Meat Decontamination 63on adipose tissue were 3.24 – 4.39 after treat-
ment and 3.74 – 4.84 after 1 day (Cutter and
Siragusa 1994b ). Following prolonged
storage, such as 21 days at 4 – 5 ° C, the pH on
the surface of meat may increase up to the
initial values of 5.5 – 5.6 (Dorsa et al. 1997a,
1998a, b, c ; van Netten et al. 1997 ). For
pathogens that cannot grow at refrigeration
temperatures, such as E. coli O157:H7, S.
aureus , C. jejuni, and S. Typhimurium, beef
decontamination with 1.5 – 5% lactic, or 1.5 –
3% acetic acid (25 – 65 ° C, 15 or 30 s) contrib-
uted to reductions of 2 – 3 log 10 CFU/cm^2 and/
or eliminated populations during storage in
air or vacuum at 4 – 5 ° C (Podolak et al. 1996 ;
Dorsa et al. 1997a, 1998a, b, c ; van Netten et
al. 1998 ; Berry and Cutter 2000 ; Cutter and
Rivera - Betancourt 2000 ; Castillo et al.
2001b ; Calicioglu et al. 2002 ; Goz á lez -
Fandos and Dominguez 2006 ). Other studies
(van Netten et al. 1997, 1998 ; Dorsa et al.
1998a, b, c ; Ikeda et al. 2003 ; Koutsoumanis
et al. 2004 ) have found that organic acids at
2% and 5% suppressed growth of the same
pathogens at 12 ° C, and of L. monocytogenes
and Y. enterocolitica during aerobic storage
or storage in vacuum sealed packages at 4 to
10 ° C. However, Uyttendaele et al. (2001)
found that treatment of beef tissues with 1%
or 2% lactic acid/sodium lactate buffer solu-
tion did not affect survival of E. coli O157:H7
on beef stored (4 ° C) aerobically. Organic
acid applications may also extend the shelf -
life of treated meat, by delaying growth of
meat spoilage bacteria. Lactic acid caused a
shift in the dominant fl ora of aerobically
stored meat from pseudomonads to yeasts
and lactic acid bacteria (van Netten et al.
1997 ; Koutsoumanis et al. 2004 ). Moreover,
treatments (25 or 55 ° C) of lamb or beef with
2 – 5% acetic or lactic acid delayed growth of
the Gram - negative aerobic fl ora and to a
lesser extend of lactic acid bacteria at − 1 to
25 ° C (Anderson et al. 1988 ; Kotula and
Thelappurate 1994 ; Goddard et al. 1996 ;
Dorsa et al. 1997a, 1998a, b, c ; van Netten et
al. 1997, 1998 ; Koutsoumanis et al. 2004 ).acid rinses (Hardin et al. 1995 ). E. coli
O157:H7 survived less on post - rigor frozen
beef tissue, treated with 2% acetic acid
(56 ° C, 15 s), compared with pre - rigor fresh
tissue, presumably due to higher bacterial
attachment on fresh than on frozen surfaces
(Cutter et al. 1997 ). In general, however, the
effi cacy of organic acid treatments is reduced
on chilled compared with hot (fresh) car-
casses, because bacterial attachment increases
with time from slaughtering to chilling,
and the temperature of the rinsing solution is
reduced by the chilled surface (Bacon et al.
2002b ).
Application of organic acid early after
slaughtering, such as after dehiding or after
evisceration, is highly effective (Prasai et al.
1991 ). For instance, pre - chilling treatment of
inoculated beef samples with lactic acid and
water resulted in 5.2 log 10 CFU/cm^2 reduc-
tions of inoculated S. Typhimurium and E.
coli O157:H7, while post - chilling lactic acid
spraying reduced these organisms by only
1.6 and 2.4 log 10 CFU/cm^2 , respectively
(Castillo et al. 2001b ). Spraying of carcass
tissue with 5% Tween 20 (a nonionic surfac-
tant) 15 minutes before acid treatment was
found to loosen or prevent bacterial attach-
ment, thereby facilitating the subsequent
decontamination by lactic acid spraying
(Calicioglu et al. 2002 ). Such methods would
probably be more effective on fat - covered
surfaces, such as briskets and ribs or poultry
skin.
In addition to initial microbial reductions,
the residual levels of acids, and thus, the
reduction of pH on treated meat surfaces,
may suppress pathogen proliferation or even
exert bactericidal effects during storage
(Koutsoumanis et al. 2004 ). Specifi cally,
spray - washing with acetic, lactic, or citric
acid at concentrations 1 – 5% reduced the pH
on the surface of lean tissues from 5.60 to
3.79 – 4.96 (with an average of 4.3 – 4.6)
immediately after treatment, whereas after 1
day, the pH rose to 5.29 – 5.39 (Cutter and
Siragusa 1994b ). The respective pH changes