EVALUATION OF WELDED AND POLISHED STAINLESS-STEEL SURFACES IN SUPPORTING SPOREFORMER BIOFILMS IN DAIRY PLANTS

Abstract

Spore-forming bacteria pose a significant challenge to the dairy industry, impacting the quality of dairy products. Bacillus species, in particular, contribute to spoilage of dairy items. Biofilm growth on stainless steel surfaces exacerbates biofouling, becoming reservoirs for persistent contamination and complicating removal due to their extracellular polysaccharide (EPS) matrix facilitating bacterial attachment. The first two studies aimed to assess biofilm growth on domestic and overseas stainless steel 316 and 304 surfaces using Geobacillus stearothermophilus (ATCC 15952), Bacillus licheniformis (ATCC 6634), Bacillus sporothermodurans (DSM 10599), and Bacillus coagulans (ATCC 5856). Among bacteria tested on domestic native 316 surfaces Geobacillus stearothermophilus and Bacillus sporothermodurans showed the least biofilm count, 4.03 and 4.05, respectively. Conversely, welded surfaces presented the highest biofilm formation for, B. licheniformis, B. coagulans, B. sporothermodurans, and G. stearothermophilus (4.86, 4.78, 4.79, and 4.73 log counts, respectively. The mean log counts across native, welded, and polished surfaces significantly differed for the four organisms (P<0.05), suggesting that polishing of weldments helps in reducing the biofilm formation. Among the findings, B. sporothermodurans exhibited minimal biofilm formation on SS 304 native surfaces with a log count of 3.87, followed by 4.04 on polished surfaces. Welded surfaces displayed the highest biofilm growth among all surface types tested, while polished surfaces exhibited lower biofilm formation compared to welded surfaces." Overall, for native, welded, and polished surfaces, the average log counts were significantly different for the four organisms (P<0.05) tested. The results indicate that polishing of weldments helps in reducing biofilm formation. For the overseas coupons, the result indicated that all bacteria tested showed a similar biofilm growth on SS316 native surfaces. However, on polished SS 316 surfaces, G. stearothermophilus demonstrated the highest biofilm growth, followed by B. licheniformis, while B. coagulans and B. sporothermodurans had similar biofilm counts. On welded SS 316 surfaces, G. stearothermophilus exhibited the highest biofilm formation, followed by B. licheniformis and B. sporothermodurans, while B. coagulans showed the least biofilm formation. The highest observed biofilm formation among the tested bacteria on SS 304 native surfaces was for B. coagulans at 5.97 logs, followed by B. licheniformis 5.4 logs. Bacillus coagulans showed more biofilm formation on SS 304 polished surfaces among the four bacteria tested. Overall, for native, welded, and polished surfaces, the average log counts were significantly different for the four organisms (P<0.05) tested. The results indicate that polishing of weldments helps in reducing biofilm formation. These studies demonstrated that SS 304 exhibited higher biofilm formation compared to SS 316 in both domestic and overseas coupon samples. Based on the anticipated result it is likely to find higher biofilm in 304 more than 316 SS surfaces. The third study was conducted to evaluate the SS surfaces roughness changes after applying CIP chemical solution for 10 consecutive cycles following 3 CIP protocols. The result indicated that the surface roughness had a slight change after the fifth cycle, while the greatest change happened after the 10th cycle. Applying frequent CIP to stainless steel could increase the roughness which supports biofilm formation.

The last study was to evaluate the effect of CIP chemical solution on elastomer material such as EPDM, Teflon, Silicon, and Viton gaskets. The results showed that the surface roughness of all gasket types slightly increased after the first CIP cycle compared to pre-CIP measurements. However, the surface roughness measurements increased over time, as shown by the measurements after the third and fifth CIP cycles. This escalating surface roughness phenomenon precipitated an associated elevation in biofilm formation, thereby influencing the overall product quality.