International Specialty Supply
Supplying Sprout Companies Throughout the World
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International Specialty Supply Supplying Sprout Companies Throughout the World
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820 East 20th Street Cookeville, TN 38501 USA 931 526 1106
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Dear
Bob,
Thanks for your interest in our work on alfalfa seed decontamination which
was summarized in the November 1999 At-A-Glance. We are confident in these
data, yet this was a preliminary study. I am attaching the text of the
article for your use in part or whole, to send to sprout growers. However,
I would ask you to please indicate in your communication that results are
preliminary. Best
wishes for 2000! Sincerely, (Dr
Beuchat's team at The Center for Food Safety and Quality Enhancement,
Griffin, GA has done much research on pathogens in sprouts. It was Larry
work that directed growers toward the 20,000 ppm Calcium Hypochlorite sanitation
procedures.) Plant
Compounds Evaluated as Alfalfa Seed Disinfectants (Allyl
isothiocyanate has potential) Outbreaks
of Salmonella and Escherichia coli O157:H7 infections associated
with seed sprouts continue to occur. At least five outbreaks of salmonellosis
associated with alfalfa or clover sprouts have been documented in the US in
1999. Hydrophobic
aqueous solutions of chlorine, chlorine dioxide, hydrogen peroxide, organic
acids, or trisodium phosphate, at concentrations known to otherwise be lethal,
are minimally effective in killing Salmonella and E. coli O157:H7
on seeds intended for sprout production. The hypothesis is that these sanitizers
do not come in contact, at least in an active form, with cells lodged in cracks
and crevices on the surface of seeds. This gave impetus to evaluating volatile
plant components for their efficacy in killing E. coli O157:H7 inoculated
onto alfalfa seeds. It was surmised that volatile antimicrobial compounds could
more easily reach cells of E. coli O157:H7 in areas protected from
contact with hydrophobia aqueous solutions. Gaseous
treatment of a surface-inoculated agar medium with up to 50 ppm of eugenol,
carvacol, linalool, or methyl jasmonate for 48 h at 20 - 47EC failed to inhibit
colony formation by E. coli O157:H7. However, exposure of cells to 8 ppm allyl
isothiocyanate (AIT), a volatile compound resulting from hydrolysis of glucosinolates
in cruciferous plants such as mustard and horseradish, resulted in more
than a 7-log reduction of the pathogen with 48 h at 37EC. Significant
reduction in populations also occurred upon exposure of cells to 4 ppm AIT.
Treatment with 10 ppm AIT for 5 h at 47EC resulted in death of 6 log10
of E. coli O157:H7. The
efficacy of low concentrations of AIT in killing E. coli O157:H7 on dry
and wet alfalfa seeds was not quite as promising. The pathogen, at an initial
population of 2.9 log10 cfu/g of dry seeds, was not completely
eliminated by treatment for 24 h with 100 ppm of AIT at temperatures as high as
47EC. The pathogen, at an initial population of 2.7 log10 cfu/g of
wet seeds, on the other hand, was not recovered after treatment with 50 ppm AIT
for 24 h at 37EC or 47EC. Unfortunately, the enhanced effectiveness of AIT in
killing E. coli O157:H7 on wet seeds is offset by a dramatic reduction in
seed viability. The lethal mode of action of AIT against microbial cells is
thought to involve respiratory inhibition. AIT apparently also adversely affects
respiratory mechanisms in alfalfa seeds. Notwithstanding
the potential adverse effect of AIT on germination of alfalfa seeds, which is
apparently influenced by moisture content, the use of AIT as an alternative to
chlorine for the purpose of killing E. coli O157:H7 and perhaps other
pathogens holds promise. We are currently evaluating the effectiveness of AIT
and other natural volatile plant compounds in killing Salmonella on
alfalfa seeds. |