Inhibition of Non-proteolytic Clostridium botulinum with Lactic Acid Bacteria in Extended Shelf-Life Cook-Chill Soups

Abstract

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.

Acknowledgments

The authors thank Kevin Woodman, Mitrol Technology Pty. Ltd., for his encouragement and enthusiasm about the potential of using bacterial cultures in food preservation.