Growth and toxin production by Clostridium botulinum on sliced raw potatoes in a modified atmosphere with and without sulfite.

The ability of Clostridium botulinum type A or B spores to grow and produce toxin on fresh raw potatoes in a modified atmosphere with or without sulfite was investigated at 22 degrees C. Fresh, peeled, sliced potatoes, untreated or dipped for 2 min into 0.7% sulfite solution and drained, were surface-inoculated at several concentration levels with a mixture of C. botulinum spores, either type A or B. They were placed in a modified atmosphere (30% N/70% CO2) within oxygen-impermeable bags (200 g/bag) and incubated at room temperature (22 degrees C). Toxicity was tested on days 0, 3, 4, 5, 6, and 7. 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 4 to 5 days, which coincided with the sensory evaluation "unfit for human consumption". Potatoes treated with NaHSO3 regardless of inoculum size or residual SO2 levels appeared acceptable for human consumption through day 7, even though they were toxic after 4 days of incubation. Although toxicity from type B spores occurred later and in fewer test samples than toxicity from type A, some potatoes again 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 conditions.