Effect of rapeseed meal on hepatic trimethylamine oxidase activity in the domestic fowl in relation to egg taint

Abstract

Abstract Shaver 585 hens were classified as ‘tainters’ or ‘non‐tainters’ according to their ability to produce eggs tainted with trimethylamine (TMA) when fed a diet containing 10% rapeseed meal (from Brassica napus ). All were then fed this diet, or one containing an equivalent amount of soya‐bean and fish meals for 16 weeks. Hepatic microsomal TMA oxidase activity was much lower in the rapeseed groups and was particularly low in the ‘tainters ’The apparent Michaelis constant of the enzyme was considerably higher in the rapeseed groups suggesting interference with the access or binding of the substrate. It was concluded that ‘tainters ’have an inherently low capacity for synthesising TMA oxidase and that the drastic reduction in its activity, which occurs when rapeseed meal is fed, allows TMA to pass into the egg. Preparations of the enzyme from ‘tainters ’and ‘non‐tainters ’on the control diet were strongly and similarly inhibited by sinapine in vitro and their apparent Michaelis constants were increased about six‐fold. Acetone and methanol extracts of rapeseed meal had a similar effect which was attributable to their sinapine content. Another inhibitor appeared to be present in a low sinapine fraction obtained by passing an aqueous solution of the methanol extract over a cation exchange resin.