Effect of Hydrogen Peroxide Treatment on the Nutritional Quality of Rapeseed Flour Fed to Weanling Rats

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Abstract
The effect of treating rapeseed flours with hydrogen peroxide on the glucosinolate content and nutritional value of the protein was examined. Four flours were prepared from Target variety rapeseed (Brassica napus) by dehulling and defatting the seed (sample RF), by heat treating and water washing the dehulled seed prior to defatting (sample WWRF), and by treating a part of samples RF and WWRF with solutions of 7 and 3% hydrogen peroxide, respectively. Chemical analysis showed that the hydrogen peroxide treatment lowered the glucosinolate content of the flour but was not as effective as the water extraction. The hydrogen peroxide treatment also oxidized methionine to its sulfoxide and sulfone and cysteine to cysteic acid. In the first experiment, weanling rats were fed for 3 weeks diets in which casein or each of the flour preparations provided 5, 10, or 20% protein. Rats fed the high glucosinolate-containing flour (sample RF) at the 10 or 20% protein level died, while those fed 5% survived but lost weight. Those fed the hydrogen peroxide-treated flours survived, but weight gains and food consumption were low compared with the values of the casein- or WWRF-fed groups. Rats fed sample RF exhibited enlarged thyroids. Those fed the peroxide-treated samples had high plasma levels of methionine sulfoxide and sulfone. In the second experiment, additions of 0.15 or 0.30% methionine to the 10% protein diets resulted in increased weight gains of the groups fed the peroxide-treated flours. It was concluded that the hydrogen peroxide treatment was effective in reducing the glucosinolate content of the rapeseed flour. However, the production of the oxidized sulfur amino acids, in particular methionine sulfone, reduced considerably the nutritional value of the protein.

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