Plant Compounds Evaluated As Alfalfa Seed Disinfectants
Thanks for your interest in our work on alfalfa seed decontamination whichwas summarized in the November 1999 At-A-Glance. We are confident in thesedata, yet this was a preliminary study. I am attaching the text of thearticle 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 arepreliminary.
Bestwishes for 2000!
Larry R. Beuchat
(DrBeuchat’s team at The Center for Food Safety and Quality Enhancement,Griffin, GA has done much research on pathogens in sprouts. It was Larrywork that directed growers toward the 20,000 ppm Calcium Hypochlorite sanitationprocedures.)
PlantCompounds Evaluated as Alfalfa Seed Disinfectants
(Allylisothiocyanate has potential)
Outbreaksof Salmonella and Escherichia coli O157:H7 infections associatedwith seed sprouts continue to occur. At least five outbreaks of salmonellosisassociated with alfalfa or clover sprouts have been documented in the US in1999.
Hydrophobicaqueous solutions of chlorine, chlorine dioxide, hydrogen peroxide, organicacids, or trisodium phosphate, at concentrations known to otherwise be lethal,are minimally effective in killing Salmonella and E. coli O157:H7on seeds intended for sprout production. The hypothesis is that these sanitizersdo not come in contact, at least in an active form, with cells lodged in cracksand crevices on the surface of seeds. This gave impetus to evaluating volatileplant components for their efficacy in killing E. coli O157:H7 inoculatedonto alfalfa seeds. It was surmised that volatile antimicrobial compounds couldmore easily reach cells of E. coli O157:H7 in areas protected fromcontact with hydrophobia aqueous solutions.
Gaseoustreatment 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 inhibitcolony formation by E. coli O157:H7. However, exposure of cells to 8 ppm allylisothiocyanate (AIT), a volatile compound resulting from hydrolysis of glucosinolatesin cruciferous plants such as mustard and horseradish, resulted in morethan a 7-log reduction of the pathogen with 48 h at 37EC.
Significantreduction 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 log10of E. coliO157:H7.
Theefficacy of low concentrations of AIT in killing E. coli O157:H7 on dryand wet alfalfa seeds was not quite as promising. The pathogen, at an initialpopulation of 2.9 log10 cfu/g of dry seeds, was not completelyeliminated by treatment for 24 h with 100 ppm of AIT at temperatures as high as47EC. The pathogen, at an initial population of 2.7 log10 cfu/g ofwet seeds, on the other hand, was not recovered after treatment with 50 ppm AITfor 24 h at 37EC or 47EC. Unfortunately, the enhanced effectiveness of AIT inkilling E. coli O157:H7 on wet seeds is offset by a dramatic reduction inseed viability. The lethal mode of action of AIT against microbial cells isthought to involve respiratory inhibition. AIT apparently also adversely affectsrespiratory mechanisms in alfalfa seeds.
Notwithstandingthe potential adverse effect of AIT on germination of alfalfa seeds, which isapparently influenced by moisture content, the use of AIT as an alternative tochlorine for the purpose of killing E. coli O157:H7 and perhaps otherpathogens holds promise. We are currently evaluating the effectiveness of AITand other natural volatile plant compounds in killing Salmonella onalfalfa seeds.