which is the active antimicrobial agent in both anaerobic MAP and VP (Sebranek & Houser, 2006). When CO2 is introduced into the headspace of a package, its concentration will decline as CO2 is absorbed into themeat. Dixon and Kell (1989) reported that CO2 gas dissolves readily into the aqueous phase of the meat and produce carbonic acid (H2CO3) which results in decreased meat pH and microbial growth. Carbon dioxide usually results in a decrease in pH of 0.05–0.35 units in the meat product (Huffman, Davis, Marple, & McGuire, 1975; Rousset & Renerre, 1991). The increase in pH observed in all PVC treatments may have been caused by production of alkaline by-products during growth and stationary phase of the microorganisms.