The physicochemical properties of fruit powders and their residence time on stainless steel surfaces are associated with their ease of removal by brushing

Factors Affecting the Adhesion of Flour Particles to Stainless-steel Surfaces and Vacuum Dry-cleaning

Recent outbreaks and recalls linked to flour-based products have highlighted the need for improved cleaning methods in low-moisture environments. The factors affecting adhesion forces of flour particles, and the vacuum cleaning methodologies to overcome these forces, need to be better understood. The objectives of this study were to: (1) Measure electrostatic charge build-up in flour under different environmental conditions (20, 40, 60% relative humidity at room temperature), (2) quantify how powder size (US standard No. 60-80 or 80-100 mesh), electrostatic charge (charged and uncharged), and relative humidity impact the force required to remove the powder from an electropolished 304 stainless steel coupon (8 × 8 × 0.2 cm), and (3) determine the most effective vacuum nozzle angle (0, 45, 90° relative to the surface) for cleaning. Chargeability (nC) of flour samples was assessed using Faraday cup electrometry, while the surface adhesion force of the flour particles was measured using a custom-built impact tester. The surface cleanliness after vacuum treatments was assessed using ATP (adenosine triphosphate) swabs and a luminometer. Charged flour samples at 20% relative humidity (RH) exhibited a significantly higher charge compared to those at 40 and 60% RH. Within the 60-80 mesh range, charged flour showed higher adhesion rates than uncharged samples at both 20 and 40% RH. However, in the 80-100 mesh range, charged flour did not show a significant difference in adhesion when compared to uncharged samples at any RH level. Additionally, at 60% RH, surface residues measured by ATP were significantly lower for a vacuum angle of 90° than for 0° across both 60-80 mesh and 80-100 mesh size ranges of wheat flour. The vacuum cleaning treatment proved capable of overcoming the increase in adhesion from triboelectric forces; however, trace flour residues were still detected on stainless steel surfaces postvacuuming, indicating that vacuuming alone may be insufficient.

Survival of Salmonella enterica and Enterococcus faecium on Abiotic Surfaces During Storage at Low Relative Humidity

Currently, there is limited knowledge on the survival of bacteria on surfaces during postharvest handling of dry products such as onions. Extended survival of microorganisms, coupled with a lack of established and regular, validated cleaning or sanitation methods could enable cross-contamination of these products. The aim of the study was to evaluate the survival of a potential surrogate, Enterococcus faecium, and Salmonella enterica on typical onion handling surfaces, polyurethane (PU), and stainless steel (SS), under low relative humidity. The influence of onion extract on the survival of E. faecium and Salmonella on PU and SS was also investigated. Rifampin-resistant E. faecium NRRL B-2354 and a five-strain cocktail of Salmonella suspended in 0.1% peptone or onion extract were separately inoculated onto PU and SS coupons (2 × 2 cm), at high, moderate, or low (7, 5, or 3 log CFU/cm2) levels. The inoculated surfaces were stored at ∼34% relative humidity and 21°C for up to 84 days. Triplicate samples were enumerated at regular intervals in replicate trials. Samples were enriched when populations fell below the limit of detection by plating (0.48 log CFU/cm2). Scanning electron microscopy was used to observe the cell distribution on the coupons. Reductions of E. faecium of less than ∼2 log were observed on PU and SS over 12 weeks at all inoculum levels and with both inoculum carriers. In 0.1% peptone, Salmonella populations declined by 2 to 3 log over 12 weeks at the high and moderate inoculum levels; at the low inoculum level, Salmonella could not be recovered by enrichment at 84 days. Survival of E. faecium and Salmonella was significantly (P < 0.05) enhanced over 84 days of storage when suspended in onion extract, where cells were covered by a layer of onion extract. E. faecium might have utility as a conservative surrogate for Salmonella when evaluating microbial survival on dry food-contact surfaces.

A review of food safety in low-moisture foods with current and potential dry-cleaning methods

Food is one of the basic needs of human life. With the increasing population, the production and supply of safe and quality foods are critical. Foods can be classified into different categories including low moisture, intermediate moisture, and high moisture content. Historically, low-moisture foods have been considered safe for human consumption due to the limited amount of moisture for microbial activity. Recalls of these foods due to pathogens such as Salmonella and undeclared allergens have brought attention to the need for improved cleaning and sanitization in dry food manufacturing facilities. In the food industry, cleaning and sanitation activities are the most efficient methods to prevent microbial contamination; however, water is most often required to deliver cleaning and sanitation agents. A well-written and properly implemented sanitation standard operating procedure can take care of microbial and allergen cross-contamination. Nevertheless, there are unique challenges to cleaning and sanitation processes for low-moisture food manufacturing facilities. The introduction of moisture into a low-moisture food environment increases the likelihood of cross-contamination by microbial pathogens. Hence, the use of water during cleaning and sanitation of dry food manufacturing facilities should be limited. However, much less research has been done on these dry methods compared to wet sanitation methods. This review discusses recent foodborne outbreaks and recalls associated with low-moisture foods the accepted methods for cleaning and sanitation in dry food manufacturing facilities and the limitations of these methods. The potential for air impingement as a dry-cleaning method is also detailed.

Surface inoculation method impacts microbial reduction and transfer of Salmonella Enteritidis PT 30 and potential surrogates during dry sanitation

Dry sanitation methods are often limited to physical removal strategies such as brushing or wiping with sanitary cleaning tools. However, the relative efficacy of these approaches to remove microbiota on surfaces, and the risk of transferring cells to other surfaces via the cleaning tool, is unclear. The effect of dry wiping with a single-use towel on the removal of four different bacteria (Salmonella Enteritidis, Enterococcus faecium, Listeria innocua, Escherichia coli) was investigated. We also quantified the number of cells transferred to the towel itself during dry cleaning. Three different surface inoculation methods (spot, glass bead, contaminated milk powder) were assessed and significantly impacted initial surface microbial load. Higher initial counts corresponded to lower transfer coefficients (e.g., proportion of transferred cells). The effect of bacterial identity was significant on reduction after dry wiping for all three inoculation methods. Moreover, both bacterial identity and inoculation method had significant effects on the number of cells transferred to the towel. In most scenarios, dry wiping resulted in a reduction <1.0 log CFU/coupon. Although, on surfaces inoculated via contaminated milk powder, reductions of up to 1.6 ± 0.3 log CFU/coupon were obtained. Overall, E. faecium transferred more readily to the towel. These results may help guide experimental design for future research on dry sanitation.