Influence of water activity and storage conditions on survival and growth of proteolytic Clostridium botulinum in peanut spread Original Research Article

Outgrowth of Clostridium botulinum spores followed by toxin production in peanut spread at Aw0·98, 0·96, 0·94 and 0·92 stored at 30°C under anaerobic or aerobic conditions for 0, 3, 7 and 16 weeks or 0, 1, 9 and 16 weeks, respectively, was investigated. Botulinal toxin was not detected in peanut spreads stored under anaerobic conditions for 16 weeks. Peanut spreads at Aw0·98 and two of three samples at Aw0·96 stored aerobically became toxic after 9 and 16 weeks, respectively. Clostridium botulinum in peanut spread at Aw0·98 and 0·96 grew to populations of 106and 105cfu g−1, respectively, within 16 weeks. Lactic acid bacteria grew within 3 days in peanut spread at Aw0·98 and 0·96 stored under aerobic or anaerobic conditions. Regardless of Aw, populations of aerobic and anaerobic micro-organisms decreased in peanut spread stored under anaerobic conditions. Only slight decreases occurred in samples stored under aerobic conditions. The pH of inoculated and uninoculated peanut spread at Aw0·98 and 0·96 increased from 4·8 to 7·0 within 16 weeks and was attributed to growth of Penicillium andMucor spp. Similarly, redox potential (Eh) of peanut spread stored under anaerobic conditions for 3 weeks, decreased as the Awwas increased. Significantly lower Eh values in peanut spread samples at Aw0·98 or 0·96 stored under aerobic conditions occurred within 1 week and/or 9 weeks compared to peanut spread at Aw0·92 or 0·94. Peanut spreads were judged inedible due to growth of lactic acid bacteria and molds which resulted in ‘off’ aromas before toxicity developed, thus greatly minimizing the likelihood of consumption.