The potential use of ricin and Shiga toxins (Stxs) as bioterror weapons in the
food supply is a major concern for homeland security. Denaturation effects of
thermal and chemical treatments are expected to reduce the toxicity of ricin and
Shiga toxins in water solutions, but their effectiveness and stabilities in food
matrices are largely unknown.
The objective of this project was the identification of heat and chemical
treatments capable of inactivating ricin and Shiga toxins in orange juice so that
large quantities can be safely disposed in the event of an intentional attack.
Diluted ricin was mixed with orange juice for inactivation studies. Thermal
stability was determined in capillary tubes using a water bath at high
temperatures typical of pasteurization. For chemical inactivation, sodium
hypochlorite (NaOCl), sodium hydroxide (NaOH) and peracetic acid (PA) were
added alone or in combination to samples with or without thermal treatment.
The ricin concentration in samples was determined using an ELISA. The
Arrhenius model was used to evaluate temperature dependence. Enterohemorrhagic Escherichia coli strains were used to produce Shiga toxin 1
(Stx1) and Shiga toxin 2 (Stx2). Shiga toxins were added into phosphate
buffered saline (PBS) or orange juice to study the inactivation effects. The same
inactivation method was also used for heat treatment of Stxs. The concentration
of Stxs was determined by an ELISA and a cytotoxicity assay was conducted to
confirm the inactivation. Kinetics studies were done to evaluate inactivation parameters. Heat inactivation of ricin followed first-order kinetics. The half-life (t1/2) of ricin at
72, 80, 85 and 90°C were 72.6, 9.0, 2.0 and 0.5 min, respectively. The Z value
was 8.8°C indicating high temperature sensitivity. When the concentration of
each chemical was increased to a sufficient amount, the detection limit of the ELISA kit was reached when measuring ricin inactivated within 5 s at room
temperature. A significant synergism between NaOCl and NaOH and
considerable efficacy with treatment with PA alone were observed.
The heat inactivation of Stxs in PBS and orange juice also followed first-order
reaction kinetics. Both Shiga toxins in PBS and orange juice would reach the
concentration that was not detectable with ELISA within 30 s at 90°C and 120 s
at 85°C. The Z values for Stx1 and Stx2 were 6.7 and 7.2°C in PBS as well as
8.7 and 6.9°C in orange juice, respectively.
This study delivered the first series of time/temperature/concentration
conditions that would serve as the basis for recommendations for treating
orange juice subjected to intentional adulteration with ricin or Shiga toxins in an
orange juice plant with typical pasteurization equipment so it can be safely
disposed into the environment.
University of Minnesota M.S. thesis. January 2010. Major: Food Science. Advisors: Dr. Francisco Diez-Gonzalez and Dr. Theodore P. Labuza. 1 computer file (PDF); xii, 117 pages, appendices pages 116-117. Ill. (some col.)
Thermal and chemical inactivation of ricin and Shiga toxins in orange juice..
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