Abstract
The official Japanese method for analysis of aflatoxins, Kanshoku No.128, is a combined method of the AOAC, BF and CB methods, using extraction of BF and clean-up procedures of the CB method. In the Kanshoku method, samples are mixed with methanol containing a 1%NaCl solution and hexane, and then, an aqueous methanol fraction separated from a hexane fraction is extracted with chloroform. The chloroform extracts are concentrated to 50ml to be applied on silica gel column for clean-up. The purpose of this study is to clarify whether the concentrated chloroform extracts in the Kanshoku method contain a small amount of methanol, which might disturb clean-up of aflatoxins with a silica gel column. Determination of methanol and chloroform concentrations in the aqueous methanol and chloroform fractions before and after shaking revealed that methanol was transferred from the aqueous methanol to the chloroform fraction. To examine whether the presence of methanol in the chloroform fraction separated after shaking disturbed the clean-up of aflatoxins with a column, aflatoxin B1 was added to the chloroform fraction separated from the aqueous methanol fraction after shaking. After being treated according to the Kanshoku or CB method, the chloroform fraction was applied on a silica gel column, and aflatoxin B1 content recovered in eluted fractions from the column was determined by the thin layer chromatography method. A large amount of aflatoxin B1 was recovered in the solution after washing the column when the Kanshoku method was used, and in the eluted solution after washing when the CB method was used. Aflatoxin B1 added to comminuted raw shelled peanuts was recovered at 91.9±6.0% (Mean±S.D., N=7, 5-10 repetition) with a coefficient variation of 3.8±1.0% of by the Kanshoku method using evaporation of chloroform extracts to dryness instead of to 50ml . Coefficient variations for naturally contaminated raw shelled peanuts and cream-type peanut butter were 14.0±6.0 (Mean±S.D., N=23, 3-11 repetition) and 6.6±4.1% (Mean±S.D., N =13, 3-7 repetition), respectively.
