Growth and survival of exponential and stationary phase Salmonella during sausage fermentation

Abstract

When raw meat is contaminated with enteropathogens, the growth state may appear in a mixture of phases. Survival for exponential and stationary phase cells differs, with stationary phase cells being generally more resistant. Our aim of this study was to investigate the survival of exponential and stationary phase Salmonella during freezing and to follow the survival/growth of these cells during subsequent sausage fermentation. Minced meat was inoculated with exponential and stationary phase Salmonella Thyphimurium, respectively, and frozen at -20oC for up to 35 days. The meat was thawed overnight at 5oC prior to sausage production. The sausages were fermented at 25oC and growth/survival was observed for 3 days. In the freezing period before sausage production, no reduction of stationary phase cells was observed after more than 35 days whereas exponential phase cells were reduced more than 1.5 log10 units. Despite this reduction, exponential phase cells was able to grow to the same level as the stationary phase cells during fermentation of sausages simulating failure of the starter culture. However, the pH drop caused by the starter culture prevented growth of both exponential as well as stationary phase Salmonella. These results show that failure of a starter culture to lower pH may lead to growth of Salmonella, independent of the phases.