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

tgrowth of Clostridium botulinum spores followed by toxin production in pea nut spread at A(w) 0.98, 0.96 0.94 and 0.92 stored at 30 degrees C under an aerobic or aerobic conditions for 0, 3, 7 and 16 weeks or 0, 1, 9 and 16 we eks, respectively was investigated. Botulinal toxin was not detected in pea nut spreads stored under anaerobic conditions for 16 weeks. Peanut spreads at A(w), 0.98 and two of three samples at A(w) 0.96 stored aerobically beca me toxic after 9 and 16 weeks, respectively: Clostridium botulinum in peanu t spread at A(w) 0.98 and 0.96 grew to populations of 10(6) and 10(5) cfu g (-1),respectively, within 16 weeks. Lactic acid bacteria grew within 3 days in peanut spread at A(w) 0.98 and 0.96 stored under aerobic or anaerobic c onditions Regardless of A(w), populations of aerobic and anaerobic micro-or ganisms decreased in peanut spread stored under anaerobic conditions. Only slight decreases occurred in samples stored under aerobic conditions. The p H of inoculated and uninoculated peanut spread at A(w) 0.98 and 0.96 increa sed from 4.8 to 7.0 within 16 weeks and was attributed to growth of Penicil lium and Mucor spp. Similarly, redox potential (Eh) of peanut spread stored under anaerobic conditions for 3 weeks, decreased as the A(w) was increase d Significantly lower Eh values in peanut spread samples at A(w) 0.98 or 0. 96 stored cinder aerobic conditions occurred within I week and/or 9 weeks c ompared to peanut spread at A(w) 0.92 or 0.94. Peanut spreads were judged i nedible due to growth of lactic acid bacteria and molds which resulted in ' off' aromas before toxicity developed, thus greatly minimizing the likeliho od of consumption. (C) 2000 Academic Press.