GROWTH DEPRESSING FACTORS IN RAPESEED OIL MEAL: V. THE EFFECTS OF MYROSINASE ACTIVITY ON THE TOXICITY OF THE MEAL

Abstract

A study was made of the effects of adding 0.1 per cent myrosinase (a thioglucoside-splitting enzyme) to mouse diets containing Swedish or Polish type rapeseed oil meal and hot water-treated fractions of the meal. The latter were devoid of active enzyme but contained known quantities of the thioglucosides, precursors of the toxic isothiocyanates (I) and thiooxazolidones (T).Hot water extraction of the meals resulted in about 20 per cent of the dry matter being extracted and in significant alteration in the proportions and amounts of I and T.The addition of myrosinase to untreated rapeseed oil meals failed to increase the toxicity, presumably because there was already sufficient enzyme in the meals to reduce gains to about 25 per cent of normal. Addition of enzyme to the extracted residue (containing about one-third of the original thioglucosides of the meal) also failed to increase the toxicity. Enzyme addition to diets containing the water-soluble components resulted in significant growth depression but the full potential toxicity was not obtained.It is concluded that the enzyme myrosinase is an important factor affecting the toxicity of rapeseed oil meal in animal feeding, although conditions for its optimum activity were not achieved in this experiment where semi-purified enzyme was employed as a dietary supplement.