Microbiological Studies on Gas-Packaged Crumpets

English-style crumpets, a chemically leavened bakery product, had a shelf life of 14 d when packaged in a CO₂:N₂ (3:2) gas atmosphere and stored at ambient temperature. Packages were visibly swollen after 14 d due to additional CO₂ production, and the product had a distinct fruity odor when opened. Initial microbiota of the product, isolated from anaerobic plates, consisted entirely of facultative anaerobic spore-forming strains of Bacillus licheniformis . After 7 d at 25°C the spoilage pattern changed, with lactic acid bacteria (LAB) accounting for almost 100% of the total anaerobic plate counts (TPC) on APT and MRS (pH 5.5) agar media. Subsequently, the number of LAB declined slightly in relation to the TPC, and B. licheniformis strains reappeared. As the LAB increased in numbers, there was a concomittant increase in CO₂ and lactic acid production and a drop in pH of the product. Metabolic activity continued even after the LAB were in the maximum stationary phase. Leuconostoc mesenteroides was subsequently identified as the major CO₂-producing isolate.