Initial challenge studies with spores of proteolytic Clostridium botulinum types A and B (~104 spores/g) showed that while air- and gas-packaged English-style crumpets (aw 0.990) and pizza crust (aw 0.960) were toxic after 42-days storage at ambient temperature (25°C), no neurotoxin was detected in bagels (a w 0.944). Further challenge studies with similarly packaged crumpets inoculated with C. botulinum (~102 spores/g), pre- or post-baking, demonstrated that all crumpets were toxic within 4 to 6 days at 25°C and that toxigenesis preceded spoilage. Furthermore, reformulating crumpets to pH 8.3 and packaging in 100% CO2 had little effect in delaying the growth of C. botulinum compared to crumpets formulated to pH 6.5 and packaged in 60% CO2. / Subsequent studies were directed at determining the levels of additional barriers that could be used to ensure the safety of high-moisture MAP crumpets. While ethanol vapour proved to be an effective additional barrier in crumpets (100-g, [aw 0.990, pH 6.5]) challenged with ~102 spores/g of C. botulinum, spoilage preceded toxigenesis due to absorption of ethanol from the package headspace by crumpets. Modelling studies in Trypticase Peptone Glucose Yeast (TPGY) broth confirmed the anti-botulinal nature of ethanol and showed that a level of ~4% (vol/vol) could be used for complete inhibition of this pathogen, depending on the aw and pH of the growth medium. However, while ethanol vapour could be used to inhibit the growth of C. botulinum in high-moisture crumpets, its anti-botulinal efficacy was influenced by the method of crumpet leavening (yeast v chemical). / Preliminary studies were also done to assess the potential of mastic oil, a novel inhibitor, against C. botulinum. While direct and indirect application of ethanolic extracts of mastic oil inhibited the growth of C. botulinum in vivo, they failed to do so in crumpets.

Previous results indicated that lactic acid bacteria (LAB) and Bacillus spores were the predominant spoilage microorganisms in minimally processed products after 35 days storage at 15$ sp circ$C. Furthermore, most packages were swollen due to carbon dioxide production by the LAB. The fact that spores survived mild heat treatment is of concern since it implies that other more pathogenic spores, e.g. Clostridium botulinum would also survive and may pose a public health problem in products stored at 15$ sp circ$C. As such, the influence of combination treatments (viz., mild heat processing treatment, pH, water activity, storage temperature, lactic acid bacteria) were evaluated through challenge studies with selected strains of C. botulinum type A, B, and E spores. The shelf life and safety of the products following a 13D process at 75$ sp circ$C, could be extended to $ ge$42 days by a combination of pH $ le$ 5.0 and storage at 5$ sp circ$C. Other combination treatments were also effective in controlling growth of, and toxin formation in the products by C. botulinum. For instance, botulinum toxin was not detected until day 35 in inoculated spaghetti and meat sauce products (pH 5.25 and a$ sb{w}$ 0.992) with type A and B spores and stored at 15$ sp circ$C. Shelf life extension and inhibition of toxin production was also possible through reductions in a$ sb{w}$ levels achieved by addition of 1-3% salt (w/w) to the products. Water activity levels of $ le$0.983 prevented botulinum toxin production in the minimally processed spaghetti and meat sauce product for $ ge$42 days during storage at 15$ sp circ$C. / Similar trends were observed in sous-vide rice and salmon products. Furthermore, when sodium lactate was used as the humectant to lower the a$ sb{w}$ of this product, toxin production was also delayed, but not to the same extent as achieved with NaCl. When two strains of bacteriocin-producing lactic acid bacteria were co-inoculated separately in the sous-vide rice and salmon products that had been challenged with C. botulinum type E spores, toxin formation was only slightly delayed in products with added NaCl (1%), while toxin formation was neither delayed nor prevented in similarly lactic acid bacteria-treated samples with no added NaCl. Furthermore, in most of the products in which botulinum toxin was detected, spoilage preceded toxigenesis, however, in some samples stored at 5$ sp circ$C toxigenesis preceded spoilage. Addition of $ alpha$-2-macroglobulin at a level of 2.7 ppm did not delay or prevent toxin formation in the product. Microwave heating of products at half-power or full power (800 Watts) for 5 to 10 min proved effective in inactivating all of the pre-formed toxin in toxic samples. (Abstract shortened by UMI.)

