The fate of labelled insecticide residues in food products. II. —The nature of methyl bromide residues in fumigated wheat

Abstract

The chemical fate of methyl bromide absorbed by wheat under the conditions of fumigation has been studied. Whole-wheat flour was exposed to 14C-labelled methyl bromide. The fat, starch, gluten, and water-soluble fractions were prepared from the exposed flour and their I4C-content assayed. The gluten or protein fraction was responsible for some 8004 of the decomposition of the absorbed fumigant. By measuring the 14C of the volatile products obtained on treating the gluten with sodium hydroxide or hydriodic acid under different conditions, it was shown that the decomposition of methyl bromide in gluten was due almost entirely to methylation with the formation of 50% of N-methyl derivatives, 30% of dimethyl sulphonium derivatives, and of 20% of methoxyl and thiomethoxyl derivatives in about equal proportions. Similar results were obtained when gluten alone was exposed to the labelled fumigant. The production of free methanol in the flour by hydrolysis of the absorbed fumigant was about 10% or less. The rate of spontaneous decomposition of the dimethyl sulphonium compounds formed as a result of fumigation was estimated by using wheat which had been grown on 35S-labelled sulphate.'

Sorption of phosphine by cereal products

“…The greater uptake of PH3 by second patent (bakers') flour as compared with first patent flour (Table I) may be a reflection of the greater ash content of the former. The protein content of gluten powder is more than six tmes that of flour, but differences in the protein constitution may also account for the greater chemisorption of PH3 by gluten powder compared to that of flour or wheat germ In this connection, chemisorption of methyl bromide h as been related to -SH groups in flour protein (Lewis and Eccleston, 1946; Page and Lubatti, 1940), and to methylation of amino acids of wheat protein (Bridges, 1956;Winteringham et al, 1955). Bromide residues that resulted from fumigation with methyl bromide increased with increasing protein content of mill fractions (Gibich and Pedersen, 1963).…”

Effects of methyl bromide on phosphorus metabolism in the adult housefly, Musca domestica L.

“…Methyl bromide readily and irreversibly methylates certain free and protein amino acids, especially the SH groups of cysteine and reduced glutathione, the S -CH, group of methionine, and the imidazole group of histidine (Blackburn, Consden & Phillips, 1944;Winteringham & Harrison, 1946;Lewis & Eccleston, 1946;Lewis, 1948;Winteringham, Harrison, Bridges & Bridges, 1955b;. The rapid blocking of the free SH groups of the tissues of Calliphora erythrocephala larvae in vivo by high concentrations of methyl bromide vapour has been demonstrated (Loveday & Winteringham, 1951).…”

Nutrients in Wheat Products, Review of Proteins of Wheat Flour

“…A recent series of papers, somewhat unrelated to the preceding topics, is worthy of brief comment, principally because of growing concern with public health aspects of food materials. Winteringham and associates (5,42,43) have studied the products formed in wheat and flour as a result of fumigation with methyl bromide. Nearly all of the reagent is taken up by the protein fraction.…”