Time-Course Study of the Antibacterial Activity of an Amorphous SiOxCyHz Coating Certified for Food Contact

Abstract

One of the most-used food contact materials is stainless steel (AISI 304L or AISI 316L), owing to its high mechanical strength, cleanability, and corrosion resistance. However, due to the presence of minimal crevices, stainless-steel is subject to microbial contamination with consequent significant reverb on health and industry costs due to the lack of effective reliability of sanitizing agents and procedures. In this study, we evaluated the noncytotoxic effect of an amorphous SiO_xC_yH_z coating deposited on stainless-steel disks and performed a time-course evaluation for four Gram-negative bacteria and four Gram-positive bacteria. A low cytotoxicity of the SiO_xC_yH_z coating was observed; moreover, except for some samples, a five-logarithm decrease was visible after 1 h on coated surfaces without any sanitizing treatment and inoculated with Gram-negative and Gram-positive bacteria. Conversely, a complete bacterial removal was observed after 30 s^-1 min application of alcohol and already after 15 s under UVC irradiation against both bacterial groups. Moreover, coating deposition changed the wetting behaviors of treated samples, with contact angles increasing from 90.25° to 113.73°, realizing a transformation from hydrophilicity to hydrophobicity, with tremendous repercussions in various technological applications, including the food industry.

Keywords: SiOxCyHz coating; antibacterial activity; food contact material; hydrophobicity; stainless steel.

Figure 1

Graphical representation of the different exposure times of uncoated disks with different surface roughness (R0.25, R0.5, and R1) unsanitized (control) and subjected to two sanitizing methods (UVC and alcohol) against (A–C) Escherichia coli ATCC 25922, (D–F) Salmonella Typhimurium ATCC 1402, (G–I) Pseudomonas aeruginosa ATCC 27588 and (J–L) Yersinia enterocolitica ATCC 9610.

Figure 2

Graphical representation of the different exposure times of SiO_xC_yH_z-coated disks with different surface roughness (R0.25, R0.5, and R1) unsanitized (control) and subjected to two sanitizing methods (UVC and alcohol) against (A–C) Escherichia coli ATCC 25922, (D–F) Salmonella Typhimurium ATCC 1402, (G–I) Pseudomonas aeruginosa ATCC 27588 and (J–L) Yersinia enterocolitica ATCC 9610.

Figure 3

Graphical representation of the different exposure times of uncoated disks with different surface roughness (R0.25, R0.5, and R1) unsanitized (control) and subjected to two sanitizing methods (UVC and alcohol) against (A–C) Staphylococcus aureus ATCC 6538, (D–F) Listeria monocytogenes NCTT 10888, (G–I) Bacillus cereus ATCC 14579 and (J–L) Enterococcus faecalis ATCC 29212.

Figure 4

Graphical representation of the different exposure times of SiO_xC_yH_z-coated disks with different surface roughness (R0.25, R0.5, and R1) unsanitized (control) and subjected to two sanitizing methods (UVC and alcohol) against (A–C) Staphylococcus aureus ATCC 6538, (D–F) Listeria monocytogenes NCTT 10888, (G–I) Bacillus cereus ATCC 14579 and (J–L) Enterococcus faecalis ATCC 29212.

Figure 5

Graphical representation of (A) morphological grading score, (B) cell viability, and (C–F) microscopic images (10×) of vehicle, negative and positive control, and SiO_xC_yH_z coating, respectively; * p < 0.05 and **** p < 0.0001.

Figure 6

Environmental scanning electron microscope morphological analysis on (A) uncoated and (C) SiO_xC_yH_z-coated stainless-steel disks observed at 300 μm, along with their respective (B,D) X-EDS microanalysis.

Figure 7

Representative contact angle images of (A,C) water and (B,D) diiodomethane on uncoated and coated sample, respectively.

Figure 8

Representative image of stainless-steel disks of different R_a (A–C) uncoated and (D–F) SiO_xC_yH_z-coated.