54 Chapter 3
beef adipose tissue with hot water (74 ° C),
whereas subsequent storage at 4 ° C allowed
APC to reach only 4.3 log 10 CFU/cm^2 com-
pared with untreated samples in which APC
exceeded the level of 6 log 10 CFU/cm^2. This
is potentially due to cell injury caused by
hot - water treatments.
In conclusion, hot water is more effective
than cold water in reducing microbial
spoilage and pathogenic contamination of
carcasses. However, proper selection of
pressures, temperature, and duration of the
application is necessary in order to ensure
microbial reductions and avoid permanent
discoloration of the carcass tissue.
Furthermore, hot water is a physical inter-
vention that involves no chemical risk
and requires lower capital investment. For
these reasons, it has received commercial
application in meat - processing industries
worldwide.Steam Pasteurization
Use of steam, instead of hot water, is an alter-
native thermal decontamination treatment. A
patented (Steam pasteurization ™ ) process
has been approved by FSIS for application in
the United States (USDA - FSIS, 1996a ) and
is used commercially at the post - evisceration
stage, after fi nal washing and before chilling
(Gill and Bryant 1997b ; Nutsch et al. 1997 )
(Fig. 3.1 ). Steam pasteurization ™ consists of
the following steps (Bacon 2005 ): (i) removal
of water by vacuum from the meat surface in
order to allow better penetration of steam; (ii)
application of “ saturated ” steam (commonly
for 6.5 – 10 s) raising surface temperature to
80 – 90 ° C; and, (iii) cooling of treated tissues
in order to prevent visual defects or microbial
growth. Moist heat treatment using a com-
mercial steam cabinet was more effective in
reducing bacterial counts than cold (15 ° C)
or warm (54 ° C) water, but equally effective
for hot (82 ° C) water, on lamb carcasses
at pre - evisceration after water - washingtions, such as > 20 seconds at temperatures
80 – 85 ° C, do not improve the decontamina-
tion effi ciency of hot water, while they may
cause irreversible discoloration of meat (Gill
et al. 1995, 1999, 2001 ; Edwards and Fung
2006 ). Deleterious effects on the color of
meat are also caused by very high water tem-
peratures (e.g., 90 ° C), irrespective of expo-
sure time (Barkate et al. 1993 ; Gill et al.
1995 ; Gill and Badoni 1997 ).
Apart from the immediate impact on
microbial reduction, hot - water sprays have
no residual antimicrobial effects during
product storage, while in some cases hot -
water application may actually enhance
microbial growth; however, it may facilitate
reduction or inhibition of growth of injured
cells by subsequent organic acid treatments
(Ikeda et al. 2003 ; Koutsoumanis et al. 2004 ).
Specifi cally, although application of hot (72
or 74 ° C) or cold (33 ° C) water for 12 seconds
on beef tissue caused 2.1 – 2.6 log 10 CFU/cm^2
reductions in APC, TCC, L. innocua , E. coli
O157:H7, and C. sporogenes, microbial
growth occurred at least 1000 - fold within 21
days of storage at 4 – 5 ° C in vacuum pack-
ages, with no pronounced differences in bac-
terial counts compared to untreated samples
(Dorsa et al. 1997a, 1998a, b, c ). Furthermore,
hot water (75 ° C, 30 s) enhanced growth of L.
monocytogenes during subsequent storage of
treated meat in vacuum packages at tempera-
tures of 4, 10, and 25 ° C, compared to colder
(55 ° C) water or untreated meat (Ikeda et al.
2003 ; Koutsoumanis et al. 2004 ). This has
been attributed to the potential of hot water
to increase available nutrients on the surface
of meat possibly via denaturation of compo-
nents or extraction from inner tissue, reduce
natural psychrotrophic competitors of the
pathogen, and increase free water available
for microbial growth (Ikeda et al. 2003 ).
Signifi cant delay in growth of natural spoil-
age fl ora has been reported on adipose tissue
treated with hot water. Gorman et al. (1997)
observed that APC were reduced by 0.8 –
2.8 log 10 CFU/cm^2 following treatment of