68 Chapter 3
whereas E. coli and coliforms counts
remained stable (Gill and Landers 2003b ).
However, pre - chilling decontamination inter-
ventions, such as pre - and post - evisceration
spraying with 2% lactic acid and steam or hot
water pasteurization, markedly reduced the
populations of E. coli and coliforms during
chilling (Gill and Landers 2003b ). The latter
may be associated with a pre - chilling injury
of cells due to the decontamination treat-
ments and the subsequent death or inability
of cells to repair their damage during
chilling.
In addition to lactic acid, other chemical
agents, such as 0.1 or 0.5% CPC, 0.05 – 0.1%
ammonium hydroxide, 0.12% ASC, 0.02%
PAA, 0.01% NaOH, or 0.005% sodium
hypochlorite within 48 hours of chilling of
beef carcass at 3 ° C to 1 ° C have been reported
to reduce inoculated E. coli O157:H7 by 1 to
3 log 10 CFU/cm^2 , that is 0.5 to 2 log 10 CFU/
cm^2 higher than spray - chilling with water
alone (Dickson 1991 ; Stopforth et al. 2004 ).
Stopforth et al. (2004) evaluated the above
chemicals in simulated spray - chilling of beef
adipose tissue and found that CPC, followed
by lactic acid, were the most effective chemi-
cal agents, followed by PAA and ASC.
However, acid - habituated E. coli O157:H7
cells (in acidic washings of pH 4.12) remained
at higher levels than non - acid - habituated cul-
tures after 10 hours of spray - chilling with
CPC and after spray - chilling with lactic acid
and 48 hours of storage of chilled tissues at
1 ° C (Stopforth et al. 2004 ). Commercial
evaluation of spray - chilling in three poultry
processing plants showed that chlorine (20 –
50 ppm) and ClO 2 (500 – 1200 ppm ASC)
spray - chilling caused up to 1.2 log 10 CFU/
cm^2 reductions of APC and TCC on poultry
carcasses (Stopforth et al. 2007 ). A mixture
of peracetic acid and hydrogen peroxide
(PAHP), approved for use in poultry chillers
in the United States, reduced Salmonella and
Campylobacter positive poultry carcass
samples by 92% and 43% exiting the chiller,
respectively, when applied at 85 ppm in aor steam pasteurization, post - evisceration
washing, chemical rinses, and chilling, that
reduce contamination of E. coli O157:H7
from above 50% on animal hides to less than
0.5% on carcasses.
Chilling
At the end of the dressing process, carcass -
chilling takes place in cold ( − 5 to 4 ° C) air
chambers with or without intermittent spray-
ing (or misting) carcasses with cold water for
variable durations within 12 – 24 hours, while
the total chilling process lasts 24 – 48 hours
(Dickson and Anderson 1991 ; Hippe et al.
1991 ; Strydom and Buys 1995 ; Gill and
Bryant 1997a ; Gill and Jones 1997b ; Greer
and Jones 1997 ; Stopforth and Sofos 2005 ;
Simpson et al. 2006 ). Spray - chilling has been
adopted in various beef plants because it
facilitates temperature reductions and reduces
losses of carcass surface moisture and weight.
Such a process may cause bacterial injury
and death either due to localized freezing of
surface moisture when cooling below 0 ° C
occurs or due to the evaporative water losses
on the carcass surface (Sheridan 2004 ;
Simpson et al. 2006 ). However, chilling is a
step for control of microbial growth rather
than a decontamination intervention, since it
relies mainly on cold temperatures, unless
pre - chilling decontamination interventions
have been applied, or antimicrobials are
added into the spray - chilling water, which,
combined with cold temperatures, may lead
to the death of injured cells. Indeed, chilling
of pig, lamb, and beef carcasses with cold
water may increase numbers of psychro-
trophs and inhibit growth of E. coli and coli-
forms (Gill and Bryant 1997a ; Gill and Jones
1997b ; Jericho et al. 1998 ). In a study moni-
toring the microbiological changes on the
surface of carcasses after 22 – 36 hours of
chilling with cold water to average tempera-
tures of − 1.4 to 2.5 ° C in four beef packing
plants, the total aerobic counts on carcass
surfaces increased by 1 – 2 log 10 CFU/cm^2 ,