Survival of Salmonella in pasteurized tahini

Salmonella enterica is the leading human pathogen responsible for bacterial foodborne outbreaks worldwide. In recent years, low water activity foods have gained the attention as transmission agents, where contamination can occur at multiple steps along the food chain. Our research focuses on the foodstuff tahini, which is often linked to Salmonella infection cases. Thermal treatments are suggested to reduce pathogen populations in low water and high fat content food (LW-HF). However, it is a challenging task in the industry since heat may impact the food quality and also, little is known about Salmonella’s behavior and resistance in a LW-HF environment.

This research, studies the survival mechanisms of Salmonella Typhimurium in pasteurized tahini at elevated temperatures by identifying food related factors such as water content (0-90 % w/w) that could influence this issue. We found that thermal treatments are suitable to kill a partial population of Salmonella but not practical to kill all cells. To achieve a 7-log reduction, a long heat exposure is needed (12 hours at 70° C; 7 hours at 80° C) and would affect the properties of the tahini. The survival of Salmonella in 100 % tahini, resulted significantly higher than in the tahini/water emulsions tested. We further analyzed the distribution of Salmonella cells expressing fluorescent protein throughout tahini oil and observed that they aggregate in 100 % oil while they spread in oil/water emulsions (50 and 90 w/w %). The distribution of Salmonella cells in the oil matrix could elucidate a local protection during heat treatments.