Microwave treatment of dehulled rapeseed to inactivate myrosinase and its effect on oil and meal quality

Rapeseed was dehulled using a Palyi pneumatic attrition system which produced 62–66% clean dehulled seed. Dehulled rapeseed was preconditioned to 7, 10 and 13% moisture levels, exposed to micro-wave irradiation for periods of up to 2.5 min and analyzed for residual thioglucoside glucohydrolase (myrosinase) activity. The 7% moisture samples heated slowly and required at least a 2.5 min treatment whereas 10 and 13% moisture samples heated more rapidly and required microwave exposures of 1.5 min or less for complete inactivation of the enzyme. The sulfur content of oils obtained from adequately microwave-treated samples (1.5 min for 10 and 13% and 2.5 min for 7% moisture samples) was equal to or lower than commercially processed crude rapeseed oils. The shorter microwave treatment of dehulled rapeseed produced considerably lighter oils and did not adversely affect the color of the meal. It also destroyed some of the rapeseed glucosinolates and improved the meal palatability. However, goitrogenic properties of microwave-treated rapeseed meal evaluated by mice feeding experiments did not appear different from untreated rapeseed meal.