium avenaceum, F. culmorum, F. graminearum and F. oxysporum. However, great variation in growth inhibition was observed between different Fusarium species and even between strains. The antifungal potential of Lact. plantarum E76 culture, including cells and spent medium, was also examined in laboratory-scale malting with naturally contaminated two-rowed barley from the crops of 1990-96. The growth of the indigenous Fusarium flora was restricted by the addition of Lact. plantarum E76 to the steeping water. However, the antifungal effect was greatly dependent on the contamination level and the fungal species ⁄ strains present on barley in different years. Conclusions: Lactobacillus plantarum strains E76 and E98 had a fungistatic effect against different plant pathogenic, toxigenic and gushing-active Fusarium fungi. Significance and Impact of the Study: The present study indicates that Lact. plantarum strains with known and selected characteristics could be used as a natural, food-grade biocontrol agent for management of problems caused by Fusarium fungi during germination of cereals.

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