Effect of NaOH (caustic wash) on the viability, surface characteristics and adhesion of spores of a Geobacillus sp. isolated from a milk powder production line

Aim: To investigate the viability, surface characteristics and ability of spores of a Geobacillus sp. isolated from a milk powder production line to adhere to stainless steel surfaces before and after a caustic (NaOH) wash used in clean-in-place regimes. Methods and Results: Exposing sessile spores to 1% NaOH at 65 degrees C for 30 min decreased spore viability by two orders of magnitude. The zeta potential of the caustic treated spores decreased from -20 to -32 mV and they became more hydrophobic. Transmission electron microscopy revealed that caustic treated spores contained breaks in their spore coat. Under flow conditions, caustic treated spores suspended in 0 center dot 1 mol l-1 KCl were shown to attach to stainless steel in significantly greater numbers (4 center dot 6 log(10) CFU cm-2) than untreated spores (3 center dot 6 log(10) CFU cm-2). Conclusions: This research suggests that spores surviving a caustic wash will have a greater propensity to attach to stainless steel surfaces. Significance of Study: The practice of recycling caustic wash solutions may increase the risk of contaminating dairy processing surfaces with spores.