Meat Decontamination 51tively more effective when the initial con-
tamination level is high (Gill and Landers
2003b ). This may be explained on the basis
that large numbers of bacteria are likely asso-
ciated with solid particles, which are easily
washed off, whereas lower bacterial popula-
tions may be associated more fi rmly with
surface tissue (Gill and Landers 2003b ).
Another reason could be that the higher the
initial contamination the more bacteria exist
to be removed.
The effi cacy of cold water (2 to 40 ° C) in
reducing microbial contamination of car-
casses may be enhanced as spraying pressure
increases from 27 to 41 bar (1 bar = 100 kPa),
and/or as contact time increases from 5 to 90
seconds (Kelly et al. 1981 ; Gorman et al.
1995a, b ; Gill et al. 1996 ; Bell 1997 ; Castillo
et al. 1998c ; Kain et al. 2001 ; Yang et al.
2001 ; Edwards and Fung 2006 ). For example,
an approximately tenfold increase in spray-
ing pressure (i.e., from 2 – 13 to 20 – 27 bar) of
water (16 – 35 ° C) increased the reduction of
APC from < 1 log 10 to 1.24 – 1.35 CFU/cm^2 on
beef (Gorman et al. 1995a, b ) and lamb
adipose tissue (Kochevar et al., 1997b ).
Certainly, the increase in pressure also
improves the presentation of carcasses
(Kochevar et al. 1997b ). However, careful
selection of washing pressure needs to be
made, because application of high pressure
water - washing may lead to potential penetra-
tion of bacterial contamination to inner layers
of tissue, while low pressures may simply
result in translocation of the microbial cells
on the carcass surface (De Zuniga et al. 1991 ;
Anderson et al. 1992 ; Ellerboek et al. 1993 ;
Gorman et al. 1995a ). Castillo et al. (1998c)
inoculated beef carcass tissue with feces
mixed with S. Typhimurium and E. coli
O157:H7 and found that spray - washing with
water caused spreading of 0.7 and 1.8 log 10
CFU/cm^2 of the above microorganisms,
respectively, to sites of carcasses adjacent to
the inoculated areas. This was attributed
to washing run - off. Likewise, Bell (1997)
found that pre - chilling washing (517.5 kPa)Common temperatures of water - washing
range from 10 to 40 ° C (and rarely up to
56 ° C) and pressures from 343 to 4134 kPa,
whereas the duration varies from 5 seconds
up to 2 or 10 minutes for manual spraying
(Sheridan 2004 ; Bacon 2005 ). In contrast to
automated spraying systems, hand - washing
lacks consistency because of human error,
such as lack of operator attention and fatigue
(Anderson et al. 1981 ; Sheridan 2004 ).
Studies evaluating the effectiveness of spray -
washing on whole carcasses or excised
carcass tissues have used either commercial
or model spray - washing cabinets. Specifi cally,
pre - evisceration washing of beef, veal, sheep,
or lamp carcasses with cold (2 to 35 ° C) or
slightly warm water (e.g., 40 or 56 ° C) for
5 – 90 seconds, reduced counts of total
bacteria and indicator organisms, such as E.
coli and coliforms by < 1 to 2.3 log 10 CFU/
cm^2 , either inoculated through fecal paste
(Gorman et al. 1995a, b ; Reagan et al. 1996 ;
Dorsa et al. 1996b, 1997a, 1998a, b, c ;
Kochevar et al. 1997b ; Graves Delmore et al.
1997, 1998 ; Castillo et al. 1998b, c ; Penney
et al. 2007 ) or naturally present on carcasses
(Gill et al. 1996 ; Kain et al. 2001 ). The
reported reductions for pathogens such as E.
coli O157:H7 and Salmonella inoculated on
carcass tissues are in the range 1.9 to 3.5 log 10
CFU/cm^2 (Castillo et al. 1998b, c ; Hardin
et al. 1995 ; Cutter and Rivera - Betancourt
2000 ).
In addition to washing time, temperature
and pressure, the effectiveness of washing
also depends on bacterial population densi-
ties, the condition (temperature of carcass
based on postmortem and/or pre - chilling
time) of the tissue, and the extent of bacterial
attachment (Bacon 2005 ; Hardin et al. 1995 ).
Bacterial adhesion, which depends on factors
such as formation of exopolymeric sub-
stances, wool, moisture of tissue, and micro-
bial species, as indicated, also increases with
time of carcass tissue exposure to fecal con-
tamination (Bacon 2005 ). Furthermore, it has
been suggested that washing appears rela-