Abstract
Stainless steel, widely present in the food industry, is frequently exposed to bacterial colonization with possible consequences on consumers’ health. 288 stainless steel disks with different roughness (0.25, 0.5 and 1 μm) were challenged with four Gram-negative (Escherichia coli ATCC 25922, Salmonella typhimurium ATCC 1402, Yersinia enterocolitica ATCC 9610 and Pseudomonas aeruginosa ATCC 27588) and four Gram-positive bacteria (Staphylococcus aureus ATCC 6538, Enterococcus faecalis ATCC 29212, Bacillus cereus ATCC 14579 and Listeria monocytogenes NCTT 10888) and underwent three different sanitizing treatments (UVC, alcohol 70% v/v and Gold lotion). Moreover, the same procedure was carried out onto the same surfaces after a nanotechnological surface coating (nanoXHAM® D). A significant bactericidal effect was exerted by all of the sanitizing treatments against all bacterial strains regardless of roughness and surface coating. The nanoXHAM® D coating itself induced an overall bactericidal effect as well as in synergy with all sanitizing treatments regardless of roughness. Stainless steel surface roughness is poorly correlated with bacterial adhesion and only sanitizing treatments can exert significant bactericidal effects. Most of sanitizing treatments are toxic and corrosive causing the onset of crevices that are able to facilitate bacterial nesting and growth. This nanotechnological coating can reduce surface adhesion with consequent reduction of bacterial adhesion, nesting, and growth.
Highlights
EN 10204 3.1) disks (SEGAT GIANNI Srl, Gerenzano, Italy) with a 5 cm diameter was analyzed by profilometer (SURFTEST SJ-210, Mitutoyo Italiana S.r.l., Milano, Italy) resulting in three different roughness average values (Ra): 0.25 ± 0.02, 0.5 ± 0.03 and 1 ± 0.06 μm
We reported the significant bactericidal effect exerted by all the three sanitizing treatments tested against all bacterial strains, with respect to the initial inoculum sanitizing treatments testedofagainst alland bacterial with to itthe initial inocu
We can conclude that untreated stainless steel surface roughness is poorly correlated with bacterial adhesion and only sanitizing treatments can exert significant bactericidal effects
Summary
Stainless steel is widely present in the food industry as the main component of work surfaces, cookware, pasteurizers, homogenizers, separators, decanters, mixing, process and storage tanks, fittings, valves, pumps, and pipework [1,2,3]. Based on the high resistance to corrosion by acidic or sulfur dioxide-containing foods and cleanability, AISI 316 or. 316 L stainless steel should be preferred to AISI 302 or AISI 304 [2,4]. Naturally passivated by air or other oxidizers, stainless steel needs to undergo additional surface treatments (pickling, electropolishing, and mechanical cleaning) to improve its strength [5].
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