Stability of nonfouling stainless steel heat exchanger plates against commercial cleaning agents

Oregano Essential Oil versus Conventional Disinfectants against Salmonella Typhimurium and Escherichia coli O157:H7 Biofilms and Damage to Stainless-Steel Surfaces

This study compared the effect of oregano essential oil versus sodium hypochlorite, hydrogen peroxide, and benzalkonium chloride against the viability of adhered Salmonella Typhimurium and Escherichia coli O157:H7 on 304 stainless steel. Oregano essential oil was effective in disrupting the biofilms of both bacteria at concentrations ranging from 0.15 to 0.52 mg mL-1. In addition, damage to stainless-steel surfaces following disinfection treatments was assessed by weight loss analysis and via visual inspection using light microscopy. Compared to the other treatments, oregano oil caused the least damage to stainless steel (~0.001% weight loss), whereas sodium hypochlorite caused the most severe damage (0.00817% weight loss) when applied at 0.5 mg mL-1. Moreover, oregano oil also had an apparent protective impact on the stainless steel as weight losses were less than for the control surfaces (distilled water only). On the other hand, sodium hypochlorite caused the most severe damage to stainless steel (0.00817% weight loss). In conclusion, oregano oil eliminated monoculture biofilms of two important foodborne pathogens on 304 stainless-steel surfaces, while at the same time minimizing damage to the surfaces compared with conventional disinfectant treatments.

Evaluation of modified stainless steel surfaces targeted to reduce biofilm formation by common milk sporeformers

The development of bacterial biofilms on stainless steel (SS) surfaces poses a great threat to the quality of milk and other dairy products as the biofilm-embedded bacteria can survive thermal processing. Established biofilms offer cleaning challenges because they are resistant to most of the regular cleaning protocols. Sporeforming thermoduric organisms entrapped within biofilm matrix can also form heat-resistant spores, and may result in a long-term persistent contamination. The main objective of this study was to evaluate the efficacy of different nonfouling coatings [AMC 18 (Advanced Materials Components Express, Lemont, PA), Dursan (SilcoTek Corporation, Bellefonte, PA), Ni-P-polytetrafluoroethylene (PTFE, Avtec Finishing Systems, New Hope, MN), and Lectrofluor 641 (General Magnaplate Corporation, Linden, NJ)] on SS plate heat exchanger surfaces, to resist the formation of bacterial biofilms. It was hypothesized that modified SS surfaces would promote a lesser amount of deposit buildup and bacterial adhesion as compared with the native SS surface. Vegetative cells of aerobic sporeformers, Geobacillus stearothermophilus (ATCC 15952), Bacillus licheniformis (ATCC 6634), and Bacillus sporothermodurans (DSM 10599), were used to study biofilm development on the modified and native SS surfaces. The adherence of these organisms, though influenced by surface energy and hydrophobicity, exhibited no apparent relation with surface roughness. The Ni-P-PTFE coating exhibited the least bacterial attachment and milk solid deposition, and hence, was the most resistant to biofilm formation. Scanning electron microscopy, which was used to visualize the extent of biofilm formation on modified and native SS surfaces, also revealed lower bacterial attachment on the Ni-P-PTFE as compared with the native SS surface. This study thus provides evidence of reduced biofilm formation on the modified SS surfaces.

Adhesion and removal kinetics of Bacillus cereus biofilms on Ni-PTFE modified stainless steel

Biofilm control remains a challenge to food safety. A well-studied non-fouling coating involves codeposition of polytetrafluoroethylene (PTFE) during electroless plating. This coating has been reported to reduce foulant build-up during pasteurization, but opportunities remain in demonstrating its efficacy in inhibiting biofilm formation. Herein, the initial adhesion, biofilm formation, and removal kinetics of Bacillus cereus on Ni-PTFE-modified stainless steel (SS) are characterized. Coatings lowered the surface energy of SS and reduced biofilm formation by > 2 log CFU cm(-2). Characterization of the kinetics of biofilm removal during cleaning demonstrated improved cleanability on the Ni-PTFE coated steel. There was no evidence of biofilm after cleaning by either solution on the Ni-PTFE coated steel, whereas more than 3 log and 1 log CFU cm(-2) of bacteria remained on the native steel after cleaning with water and an alkaline cleaner, respectively. This work demonstrates the potential application of Ni-PTFE non-fouling coatings on SS to improve food safety by reducing biofilm formation and improving the cleaning efficiency of food processing equipment.

The effect of pre-adsorption of OVA or WPC on subsequent OVA or WPC fouling on heated stainless steel surface

Fouling on the heat exchanger surface during food processing has been researched extensively due to its great importance in energy efficiency, product quality and food safety. The nature of heat exchanger surface has an effect on the initial deposition behavior and deposit removal behavior to some degree. Protein adsorption on surface is considered to be the initial stage in fouling. In the current study, protein 'pre-adsorption' at room temperature on stainless steel has been investigated as a means to influence the behavior of protein fouling at pasteurization temperatures. Pre-adsorption was carried out with whey protein concentrate (WPC) and ovalbumin (OVA), respectively, which reduced the fouling of OVA (∼20-30% energy saving in the processing time examined). However, the pre-adsorption had little effect on fouling of whey protein concentrate. Contact angles were measured to show the surface change due to protein pre-adsorption. Protein pre-adsorption made the surfaces more hydrophilic.