Decontamination of Spores on Model Stainless-Steel Surface by Using Foams Based on Alkyl Polyglucosides

Abstract

In the food industry, the surfaces of processing equipment are considered to be major factors in the risk of food contamination. The cleaning process of solid surfaces is essential, but it requires a significant amount of water and chemicals. Herein, we report the use of foam flows based on alkyl polyglucosides (APGs) to remove spores of Bacillus subtilis on stainless-steel surfaces as the model-contaminated surface. Sodium dodecyl sulfate (SDS) was also studied as an anionic surfactant. Foams were characterized during flows by measuring the foam stability and the bubble size. The efficiency of spores' removal was assessed by enumerations. We showed that foams based on APGs could remove efficiently the spores from the surfaces, but slightly less than foams based on SDS due to an effect of SDS itself on spores removal. The destabilization of the foams at the end of the process and the recovery of surfactant solutions were also evaluated by using filtration. Following a life cycle assessment (LCA) approach, we evaluated the impact of the foam flow on the global environmental footprint of the process. We showed significant environmental impact benefits with a reduction in water and energy consumption for foam cleaning. APGs are a good choice as surfactants as they decrease further the environmental impacts.

Keywords: cleaning; foam; life cycle analysis; spore; surface hygiene.

Figure 1

Spores log reduction on the plate under static dipping conditions as a function of the surfactant in comparison to water. The small letters a–b indicate groups of statistical differences according to Tukey’s test (p < 0.05).

Figure 2

Spores log reduction on the plate in dynamic condition during foam flow cleaning after 1 and 30 min of foam flow as a function of the surfactant in comparison to water. The small letters a–d indicate groups of statistical differences according to Tukey’s test (p < 0.05) between the water and the surfactants for 1 min of foam flow cleaning and for 30 min of foam flow cleaning.

Figure 3

Epifluorescence microscopy pictures of a stainless-steel plate contaminated by spores and stained with acridine orange: (a) before cleaning by foam flow, (b) after one minute of foam flow cleaning based on DG, and (c) after 30 min of foam flow cleaning based on DG. The scale bar represents 1 mm for all the pictures.

Figure 4

Evolution of the foam height for SDS, DG, and LG: (a) before the foam passed through the duct containing the plate contaminated with spores and (b) after the foam passed through the duct.

Figure 5

Mean bubbles area of the foams produced with SDS, DG, and LG with the corresponding microscopic pictures: (a) before the foam passed through the duct containing the plate contaminated with spores and (b) after the foam passed through the duct. The scale bar represents 1 mm for all the foam pictures. The small letters a–b indicate groups of statistical differences according to Tukey’s test (p < 0.05).

Figure 6

Pictures of the foams produced from the surfactants solution (SDS, DG, and LG) before and after filtration to remove the spores, showing a similar foamability and foam stability around 5 min after producing the foam. The scale bar represents 2 cm for all the pictures.

Figure 7

Environmental comparison between foam cleaning process with APG and foam cleaning process with SDS (reference system) by impact category (ReCiPe midpoint H).

Figure 8

Different steps of stainless-steel plate surface preparation methodology: (1) 15 cycles of immersion of the plate in milk at room temperature for 30 min and in sodium hydroxide at 70 °C for 30 min; (2) biofilm formation on the plate; (3) rubbing of the plate with commercial undiluted surfactant (RBS) followed by immersion of the plate in surfactant aqueous solution at 5 wt.% at 60 °C for 10 min; (4) the plate sterilization in a hot air oven at 180 °C for 1 h; (5) soiling of the plate with 5 drops of 1 μL of the spore suspension at a concentration of 10⁸ CFU.mL⁻¹.

Figure 9

The process flowchart for the foam cleaning process formulated with: (a) SDS and (b) APG.