GROWTH-DEPRESSING FACTORS IN RAPESEED OIL MEAL: VII. EFFECTS OF MYROSINASE ACTIVITY ON TOXICITY FOLLOWING TREATMENT WITH BUFFERED SOLUTIONS

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Abstract
Solvent-process, uncooked rapeseed meal of Brassica napus L. (summer) origin was autoclaved at 0.7 kg/cm2 to destroy myrosinase and compared with uncooked meal. Each type of meal was treated with buffer solutions at pH 3.0, 6.0, and 9.0 for 1 hour at temperatures of 22 °C and 50 °C. Unextracted meals were air-dried after buffer solution treatment; extracted meals were filtered under vacuum and washed twice with similar buffer solution before drying. The resulting meals were assayed chemically for isothiocyanate (I) and oxazolidinethione (O) and tested for toxicity with mice using diets containing up to 0.07% I+O.Treatment of myrosinase-free rapeseed meal at any pH resulted in no apparent change in toxicity provided the sample was not filtered. Extraction of soluble matter removed over 80% of the I+O, but growth was depressed on meal processed at pH 3.0. Some of the thioglucosides apparently were converted into other non-water-soluble compounds.Exposure of enzyme-active meal to buffer solutions without subsequent filtration resulted in a one-third reduction in I+O at pH 3.0, one-half reduction at pH 6.0, and two-thirds reduction at pH 9.0. Further losses occurred upon filtration but all of these meals contained significantly more I+O than did enzyme-free meals similarly processed. Chemically determined I and O may fail to measure the potential toxicity of rapeseed meals in which enzyme activity has occurred.

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