The fish processing industry is actively seeking for alternative methods of shelf life preservation and marketability of fresh fish, while at the same time economizing on energy costs. Two methods which fulfill both objectives are modified atmosphere packaging (MAP) and glucose oxidase (GOX)/Glucose dipping solutions. MAP is the packaging of perishable products in an atmosphere other than that of air and is used for the shelf life extension of beef, pork, fruits, vegetables and bakery products. GOX, either alone or in conjunction with MAP has the potential for shelf life extension of fresh fish. / The objectives of this study were to determine the combined effect of glucose oxidase/glucose or gluconic acid dipping solutions and modified atmosphere packaging in conjunction with refrigeration on the shelf life extension of mackerel and cod. / This study has shown that the shelf life of fresh fish can be extended through the combined use of MAP/dipping solutions and refrigeration. This novel process of "dipping" in GOX solution in conjunction with modified atmosphere packaging (MAP) will have a significant effect in the area of fish hygiene and will minimize fish losses incurred through spoilage.

The combined effect of various gas packaging atmospheres (air, vacuum and gas packaging), films of different oxygen transmission rate (OTR) and storage temperature (4 and 12°C) were investigated on the shelf-life and safety of flesh rainbow trout fillets. / Preliminary studies were done to determine the optimum packaging atmospheres to maintain the bright pink color of trout packaged in a high gas barrier film. Both vacuum and gas packaging (85% CO2:15%N2) resulted in the longest shelf-life (~28 days) in terms of color at 4°C. Based on these optimum gas atmospheres for color, shelf-life studies were performed at both refrigerated and temperature abuse conditions (12°C). / Challenges studies were also done with Listeria monocytogenes and Clostridium botulinum type E, two psychrotrophic pathogens of concern in modified atmosphere packaged (MAP) fish. / Subsequent studies were done to determine the effect of various levels of headspace oxygen (0--100%, balance CO2) or film OTR on the time to toxicity in trout stored at 12°C. (Abstract shortened by UMI.)

Value-added trout burgers and trout wontons were prepared from minced trout trimmings, oats, dried onion flakes, white pepper, cayenne pepper, garlic powder, soy sauce, spice mix and eggs. The trout burgers were coated with crushed cornflakes and then partially cooked (2 min at 140ºC) or frilly cooked (5 min at 140ºC) in hot oil. Similar fillings were used to prepare trout wontons by wrapping the mixture with Chinese wonton dough and 2 products were made: raw wonton (uncooked) and fried wonton (fried for 8 min at 140ºC). / Storage trials were performed on raw and fried trout wontons (a w 0.98--0.95, pH 6.5), and partially and fully cooked trout burgers (aw 0.97--0.96, pH 6.4). Products were packaged in air and under various modified atmospheres (MAP), and stored at 4 and 12ºC. A microbiological shelf-life of >28 days was possible for the cooked trout burgers and fried wontons stored at 4ºC. In general, the microbiological shelf-life preceded the sensory shelf-life. / Subsequent challenge studies were done to address the safety concerns associated with MAP food. All products were inoculated with 102 CFU/g of Listeria monocytogenes and 102 spores/g of Clostridium botulinum type E spores. Gas packaging with 80% CO2 (balance N2) inhibited the growth of L. monocytogenes in products stored at 4ºC. However, counts of L. monocytogenes increased in all other packaging conditions. In challenge studies with C. botulinum type E, toxin was not detected in any products after 28--60 days.

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