These films are very difficult to remove
during the cleaning operation. Microorgan-
isms that appear to be more of a problem to
remove because of biofilm protection are
PseudomonasandL. monocytogenes. Cur-
rent information suggests that the applica-
tion of heat appears to be more effective
than that of chemical sanitizers, and Teflon
appears to be easier to clear of biofilm than
does stainless steel.
Biofilms protect against the penetration of
water-soluble chemicals such as caustics,
bleaches, iodophors, phenols, and quater-
nary ammonium sanitizers. Therefore, the
organisms within them may not be
destroyed. According to Kramer (1992),
there are no procedural specifications or reg-
ulations on the removal and disinfection of
biofilms. A biocide may require use at 10 to
100 times normal strength to achieve inacti-
vation.
In tests of sanitizers-including hot water at
82ºC; chlorine at 20, 50, and 200 ppm; and
iodine at 25 ppm-the bacteria on stainless
steel chips survived, even after immersion in
the sanitizer for 5 minutes. The only true ger-
micide tested was a hydrogen-peroxide-based
powder that was found to be effective against
biofilms at 3% and 6% solutions (Felix, 1991).
Relationship of Amount of Contamination,
Temperature, and Time
to Microbial Growth
As temperature decreases, the generation
interval(time required for one bacterial cell
to become two cells) is increased. This is
especially true when the temperature goes
below 4ºC. The effect of temperature on
microbial proliferation is illustrated in Fig-
ure 3–2. For example, freshly ground beef
usually contains approximately 1 million
bacteria/g. When the number of this micro-
bial population reaches approximately 300
million/g, abnormal odor and some slime
development, with resultant spoilage, can
occur. This trend does not apply to all gen-
era and species of bacteria. However, it can
be determined from these data that initial
contamination and storage temperature dra-
matically affect the shelf life of food. The
storage life of ground beef that contains 1
million bacteria/g is approximately 28 hours
at 15.5ºC. At normal refrigerated storage
temperature of approximately −1ºC to 3ºC,
the storage life exceeds 96 hours.Effects of microorganisms on spoilage....................................................
Food is considered spoiled when it
becomes unfit for human consumption.
Spoilage is usually equated with the decom-
position and putrefaction that results from
microorganisms. Davidson (2003) defined
spoilage as an undesirable change in the fla-
vor, odor, texture, or color of food caused by
growth of microorganisms and ultimately
the action of their enzymes.Physical Changes
The physical changes caused by microor-
ganisms usually are more apparent than the
chemical changes. Microbial spoilage usually
results in an obvious change in physical char-
acteristics such as color, body, thickening,
odor, and flavor degradation. Food spoilage
is normally classified as being either aerobic
or anaerobic, depending on the spoilage con-
ditions, including whether the principal
microorganisms causing the spoilage were
bacteria, molds, or yeasts.
Aerobic spoilage of foods from molds is
normally limited to the food surface, where
oxygen is available. Molded surfaces of foods
such as meats and cheeses can be trimmed
off, and the remainder is generally acceptable
for consumption. This is especially true for
aged meats and cheeses. When these surface
molds are trimmed, surfaces underneath