Soluble and total myrosinase activity in defatted Crambe abyssinica meal

Crambe defatted meal contains 4-6% w/w of glucosinolates, with epiprogoitrin accounting for >90% of the total. This feature limits the use of the meal as feed due to the antinutritional properties of myrosinase-glucosinolate breakdown products. In this context, myrosinase activity assumes particular importance. In this study the total and soluble myrosinase activities have been evaluated directly on defatted meals of eight Crambe abyssinica varieties. The pH-stat method, which is the most suitable for assays in heterogeneous solid-water systems, was used. The total myrosinase activity in C. abyssinica varieties, determined using epiprogoitrin as substrate, ranged from 288 to 653 units g(-1). These activity values were up to 26 times higher than those obtained using other substrates, namely, sinigrin, glucosinalbin, glucotropaeolin, progoitrin, and glucoraphenin. Crambe myrosinase is unusual in that, unlike other Brassicaceae containing a typical main glucosinolate, it does not show the same specificity toward its natural substrates.