48 Chapter 3
of carcasses are the fi rst interventions after
hide removal, applied for removal of visible
soil from external surfaces of carcasses.
Such treatments include knife - trimming and
steam - vacuuming. Both spot - carcass inter-
ventions are approved by FSIS for use in
meat processing in order to achieve zero tol-
erance of visible contamination on carcasses.
However, given that such interventions are
based on visual inspection, and thus, invisi-
ble carcass contamination may be over-
looked, they should be combined with
pre - and/or post - evisceration decontamina-
tion treatments.
Knife - Trimming
As indicated, knife - trimming is required by
FSIS in the United States for removal of
visible contamination (i.e., feces, soil, hair,
milk fl uids, and bruised tissue) from car-
casses before any spraying with water or
decontamination liquids. In addition to
cosmetic reasons, it is assumed that knife -
trimming removes microbial contamination
through proper removal of soiled tissue
(Sofos and Smith 1998 ; Sofos 2002 ). The
magnitude of reported reductions of naturally
occurring total bacteria and coliforms by
knife - trimming of beef carcasses ranges
from < 1 to 2 log 10 /cm^2 (Gorman et al. 1995b ;
Reagan et al. 1996 ; Kochevar et al. 1997b ;
Phebus et al. 1997 ; Castillo et al. 1998c ).
Higher reductions, such as 2.9 to 4.9 log 10 /
cm^2 , have been observed on inoculated S.
Typhimurium, E. coli O157:H7 and L. mono-
cytogenes , which may be associated with the
higher inoculum levels applied on the beef
tissue compared with naturally occurring
levels of contamination on carcasses (Hardin
et al. 1995 ; Cabedo et al. 1996 ; Phebus et al.
1997 ; Castillo et al. 1998c ). However, knife -
trimming may also increase microbial load of
treated spots (Gill et al. 1996 ) or disperse
contamination to adjacent areas (Gorman et
al. 1995a ). The effi ciency of this intervention
depends on the skills of personnel perform-
chemicals (SS and hydrogen peroxide)
released by the dehairing process from
coming in contact with dehided carcasses.
Concerns with chemical dehairing include
the corrosiveness and hazardous potential of
the sulfi des and their potential effect on the
skin and mucus membranes of workers
(Edwards and Fung 2006 ). Moreover, recy-
cling systems are needed to treat and recover
the liquid waste generated by dehairing
(Edwards and Fung 2006 ).
In contrast to cattle, pigs and chickens are
rarely skinned, as they are scalded (with hot
water that may contain wetting agents or
alkali at up to 66 ° C) immediately after bleed-
ing (Gill and Bryant 1992 ; Bolton et al.
2002 ). Scalding and singeing are known to
cause up to 4.5 log 10 CFU/cm^2 reductions of
total aerobic bacteria and 6.0 log 10 CFU/cm^2
reductions of pathogens, such as S.
Typhimurium and C. jejuni, on poultry (Yang
et al. 2001 ) or swine carcasses (Gill and
Bryant 1992 ; Yu et al. 1999 ). However,
despite these potential reductions in micro-
bial counts, contamination levels may
increase on scalded pork carcasses during
subsequent polishing and/or mechanical
shaving (Gill and Bryant 1992 ; Gill and
Jones 1997a ; Yu et al. 1999 ; Gill et al.
2000 ), and on poultry carcasses during chill-
ing. Therefore, there is a need for strict
hygiene control and additional decontamina-
tion strategies in the slaughtering and chilling
process, in order to reduce microbial con-
tamination on carcasses and maintain it at
low levels.
Spot - Carcass Decontamination
Treatments
Knife incision for bleeding (sticking) and for
hide removal (skinning) is the fi rst exposure
of carcasses and muscle to contamination;
the hide also introduces animal contamina-
tion on the carcass and in the plant environ-
ment, equipment, and workers as it is removed
from the carcass. Therefore, spot - treatments