Thermal Inactivation of Salmonella and Enterococcus faecium during Pecan Conditioning Treatments

Introduction: Validating the processes and equipment used by the nut industry is necessary under the Food Safety and Modernization Act. Currently, FDA recommends nut processors (except almonds) to use a process that is validated to reduce Salmonella by 5 log CFU/g. The use of non-pathogenic surrogate instead of the pathogen is recommended for validation studies.

Purpose: Our objective was to evaluate the suitability of Enterococcus faecium (ATCC 8459) as a surrogate of Salmonella during hot water conditioning treatment of pecans.

Methods: In-shell pecans (Southern Improved) were inoculated to ca. 7 log CFU/g after drying to the original moisture content and water activity, with either a 5-strain Salmonella cocktail or E. faecium. The cocktail of Salmonella included serotypes Enteritidis PT 30, Enteritidis PT 9c, Oranienburg, Seftenberg and Tennessee. In-shell pecans (50 g) were submerged in a water bath (n = 6) at 75 ± 1°C (20, 40, 80, 120 s), 80 ± 1°C (20, 40, 80, 120 s), 85 ± 1 (20 40, 80, 120 s), 90 ± 1°C (20, 40, 60, 80 s) and 95 ± 1°C (20, 40, 60, 80 s). Treated nuts were added to 100 ml of cold TSB, cracked with a hammer and stomached for 1 min. Populations were enumerated onto selective and non-selective media supplemented with nalidixic acid (50 µg/ml).

Results: Under all treatment conditions, log reductions (log N/No) of E. faecium were either not significantly different from (P > 0.05), or significantly lower than (P < 0.05), Salmonella. A maximum of 4.8-log reduction was observed following exposure to 95 ± 1°C water for 80 s. Reduction data did not fit into a linear or Weibull model.

Significance: E. faecium can be successfully used by pecan industry to validate hot water conditioning treatments. As no model to predict reductions during conditioning was developed, the pecan industry should validate individual protocols for achieved log reductions.