Sample preparation and presampling of pistachios.

A theory has been developed to quantify the reduction of subsample variance of aflatoxin contamination, which is observed when granular materials are wet slurried, rather than dry ground, during subsample homogenization. A coefficient of variation, based on particle size distribution, subsample size, and probability of contamination, is predicted. The theory is tested with dry ground and with wet slurried pistachios, and excellent quantitative agreement is obtained. A 32% increase in the mean aflatoxin level is observed as well when wet slurrying is applied. Although no statistical explanation for this effect can be found, it is suggested that it is related to physiochemical binding between the nut matrix, which is (partly) broken by wet slurrying, and aflatoxin, making the extraction of more toxin possible. Other parameters that may affect slurrying results have been investigated as well.