Effect of a Dietary Rapeseed Protein Concentrate on the Contents of α-Tocopherol and Zinc in Serum, Liver and Tibia of Rats

Abstract

In order to study the effects of a dietary rapeseed protein concentrate (RPC) on tocopherol and zinc levels in serum, liver and tibia, female rats were fed a tocopherol-reduced diet for a 3-week period and were then transferred to either of a RPC diet or a control diet containing casein at 20% levels of protein. No unfavourable effects on food intakes or weight gains were recorded. The serum zinc content of the RPC group was slightly reduced and the serum tocopherol values significantly lowered in comparison to the control group. Zinc and tocopherol contents of the livers were not changed. Precipitation of sera by dextran sulphate in the presence of calcium ions indicated a reduced level of low density lipoproteins in rats fed RPC diet. In a second experiment, male and female rats were fed diets containing 10% of protein derived either from RPC or casein. Low zinc contents of tibiae indicated a low biological availability of the zinc present in the RPC diet. Rats on RPC diet also showed reduced levels of tocopherol in serum. Despite a lowered zinc status in rats fed RPC diet there was no reduction in food intake, weight gain or growth of tibia in these groups.

Levels of Minerals, Lipoproteins and Lipids in Plasma, Liver and Tibia from Female Rats Fed on a Zinc-Supplemented Rapeseed Protein Diet

“…On the other hand, one or more components of RPC, and maybe other vegetable protein products, may by some heretofore unknown mechanism alter the metabolism of lipoproteins in such a way as to produce reduced plasma levels of lipoproteins of lower density classes. The comparatively high total lipid contents of the livers of RPC-fed rats are in agreement with a previous report (10). This finding in connection with the low plasma level of lower density lipoproteins may indicate some interference with the hepatic synthesis or secretion of lipoproteins.…”

“…Experiments carried out by Eklund and Rask (3), Eklund (9) and Eklund and Agren (10) have indicated significantly increased zinc requirements as well as decreased serum tocopherol contents in rats fed on rapeseed protein. Changes in the levels of serum lipoproteins and liver lipids were also reported from these experiments (3,10). Recently Lieden and Hambraeus (11) claimed that the toxicity of rapeseed protein for the pregnant rat was not due to phytic acid but to the presence of another distinct low molecular weight substance soluble in methanol at 65 °C.…”

Zinc Status and Serum Levels of Retinol-Binding Protein, Tocopherol and Lower Density Lipoproteins in Male and Female Rats Fed on Semi-Purified Diets Containing Rapeseed Protein or Casein

“…Other studies have demonstrated effects of dietary RPC on tissue zinc (3,4) and serum tocopherol contents (4,5) in pregnant as well as non-pregnant rats. Changes in the levels of serum lipoproteins and liver lipids have also been observed in these rats (4).…”