Shelf‐life and quality of fresh fishery products can be extended by the use of a modified atmosphere (MA) and high barrier film packaging coupled with refrigerated storage. MAs with elevated levels of carbon dioxide inhibit or slow the growth of various aerobic spoilage bacteria of fishery products by extending the lag phase. However, at the same time, MAs provide conditions for the growth of Grampositive bacteria and food pathogens within the package. The extension of the storage life of the refrigerated MA products may enable the slower‐growing Gram‐positive bacteria to reach high populations. The shelf‐life of fishery products packaged under MAs rich in carbon dioxide coupled with storage at 8.0°C or below can be extended more than 100%. Major safety concerns regarding the risk of foodborne botulism can result from MA packaging of fresh fishery products that contain the spores of nonproteolytic C. botulinum and are subsequently temperature‐abused. Minimizing the risk of foodborne botulism by including inhibitory factors such as antimicrobial agents before packaging fishery products under MAs and strict adherence to refrigerated storage temperatures are discussed.

To improve the accuracy and precision of the mouse assay for botulinum toxins found in foods and body fluids, a stable reference standard of botulinum toxin has been developed. It contains 100 ng crystalline type A botulinum toxin/ml 0.05M pH 4.2 sodium acetate buffer which contains 3 mg bovine serum albumin and 2 mg gelatin/ml. The albumin and gelatin stabilize the toxin. For distribution to laboratories carrying out the assay, 0.5 ml of the standard is sealed in 1 ml glass vials. The standard reference toxin, used as directed, enables the assayer to establish the response of laboratory mice, under a specific set of conditions, to a definite amount of toxin and to express the toxin content of an unknown in terms of ng toxin/g or ml food or body fluid. The mouse assay by itself is not specific for botulinum toxin, but when used in conjunction with specific antisera for identification and typing, it is the most reliable test available.

We investigated the shelf life of fresh Tilapia spp. fillets packaged in high-barrier film under both 100% air and a modified atmosphere (MA) of 75% CO2:25% N2, and stored under refrigeration (4°C) and abuse temperatures (8 and 16°C). The chemical spoilage indicators trimethylamine, K-value, and surface pH, as well as microbial counts, were compared with the sensory characteristics of spoilage. For fillets packaged under 100% air, the shelf life was 9 to 13 days at a storage temperature of 4°C, but decreased to 3 to 6 days at 16°C. However, the shelf life of MA-packaged fillets stored at 4°C increased to >25 days when the lag phase and generation time of the bacteria were extended. MA packaged fillets stored under temperature-abuse conditions (8 and 16°C) had a shorter shelf life. The trimethylamine content associated with onset of sensory spoilage for MA packaged fillets increased as storage temperature increased and differed for each temperature. The surface pH and K-values of MA-packaged fillets were not good indicators of spoilage onset.

An improved selective medium, Tryptose-sulfite-cycloserine (TSC) agar, for the enumeration of Clostridium perfringens is described. It consists of the same basal medium as Shahidi-Ferguson-perfringens (SFP) agar, but with 400 p,g of D-cyclOserine per ml substituted for the kanamycin and polymyxin. Tolerance of C. perfringens for D-cycloserine, its production of lecithinase, and its ability to reduce sulfite were used as the basis for development of this medium. Comparisons were made between TSC and SFP agars for the recovery of vegetative cells of C. perfringens by using statistical methods. The results showed that TSC allowed virtually complete recovery of most of the C. perfringens strains while inhibiting practically all facultative anaerobes tested. SFP agar allowed a slightly higher rate of recovery of C. perfringens but was found to be much less selective.

The ability of Salmonella spp. to grow on the interior tissues of cantaloupe, watermelon, and honeydew melons was investigated. Pieces of rind-free melons (pH 5.90–6.67) and tryptic soy broth (TSB, pH 5.90) were inoculated with a mixed culture (approximately 100 CFU/g or ml) containing equal proportions of five species of Salmonella (S. anatum, S. Chester, S. havana, S. poona, and S. senftenberg). Inoculated melon pieces and TSB were incubated for 24 h at 5 or 23°C. Viable populations of salmonellae were determined by surface plating test portions on Hektoen enteric agar. Results indicated that Salmonella growth was rapid and prolific on the melons and in TSB at 23°C incubation. Final populations on watermelons were approximately 1.0 log10 greater than populations on cantaloupe and honeydew and in TSB. Although viable Salmonella populations on melons and in TSB did not increase during the 24-h incubation at 5°C, little or no decrease in viable populations was observed.