African Journal of Biotechnology

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Toxin production in food as influenced by pH, thermal treatment and chemical preservatives

IC Oladipo, AO Adebiyi, AA Ayandele


Sixteen foods borne bacteria were isolated from raw food samples including okro, carrot, spinach, pepper, tomato, onion and cooked food samples (rice, yam, beans, meat and plantain). The isolates
were characterized and identified as Bacillus brevis, Bacillus congulans, Bacillus polymyxa, Bacillus lentus, Bacillus megaterium, Bacillus subtilis, Acinetobacter spp., Citrobacter freundii, Klebsiella aerogenes, Streptococcus agalactiae, Alcaligenes spp., Corynebacterium spp., Enterobacter aerogenes, Enterobacter spp. and Staphylococcus epidermidis. These isolates were screened on egg yolk agar for
toxigenic properties and thirteen of the sixteen were positive for toxin production while three were negative. Six out of the thirteen toxigenic bacterial were selected for further work. These were; E. coli,
K. aerogenes, C. freundii, B. polymyxa, S. epidermidis and E. aerogenes. The effect of pH, thermal treatment and chemical preservatives on the growth rate and toxin elaboration of E. coli, K. aerogenes, C. freundii, B. polymyxa, S. epidermidis and E. aerogenes was studied. It was observed that E. coli had no viable growth until 48 h of incubation, while the other five isolates had visible growth right from the 24 h of incubation. Also E. coli did not produce toxin until the 96th hour of incubation; K. aerogenes and E. aerogenes were able to produce toxin at 24 h of incubation, while C. freundii, B. polymyxa and S.epidermidis produced toxin at 48 h of incubation. Also, 44°C was not suitable for toxin production. pH 3 and 5 were less favorable for toxin production despite the fact that isolates were able to grow at different temperature and pH ranges. The isolate were more sensitive to sodium metabisulfite than benzoic acid. Also, E. coli and K. aerogenes were able to elaborate toxin in their dormant state with 750mg of sodium metabisulfite.
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