Effect of alkanol-ammonia-water treatment on the glucosinolate content of rapeseed meal

Abstract

The effect of alkanol and alkanol-ammonia treatment, with and without water, on the glucosinolate content of laboratory-prepared Altex and commercial rapeseed meals was studied. The meals were treated with methanol, ethanol, isopropanol and t-butanol, and with the same alkanols containing anhydrous ammonia (0-15% for methanol and 10% for other alkanols), and water (0-35%). The results showed that methanol was the most effective alkanol for the removal of glucosinolates. The treatment of laboratory-prepared meal with methanol removed about 55% of the glucosinolates initially present in the meal. Methanol containing 35% water removed 80% of the glucosinolates. However, treatment of this meal with 10% ammonia in methanol reduced the glucosinolates content to 0.2mg/g after a quiescent period of 15 minutes. The addition of water to the methanol-ammonia solutions further reduced the glucosinolates to trace levels. Methanol or methanol-ammonia were less effective in reducing the glucosinolate content of commercial meal. This suggests that the treatment of the meal during processing reduces the extractability of the glucosinolates. The effectiveness of glucosinolate removal by alkanols and solutions containing ammonia and water could be ranked as follows:methanol>ethanol>isopropanol>t-butanolThe preferred solvent mixture for the removal of glucosinolates is 10% NH3 in methanol containing 5% H2O.