Soya bean tempe extracts show antibacterial activity against Bacillus cereus cells and spores.
OBJECTIVE
Tempe, a Rhizopus ssp.-fermented soya bean food product, was investigated for bacteriostatic and/or bactericidal effects against cells and spores of the food-borne pathogen Bacillus cereus.


RESULTS
Tempe extract showed a high antibacterial activity against B. cereus ATCC 14579 based on optical density and viable count measurements. This growth inhibition was manifested by a 4 log CFU ml(-1) reduction, within the first 15 min of exposure. Tempe extracts also rapidly inactivated B. cereus spores upon germination. Viability and membrane permeability assessments using fluorescence probes showed rapid inactivation and permeabilization of the cytoplasmic membrane confirming the bactericidal mode of action. Cooked beans and Rhizopus grown on different media did not show antibacterial activity, indicating the unique association of the antibacterial activity with tempe. Subsequent characterization of the antibacterial activity revealed that heat treatment and protease addition nullified the bactericidal effect, indicating the proteinaceous nature of the bioactive compound.


CONCLUSIONS
During fermentation of soya beans with Rhizopus, compounds are released with extensive antibacterial activity against B. cereus cells and spores.


CONCLUSIONS
The results show the potential of producing natural antibacterial compounds that could be used as ingredients in food preservation and pathogen control.
Roubos-van den Hil
P J
PJ
Laboratory of Food Microbiology, Wageningen University, Wageningen, the Netherlands. Petra.Roubos@wur.nl
Dalmas
E
E
Nout
M J R
MJ
Abee
T
T
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001409:Bacillus cereus / Q000187:drug effects* / Q000254:growth & development; D018533:Biomass; D002463:Cell Membrane Permeability; D015169:Colony Count, Microbial; D005285:Fermentation; D005516:Food Microbiology; D050296:Microbial Viability; D010936:Plant Extracts / Q000494:pharmacology*; D012233:Rhizopus; D045730:Soy Foods / Q000382:microbiology; D013025:Glycine max / Q000737:chemistry* / Q000382:microbiology; D013171:Spores, Bacterial / Q000187:drug effects / Q000254:growth & development
D000900:Anti-Bacterial Agents; D010936:Plant Extracts