Agriculture Reference
In-Depth Information
product quality. In a sequential combination, sanitization of whole produce prior to
irradiation has been shown to synergistically lower the microbial load of fresh- cut
produce. Fan and others ( 2008a ) surface - pasteurized whole cantaloupes with 76 ° C
water for 3min. Fresh-cut cantaloupe pieces prepared from the pasteurized whole
fruits were then packaged in clamshell containers and exposed to 0.5 kGy radiation.
They found that samples treated with combined heat and low-dose radiation had lower
microfl ora populations than either treatment alone and maintained the quality of the
product. Overall, the studies conducted in the last decade demonstrated that most
fresh-cut fruits and vegetables can tolerate up to 1 kGy radiation without deleterious
sensory impact.
Microbial Safety of Irradiated Produce
Irradiation doses suffi cient to achieve a 1-log reduction for surface-contaminating
bacterial pathogens are typically in the range of 0.2-0.8 kGy. Viruses and fungi are
generally more resistant, often requiring 1-3 kGy to achieve the same level of reduc-
tion (Niemira and Sommers 2006). Doses required for 3-log reductions of viruses and
fungi are deleterious for most types of produce. However, it is important to recognize
that the majority of serious foodborne illnesses resulting in hospitalizations and deaths
(60% and 72% of the total, respectively) are attributed to bacterial pathogens (Mead
and others 1999). Irradiation is therefore suitable for inactivating bacterial pathogens
such as
E. coli
O157:H7,
Salmonella
, and
Listeria
, the most serious safety threats for
consumers of fruits and vegetables.
Relatively low doses of irradiation can result in signifi cant reductions of foodborne
pathogens. A 1 kGy dose resulted in a 4-log reduction of total aerobic plate counts
(TAPC) and
L. monocytogenes
on bell peppers (Farkas and others 1997). The same
degree of reduction of TAPC was obtained on peeled, ready-to-use carrots (Lafortune
and others 2005). In that study, reductions increased to 4.5 log when MAP was sub-
stituted for air packaging. A 1 kGy dose also produced a 5-log reduction of
E. coli
and
L. monocytogenes
on diced celery (Prakash and others 2000b). These studies yielded
a D
10
for these pathogens of 0.2-0.3 kGy. D
10
values for
E. coli
O157:H7 on radish,
alfalfa, and broccoli sprouts were 0.34, 0.27, and 0.26 kGy, respectively (Rajkowski
and Thayer 2000). Bari and others (2004) obtained D
10
of 0.3 kGy for both
E. coli
O157:H7 and
Salmonella
on radish sprouts, but lower values (0.16-0.18kGy) on
mung bean sprouts.
Irradiation of melons at 0.5 or 1.0 kGy reduced the microbial load and improved
the keeping quality in storage (Boynton and others 2006). Apple slices treated with
the antibrowning agent calcium ascorbate required higher irradiation doses to inacti-
vate inoculated
L. monocytogenes
(Fan and others 2005b). However, the compound
also protected apple slices from the negative sensory effect impact resulting from the
higher dose. Irradiation of sliced carrot (2 kGy) reduced
E. coli
,
Yersinia enteroco-
litica
, and
L. monocytogenes
to undetectable levels (Kamat and others 2005). The
D
10
values were calculated to be 0.12 kGy for
E. coli
, 0.26 kGy for
Y. enterocolitica
, and
0.3 - 0.5 kGy for
L. monocytogenes
. In the same study, irradiated carrots showed insig-
nifi cant losses in sucrose, total carotenes, and ascorbic acid, and had two- to fourfold
increases in the refrigerated shelf life. Several isolates of
Salmonella
inoculated onto
