Inhibition of non-proteolytic Clostridium botulinum with lactic acid bacteria in extended shelf-life cook-chill soups

The possibility of protecting cook-chill foods with microbial cultures against the risk of botulism was demonstrated. Three commercial soups were incubated with Clostridium botulinum 17B (103 spores/g) and protective cultures (PCs) during 10-15 days at 10°C. The PCs populations were enumerated on M17, MRS and maltose tryptic soy agar, C. botulinum - on sorbitol tryptic soy agar, botulinal toxin was detected by the immunoassay, bacteriocins - by well diffusion assay. C. botulinum did not grow in two soups with low pH (5.2-5.5) and was unaffected by the PCs. In seafood chowder (pH 6.2) C. botulinum populations reached 108 cfu/g. The co-incubation with the PCs, nisin-producing Lactococcus lactis (107 cfu/g) or pediocin-producing Pediococcus pentosaceus (3×108 cfu/g) singularly and as a mixture, prevented toxigenesis as well as reduced the product pH to 4.8-5.0 and C. botulinum populations to undetectable levels. Color, mouth-feel, texture, flavor and the overall acceptability of seafood chowder was not affected by the presence of the PCs.