In vitro model study for biofilm formation by Bacillus cereus in dairy chilling tanks and optimization of clean-in-place (CIP) regimes using response surface methodology

Abstract

An in vitro model study was carried out to check biofilm formation by a selected strain of Bacillus cereus isolated from a chilling tank where pasteurized milk was stored. The strain was able to form biofilm even at 4 °C. From the study of different simulated conditions it was found that B. cereus cell count reached up to 106 cfu/cm2 of the surface of stainless steel tank if inadequately cleaned tanker is left to stand empty at room temperature. Prevalence of biofilm in dairy environment is a matter of concern as it can be an important reservoir for food spoilage and can lead to foodborne outbreaks. In the present study response surface methodology (RSM) was used to optimize parameters influencing biofilm cell removal. The RSM results were used to design an optimized clean-in-place (CIP) regime which consisted of 1.5% NaOH at 65 °C for 30 min – water rinse – 1% HNO3 at 65 °C for 10 min – water rinse. Effectiveness of reference CIP (1% NaOH at 65 °C for 10 min – water rinse – 1% HNO3 at 65 °C for 10 min – water rinse) and optimized CIP was assessed against 24 h-old biofilm. While the reference CIP caused 3.29 log reduction/cm2 in B. cereus biofilm cells, the optimized CIP achieved 4.77 log reduction/cm2 in biofilm cell count. Thus, the optimized CIP regime designed in the present study was found to be significantly (p < 0.05) more effective in biofilm cell removal as compared to the reference CIP.