Novel Technologies for Microbial Spoilage Prevention 267otic cells. To our knowledge, sensory data
demonstrating that phage treatments do not
alter the appearance or fl avor of foods have
not been published.
Among the many potential drawbacks of
phage technology, limited host range is con-
sidered most important. Most reported studies
were performed on experimentally inocu-
lated refrigerated meats and demonstrated
effi cacy against spoilage psychrotrophs and
psychrophiles (Greer 1986, 1988 ; Greer and
Dilts 2002 ; Greer et al. 2007 ). Greer (1988)
showed that homologous phage can replicate
and limit bacterial growth on inoculated and
refrigerated phage - treated beef. Maximum
shelf life extension was seen with an initial
bacteria density in excess of 3 log 10 CFU/cm^2
and phage concentrations above 7 log 10 PFU/
cm^2. Greer and Dilts (2002) were able to
extend the shelf life of inoculated ( B. ther-
mosphacta ) and homologous phage - treated
refrigerated pork adipose tissue from 4 to 8
days. Leuconostoc gelidum phage isolated
from vacuum - packaged pork loin was able to
limit growth of the corresponding host on
inoculated pork adipose tissue stored at 4 ° C
in air or vacuum (Greer et al. 2007 ). However,
the same research group (Greer and Dilts
1990 ) showed that a pool of seven phage
strains failed to lyse 43.8% of 1,023 strains
of naturally isolated pseudomonads from
beef, pork, and lamb. When added to refrig-
erated, naturally contaminated beef rib - eye
steaks, the same phage pool remained
viable throughout the study and signifi cantly
reduced Pseudomonas growth, but did not
signifi cantly affect shelf - life duration. The
authors concluded that phage inability to
prolong shelf life of meat was caused by the
narrow host range of the phage pool.
Development of phage - resistant bacterial
mutants is another point of concern that may
be overcome using a pool of phage strains,
with each targeting different receptors on the
bacterial cell - wall surface. On the other hand,
phages continuously co - evolve with bacteria,Several advantages of phage technology
for meat spoilage control are described by
others (Greer 2005 ; Hudson et al. 2005 ). For
example, phages are self - reproducible and
release more phage after bacterial lysis.
Phage specifi city may be an advantage if
selective for spoilage microfl ora only. On the
other hand, specifi city may diminish phage
activity against broad - spectrum spoilage
microfl ora. Whitman and Marshall (1971a)
noticed that phages from bacteriophage - host
systems isolated from refrigerated food prod-
ucts usually attacked only those hosts upon
which they were isolated. Phages are gener-
ally more stable than their hosts and can
survive processing (Koo et al. 2000 ). Greer
(1988) showed that phage concentration
remained stable (5 to 6 log 10 PFU/cm^2 ) on the
surface of refrigerated (4 ° C) beef rib - eye
steaks during 14 days of storage in air.
Whitman and Marshall (1971b) showed that
some Pseudomonas phages isolated from
beef may remain infectious after heating to
60 ° C, pH change to 4.0, and exposure to 4 M
NaCl. Phages are naturally present entities
and constitute part of the environment.
Whitman and Marshall (1971a) isolated a
total of 38 host - phage pairings from ground
beef, sausage, chicken, raw milk, and oysters.
Phage concentration as high as 6.3 × 1 0^6 PFU/g
was found on chicken skin. Not surprisingly,
most isolated were invaders of Pseudomonas
spp., followed by Gram - positive cocci and
members of the Enterobacteriacea family.
Similarly, Atterbury et al. (2003) isolated 34
Campylobacter phages from retail chicken
meat.
Because of the naturally wide prevalence
of phages on raw meats, one may conclude
that phage addition to food products is not
adding a foreign entity. Phages used to
control food spoilage bacteria can be
derived from corresponding foods and food -
processing environments. Because phages
are highly specifi c to prokaryotes, it is
unlikely that they can target human eukary-