The reduction of chemical and microbial contaminants in wheat

Abstract

This study was undertaken to investigate alternative procedures for cleaning wheat prior to milling. Overall it concluded that scouring wheat prior to milling is unlikely to result in sufficiently substantial reductions in either pesticide residue levels or microbial loads to justify the inclusion of such equipment in commercial mills.

On the basis that pesticide residues and microbes in wheat are concentrated in the branny layers of the kernel, wheat samples were subjected to frictional cleaning in a Westrup Laboratory Scarifier type LA-H to remove part of the bran coat. Scouring regimes were chosen on the grounds of practical application in a commercial mill. Thus, only 3-6% of the bran coat was removed and no attempt was made to study wet scouring.

Wheat samples were treated at the same application rate of 4mg/kg with two formulations (2% dust and 25% emulsifiable concentrate) of pirimiphos-methyl and stored for 1, 3 and 6 months prior to scouring and laboratory milling. Pesticide residue analysis of the mill stocks showed that greater reductions were achieved when the pesticide had been applied as a dust formulation than an emulsifiable concentrate and that with longer storage times it became increasingly difficult to remove the pesticide when applied in the form of an emulsifiable concentrate. However, the scouring regimes employed resulted in only slight overall reductions (17-28%) over and above conventional cleaning.

Wheat samples with naturally occurring microbial loads were subjected to scouring and milling and the mill stocks tested for total viable count, moulds and yeasts and coliform bacteria. Neither scouring regime employed was particularly effective in reducing the microbial load in flour - tenfold reduction being the best result obtained.