varieties ranging from 6.66 to 17.39 and 2.6 to 2.92 mg/kg, respectively (Rekas et al.
2016).
2.3.6 Antinutritional Factors
Rapeseed contains several antinutritional factors such as glucosinolates, tannins,
phytates, erucic acid, etc., which affect the nutrient’s bioavailability adversely and
reduce the growth and performance of the animals.
2.3.6.1 Glucosinolates
Glucosinolates, chemically, are a class of water-soluble, sulfur- or nitrogencontaining glucosides that occur as secondary metabolites in virtually all species
of Brassica (Boot 2016). Traditional rapeseed is reported to contain 120–150 μmol
glucosinolates/g of rapeseed meal. Through breeding techniques, the amount of
glucosinolates has been reduced to 4–10 μmol/g (approximately 10–12% of original
level) in canola meal. The most common glucosinolates in canola meal are progoitrin
(2(R)-2-hydroxy-3-butenyl glucosinolate), gluconapin (3-butenylglucosinolate),
gluconapoleiferin (2-hydroxy-4-pentenyl glucosinolate), glucobrassicanapin
(4-pentenyl glucosinolate) (Konkol et al. 2019). In their natural and
non-hydrolyzed form, glucosinolates are not harmful to animals or humans. However, in presence of myrosinase (naturally present in seed), glucosinolates get
hydrolyze and produce glucosinolate derivatives including isothiocyanates, nitriles,
thiocyanates,
and
5-vinyloxazolidine-2-thione
(VOT)
(Liang
2000).
Isothiocyanates, thiocyanates, and VOT have been reported to interfere with iodine
uptake by thyroid gland and induce goitrogenic effects in humans. On the other
hand, nitriles are toxic and have shown to interfering with liver and kidney functions.
Glucosinolate levels of 18–30 μmol/g canola meal have been reported to have
antinutritional or toxic effects in animal studies (Boot 2016) (Fig. 2.3).
2.3.6.2 Phytic Acid/Phytates
Phytate (myoinositol 1,2,3,4,5,6-hexakis dihydrogen phosphate or inositol
hexaphosphate, InsP6) represents the major storage form of phosphorus and inositol
in plant species. Whole canola/rapeseed contains about 2–4 g/100 g phosphorus, of
which approximately 65% is present in the form of phytates, which are salts of phytic
acid with divalent minerals) (Thompson 1990; Liang 2000). Phytates act as
antinutrients and bind with divalent cations such as Zn, Ca, Fe, Cu, Mn, etc. in gut
of monogastric animals including poultry and humans. Monogastric animals are not
able to digest phytates due to deficiency of hydrolyzing enzyme (phytase). Thus,
phytates reduce the bioavailability of essential ions and adversely affect the
56
A. Goyal et al.
2016).
2.3.6 Antinutritional Factors
Rapeseed contains several antinutritional factors such as glucosinolates, tannins,
phytates, erucic acid, etc., which affect the nutrient’s bioavailability adversely and
reduce the growth and performance of the animals.
2.3.6.1 Glucosinolates
Glucosinolates, chemically, are a class of water-soluble, sulfur- or nitrogencontaining glucosides that occur as secondary metabolites in virtually all species
of Brassica (Boot 2016). Traditional rapeseed is reported to contain 120–150 μmol
glucosinolates/g of rapeseed meal. Through breeding techniques, the amount of
glucosinolates has been reduced to 4–10 μmol/g (approximately 10–12% of original
level) in canola meal. The most common glucosinolates in canola meal are progoitrin
(2(R)-2-hydroxy-3-butenyl glucosinolate), gluconapin (3-butenylglucosinolate),
gluconapoleiferin (2-hydroxy-4-pentenyl glucosinolate), glucobrassicanapin
(4-pentenyl glucosinolate) (Konkol et al. 2019). In their natural and
non-hydrolyzed form, glucosinolates are not harmful to animals or humans. However, in presence of myrosinase (naturally present in seed), glucosinolates get
hydrolyze and produce glucosinolate derivatives including isothiocyanates, nitriles,
thiocyanates,
and
5-vinyloxazolidine-2-thione
(VOT)
(Liang
2000).
Isothiocyanates, thiocyanates, and VOT have been reported to interfere with iodine
uptake by thyroid gland and induce goitrogenic effects in humans. On the other
hand, nitriles are toxic and have shown to interfering with liver and kidney functions.
Glucosinolate levels of 18–30 μmol/g canola meal have been reported to have
antinutritional or toxic effects in animal studies (Boot 2016) (Fig. 2.3).
2.3.6.2 Phytic Acid/Phytates
Phytate (myoinositol 1,2,3,4,5,6-hexakis dihydrogen phosphate or inositol
hexaphosphate, InsP6) represents the major storage form of phosphorus and inositol
in plant species. Whole canola/rapeseed contains about 2–4 g/100 g phosphorus, of
which approximately 65% is present in the form of phytates, which are salts of phytic
acid with divalent minerals) (Thompson 1990; Liang 2000). Phytates act as
antinutrients and bind with divalent cations such as Zn, Ca, Fe, Cu, Mn, etc. in gut
of monogastric animals including poultry and humans. Monogastric animals are not
able to digest phytates due to deficiency of hydrolyzing enzyme (phytase). Thus,
phytates reduce the bioavailability of essential ions and adversely affect the
56
A. Goyal et al.