Cleaning and Sanitation of Salmonella-contaminated Peanut Butter Processing Equipment

Introduction: Contamination of peanut butter and nut butter products by pathogenic Salmonella serovars have led to an increasing number of product recalls and foodborne outbreaks. Post-processing contamination of peanut butter poses a significant health risk to consumers as Salmonella can remain viable throughout the shelf-life of the product. Effective cleaning and sanitation of nut butter lines are essential for preventing cross-contamination of microbial hazards such as Salmonella.

Purpose: The objective of this study was to evaluate the efficacy of commonly used commercial cleaning methods, hot oil and isopropanol, on Salmonellasurvival and/or removal from pilot-scale peanut butter processing equipment.

Methods:   Peanut butter inoculated with a cocktail of four Salmonella serovars (inoculation level ~7 log CFU/g) was used to contaminate peanut butter processing equipment (capacity ~75 l).  The system was drained of peanut butter, and treated with hot oil (93°C) for 2 h and then 60% isopropanol for 1 h (via continuous recirculation). Microbial analysis of environmental (swabs of 8 different locations in the processing line) and product (peanut butter and oil) samples obtained during the cleaning procedures was conducted using trypticase soy agar with yeast extract (TSAYE) and xylose lysine deoxycholate (XLD) agar.

Results: Samples of oil obtained after the 2 h cleaning treatment contained ~3.2 log CFU/g on both TSAYE and XLD, indicating the hot oil treatment was not sufficient to inactivate the contamination in the processing line. Following hot oil circulation, environmental sampling of various locations in the processing line found 2.5-7.0 log CFU/cm² remaining on processing equipment surfaces as measured on TSAYE and XLD. After the 60% isopropanol sanitation treatment, no Salmonella was detected in environmental samples cultured on XLD (detection limit = 1.0 log CFU/cm²).

Significance: These data suggest that a two-step process consisting of a hot oil cleaning step followed by a 60% isopropanol sanitization treatment may eliminate pathogenic Salmonella from a contaminated peanut butter processing line.