Competitive inhibition of Clostridium botulinum type E by Bacillus speciesin a value-added seafood product packaged under a modified atmosphere

Challenge studies were carried out on raw, cooked, and sterilized surimi nu ggets, inoculated with 10(4) spores g(-1) of C. botulinum type E spores. Al l products were packaged in air and air with an Ageless SS oxygen absorbent and stored at 4, 12 and 25 degrees C. Toxin was not detected in any raw pr oduct throughout storage (28 days). The absence of toxigenesis was attribut ed to the low pH (4.1-4.3) due mainly to the growth of lactic acid bacteria (10(7) CFU g(-1)). Toxin was also not detected in any cooked product after 28 days. Product pH did not decrease as previously (due to the absence of LAB), but counts of C. botulinum still decreased throughout storage. The ab sence of toxin in cooked nuggets was attributed to the anti-botulinal role by Bacillus species, the predominant spoilage bacteria in cooked nuggets. A total of 27 Bacillus isolates were isolated from value-added surimi nugget s and identified as B. subtilis (18/27), B. cereus (7/27), B, licheniformis (1/27), and B. pumilus (1/27). Each isolate was tested for its antimicrobi al activity against proteolytic strains of C. botulinum types A and B, and non-proteolytic strains of C. botulinum types B and E by a deferred antagon ism method. All strains of C, botulinum were sensitive to the bacteriocin-l ike inhibitory substances (BLIS) produced by B. subtilis, while all other B acillus isolates were effective mainly against non-proteolytic strains of C . botulinum. B, licheniformis produced the largest zones of inhibition agai nst C. botulinum type E. This study has confirmed that the absence of growt h of, and toxin production by, C. botulinum type E in challenge studies wit h cooked surimi nuggets was due to Bacillus spp, present in the cooked prod ucts. (C) 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.