Mitsuru Fukuda

Effects of Lactobacillus Fermented Soymilk and Soy Yogurt on Hepatic Lipid Accumulation in Rats Fed a Cholesterol-Free Diet

We examined the effects of lactic acid fermented soymilk, in which part of the soymilk was replaced with okara (soy yogurt), on plasma and hepatic lipid profiles in rats fed a cholesterol-free diet. Additionally, we investigated the effects of soy yogurt on hepatic gene expression in rats using DNA microarray analysis. Male Sprague-Dawley rats aged 5 weeks (n=5/group) were fed a control diet (AIN-93) or a test diet in which 20% of the diet was replaced by soy yogurt for 7 weeks. Soy yogurt consumption did not affect body weight or adipose tissue weight as compared with control diet. In the soy yogurt group, the liver weight and hepatic triglyceride content were significantly lower than the control group, and the level of plasma cholesterol was also lower. Furthermore, DNA microarray analysis indicated that soy yogurt ingestion down-regulated the expression of the SREBP-1 gene and enzymes related to lipogenesis in the rat liver, while expression of β-oxidation-related genes was up-regulated. These results suggest that soy yogurt is beneficial in preventing hepatic lipid accumulation in rats.

Hypocholesterolemic Effects of Lactic Acid-Fermented Soymilk on Rats Fed a High Cholesterol Diet

The effect of fermented soymilk on rats fed a high cholesterol diet was investigated to clarify the cholesterol-lowering function. Male Sprague-Dawley rats aged 7 weeks were fed a control diet (1% cholesterol, high cholesterol diet), high cholesterol diet containing 11.7% fermented soymilk diet (5% soy protein as final concentration, F-5), or high cholesterol diet containing 23.4% fermented soymilk diet (10% soy protein as final concentration, F-10) for 5 weeks. The liver weight and fat mass were decreased by the ingestion of fermented soymilk. The hepatic triglyceride and cholesterol levels in the F-5 and F-10 groups were significantly lowered compared to those in the control group. The plasma total cholesterol level of the F-10 group was significantly decreased. The expression of SREBP-2, a cholesterol synthesis-related gene, was significantly decreased in liver of the F-5 group, but the expression of CYP7a1, a cholesterol catabolism-related gene, was significantly increased. These results suggest that fermented soymilk can modulate the cholesterol metabolism in rats fed a high cholesterol diet.

Effects of Lactic Acid-Fermented Soymilk on Lipid Metabolism-Related Gene Expression in Rat Liver

We examined the effects of lactic acid fermentation of soymilk on the lipid profile and lipid metabolism-related gene expression in rat liver. Male Sprague-Dawley rats aged 7 weeks were fed a control diet (AIN-93), soymilk diet, or fermented soymilk diet for 1 week or 5 weeks. The hepatic triglyceride and cholesterol contents in the soymilk (SM) group and the fermented soymilk (FSM) group were significantly lower than those in the control group after 5 weeks, but these changes had not become apparent until after 1 week. The fatty acid synthesis-related genes were more markedly down-regulated after 1 week than after 5 weeks, whereas the cytochrome p450 family 7 subfamily a polypeptide 1 (CYP7al) gene related to cholesterol catabolism was more markedly up-regulated after 5 weeks than after 1 week. This up-regulation was higher in the FSM group than in the SM group. It is assumed that the bioactive components produced by lactic acid fermentation induced the up-regulation of CYP7a1.

Isoflavone and protein constituents of lactic acid-fermented soy milk combine to prevent dyslipidemia in rats fed a high cholesterol diet.

