44 Chapter 3
sure, sonication and pulsed light, or pulsed
electric fi elds (Cutter and Siragusa 1994a ;
Reagan et al. 1996 ; Naidu and Bidlack 1998 ;
Sofos and Smith 1998 ; Huffman 2002 ;
Castillo et al. 2003 ; Sofos 2005 ; Aymerich et
al. 2008 ; Kalchayanand et al. 2008 ). However,
most of these alternatives are still under
investigation and have not been applied in
practice yet. The main focus of the following
paragraphs is to discuss commercially applied
decontamination interventions on animals
and carcasses.Animal Washing
Before slaughter, internal tissues of healthy
animals are considered sterile (Sofos 1994 ).
Microbial contamination of meat usually
starts during conversion of live animals into
carcasses and meat by the slaughter/dressing
process and more specifi cally by the removal
of the hide, pelt or feathers, and viscera.
Contamination is an unavoidable problem,
which may occur even in the best - managed
slaughter facilities. Nevertheless, highly
soiled animals with long wool and visible
fecal contamination are expected to introduce
in the slaughter plant higher microbial popu-
lations than shorn and “ clean ” animals (Biss
and Hathaway 1995 ; Hadley et al. 1997 ;
Duffy et al. 2005 ; Childs et al. 2006 ).
Therefore, presentation of clean animals for
slaughter is desirable because it reduces the
likelihood of pathogen presence and transfer
onto carcasses (Biss and Hathaway 1995 ;
Hadley et al. 1997 ; Bolton et al. 2002 ; Arthur
et al. 2004 ; Duffy et al. 2005 ).
A fi rst step in efforts to minimize sources
of carcass contamination at slaughter is to
wash animals before knife incision (Sofos
and Smith 1998 ). Pre - slaughter washing of
sheep is a common intervention in New
Zealand (Biss and Hathaway 1995 ). In addi-
tion, Australia has adopted washing of cattle,
which is also practiced in certain slaughter
plants in the United States (Sofos 2002 ). The
outcome of animal washing is variable andcarcasses for E. coli for verifi cation of the
effectiveness of control measures against
fecal contamination; and (iii) establishment
of microbiological performance standards for
Salmonella prevalence as a means of tracking
pathogen reduction (USDA - FSIS 1996c ;
Sofos et al. 1999a, b, c, d ; Rose et al. 2002 ).
The need for compliance with zero tolerance
and microbiological criteria imposed by reg-
ulatory authorities or the industry, as well as
the fact that knife - trimming may not be ade-
quate for effi cient removal of microbial con-
tamination, resulted in evaluation and
commercial application of washing and
decontamination treatments (Smulders and
Greer 1998 ; Sofos and Smith 1998 ; Sofos
2005 ; Stopforth and Sofos 2006 ) before
slaughtering, during slaughtering at the pre -
and post - evisceration stage, during chilling,
and post - chilling (Fig. 3.1 ).
Decontamination treatments may be
physical or chemical in nature, while the
combination of both as multiple interventions
is also used (Smulders and Greer 1998 ; Sofos
and Smith 1998 ; Bacon et al. 2000 ; Geornaras
and Sofos 2005 ; Kalchayanand et al. 2008 ).
Physical methods aim to mechanically
remove soil from the external surfaces of
animals (e.g., hides) or carcasses, as well
as to reduce microbial populations. They
include animal washing/cleaning and/or hair -
trimming before slaughtering, dehairing and
defeathering, knife - trimming, and washing
of carcasses, as well as thermal treatments,
such as use of steam/hot water - vacuum gen-
erating equipment for spot - cleaning, “ steam
pasteurization, ” or spraying with hot water.
Chemical treatments involve the application
of organic acid or other chemical solutions
for chemical dehairing and as rinses for
contamination reduction. Thermal treatments
(hot water and steam) or organic acid
solutions are commonly used alone or in
combination (Sofos 2005 ). Alternative
decontamination methods/agents include
ionizing radiation, ozonated water, nisin, glu-
conic acid, lactoferrin, high hydrostatic pres-