Scientific
Publications - Work Done by Microbiology Reader Bioscreen C
Karwoski, Merja, Applications of automated direct and
indirect methods for food microbiology, Doctoral thesis, 1994. VTT, Espoo.
121 p. + app. 69 p., VTT Publications : 194, ISBN 951-38-4632-6
ABSTRACT
Abstract: The microbiological laboratory of the
future will have increased automation and instrumentation. More efforts should
be focused on the practical and novel applications of improved conventional and
new commercial systems. In this thesis two direct and two indirect automated
microbiological methods were studied in order to gather more information about
their use and applications in the field of food microbiology.
The Spiral system Spiral Plater used in this work
offered substantial savings over conventional plating, in the recycling of
glassware, agar, Petri plates and diluent, in time, space and support labor. The
Spiral method could be used for plating when enumerating pure bacterial, yeast
and some mold cultures, raw milk and minced beef samples as an alternative to
the conventional Aerobic Plate Count (APC) method when plates were counted
manually. Microbial pure culture, raw milk (manual or automatic counting) and
minced beef (manual counting) results showed that the Spiral method had higher
overall recovery when compared with the pour plating method. The Spiral system
Laser Colony Scanner connected to the CASBATM Bacterial Enumeration Program
could replace manual counting of APC plates when pure bacterial, yeast and some
mold cultures were studied. The findings with raw milk, pork loin surface and
minced beef samples emphasized the need for careful adjustment of the settings
of the automatic colony counter.
Another direct method included in this thesis was
the Direct Epifluorescent Filter Technique (DEFT). The combined use of
semi-automated DEFT and the conventional APC method could identify irradiated
(doses ³5 kGy) spices, herbs and seasonings from unirradiated ones. The results
had to be confirmed by chemical/physicochemical methods to reveal possible heat
treatment or fumigation of samples. The combined DEFT+APC method proved to be a
useful screening method for indication of the use of irradiation of
spices/herbs/seasonings and it also provided an estimate of the microbiological
quality of products prior to and after the irradiation process. The method is
easily adaptable as a part of routine microbiological quality control systems.
The semi-automated counting equipment used in the DEFT method offered an
advantage when many samples were analysed. The DEFT counts could be obtained
very quickly and there was no operator fatigue.
Two indirect automated microbiological systems
included in this thesis were the Bioscreen analysing system and the OmnispecTM
4000 bioactivity monitor system. Both systems measure growth or growth-related
microbial processes during incubation of samples. The Bioscreen analysing system
turbidometer measured turbidity changes and the OmnispecTM 4000 bioactivity
monitor system reflectance colorimeter measured color changes in samples. Both
systems offered several advantages that could help food microbiologists provide
quality assurance rather than merely quality control. With these automated
systems, detection times were shorter than with conventional methods, more
frequent readings were possible than by hand with the same number of samples,
monitoring the growth of microorganisms in the samples was not time-consuming,
data could be further processed, e.g. for statistical analyses. Furthermore, the
systems had high capacity and the cost per test due to labor and media was
reduced. Both systems were easy to use and had considerable temperature
flexibility and both were versatile, providing possibilities for several
applications.
