Determining the Shelf Life of Ready-to-Eat Deli Products Held at 40ºF, 45ºF and 50ºF Using Total Aerobic Plate Count as a Surrogate Growth Indicator of Listeria monocytogenes

Introduction: Shelf Life Determination of Ready-to-Eat Deli products varies within the food industry. Food Safety Shelf Life, relying on product Total Aerobic Plate Count may not reflect the growth of pathogens such as Listeria monocytogenes. This study evaluated product Total Aerobic Plate Count in parallel with a product Challenge using a five-strain cocktail of Listeria monocytogenes.

Purpose: Determine if Total Aerobic Plate Count values correlate with Listeria monocytogenes growth values at 40°F, 45°F and 50°F and may be used to establish a Food Safety Shelf Life for Ready-to-Eat Deli Products.

Methods: Ready-to-Eat Deli Products (Salads and Meats) were separated into two groups and held at 40°F, 45°F, 50°F for the duration of the Shelf Life Study of 30 days. Group I was analyzed for Total Aerobic Plate Count (TAPC). Corresponding Group II was inoculated using a five-strain cocktail of Listeria monocytogenes. Samples were quantitatively evaluated at weekly intervals using Standard Methods agar for TAPC and MOX media for Listeria monocytogenes.

Results: Correlation of TAPC growth and Listeria monocytogenes growth is product dependent. Intrinsic product factors were more influential on growth than storage temperature. A challenge provides an accurate reproducible method to Determine Food Safety Shelf Life as opposed to quantitating Total Aerobic Plate Count.

Significance: Food Safety Shelf Life determination should be based on a reproducible quantifiable method such as an active challenge. Basing Shelf Life on a passive indicator test like TAPC, with product variability may not be an accurate predictor of Food Safety Shelf Life.