Growth and Toxin Production by Clostridium botulinum in Sliced Raw Potatoes Under Vacuum With and Without Sulfite

The ability of Clostridium botulinum type A or B spores to grow and produce toxin in fresh raw potatoes under vacuum with or without sulfite at 22°C was investigated. Fresh, peeled, sliced potatoes, untreated or dipped for 2 min in sulfite (NaHSO₃) and drained, were surface-inoculated at several levels with a mixture of C. botulinum spores, either type A or B, and placed in oxygen-impermeable bags (200 g/bag) that were then vacuum-sealed and incubated at room temperature (22°C). Toxicity was tested on days 0, 3, 4, 5 and 6. After incubation, the potatoes were blended and centrifuged, and the millipore-filtered supernatant fluid was injected intraperitoneally into mice. Sensory evaluation, except taste, was also performed. Potatoes inoculated with C. botulinum type A spores, but untreated with NaHSO₃ became toxic in 3 days, which coincided with the sensory evaluation, "Unfit for human consumption." However, despite inoculum size or residual SO₂ levels, potatoes treated with NaHSO₃ appeared acceptable for human consumption through day 6, even though they were toxic after 4 days of incubation. Toxicity from type B spores occurred later and in fewer test samples than type A. Again, the potatoes appeared acceptable but were toxic. Thus, although NaHSO₃ markedly extended the consumer acceptability of peeled, sliced, raw potatoes at the abuse temperature, it did not inhibit outgrowth and toxin production by C. botulinum under these same conditions.