Nutritional evaluation of low-glucosinolate rapeseed meals obtained by various processes

Defatted meals were prepared from two new varieties of rapeseed, the 'high-glucosinolate' variety, Brassica napus, Lesira, and the 'low-glucosinolate' variety, Brassica napus, Erglu, by each of the following processes: (1) defatting of the ground seed with hexane; (2) extraction of the myrosinase-deactivated ground seed with 70% aqueous acetone for the removal of glucosinolates followed by defatting with pure acetone, and (3) autolysis of the ground seed for the decomposition of glucosinolates followed by defatting and simultaneous removal of the decomposition products with hexane. The defatted meals obtained after extraction with aqueous acetone of autolysis contain very little glucosinolates and their degradation products as compared to those obtained by defatting with hexane only. The contents of available lysine and of phytates in the meals are, to some extent, affected by the treatment for the removal of glucosinolates. The rapeseed meals were fed at different levels to protein-depleted chicks and weanling rats. The animals fed low-glucosinolate meals prepared both from high-glucosinolate and low-glucosinolate varieties of rapeseed gave superior performance with regard to the feed conversion and protein efficiency ratio as compared to the animals fed the corresponding meals which were obtained simply by defatting the seeds with hexane. The levels of thyroxine (T4) and triiodothyronine (T3) in the serum of rats fed low-glucosinolate meals indicated normal function of the thyroid, whereas those in rats fed high-glucosinolate meals revealed hypothyroidism of the animals.