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Growth and aflatoxin production of Aspergillus flavus in the presence of Lactobacillus species

Hassan Gourama, University of Nebraska - Lincoln

Abstract

A commercial silage inoculant mixture of Lactobacillus species inhibited aflatoxin production by Aspergillus flavus subsp parasiticus. Germination of mold spores was inhibited by actively growing Lactobacillus cells, however Lactobacillus cell free supernatant did not affect mold spore viability. Aflatoxin production was inhibited in Lablemco Tryptone Broth (LTB) by Lactobacillus species growing inside dialysis sacks (molecular weight cutoffs of 1000, 6-8000 and 12-14,000) immersed in the LTB. Aflatoxin levels were also significantly reduced when Lactobacillus species were inoculated into a growing mold culture, and also when mold spores were injected into Lactobacillus cultures. Different Lactobacillus isolates were purified from the silage inoculant mixture. Some of the isolates had no effect on mold growth and aflatoxin production. Other Lactobacillus isolates showed various degrees of aflatoxin inhibition. Lactobacillus isolate 371, which was identified as Lactobacillus casei pseudoplantarum, was found to greatly inhibit the production of aflatoxins B1 and G1. The inhibition of aflatoxins by Lactobacillus casei pseudoplantarum 371 was not eliminated by replacing an amount of glucose equal to the amount used by Lactobacillus sp before inoculation of the mold. The inhibitory principle in a Lactobacillus cell free supernatant was found to be sensitive to trypsin and $\alpha$-chymotrypsin, but not to pepsin. Dialyzed protein concentrate of the Lactobacillus cell free supernatant greatly inhibited aflatoxin formation. The antiaflatoxigenic activity of the supernatant was destroyed at 100 C within 10 mn. While Lactobacillus casei pseudoplantarum 371 inhibited aflatoxin production in broth, it did not have any effect on mold growth and aflatoxin production in sterile steamed rice, when mold growth was monitored by ergosterol and plate count techniques. Ergosterol determination was found to be a sensitive indicator of low levels of fungal activity and aflatoxin production in rice. Ergosterol formation in rice followed the same trend as aflatoxin B1 production. The inhibitory activity of the Lactobacillus isolate was shown to inactivate the enzymatic system required for the production of aflatoxin B1.

Subject Area

Food science|Microbiology

Recommended Citation

Gourama, Hassan, "Growth and aflatoxin production of Aspergillus flavus in the presence of Lactobacillus species" (1991). ETD collection for University of Nebraska - Lincoln. AAI9208107.
https://digitalcommons.unl.edu/dissertations/AAI9208107

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