ABSTRACT
Geobacillus species are important contaminants in the dairy industry, and their presence is often considered an indicator of poor plant hygiene with the potential to cause spoilage. They can form heat-resistant spores that adhere to surfaces of processing equipment and germinate to form biofilms. Therefore, strategies aimed toward preventing or controlling biofilm formation in the dairy industry are desirable. In this study, we demonstrated that the preferred temperature for biofilm and spore formation among Geobacillus stearothermophilus A1, D1, P3, and ATCC 12980 was 65°C. Increasing the total dissolved milk solid concentration to 20% (wt/vol) caused an apparent delay in the onset of biofilm and spore formation to detectable concentrations among all the strains at 55°C. Compared to the onset time of the biofilm formation of A1 in 10% (wt/vol) reconstituted skim milk, addition of milk protein (whey protein and sodium caseinate) caused an apparent delay in the onset of biofilm formation to detectable concentrations by an average of 10 h at 55°C. This study proposes that temperature and total dissolved solid concentration have a cumulative effect on biofilm and spore formation by G. stearothermophilus A1, D1, P3, and ATCC 12980. In addition, the findings from this study may indicate that preconditioning of stainless steel surfaces with adsorbed milk proteins may delay the onset of biofilm and spore formation by thermophilic bacteria during milk powder manufacture.
IMPORTANCE The thermophilic bacillus Geobacillus stearothermophilus is a predominant spoilage bacterium in milk powder manufacturing plants. If its numbers exceed the accepted levels, financial losses may be incurred because of the need to lower the price of the end product. Furthermore, G. stearothermophilus bacilli can form heat-resistant spores which adhere to processing surfaces and can germinate to form biofilms. Previously conducted research had highlighted the variation in the spore and biofilm formation among three specific strains of G. stearothermophilus isolated from a milk powder manufacturing plant in New Zealand. The significance of our research is in demonstrating the effects of two abiotic factors, namely, temperature and total dissolved solid concentration, on biofilm and spore formation by these three dairy isolates, leading to modifications in the thermal processing steps aimed toward controlling biofilm and spore formation by G. stearothermophilus in the dairy industry.
Innovative Control of Biofilms on Stainless Steel Surfaces Using Electrolyzed Water in the Dairy Industry
