Glucosinolates in rape and camelina: composition, concentrations, toxicity and anti-nutritive effects in poultry, methods of neutralization - a mini-review

During the last decades animal nutrition and feed production in the World encounter the increasingly important problem of the deficit of feed-grade protein especially urgent for the regions (including Russian Federation) where the soybeans (considered an “ideal” protein source in feeds for all animal and poultry species) cannot be effectively cultivated. To solve this problem, decrease feeding costs and dependence on the imported soybeans the local vegetable protein sources are increasingly used including Brassicaceae oil crops rape ( Brassica napus L.) and camelina ( Camelina sativa L.) which are highly tolerant to the conditions of cultivation. Though cakes and meals of these crops are rich in protein they contain certain anti-nutritive factors including glycosides called glucosinolates (GLs), a vast group of protective secondary plant metabolites, alkyl-aldoxime O-sulphates containing the residue of β-D-thioglucopyranoside bonded to the hydroximine carbon in cis -position to the sulphate group. At present over 120 natural GLs are identified (B.A. Halkier and J. Gershenzon, 2006). The toxic and anti-nutritive effects of the GLs in rapeseed and methods for their neutralization are relatively well studied; however, the effects of GLs in camelina are still understudied (due to its relatively short history of large-scale cultivation) and hence the data obtained on rape should be used for the assessment of possible effects of camelina. The detrimental biological effects of the GLs on poultry, their mechanisms and methods of neutralization are reviewed herein. The GLs per se are non-toxic and their protective role in the plants is related to the endogenous plant enzymes β-thioglucosidases (myrosinases): GLs and myrosinases normally (in an intact plant) localized in different tissues contact after the damage of the plant (e.g. by insects or other herbivores) resulting in the enzymatic hydrolysis of the GLs and transformation of their aglycone residues into the potentially toxic products: isothiocyanates, thiocyanates, oxazolydine-thiones, nitriles, epithionitriles (D.J. Kliebenstein et al., 2005). Similar processes could be also induced by the enzymes of intestinal microbiota in poultry. Main toxic effect of almost all these products is goitrogenicity involving disturbance of the synthesis and secretion of thyroid hormones into the bloodstream and (in cases of heavier exposure) hypertrophy of the thyroid gland and formation of the goiter. In sub-toxic doses these GL metabolites can hamper the growth in young poultry, decrease egg production and quality in adult hens, induce “fishy taint” of the eggs. Since 1960s the rape has been intensively selected for decreased GL content and a wide range of low-GL cultivars are now present in the market; similar work with the camelina is still at its start. Concentrations of the GLs in cakes and meals of these crops can be decreased by thermal treatment (at ca. 100 °С), soaking in water, treatments with solutions of alkali or copper sulphate, solid-phase microbial fermentation, micronization, extrusion, etc. (M.K. Tripathi and A.S. Mishra, 2007). Maximal permissible level of the GLs in diets for poultry is apparently 5-6 mM/kg, corresponding to dietary levels of the products of the native rape ca. 10 %, low-GL rape varieties 15-20 %, camelina products 5-10 %. The studies on the toxic and anti-nutritive effects of rape and especially camelina are necessary for the practice of poultry nutrition and important for further genetic improvement of these crops.