Growth of Escherichia coli and Salmonella typhimurium on high-pH beef packed under vacuum or carbon dioxide.

A strain each of Escherichia coli and Salmonella typhimurium, were inoculated onto samples of high-pH (greater than 6.0) beef. Samples were packaged under vacuum or CO2 and stored at 8, 10, 12, 15, 20 or 30 degrees C. In vacuum packs, E. coli and S. typhimurium grew at all storage temperatures. At temperatures between 8 and 12 degrees C inclusive, both organisms grew at rates less or no more than those of the spoilage flora after significant lag periods. At temperatures of 15 degrees C or above, growth rates were equal to or greater than those of the spoilage flora, and lag periods were insignificant. In CO2 packs, neither organism grew at 8 degrees C, and S. typhimurium did not grow at 10 degrees C. Subsequent tests showed that E. coli did not grow at 9 degrees C, nor S. typhimurium at 11 degrees C. At 12 degrees C, both organisms grew, after prolonged lags, at rates markedly slower than that of the spoilage flora. At 15 degrees C, their growth rates were similar to that of the spoilage flora. At higher temperatures, both organisms grew without significant lags at rates greater than that of the spoilage flora.