Growth of Yersinia enterocolitica and spoilage microorganisms on fresh pork and minimally processed broccoli packaged in modified atmospheres

Fresh broccoli was inoculated with 3 to 4 log CFU/g Y. enterocolitica immersed in a salt solution, packaged in air, MA and under vacuum and stored at 4 and 10{dollar}spcirc{dollar}C. Phenotypic characteristics of Y. enterocolitica were used to detect presence of the virulence plasmid after exposure to each packaging and storage regime. These included Congo red uptake, calcium dependence, and autoagglutination in methyl red-Vogues Proskauer broth and tissue culture medium. Populations of Y. enterocolitica increased in untreated and salt-treated broccoli during storage at 4 and 10{dollar}spcirc{dollar}C. Salt treatment of broccoli did not inhibit growth of Y. enterocolitica in each packaging treatment. The virulence plasmid of Y. enterocolitica was detected in 13-22% of isolates following salt treatment and storage on minimally processed broccoli.; The microbiological quality of salt-treated minimally processed broccoli packaged and stored at 4 and 10{dollar}spcirc{dollar}C in MA was studied by examining the fate of spoilage bacteria. Fresh untreated broccoli packaged in air and MA maintained a crisp green appearance for 9 days at 4{dollar}spcirc{dollar}C and 6 days at 10{dollar}spcirc{dollar}C. Vacuum packaged fresh broccoli had an extended shelf-life of up to 15 days at 4{dollar}spcirc{dollar}C. Vacuum packaged salt-treated broccoli showed signs of deterioration within 3 days of packaging, while salt-treated broccoli packaged in air and MA began to deteriorate within 3 to 6 days at 4 and 10{dollar}spcirc{dollar}C.; Slices of high (pH {dollar}>{dollar} 6.0) and normal (pH {dollar}<{dollar} 5.8) pH pork striploin were inoculated with Y. enterocolitica, vacuum packaged or packaged under 100% CO{dollar}sb2{dollar} in barrier bags, and stored at 4{dollar}spcirc{dollar}C. Numbers of Y. enterocolitica on the lean surface of high pH pork slices increased approximately 3.0 log CFU/cm{dollar}sp2{dollar} when vacuum packaged and stored at 4{dollar}spcirc{dollar}C for 30 days. Storage of inoculated normal pH pork in 100% CO{dollar}sb2{dollar} resulted in Y. enterocolitica remaining in lag phase throughout the storage period. The virulence plasmid of Y. enterocolitica was maintained in 10-21% of isolates for the duration of storage on vacuum and CO{dollar}sb2{dollar} packaged pork.