Food Protection with Modified Atmospheres 363 CO2 + 85% N2 , 80% CO2 + 20% N2 , under vacuum, and in pure nitrogen at 4◦ C for up to weeks In another study of C jejuni in beef, two of three strains decreased slightly when stored at 20◦ C and 4◦ C for 48 hours but increased when stored at 37◦ C under all gas mixtures used.44 The storage conditions consisted of vacuum packaging, 20% CO2 + 80% N2 , 5% O2 + 10% CO2 + 85% N2 , and the background biota apparently had no effect on C jejuni When heat-injured and uninjured cells of Aeromonas hydrophila were stored at 5◦ C for 22 days under 100% N2 or 100% CO2 , both types steadily declined in numbers, but growth of both was enhanced when incubated under N2 33 The heat-injured cells apparently were not particularly disadvantaged under the conditions noted In a study of raw crayfish stored at 4–10◦ C for up to 30 days, Aeromonas hydrophila, S aureus, C perfringens, and C botulinum type E were not found.63 When cooked crawfish was inoculated with 103 cfu of C botulinum type E spores/g of crawfish tail, vacuum packaged with both high-barrier film and air-impermeable bags followed by storage at and 10◦ C for 30 days, type E toxin was not detected in any packages.63 SPOILAGE OF MAP AND VACUUM-PACKAGED MEATS From the research of many groups, it is clear that when vacuum-packaged meats undergo long-term refrigerator spoilage, often the predominant organisms are lactobacilli, other lactics, B thermosphacta, or all of these Other organisms can be found and, indeed, others may predominate Among the determining factors are the following: whether the product is raw or cooked; concentration of nitrites present; relative load of psychrotrophic bacteria; the degree to which the vacuum-package film excludes O2 ; product pH Cooked or partially cooked meats, along with dark, firm, and dry (DFD) and dark-cutting meats, have a higher pH than raw and light-cutting meats, and the organisms that dominate these products during vacuum storage are generally different from those found in vacuum-packaged normal meats In vacuum-packaged DFD meats held at 2◦ C for weeks, the dominant biota consisted of Yersinia enterocolitica, Serratia liquefaciens, Shewanella putrefaciens, and a Lactobacillus sp.32 S putrefaciens caused greening of product, but a pH