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P1-172 Impact of the Local Microenvironment in a Food Matrix on Salmonella Survival

Monday, July 23, 2012
Exhibit Hall (Rhode Island Convention Center)
Haiping Li, U.S. Food and Drug Administration, Bedford Park, IL
Anuhya Goutham Bhaskara, Illinois Institute of Technology (IFSH), Bedford Park, IL
Christina Megalis, U.S. Food and Drug Administration, Bedford Park, IL
Fei Yang, Illinois Institute of Technology (IFSH), Bedford Park, IL
Gregory Fleischman, U.S. Food and Drug Administration, Bedford Park, IL
John Koontz, U.S. Food and Drug Administration, Bedford Park, IL
Mary Lou Tortorello, U.S. Food and Drug Administration, Bedford Park, IL
Introduction: Multiphasicfoods can be problematic in process validations. Ingredients can create local microenvironments that may determine process effectiveness and be more critical to pathogen survival than the overall physicochemical properties of the food. Although it has been speculated that local microenvironments can affect pathogen survival, experimental validation of this concept has not been performed.

Purpose: To study the impact of the local microenvironments on the survival of Salmonella in model multiphasicfood systems.

Methods: Non-fat dry milk powder (NFDM) and creamy peanut butter (PB) were combined to create model multiphasic systems having identical compositions but different physicochemical local microenvironments. Salmonella cells were mixed into either matrix, and then combined with the other in different sequential order, as follows: 10 log CFU Salmonella cells in 0.5 ml of PBS was added to 5 g NFDM or 20 g PB, homogenized, and then mixed into 20 g PB and 5 g NFDM, respectively. Cells were also inoculated into 25 g pure PB and NFDM, respectively, as control systems. Viable cells were enumerated by plate counting within 1 h of inoculation and after 5 weeks of storage at 25ºC. The distribution of water, lipid, and protein in the microenvironment was analyzed by micro-FT-IR using a mid-IR ATR image analysis system. Three independent experiments were carried out using duplicate samples in each. Data were analyzed using One-Way ANOVA and TukeyHSD test.

Results: Each inoculated model system showed a statistically uniform distribution in terms of bacterial counts per gram, but not homogenous absorptions of amines, OH, C-C, and C=C groups, as determined by FT-IR imaging with chemical specificity and high spatial resolution analysis. Within one hour of inoculation, the log reduction was about 4-fold greater (P < 0.05) in the system with NFDM (2-log reduction) as the first ingredient than the one in which PB was first (0.55-log reduction). This log reduction pattern was consistent between the pure NFDM (2.5-log reduction) and pure PB (0.67-log reduction) (P < 0.01). After 5 weeks of equilibration, a 2-fold greater log reduction (P < 0.01) was observed in the system with NFDM (4-log reduction) as the first or only ingredient than the one in which PB was in immediate contact with cells (2-log reduction).

Significance: This study is the first report which provides evidence that characterized the local microenvironment and its role on Salmonella survival. Pathogen survival and process effectiveness may depend on whether the contaminated ingredient is miscible or remains as a discrete phase within the food.

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