The effect of aqueous leaching of glucosinolates on the nutritive quality of rapeseed meal.

Abstract

AbstractStudies were conducted with the aim to upgrade the nutritional quality of high glucosinolate rapeseed meals, via heat treatment and aqueous leaching of the glucosinolates, under various conditions of temperature and pH. Conditions for thermal pretreatment of the seeds were sought which ensured complete inactivation of the enzyme myrosinase, no reduction in available lysine, and minimal losses of soluble protein during subsequent leaching processes. This was achieved by 30 min steaming at 100°C, although kinetic studies showed that complete inactivation of the enzyme took place within 5 min. Leaching experiments were performed with full‐fat flakes and with defatted meal. The rate as well as the total amount of leached glucosinolates was higher in defatted meal compared to full‐fat flakes. Protein losses were similar with both types of rapeseed raw material and were only slightly affected by changing the pH. Oil losses from full‐fat flakes during the leaching process were significant. Raising the leaching temperature from 25 to 50°C increased substantially the rate and the total amount of leached glucosinolates, but resulted in higher losses of protein. Generally, raising the pH of the leaching medium in the range of 4–8, resulted in an increase in the rate as well as in the total amount of leached glucosinolates. Rat feeding tests (PER) of leached meals indicated that raising the leaching temperature from 25 to 50°C lowered the protein quality of the meals. On the other hand, meals leached under the same temperature conditions, in the pH range of 4–8, were not found significantly different in their protein nutritive value. Substantial heat treatment was also found necessary for improving the nutritive quality of low glucosinolate rapeseed.