Rapeseed meal and egg taint: Effects of low glucosinolate Brassica napus meal, dehulled meal and hulls, and of neomycin

Abstract

Whole meals prepared from four cultivars (Tower, ‘French’ (unknown cultivar from France), Duo and Tandem) contained sufficient progoitrin and soluble tannins to impair trimethylamine (TMA) oxidation, and thereby allow the TMA content of eggs to rise above the tainting threshold, when they were fed as protein supplements (100 g kg−1) to hens which had been bred for low TMA oxidase activity. Hulls from Tower and ‘French’ seed produced small, but detectable, effects and since the potencies of dehulled and whole meals were similar, it was established that the hulls make only a very minor contribution to the tainting potential. Although the addition of neomycin to the drinking water when the Tandem whole meal was fed appeared to diminish its effects to a certain extent, it had little value as a prophylactic measure. It was concluded that these meals could produce widespread tainting if used commercially in the UK, and that the removal from the laying hens of the genetic defect which restricts the synthesis of TMA oxidase and thereby confers susceptibility is the only effective way of eliminating the problem.

Phenolic Acids and Tannins in Rapeseed and Canola

“…Thus, the corrected concentration of tannins in rapeseed meals was 18-45% lower than those given by Clandinin and Heard (1968). In addition, Fenwick et al (1984a) demonstrated that whole and dehulled Tower meals contained 2.71 % and 3.91 % tannins, respectively. Leung et al (1979) reported that rapeseed hulls contained only 0.1 % acetone-extractable condensed tannins.…”

“…Moreover, it may have adverse effects on the palatability of rapeseed products (Appelqvist 1972). Sinapine is also linked to a crabby or fishy taint note in eggs from some brown-egg-Iaying hens (Hobson-Frohock et al 1973;Butler et al 1982;Fenwick et al 1984a) and serves as a precursor of trimethylamine (TMA; Pearson et al 1980). The egg taint is caused by the presence of low concentrations (about 1 Jlg/g) of TMA in the eggs (Hobson-Frohock et al 1973).…”

“…Furthermore, tannins in rapeseed meal are reported to cause tainting of eggs. It is postulated that they block the metabolism ofTMA by inhibiting TMA oxidase (Fenwick et al 1981;Butler et al 1982;Fenwick et al 1984a). This enzyme converts TMA to odorless and water-soluble TMA oxide.…”

Effect of dehulling on the composition of antinutritive compounds in various cultivars of rapeseed

“…5). Other investigations [16,31] also showed an unproportionally high increase of sinapine in dehulled seeds of different cultivars after dehulling.…”

Chemical tainting of foods

“…The feeding of fish protein to meat animals, especially pigs, can result in taints in the meat, possibly because of increased autoxidation of the meat lipid. Diet was also shown to be responsible for fishy taints in eggs ( Pearson et al ., 1983 ; Fenwick et al ., 1984 ): a relationship between the taint and trimethylamine was established, the use of fish meal or rapeseed meal in the poultry diets being shown to be the cause of the problem.…”