A high cholesterol diet induces dyslipidemia. This study investigated whether isoflavone aglycones in lactic acid-fermented soy milk (LFS) improve lipid metabolism in rats fed a high cholesterol diet. Male Sprague-Dawley rats aged seven weeks were fed an AIN-93G diet, a 1% cholesterol diet (a high cholesterol diet), a high-cholesterol diet containing 4% isoflavone extract of LFS (LFS extract diet), a high-cholesterol diet containing 19.4% ethanol-washed LFS (ethanol-washed LFS diet, isoflavone-poor diet), or a high cholesterol diet containing 23.2% intact LFS (intact LFS diet) for five weeks. The plasma total cholesterol (TC) level was increased in the rats fed the LFS extract diet compared with those fed the high cholesterol diet. The TC level was decreased by the intact LFS and ethanol-washed LFS diets. The cholesterol-lowering effect was stronger in the rats fed the intact LFS diet than those fed the ethanol-washed LFS diet. The plasma triglyceride (TG) level was unchanged in the rats fed the LFS extract diet, but it decreased in rats fed the intact LFS and ethanol-washed LFS diets. Although, compared with the high cholesterol diet, the LFS extract and ethanol-washed LFS diets did not reduce hepatic cholesterol and TG, both levels were remarkably lowered by the intact LFS diet. These results suggest that the improvement in lipid metabolism of rats fed a high-cholesterol diet containing LFS isoflavone aglycones is not due to an independent effect but due to a cooperative effect with soy protein.

Functional Components and Health Benefits of Fermented Soymilk

Abstract Soy foods are known to promote health, and their functional constituents include soy proteins and isoflavones. Although soymilk with beany flavor is considered unfavorable, its palatability is improved by fermentation. Soymilk can turn to a yogurt-like paste following lactic acid fermentation using Lactobacillus, Bifidobacterium, or other bacteria. Isoflavone aglycones and peptides that are produced in soymilk during fermentation have hypolipidemic effects, such as blood cholesterol lowering and prevention of hepatic lipid and visceral fat accumulation. Accordingly, physiological effects of fermented soymilk are greater than those of soymilk. Additionally, soy peptides, isoflavone aglycones, and other functional components in fermented soymilk reportedly exert many beneficial effects and can prevent cardiovascular disease, obesity, cancer, and inflammation. In conclusion, as an alternative to cow milk yogurt, fermented soymilk can provide much greater health benefits.

Transformation of soybean cotyledon cell during water absorption.

大豆の吸水時における種子の形状変化を子葉細胞の形状変化の観点から調べ,以下の知見を得た.(1) 大豆は乾燥時には球状体に近い形であるが,吸水すると種子の幅(W)方向や厚さ(T)方向と比較して,長さ(L)方向への膨潤が著しいため楕円体に変形した.しかし,小豆やいんげんは,乾燥時からL方向に長い形をしており,吸水,膨潤してもほぼ元の形状を保っていた.(2) 乾燥大豆の子葉細胞はL方向に収縮しているが,吸水,膨潤すると,L方向に特に大きく膨潤し,細胞間隙が広がることを認めた.(3) 吸水大豆の子葉細胞は,種子のL方向と垂直な長軸をもつ細長い楕円形の回転体に近い形で存在していた.(4) 乾燥大豆の子葉細胞の細胞壁には,種子のL方向と垂直なしわが存在し,子葉細胞はL方向に折りたたまれていることが明らかになった.(5) 大豆の吸水による膨潤は,枝豆種子の乾燥・収縮時における形状変化の逆過程に類似している.なお,大豆種子の吸水・乾燥によるL方向への膨潤・収縮には,皮も関与していると推察した.

The Structure of the Aleurone Layer and Its Glycine-rich Protein Content in Different Bean Seeds.

種々の豆種子を用いて, アリューロン層組織の構造とアリューロン層組織に含まれるGRP (高グリシンタンパク質) の含有量を調べ, 次に示す結果を得た。1) ダイズ (Glycine max品種エンレイ), 黒ダイズ (Glycine max, 品種タンバグロ), ツルマメ (Glycine soja) のアリューロン層細胞壁は, 赤インゲンマメ (Phaseolus vulgaris, 品種タイショウキントキ), 斑入インゲンマメ (Phaseolus vulgaris, 品種トラマメ) のものよりも厚みが増していた。2) ダイズのアリューロン層細胞壁に特異的なGRPは主としてペクチン画分に存在した。3) 3種のダイズのアリューロン層の熱水可溶性画分のGRP含有量は2種のインゲンマメのものより高かった。4) ツルマメや黒ダイズから抽出したGRPの推定分子サイズはそれぞれダイズと同じ約30kDaであった。以上の結果から, ダイズ属植物のアリューロン層のGRPはアリューロン層の細胞壁構造強化に何らかの役割を担っていると推察した。