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.
OBJECTIVE
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.


RESULTS
Exposing sessile spores to 1% NaOH at 65°C for 30min 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 log(10)  CFU cm(-2) ) than untreated spores (3·6 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.
Department of Food Science, University of Otago, Dunedin, New Zealand.
R
R
Brent Seale
S H
SH
Flint
A
A
James McQuillan
P J
PJ
Bremer
D000818:Animals; D001422:Bacterial Adhesion / Q000187:drug effects; D002424:Caustics; D003612:Dairying; D056506:Geobacillus / Q000187:drug effects* / Q000302:isolation & purification / Q000648:ultrastructure; D050296:Microbial Viability; D008892:Milk / Q000382:microbiology*; D011208:Powders; D012972:Sodium Hydroxide / Q000633:toxicity*; D013171:Spores, Bacterial / Q000187:drug effects / Q000648:ultrastructure; D013193:Stainless Steel; D013499:Surface Properties
D002424:Caustics; D011208:Powders; D013193:Stainless Steel; D012972:Sodium Hydroxide