Agriculture Reference
In-Depth Information
quality-related attributes, but care is needed in their application because continuous
fumigation can lead to taint, with thin-skinned products more prone than those that
are thicker-skinned (Tzortzakis 2007). EO vapors have shown potential for the decon-
tamination of cabbage leaves. Citral and linalool vapors produced 2- to 6-log
10
reduc-
tions of
L. monocytogenes
,
Staph. aureus
,
B. cereus
, and
Arcobacter
spp. after 8 - 24 h,
and bergamot vapors had a similar effect but did not affect
Staph. aureus
(Fisher and
Phillips 2006; Fisher and others 2007). Another EO volatile compound allyl isothio-
cyanate (AIT), derived from cruciferous plants, has been tested for the elimination of
E. coli
O157:H7 on wet and dry alfalfa seeds with mixed results. Greater than a 2-log
10
reduction (inoculum 2.7 log
10
) was achieved on wet seeds exposed to AIT for 24 h at
37 or 47 °C, although loss of seed viability was a problem. On dry seeds the effects
were not observed (Park and others 2000). An effect against
Salmonella
was, however,
noted for treatment of alfalfa seeds by thymol at 60 °C for 7 hours (Weissinger and
others 2001 ).
Essential oil vapors also have the potential to be used in combination with modifi ed
atmosphere packaging (MAP) to enhance both product safety and quality. For example,
eugenol, thymol, and carvacrol vapors have been tested separately and in combination
for antimicrobial properties on MAP-packed table grapes. Around a 2-log
10
reduction
in both yeasts and molds and aerobic mesophiles was achieved. The combination of
multiple EO allowed reduced quantities to be used, and odors associated with the EOs
were found to dissipate rapidly upon opening of the seal (Guillen and others 2007;
Valero and others 2006). Similar results were achieved in MAP sweet cherries (Serrano
and others 2005 ).
Other plant materials with potential for biocontrol use in produce include extracts
from berries, seeds, and tea. The skins, juice, and seed extracts of grapes have been
found to be inhibitory to
L. monocytogenes
,
E. coli
,
Salmonella
Poona, and
B. cereus
in vitro
(Rhodes and others 2006; Serra and others 2008). Both Gram-negative and
Gram-positive foodborne pathogens were inhibited by addition of Nordic berry
extracts to growth media, with cloudberry and raspberry the best inhibitors (Puupponen-
Pimia and others 2005). Whole tea infusions and fl avonoid extracts were inhibitory
when applied to
B. cereus
cultures on solidifi ed media (Friedman and others 2006).
Grapefruit seed extract has been tested in combination with nisin, citric acid, sodium
lactate, and potassium sorbate on fresh-cut cucumber and lettuce. Either alone or in
combination with nisin and citric acid, grapefruit seed extract caused signifi cant inhi-
bition (
2 log
10
) of
Salmonella
and
Listeria
on the vegetables (inoculum 4 log
10
) and
prolonged the sensory quality of the product (Xu and others 2007).
A completely different approach to elimination of pathogens on produce may be
to stimulate the innate pathogen defense mechanisms of the plant tissues by adding
extracted plant signaling compounds. Methyl jasmonate is known to affect plant
growth and development and is involved in responses to pathogen attack and wound-
ing. When applied as a vapor to fresh-cut celery at 10 °C, a 3-log
10
reduction in the
native fl ora was achieved and the shelf life extended. Similar effects were observed
on green pepper strips when applied as a dip (Buta and Moline 1998). Methyl jasmo-
nate vapors and dips were also effective in reducing numbers of endogenous fl ora on
fresh-cut pineapple chunks by 3 log
10
when in a sealed container (Martinez-Ferrer and
Harper 2005). Other signaling compounds of interest include the plant defense
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