294 Chapter 15
agents seems to be due to the characteristics
of extracellular polymeric substances rather
than intrinsic attributes of the cells in the
biofi lm (Pan et al. 2006 ).
The macro - cavities of porous surfaces
may play an important role in the ability of a
microorganism to colonize food - contact sur-
faces. Stone and Zottola (1985) demonstrated
that the number of cracks and irregularities
may allow the surface to harbor bacteria
and reduce the effectiveness of cleaning
procedures.
Cleaning is the most important step for
minimizing microbial colonization of meat -
processing equipment. Microorganisms are
far more sensitive to disinfectants once they
have been detached from the surfaces to
which they were adhering. Mechanical action
with brushes and medium - and high - pressure
jets is recognized as being highly effective in
eliminating biofi lm (Holah et al. 1990b ;
Carpentier and Cerf 1993 ). Acid products are
no more effective than hot water, while
chlorinated alkaline detergents are the most
effective for detaching biofi lm, followed
by nonchlorinated alkaline detergents
(Carpentier and Cerf 1993 ). Peroxides have
been reported to be effective for the removal
of bacterial biofi lms and are widely used in
the food industry (Fatemi and Frank 1999 ;
Stopforth et al. 2002 ).
Usual recommendations for choosing
materials and food equipment design are
useful to avoid biofi lm formation: use of
smooth, nonporous material and of equip-
ment without inaccessible corners; cleaning
at short intervals to prevent excessive buildup
of soil and biofi lm; and, since water is indis-
pensable for biofi lm production, drying of
the surfaces after the cleaning - disinfection
procedures whenever possible.Control of Listeria monocytogenes
in Meat - Processing Plants
Listeria monocytogenes is a pathogenic bac-
terium that is widely spread throughout the
environment. It has been isolated from soil,Water Quality
Water used for food processing, cleaning,
and sanitizing activities must be potable.
Knowing the water source available to a
food - processing plant is a must when design-
ing a sanitation program. Water functions as
a carrier for detergents and sanitizers. It also
carries soil or contaminants away from the
surface that has been cleaned and sanitized.
Water quality varies greatly, and its ability to
function in cleaning is determined by several
factors: total alkalinity, calcium hardness,
iron, pH, silica, total dissolved solids, and
standard plate count. Often problems in plant
sanitation programs are a direct result of the
raw water supply. These sanitation problems
can be prevented or minimized through
advanced knowledge of the raw water quality.
One factor of prime importance is water
hardness. Water hardness is responsible for
excessive soap and detergent consumption
(with hard water, more cleaners will be
required as minerals precipitate out with the
alkali cleaners), mineral deposits, undesir-
able fi lms, and precipitates. When hard water
( > 120 ppm CaCO 3 ) must be used for clean-
ing, the addition of chelating or sequestrating
reagents is necessary.
Biofi lm Formation
A biofi lm can be described as a group of
bacteria that have colonized a surface. The
biofi lm not only includes the bacteria but also
a complex polysaccharide - like material pro-
duced on the surface and any material trapped
within the matrix. It is generally assumed that
the biofi lms take hours or days to develop.
They are self - regulating; that is, pieces may
dislodge from the surface, allowing other
cells to attach and to entrap more food soil
inside (Hood and Zottola 1995 ) and contami-
nate the food as it passes by. There is evi-
dence that usual sanitation practices are less
effective on attached microorganisms com-
pared with free cells (Holah et al. 1990a ).
Resistance of treated biofi lms to sanitizing