Atmospheric pressure plasma spraying of silane-based coatings targeting whey protein fouling and bacterial adhesion management

Abstract

This work aims at studying the impact of silane-based coatings, generated by atmospheric pressure plasma spraying (APPS) of a liquid precursor (hexamethydisiloxane -HMDSO), on dairy antifouling and antibacterial properties of food-grade 316L stainless steel. The influence of the manufacturing parameters (precursor flow rate, nozzle-to-substrate distance and scanning speed) on the coatings properties was investigated using a wide range of characterization techniques (drop shape analysis, X-Ray Mappings, Scanning Electron Microscopy, Fourier-Transformed Infrared Spectroscopy, Atomic Force Microscopy). Coating's roughness in particular was shown to strongly increase when precursor flow rate increases. A pilot pasteurizer, fed with a model foulant solution (whey protein and calcium), allowed performing two consecutive industrial-like isothermal dairy fouling tests, revealing the promising anti-fouling properties of the HMDSO-coated steel. A fouling reduction of up to 90% compared to bare stainless steel was achieved after first cycle for all samples. The second fouling run allowed to select the best-performing sample, which kept the same antifouling properties as in the first test.Its mechanism of action was investigated, which revealed that a nanostructured, Si-O-Si rich surface was efficient to prevent isothermal dairy fouling. The adhesion of the pathogenic bacterium Staphylococcus aureus also proved to be impacted by this plasma coating, with a significant decrease of adhered cells (-30% compared to native stainless steel).

Biomimetic surface modifications of stainless steel targeting dairy fouling mitigation and bacterial adhesion

“…Furthermore, SEM and AFM analyses (Figure 2 and Figure 4) showed that PL coatings present a pronounced nano-roughness, in accordance with previous findings (Zouaghi et al, 2018).…”

“…This is probably due to the fact that S. aureus is a round-shaped bacterium and that this geometry allows it to easily penetrate into the grain boundaries of the coated surface. Indeed, the coating thickness does not permit it to fill in the grain boundaries of the SS substrate (Zouaghi et al, 2018). Figure 6 indeed reveals that a significant number of adhered S. aureus cells are located into the grain boundaries of the surface, highlighting the importance of roughness and surface morphology in the control of bacterial adhesion.…”

“…The procedures for fouling tests has been detailed in previous works (Zouaghi et al, 2018(Zouaghi et al, , 2017a. Briefly, fouling tests were carried out with a model foulant fluid (MFF) to ensure repeatability.…”

“…siloxane from the HMDSO precursor, and surface morphology, i.e. nano-roughness (Zouaghi et al, 2018).…”

Cold plasma surface treatments to prevent biofilm formation in food industries and medical sectors

“…In another research, organosilicone-based films were developed on 316L stainless steel, by atmospheric pressure plasma spraying (APPS) of HMDSO. This plasma coating showed an antifouling character and antiadhesive properties towards Staphylococcus aureus (Zouaghi et al 2018). Moreover, Kregiel and Niedzielska (2014) developed polyethylene surfaces, activated by plasma processing and modified with active organosilanes.…”