Hitoshi Furuta

Analysis of Structural Components and Molecular Construction of Soybean Soluble Polysaccharides by Stepwise Enzymatic Degradation

Soybean soluble polysaccharides (SSPS) extracted from soybean cotyledons have a pectin-like structure. The core polysaccharides after treatments with four kinds of hemicellulases and a pectinase contained approximately equal numbers of L-rhamnouse and D-galacturonate residues, suggesting the presence of the rhamnogalacturonan (RG) I structure consisting of the diglycosyl repeating unit, -4)-α-D-GalpA-(1→2)-α-L-Rhap-(1-. The lengths of RG chains were calculated as approximately 15, 28, and 100 diglycosyl repeats. The RG components linked to each other by intervention of galacturonan (GN) chains, constituting the backbone of SSPS. All arabinose residues, which constitute 21% of total SSPS sugars, were found to be in side chains from RG regions, and this was also true for galactose residues, which constitute 50% of total sugars. Of arabinose residues, 94% are present as α-1,3- or α-1,5-arabinans, and 89% of galactose residues were present as β-1,4-galactans. Galactan chains are modified with arabinose, xylose, fucose, and glucose at the sites close to the RG regions.

Structural Studies by Stepwise Enzymatic Degradation of the Main Backbone of Soybean Soluble Polysaccharides Consisting of Galacturonan and Rhamnogalacturonan

Soybean soluble polysaccharides (SSPS) extracted from soybean cotyledons are acidic polysaccharides and have a pectin-like structure. The results of a structural analysis of SSPS by using polygalacturonase (PGase) and rhamnogalacturonase (RGase) clarified that the main backbone consisted of galacturonan (GN) and rhamnogalacturonan (RG), which were composed of the diglycosyl repeating unit, -4)-α-D-GalpA-(1→2)-α-L-Rhap-(1-. The side chains of β-1,4-galactans, branched with fucose and arabinose residues, were linked to the C-4 side of rhamnose residues in the RG regions. The degree of polymerization (dps) of GN, which linked the RG regions together, was estimated to be about 4-10 residues, and some were modified with xylose residues on the C-3 side of the galacturonates. The dps of GN at the reducing end of SSPS was estimated to be about 7-9 residues. Moreover, the fragment of the basic structure of the RG region, -[4)-α-D-GalpA-(1→2)-α-L-Rhap- (1-]2-, some of which had long-chain β-1,4-galactans branched on the C-4 side of rhamnose residues, were liberated from SSPS by the RGase treatment. The dps of the galactan side chain was estimated to be about 43-47 residues by an analysis of the digestion products from the β-galactosidase treatment.

Effect of soybean soluble polysaccharides on the stability of milk protein under acidic conditions

Abstract Soybean soluble polysaccharide (SSPS) extracted from soybean cotyledons has a pectin-like structure. SSPS has been used as a dispersion stabilizer for milk protein under acidic conditions, below the isoelectric point of milk protein, in a manner similar to high methoxyl pectin. SSPS at concentrations of less than 0.2% stabilized acidic beverages prepared with 8.0% of milk solid non-fat at pH 3.4–4.4, in contrast with pectin which needed at least 0.4% concentration. To elucidate the structure of the polysaccharide, which seemed likely to have a significant influence on its ability to stabilize acidic beverages, SSPS was digested with purified pectinases and hemicellulases, and the stabilizing effects of the digestion products on acidic beverages were analyzed. The stabilizing ability of SSPS was reduced by digestion of its neutral sugar side chains, arabinan or galactan, and was only slightly changed by digestion of its galacturonan main backbone with polygalacturonase or rhamnogalacturonase. This indicates that neutral sugar side chains, which mainly consist of arabinose and galactose residues, play a significant role in the ability of SSPS to stabilize acidic beverages. In contrast, the stabilizing effect of pectin was reduced by digestion of its galacturonan backbone, and was not changed by digestion of its neutral sugar side chains. This indicates that SSPS may differ from pectin in the mechanism by which it stabilizes milk proteins under acidic conditions.

Analysis of the molecular construction of xylogalacturonan isolated from soluble soybean polysaccharides

Soluble soybean polysaccharides (SSPS) extracted from soybean cotyledons are acidic polysaccharides, and exhibited a pectin-like structure. After digesting galacturonan with polygalacturonase, two novel galacturonan (GN) fragments, which were directly linked to xylosyl oligosaccharides, were obtained. One consisted of (β-D-Xyl)7 branched at the C-3 site of 1,4-linked (α-D-GalA)4, and the other consisted of (β-D-Xyl)4 branched at the C-3 site of 1,4-linked (α-D-GalA)3.

Extraction of Water-soluble Soybean Polysaccharides under Acidic Conditions

We investigated the yield, gelation and sugar composition of water-soluble polysaccharides that had been extracted from soybean cotyledons under acidic conditions. SSPS were easily extracted at several pHs. The highest yield was about twice that reported by Morita et al., after extraction in boiling water, or by Kawamura et al., after extraction in hot water (90°C) with the stepwise addition of ammonium oxalate and 0.5% NaOH. Our results show that the average molecular weight was relatively high for both SSPS extracted in the weakly acidic pH range of 4-6 at 100-120°C and in the strongly acidic pH range of 2-3 at 40-80°C. The water-soluble polysaccharide solutions which were extracted under the former conditions remained fluid, but those which were extracted under the latter conditions gelled. However, the molecular weight distribution and sugar composition were similar for SSPS isolated by using both sets of conditions. Furthermore, water-soluble soybean polysaccharides were found to consist of rhamnogalacturonans, which could endure hydrolysis, and arabinogalactans, which were easily hydrolyzed under acidic conditions.

