essential for selection of the most appropri-
ate method and the ultimate application of
results.
During the past, many of the microbial
determination methods were culture-based, in
which microorganisms were grown on agar
plates and detected through biochemical iden-
tification. These methods have been slow,
labor intensive, and tedious to perform. Now,
the food industry utilizes several rapid micro-
bial test kits and automated systems to enable
firms to detect, identify, and correct potential
microbial hazards in their products before
they are released from the plant. These tech-
nologies (usually DNA-based) include
immunological methods (i.e., ELISA), auto-
mated biochemical identification and optical
systems (i.e., biosensors), and molecular
methods (i.e., PCR and microarrays).
Immunocapture techniques have also been
developed in which antibodies are attached to
plastic beads to facilitate recovery of
pathogens from a food matrix. The most
viable of these methods will be discussed.
Although microbial analysis may not pro-
vide precise results, it can indicate the degree
of hygiene reflected through equipment,
utensils, other portions of the environment,
and food products. In addition to reflecting
sanitary conditions, product contamination,
and potential spoilage problems, microbial
analysis can indicate anticipated shelf life.
Because several new and improved methods
are now available, it is difficult to indicate
which will be the most viable in the future.
Therefore, we will look at some potential
methods of assessment of microbial load
here. (Readers interested in more informa-
tion should review current technical micro-
biology journals.)
Aerobic Plate Count Technique
This technique is among the most repro-
ducible methods used to determine the pop-
ulation of microorganisms present on equip-
ment or food products. It may be used to
assess the amount of contamination from
the air, water, equipment surfaces, facilities,
and food products. With this technique, the
equipment, walls, or food products to be
analyzed are swabbed. The swab is diluted in
a dilutant such as peptone water or phos-
phate buffer, according to the anticipated
amount of contamination, and subse-
quently applied to a growth medium con-
taining agar in a sterile, covered plate (petri
dish). The diluted material is transferred to
a culture medium (such as standard meth-
ods agar) that nonselectively supports
microbial growth.
The number of colonies that grow on the
growth medium in the sterile, covered plate
during an incubation period of 2 to 20 days
(depending on incubation temperature and
potential microorganisms) at an incubation
temperature consistent with the environ-
ment of the product being tested reflects the
number of microorganisms contained by the
sample. This technique provides limited infor-
mation related to the specific genera and
species of the sample, although physical char-
acteristics of the colonies can provide a clue.
Special methods that permit the selective
growth of specific microorganisms are avail-
able to determine their presence and quantity.
This method is reliable, but it is slow and
laborious. The need for a faster response to a
high-volume production environment has
encouraged the investigation of more rapid
methods. Slowness of “end-product” testing
can retard production and does not provide
an actual total count. Its use continues
because of reliability and wide acceptance.Surface Contact Technique
This method of assessment, which has also
been called the contact plate technique, is sim-
ilar to the plate count technique except that