Mathematical models for the biofilm formation of Geobacillus and Anoxybacillus on stainless steel surface in whole milk
Received: Sep 29, 2020 ; Revised: Oct 28, 2020 ; Accepted: Dec 15, 2020
Published Online: Dec 21, 2020
Biofilm formation of Geobacillus thermodenitrificans, Geobacillus thermoglucosidans and Anoxybacillus flavithermus in milk on stainless steel were monitored at 55, 60, and 65 °C for various incubation times. Although species of Geobacillus showed a rapid response and produced biofilm within 4 h on stainless steel, a delay (lag time) was observed for Anoxybacillus. A hyperbolic equation and a hyperbolic equation with lag could be used to describe the biofilm formation of Geobacillus and Anoxybacillus, respectively. The highest biofilm formation amount was obtained at 60 °C for both Geobacillus and Anoxybacillus. However, the biofilm formation rates indicated that the lowest rates of formation were obtained at 60 °C for Geobacillus. Moreover, biofilm formation rates of G. thermodenitrificans (1.2-1.6 log10CFU/mL∙h) were higher than G.thermoglucosidans (0.4-0.7 log10CFU/mL∙h). Although A. flavithermus had the highest formation rate values (2.7-3.6 log10CFU/mL∙h), this was attained after the lag period (4 or 5 h). This study revealed that modeling could be used to describe the biofilm formation of thermophilic bacilli in milk.