Evaluation of Choridic Acid Cross-protection in Salmonella Typhimurium Submitted to Long-term Desiccation Stress in Peanuts

Introduction: The capacity of Salmonella to survive in the food supply chain and in the gastrointestinal tract, is partly due to defense mechanisms that are activated during stress conditions. Preexposure of microorganisms to an unfavorable environment can select resistant cells and promote cross-protection to different types of stress.

Purpose: Evaluate the behavior of SalmonellaTyphimurium against acid stress conditions after being recovered from roasted peanuts stored for a long time.

Methods:  Two types of Salmonella Typhimurium ATCC 14028 inoculum were used: one cultivated in brain heart infusion broth (control) and the other recovered from roasted peanuts stored at 28°C over 550 days. The tests were performed in tryptic soy broth with differential pH adjusted with choridic acid. Salmonellacount was determined on XLD agar every 60 min until four hours.

Results:  The cells recovered from peanuts had similar behavior (P>0.05) to the control cells during four hours of storage at pH 7.2, with growth of ca. 1.0 log cfu/g. At pH 4.5, there was a statistical difference (P<0.05) between the samples from three hours on. Cells exposed to desiccation stress did not show growth throughout four hours, whereas an increase of 0.8 log cfu/g in the control sample was observed. At pH 3.5 the control remained stable throughout the treatment, while the cells recovered from peanuts showed reduction up to 0.8 log cfu/g. At pH 3.0, the Salmonella count was reduced to below the limit of detection (1.0 log cfu/g) after one hour for inoculum recovered from peanuts and after three hours for control.

Significance: Salmonella cells exposed to low water activity environment had high sensitivity to acid stress condition.