Agriculture Reference
In-Depth Information
Bower
et al
. (2002) reported lower incidences of
powdery mildew in Charantais melons with anti-sense
gene for ACC oxidase (non-ethylene producing) as
compared to wild type Charantais melons. Since plant
tissues generally produce ethylene as a defence response to
infection, the reason for lower incidence of disease in the
anti-sense melons is unclear.
Post-harvest heat treatment shows promise for decay
control in cantaloupe. Full-slip fruits heat-treated for 3
minutes at 57°C by immersion and shrink-wrapped main-
tained good quality and low surface decay rates up to 20
days at 4°C (Lester 1989). However, irradiation treatment
(2 kiloGrays) was ineffective in controlling decay and
accelerated fruit softening, weight loss and electrolyte
leakage.
In a later study, Mayberry and Hartz (1992) applied heat
treatment to cantaloupes for 3 minutes with 60°C water
prior to storage at 3°C. Fruits had excellent appearance and
firmness and showed no stem-end decay up to 28 days of
storage; untreated control fruits, however, were unmarket-
able. 'Galia' melons were free from decay up to 8 days at
20°C following immersion in 52°C water for 2 minutes;
however, off-flavours were noted (Teitel
et al
. 1989). Dry
heating the surface of the melons to 52°C did not reduce
decay. Teitel
et al
. (1991) found that 'Galia' melons could
be dipped for 1 to 2 minutes in 55°C water and immedi-
ately wrapped with PVC plastic film; acceptable quality
was maintained for up to 9 days at 18°C storage. Heat
injury symptoms ranged from small pits to general brown-
ing up to 50% of the fruit surface.
Hot-water treatments did not reduce decay or extend
post-harvest life of winter squash. 'Delica' was immersed
for up to 12 minutes at 50°C; after 12 weeks of storage
there was no difference from untreated fruit (Arvayo-Ortiz
et al
. 1994).
samples of raw cucumber and melons, and several
outbreaks have been traced to contaminated cantaloupe
(Beuchat 1995). Pathogens have also been isolated from
vegetable salad samples of commercial establishments
(Lin
et al
. 1996) Salmonella can survive in tissues infected
with bacterial soft rot and on the surfaces of fresh-cut
produce, highlighting the necessity for maintaining
sanitary conditions during harvest, handling and distribution
(Wells & Butterfield 1997).
As a result, guidelines were published by the US
Department of Agriculture and the US Food and Drug
Administration to assist growers and handlers in maintaining
safe produce (USDA 1998). This guide outlines practical
steps to avoid cross-contamination of fresh produce with
human pathogens, beginning with production of transplants
and seeds, and continuing through production practices
related to soil and water quality, run-off situations, and
harvest, packing, storage and shipping operations. Worker
hygiene is also a critical component at each of these steps.
There is a significant amount of research being conduc-
ted to determine efficacy of post-harvest sanitizers in
reducing fruit surfaces contaminated with human patho-
gens.
Escherichia coli
O157:H7 multiplied on cantaloupe
cut surfaces and rinds at 25°C up to 3 weeks (Del Rosario &
Beuchat 1995).
Campylobacter jejuni
survived at least
6 hours on the surfaces of cut watermelon at room tem-
perature (Castillo & Escartin 1994). Immersion in chlorine
(1000 ppm) solution was more effective than hydrogen
peroxide in reducing populations of
E. coli
spp. inoculated
on whole cantaloupes, although efficacy decreased with
increased delay after inoculation (Ukuku
et al
. 2001).
Neither of these treatments completely sanitized contami-
nated surfaces.
As mentioned above, anoxic conditions can develop in
poorly designed film packages. As the oxygen level falls
below 2% in an enclosed package of low-acid produce
(such as squash and cucumber), if
Clostridium botulinum
is present, it can grow and produce a deadly neurotoxin
(Centres for Disease Control 2002). Proper temperature
management is critical in minimizing the potential for
pathogen growth. Cantaloupe and honeydew melon cubes
were inoculated with
C. botulinum
; after 9 days at15°C
toxin was detected, whereas inoculated cubes stored at 7°C
had no toxin present (Larson & Johnson 1999). Presence of
toxin was also associated with severe fruit decay, although
the presence of background flora appeared to limit growth
of
C. botulinum
.
There are numerous resources available regarding food
safety:
Food safety
Sales of fresh fruits and vegetables continue to increase due
to greater consumer awareness of health benefits. However,
precautions must be taken to minimize cross-contamination
of fresh produce with human pathogens during production
and post-production practices. Sales of a few crops have
been severely curtailed following outbreaks of illness
attributed to contaminated produce. Fortunately, consistent
application of sanitation procedures minimizes the risk.
A number of outbreaks of gastroenteritis have been
traced to the presence of human pathogens on fresh pro-
duce, mainly vegetables (Mead
et al
. 2002). Pathogenic
listeria and salmonella species have been isolated from
