|dc.description.abstract||Anoxybacillus flavithermus is a common species of thermophilic bacteria discovered in most
milk powder manufacturing plants through out New Zealand. The contamination of it’s
spores into the finished milk powder is an on-going problem as these spores are able to
survive the sterilization process. Cheating death, A. flavithermus spores were then believed
to attached on the stainless steel surface piping of the production line and germinate into a
mature bacteria. A single surviving spore could grow to produce more spores that eventually
dislodged from the colony and deposited together with the packaged milk powder. Over the
storage time, the contaminated product will gives an off flavor as it deteriorates from
bacterial action within.
Currently, the applied cleaning method is by rinsing the target section with 1% sodium
hydroxide & acid solutions before being flushed out to remove any microorganisms attached
on the interior surfaces. However, it is not very effective in removing spores and there is very
little information on the value of the spore’s adhesion force on a stainless steel surface. With
that in mind, the aim of this study is to determine a proper adhesion force value between a
dairy strain spore, A.flavithermus CM and stainless steel surface using the Atomic Force
Microscopy (AFM) system. Meanwhile, Geobacillus strearothermophilus ATCC 2641 which is
also a thermophilic organism was used over the study for comparison purpose.
To measure the adhesion force under an Atomic Force Microscopy (AFM), the crude
suspension was first purified using two-phase separation method. Polyethylene glycol (PEG)
and phosphate buffer were used as the phase separation chemicals while 0.1% polysorbate
20 was added to the freshly purified spores’ suspension to aid the imaging sequence under
the AFM. All AFM imaging and force measurements were done in air and conducted using
the silicon type CSG 11/Au cantilever. The crucial Force-Volume imaging was done on a
32x32 grid scan size (1024 samples) on a scan rate of 0.5 Hz.
It was calculated that a single A. flavithermus CM spore has an adhesive force value of 16.8
µN when attached on a stainless steel surface. It has a stronger localize adhesive value of
3.9 nN than a G.stearothermophilus ATCC 2641 spore with just 3.6 nN. However,
G.stearothermophilus ATCC 2641 has a larger adhesive force of 21.1 µN on a stainless steel
surface due to it’s larger spore size. It was also found that spore’s hydrophobicity does not
dictates the magnitude of it’s adhesion on any surface.
The results from this study have provide the dairy industry an extra sight on the quantitative
value of the adhesion force of thermophilic spores, particularly A.flavithermus CM. This will
help the dairy industry to design strategies in preventing spores from adhering to its