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

Abstract Text:

Development of bacterial biofilms on stainless steel (SS) surface of dairy equipment such as plate heat exchangers pose a great threat to the quality of milk and other dairy products, as the biofilm embedded bacteria can survive thermal processing to a greater extent. Many of these are sporeformers that also form heat resistant spores leading to a long-term persistent contamination. Biofilms also offer cleaning challenges, as they are generally resistant to regular cleaning protocols. The main objective of this study was to evaluate different surface modifications (AMC 18, Durasan, Lindgren and Magnaplate) of stainless steel for their resistance to biofilm formation. It was hypothesized that these coated surfaces would promote a lower deposit build up and bacterial adhesion. Challenge studies, using vegetative cells of common dairy related aerobic sporeformers namely Geobacillus stearothermophilus (ATCC 15952), Bacillus licheniformis (ATCC 6634), and Bacillus sporothermodurans (DSM 10599), were conducted to study the biofilm formation on the modified and native SS coupons under static conditions. Standard enumeration techniques were used to culture biofilm embedded bacteria. The adherence of these organisms was observed to be influenced by surface energy and hydrophobicity, but exhibited no relationship with surface roughness. Statistical analysis of the number of adhered cells of G. stearothermophilus to different native and modified SS surfaces, after 72 hours of incubation, revealed significant differences in counts. Lindgren was observed to be most resistant to bacterial attachment (average 3.15 log cfu/cm²), in comparison to the native SS surface that recorded a higher average bacterial adhesion of 5.11 logs. Similar results were obtained with B. licheniformis and B. sporothermodurans, the latter showing least attachment. Scanning electron microscopy provided the visual evidence of the extent of biofilm development and bacterial attachment on the surface of modified and native SS surfaces. In conclusion, Lindgren coating, being the most resistant to biofilm development, could potentially help in reducing the bacterial cross contamination of milk and dairy products during processing.

Keywords: : Biofilms, sporeformers, surface modification