Use of alkali in the isolation and preparation of aflatoxins Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5425kc89z

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  • The biological preparation of aflatoxins was accomplished by culturing the mold Aspergillus flavus on various media. Aflatoxin was isolated by chloroform extraction of the culture, and purified by column fractionation and crystallization. Rice, wheat, soya bean, peanut and YES media were found to give high yields of aflatoxin. It was also found that A. flavus could grow and produce toxin on fresh tomatoes and grapes. The pure aflatoxins B₁ and G₁ were treated separately with standardized NaOH and NH₄OH solutions. Changes in solvent system, exposure time and alkali concentration were found to affect the stability of aflatoxin. Solutions of aflatoxins B₁ and G₁ in ethanol and methanol were quite unstable when treated with strong base even after a short exposure period. The aflatoxins were quite stable, however, if treated in a chloroform solution at a lower base concentration. Several crude chloroform extracts containing aflatoxins were prepared from various culture media with different mold strains. These extracts were then shaken gently with an equal volume of 0.25 N NaOH solution for several seconds. This treatment produced final chloroform extracts which were lower in pigments, total solids, and lower R [subscript f]-value compounds than similar extracts which received no base treatment. The decolorizing ability of the alkali treatment was demonstrated by comparison of the ultraviolet absorption spectra of the treated samples and control samples. This base treatment shortened the preparation time and increased the yield of aflatoxins from crude chloroform extracts. Photodegradation of aflatoxins B₁ and G₁ was observed in both ethanol and chloroform solutions. After an induction period, the aflatoxin was degraded to low R [subscript f]-value compounds, which were then converted to non-fluorescent products. Aflatoxin G₁ was found to be more stable than aflatoxin B₁ to light exposure. Base treatment as described above was found suitable for purifying aflatoxin which contained photodegraded contaminants.
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