P1-175 Effect of Product Structure on Thermal Resistance of Salmonella Enteritidis PT30 on Whole Almonds, in Almond Meal and in Almond Butter

Monday, August 4, 2014
Exhibit Hall D (Indiana Convention Center)
Pichamon Limcharoenchat, Michigan State University, East Lansing, MI
Bradley Marks, Michigan State University, East Lansing, MI
Ian Hildebrandt, Michigan State University, East Lansing, MI
Nicole Hall, Michigan State University, East Lansing, MI
Introduction: Low-moisture products, such as almonds, can be contaminated with Salmonellain the production environment. Subsequent valued-added processes change product structure, but the impact on pathogen thermal resistance has not been reported.   

Purpose: The objective was to quantify the effect of product structure on thermal resistance of Salmonella Enteritidis PT30 inoculated onto whole almonds subsequently ground into almond meal and almond butter.

Methods: Almonds were inoculated with Salmonella Enteritidis PT30 (~108 CFU/g) and equilibrated to ~0.4 aw. After equilibration, almonds (100 g) were ground in a food processor (45 s) to produce an almond meal sized between U.S. standard sieves #20 and 80. Almond butter was produced by further milling almonds (200 g) for 15 min, with dry ice added every 2 min to control product temperature (<40°C). All products were re-equilibrated to ~0.4 aw. The inoculated almonds were individually vacuum-packed in thin layer plastic bags, and meal and butter samples (thickness < 1 mm) were packed in aluminum test cells. Samples were heated in an isothermal water bath (~80°C), with almonds pulled every 10 min for 1.25 h, and meal and butter pulled every 15 min for 2.5 h; all were cooled immediately in an ice bath, diluted in peptone water, and plated on modified TSA to enumerate survivors.

Results: Initial Salmonella populations and sample water activities were not significantly different (P > 0.05) after grinding and milling. However, D80°C values, determined by linear regression of the Salmonella survivor curves, were greater (P< 0.05) in almond meal (60.7 min) and almond butter (66.0 min) than on the whole almonds (19.1 min).

Significance: Changing the product structure, given equivalent aw and composition, significantly impacted Salmonella thermal resistance.  Therefore, it is extremely important to use product-specific inactivation parameters when validating pasteurization processes.