Detection and inactivation of saxitoxin in skim milk.
In this study, saxitoxin dihydrochloride in skim milk was reacted with sodium hydroxide and hydrogen peroxide to yield nontoxic 8-amino-6-hydroxymethyl-iminopurine-3(2H)-propionic acid (AHIPA), which was quantified by fluorescence spectroscopy using excitation and emission wavelengths  of 330 and 425 nm, respectively. Samples of saxitoxin dihydrochloride (in 20% ethanol, vol/vol) were used as controls. The limits of detection of AHIPA, based on the concentration of saxitoxin prior to inactivation, were 5 and 10 μg/ml for the control and skim milk, respectively. These  values are considerably below the concentration of saxitoxin that corresponds to the lethal dosage of 1 mg for an adult of average weight (70 kg). The inactivation of saxitoxin proceeded at a lower rate in skim milk than in the control, as its reaction rate constant was only 0.004 min(-1)  compared with 0.011 min(-1) for the control. We were unable to detect AHIPA in 2% milk contaminated with saxitoxin because of possible interference from what we believed were products of secondary reactions involving milk fat and sodium hydroxide. Our results also indicated  that the conversion of saxitoxin to AHIPA increased initially with temperature up to 40°C but decreased thereafter. We observed a decrease in the formation of AHIPA when the concentration of hydrogen peroxide was increased except at 22°C, where there was an initial increase in AHIPA  formation between 1.2 and 2.4 mg/ml hydrogen peroxide but its formation decreased thereafter.
Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Avenue, Saint Paul, Minnesota 55108, USA.
Stephen E
SE
Lumor
Bronwyn D
BD
Deen
Ian
I
Ronningen
Kenneth
K
Smith
Neal R
NR
Fredrickson
Francisco
F
Diez-Gonzalez
Theodore P
TP
Labuza
D000818:Animals; D054045:Biological Warfare Agents; D003257:Consumer Product Safety; D005506:Food Contamination / Q000032:analysis*; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D008892:Milk / Q000737:chemistry*; D011422:Propionates / Q000032:analysis / Q000737:chemistry; D012530:Saxitoxin / Q000737:chemistry* / Q000302:isolation & purification; D012680:Sensitivity and Specificity; D012972:Sodium Hydroxide / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013696:Temperature
D054045:Biological Warfare Agents; D011422:Propionates; D012530:Saxitoxin; D012972:Sodium Hydroxide; D006861:Hydrogen Peroxide