Modified atmosphere (MA) storage in conjunction with refrigeration has been shown to significantly increase the shelf life of fresh fish and other products, but the effects, if any on the outgrowth and toxigenesis of C. botulinurn are unknown. A commercial system was duplicated in the laboratory and the effects of modified atmosphere on the outgrowth of C. botulinurn types A, B, and E were observed in inoculated salmon fillets and sandwiches stored at 4.4'C and 22.2"C. Inoculated samples stored in air at the same temperatures were used as controls. No toxigensis was observed in either the air or modified samples stored at 4.4"C, but all inoculated samples held at 22.2"C were toxic within 2-3 days. Spoilage generally preceded toxigenesis. In a concurrent study, the tendency of CO2 environments to repress the growth of gram negative bacteria to a greater extent than gram positive bacteria was also noted.

Fresh figs were pureed, the puree mixed with one of three syrup variables (water, light or heavy syrup), the pH adjusted at 0.1 pH intervals from 4.6 to 5.4, and the tubes inoculated with a composite of 5 type A and 5 type B. C. botufinum spores at 2 inoculum levels (10' or lo6 spores/tube). Anaerobic incubation was at 30°C for almost 1 yr. The results of our experiments show that maintenance of pH 4.9 or below in this product will prevent the outgrowth of C. botulinurn spores. An inoculated pack utilizing commercial procedures confirmed these results.

The addition of various amounts of acetic acid to pureed cucumbers inoculated with Clostridium botulinum spores has shown that outgrowth is inhibited at pH 4.8 but not at pH 5.0. Inoculation experiments with whole cucumbers showed that as little as 0.9% acetic acid in the brine was sufficient to prevent outgrowth from spore inocula as high as 106/cucumber. It was further shown that the rapid rate of acetic acid penetration into fresh-pack pickles prevents the growth of any C. botulinum spores that may be present.

Minimization of microbial spoilage in canned foods is accomplished by application of an appropriate thermal process and by controlling post-processing contamination by controlling the microbial population in container cooling water. The most widely used means of controlling microbial population in cooling water is with the application of germicidal solutions. The amount. kind and manner of application affect the effectiveness of germicidal solutions. This report discusses the various germicidal solutions used and their effectiveness, particularly in controlling microbial populations.

Summary: Byssochlamys fulva asci are resistant to high concentrations of aqueous chlorine and iodophor solutions, but are sensitive to peracetic acid. Concentrations of 2% and 4% of peracetic acid gave 99·9% reductions in 2·5 and 1·3 min, respectively. The asci were also sensitive to methyl bromide gas (MeBr), c. 5 × 104 asci/g inoculated into tapioca starch powder (aw= 0·69) being killed in 30 days by 90 mg of MeBr/kg of starch. About 180 asci/g were killed by adding 60 mg of MeBr/kg of starch.