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The combined effect of Modified Atmosphere Packaging (MAP) involving gas packaging, oxygen absorbent and other environmental factors to control aflatoxin production by Aspergillus flavus and Aspergillus parasiticus in both synthetic media and peanuts were studied using a process optimization technique termed Response Surface Methodology (RSM). Regression analysis of the data indicated that water activity (a$ sb{ rm w}$), pH, storage temperature, initial concentration of headspace oxygen and inoculum level were all highly significant factors (p 0%). These changes in the barrier characteristics influenced the headspace gas composition within the product and under modified atmospheres hence the level of aflatoxin detected in these stored products. / In conclusion, this study has shown that the combined effect of several "barriers" can be used in conjunction with low oxygen modified atmosphere and high barrier packaging films to inhibit or reduce aflatoxin to safe and acceptable levels, particularly at abusive temperatures encountered during storage.

The effects of irradiation dose (0, 0.5 and 1.0 kGy), various gas atmospheres and storage temperature (5, 15 and 25$ sp circ$C) on the physical, chemical, microbiological, and organoleptic changes in fresh pork were studied using factorial design experiments. The effects on toxin production by Clostridium botulinum were also investigated using challenge studies. Shelf life could be extended to 21 d when product was packaged in 0% O$ sb2$, irradiated at 1.0 kGy and stored at 5$ sp circ$C compared to 4 d for control samples. While the presence of O$ sb2$ in the package headspace enhanced the antimicrobial effects of low-dose irradiation, it adversely affected the organoleptic qualities of pork. Botulinum toxin was detected after only 2 d in all inoculated treatments stored at 25$ sp circ$C. At 15$ sp circ$C, toxin was produced faster when pork was initially packaged with O$ sb2$ or low levels of CO$ sb2$ (15-30%) as compared to 100% N$ sb2$. Higher levels of CO$ sb2$ (45-75%) delayed toxin production. In most treatments, spoilage preceded toxigenesis. Models were developed relating the above factors to the time until toxin production and to the probability of toxigenesis. Temperature, initial O$ sb2$ and irradiation were all significant factors.

Listeria monocytogenes is a pathogenic, psychrotrophic microorganism that is ubiquitous in nature. L. monocytogenes has been isolated from numerous meat products, both fresh and processed, the incidence of contamination varying greatly. The ability of Listeria to grow in meats depends on temperature, pH, water activity (a$ sb{ rm w}$), nutrients, species and numbers of competing microorganisms, gaseous conditions, and levels of additional barriers. Therefore, methods to control the growth of L.monocytogenes are of great importance to food processors since this organism can grow under a wide range of environmental and storage conditions. Two methods of control, in conjunction with temperature, were studied in this project: (i) modified atmosphere packaging (MAP) and (ii) chitosan, to determine the optimum levels of these "hurdles" needed to effectively control the outgrowth of L.monocytogenes in both model broth and agar systems and in fresh pork loin. On the basis of these preliminary studies, a combination of chitosan as a dipping solution and modified atmosphere packaging were investigated to control the growth of L.monocytogenes in fresh pork loin. Pork loin samples were dipped in a 0.2% chitosan solution for 60 seconds and packaged under various atmospheres in Cryovac bags and stored at 5, 10 and 15$ sp circ$C up to 28 days. Samples were monitored for physical, chemical and microbiological changes throughout the storage period. Optimum control over the growth of L. monocytogenes was achieved using a combination of 100%N$ sb2$ + an Ageless FX oxygen absorbent and dipping in a 0.2% chitosan solution. Based on these studies, a combination of 0.2% chitosan and MAP could be used to extend the shelf life of pork without adversely affecting color, odor and exudate loss while inhibiting the growth of the pathogenic microorganism, L.monocytogenes. (Abstract shortened by UMI.)

In this research, three alternative approaches to chemical preservatives to extend the mold free shelf-life and quality of pita bread were investigated namely: Modified Atmosphere Packaging (MAP) involving gas packaging, oxygen absorbents technology and ethanol vapor generators, high pressures, and direct and indirect heating. / Gas packaging using 60%CO2 (balance N2) inhibited the growth of Aspergillus niger and Penicillium notatum from 3d (pita bread packaged in air) to 35d at ambient temperature. A longer extension in shelf-life (42d) was possible using an Ageless oxygen absorbent or a Freshmax oxygen absorbent label in conjunction with gas packaging. / Similar results were obtained with 2G--4G sachets of Ethicap, and 100--200S sachets of Negamold, a dual functional oxygen absorbent-ethanol vapor generator. / High pressures (30--400MPa) used to inhibit mold growth, resulted in delamination of the packaging film and textural changes to the pita bread. / Other alternatives, such as direct heating and microwave processing had a minimal effect in increasing the shelf-life of pita bread. (Abstract shortened by UMI.)

The use of a direct method for measuring respiration and transpiration rates may lead to better storage control systems and closer observation of storage losses. A laboratory scale environmental chamber was constructed and provided with a fan and adjustable louver to obtain variable ventilation flow rates. Flow rates were determined using a pressure sensor and fan characteristic curves which were determined experimentally. A regression equation representing the flow rate versus pressure relation was derived and used for estimating the flow rates throughout the study. / Respiration and transpiration were simulated using precision heat sources ranging from 15 to 105W in 15W interval and an evaporative pad. Measured wet and dry bulb temperatures and ventilation flow rates were used for the estimation of heat and moisture generated inside the chamber. The work was performed in two parts. In the first, precision heat sources were used and the heat balance equation components were solved. / In the second part, heat and moisture were generated inside the chamber, heat and moisture balance equations as well as psychrometric equations were solved. (Abstract shortened by UMI.)