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


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Abstract

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°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 0·1 mol l−1 KCl were shown to attach to stainless steel in significantly greater numbers (4·6 log10 CFU cm−2) than untreated spores (3·6 log10 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.

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