Effects of Protein Isolates from Radish and Spinach Leaves on Serum Lipids Levels in Rats.

Abstract

SummaryRadish and spinach leaf protein isolates (RLP and SLP, respectively) were prepared from chilled aqueous 0.2% sodium hydroxide extract of their leaves. The RLP and SLP, and those supplemented with methionine (RLP+Met and SLP+Met, respectively) to become equal to casein in methionine content, were compared with casein for their effects on serum cholesterol level in rats fed with a cholesterol-enriched diet for 14 days. Each protein isolate was incorporated into the cholesterol enriched diet to provide a 15% protein level. RLP was extremely inferior to SLP and casein for body weight gain of rats, but that of rats fed with RLP+Met diet was almost equal to that of casein and SLP groups. The serum cholesterol level in rats fed with SLP and SLP+Met diets was significantly lower as compared with that of the casein-fed rats. Both the amounts of excreted cholesterol and bile acids were significantly higher in rats fed with the SLP and SLP+Met diets than that of the casein-fed rats. These results suggest that the hypocholesterolemic action of SLP may in part have been due to the inhibition of intestinal absorption of both cholesterol and bile acids. RLP+Met diet tended to decrease the serum cholesterol level as compared to casein diet, but the difference was not significant. Key Words leaf protein isolate, radish leaf protein, spinach leaf protein, serum cholesterol It is well known that plasma cholesterol level in human and several experimen tal animals is affected by dietary proteins, and especially, plant proteins such as soybean protein isolate (1-5), sunflower seed protein isolate (6), potato protein (7), and wheat gluten (8, 9) exert hypocholesterolemic effect as compared with animal protein such as casein. Cho et al. reported that leaf protein isolates, prepared by heating green juice from Italian ryegrass and alfalfa, exert hypocholesterolemic effect in rats (10). However, the effects of other leaf protein isolates, prepared by a simiple method, on the serum cholesterol levels have not been examined. This paper describes the effects of protein isolates from radish and spinach 627

Effects of Cabbage Leaf Protein Concentrate on the Serum and Liver Lipid Concentrations in Rats.

“…It has been reported that proteins derived from plant-origin, such as soybean, sunflower, rice, spinach and radish protein isolates (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11), produce activity to maintain lower serum cholesterol concentrations as compared to those of animal proteins such as casein. These reports suggest that some other plant proteins may also have hypocholesterolemic activity; however, the influence of vegetable proteins which are consumed daily on the serum and liver lipid levels has not yet been fully examined.…”

“…These reports suggest that some other plant proteins may also have hypocholesterolemic activity; however, the influence of vegetable proteins which are consumed daily on the serum and liver lipid levels has not yet been fully examined. We have previously demonstrated that spinach leaf protein isolate, as compared to casein, had hypocholesterolemic and hypolipidemic activities, and that the supplement of methionine to the spinach leaf protein isolate diet improved the nutritive value without loss of the cholesterol-lowering effect (10,11).…”

Effects of Spinach Leaf Protein Concentrate on the Serum Cholesterol and Amino Acid Concentrations in Rats Fed a Cholesterol-free Diet.

“…The amounts of fecal total lipids, cholesterol and bile acids excreted from the rats fed the SPPC diet were signifi cantly higher than those of the control rats. The serum free amino acid concentrations of the rats fed casein and SPPC diets containing 2% corn oil are shown in Table 3, together with the amino acid compositions of SPPC and casein reported previously (12). The concentrations of threonine, serine, glutamine, glycine, cystine and isoleucine were significantly higher in the rats fed SPPC than in the control rats.…”

“…In the previous paper, we reported that protein concentrate from spinach leaves had the effect of lowering serum and liver cholesterol concentrations in rats fed a cholesterol-enriched diet, suggesting that this protein concentrate also exhibits stronger cholesterol-lowering action in the rats fed a cholesterol-free diet, analo gously to soybean protein isolate (12). On the other hand, it has been deduced that the cholesterol-lowering action of plant protein is closely related to the plasma levels of several free amino acids, which may reflected the amino acid compositions of protein isolates (2,(13)(14)(15) .…”

“…is one of the vegetable protein isolates which can be prepared by a simple extraction method and has a high nitrogen content (12). SPPC, therefore, is considered to be a favorable plant protein for comparing physiological functions of plant and animal proteins in experimental animals.…”