An electrostatic dry surface inoculation method for low-moisture food contamination experiments

Salmonella outbreaks linked to wheat flour and related products pose a significant public health concern. Additionally, dry food processing equipment currently lacks federally mandated sanitation guidelines. While existing models of pathogen transfer and adhesion provide useful insights, they may not fully represent real-world contamination scenarios. Therefore, there is a need for a replicable dry inoculation method for food powders on food-contact surfaces. The objective of this study was to develop and evaluate a novel non-aqueous surface inoculation method using an electrostatic powder-coating technique. A 1000 g wheat berry mix was inoculated with a six-serovar Salmonella cocktail, equilibrated to water activity (a_w) ∼0.45, and milled into all-purpose flour. Subsequently, 0.1 g of inoculated flour was electrostatically adhered onto circular #304 and #316L stainless steel (SS) coupons (6.43 cm diameter). Coated SS coupons were brushed 10 times vertically and 10 times horizontally to produce a visibly clean yet contaminated surface. Electrostatically coated coupons (n = 48) achieved populations of 5.5 ± 0.6 and 5.7 ± 0.2 log CFU/cm² on #304 and #316L SS, respectively. After brushing to a visibly clean state, the original populations decreased (p < 0.05) to 3.9 ± 0.6 and 4.1 ± 0.6 log CFU/cm², representing a 1-1.5 log reduction. Microscopic observation confirmed residual flour particles remained on visibly clean surfaces. No significant differences were observed between SS grades. Overall, the novel dry inoculation methodology was an effective technique for achieving consistent and substantial Salmonella inoculation levels on SS surfaces while reflecting real-world contamination and brush-based cleaning scenarios.