Ingestion of water-soluble soybean fiber improves gastrectomy-induced calcium malabsorption and osteopenia in rats

OBJECTIVE Total gastrectomy produces calcium malabsorption and osteopenia. We examined the effects of feeding water-soluble soybean fiber (WSSF), a highly fermentable dietary fiber with low viscosity, on calcium absorption and bone characteristics in totally gastrectomized rats. METHODS Male Sprague-Dawley rats were assigned to two groups: sham operation and gastrectomy. After the postoperative recovery period, rats of each group were fed diets with or without WSSF (50 g/kg diet) for 4 wk. RESULTS Net calcium absorption and femoral dry weight and calcium content and maximum breaking force were lower in the gastrectomy groups than in the sham groups. In the gastrectomy groups, calcium absorption and these femoral parameters were higher in rats fed the WSSF diet than in rats fed the WSSF-free diet. Feeding WSSF increased the concentrations of short-chain fatty acids and soluble calcium and decreased the pH in cecal contents. Net calcium absorption in gastrectomized rats correlated positively with the concentration of total short-chain fatty acids (the sum of acetic, propionic, and butyric acids) in cecal contents (r = 0.545, P < 0.05) and negatively with cecal pH (r = -0.628, P < 0.05). CONCLUSIONS These findings indicate that ingestion of WSSF partly prevents the diminished calcium absorption after total gastrectomy in rats, resulting in the improvement of postgastrectomy osteopenia. The increase of calcium absorption may be associated with cecal fermentation of WSSF.

Screening of soy protein-derived hypotriglyceridemic di-peptides in vitro and in vivo

BackgroundSoy protein and soy peptides have attracted considerable attention because of their potentially beneficial biological properties, including antihypertensive, anticarcinogenic, and hypolipidemic effects. Although soy protein isolate contains several bioactive peptides that have distinct physiological activities in lipid metabolism, it is not clear which peptide sequences are responsible for the triglyceride (TG)-lowering effects. In the present study, we investigated the effects of soy protein-derived peptides on lipid metabolism, especially TG metabolism, in HepG2 cells and obese Otsuka Long-Evans Tokushima fatty (OLETF) rats.ResultsIn the first experiment, we found that soy crude peptide (SCP)-LD3, which was prepared by hydrolyze of soy protein isolate with endo-type protease, showed hypolipidemic effects in HepG2 cells and OLETF rats. In the second experiment, we found that hydrophilic fraction, separated from SCP-LD3 with hydrophobic synthetic absorbent, revealed lipid-lowering effects in HepG2 cells and OLETF rats. In the third experiment, we found that Fraction-C (Frc-C) peptides, fractionated from hydrophilic peptides by gel permeation chromatography-high performance liquid chromatography, significantly reduced TG synthesis and apolipoprotein B (apoB) secretion in HepG2 cells. In the fourth experiment, we found that the fraction with 0.1% trifluoroacetic acid, isolated from Frc-C peptides by octadecylsilyl column chromatography, showed hypolipidemic effects in HepG2 cells. In the final experiment, we found that 3 di-peptides, Lys-Ala, Val-Lys, and Ser-Tyr, reduced TG synthesis, and Ser-Tyr additionally reduced apoB secretion in HepG2 cells.ConclusionNovel active peptides with TG-lowering effects from soy protein have been isolated.

Effect of Soluble Soybean Polysaccharide on Dispersion Stability of Acidified Milk Protein

The effect of soluble soybean polysaccharide (hereinafter referred to as SSHC) obtained frpm so-called bean-curd rewse, a by-product of bean curd and soybean protein, on the dispersion stability of yoghurt drinks was examined by measuring the viscosity, zeta potential, median diameter, precipitation quantity after centrifugation, and absorbance at 660 nm of the supernatant fluid.

Effects of Dietary Soybean Peptides on Hepatic Production of Ketone Bodies and Secretion of Triglyceride by Perfused Rat Liver

Soybean protein isolate (SPI) was digested with protease to produce a peptides containing the low-molecular fraction (LD3) or a mixture of high- and low-molecular fractions (HD1). Rats were fed a diets containing SPI, LD3, or HD1 at a protein level equivalent to the 20% casein diet for 4 weeks. The serum triglyceride concentration was lower in rats fed SPI, LD3, and HD1 diets than in rats fed the casein diet, and the differences were significant for the cholesterol-enriched diet. The value for the LD3 group was the lowest among all groups for both the cholesterol-free and -enriched diets. The level of triglyceride in the post-perfused liver was significantly lower in the LD3 and HD1 groups and the SPI group than in the casein group irrespective of the presence of cholesterol in the diet. In the cholesterol-free diet, LD3 feeding as compared to casein feeding caused a reduction in triglyceride secretion from the liver to perfusate and an increment of hepatic ketone body production. The addition of cholesterol to the diets somewhat attenuated these effects of LD3. These results suggest that the low-molecular fraction in soybean peptides causes triglyceride-lowering activity through a reduction in triglyceride secretion from the liver to the blood circulation and the stimulation of fatty acid oxidation in the liver. There is a possibility that soybean peptides modulate triglyceride metabolism by changes in the hepatic contribution.

Properties of Rice Cooked with Commercial Water-soluble Soybean Polysaccharides Extracted under Weakly Acidic Conditions from Soybean Cotyledons

It has been found that commercial water-soluble soybean polysaccharides (SSPS) can make cooked rice and noodles non-sticky and prevent rice grains and noodles from adhering to each other. We studied in detail the phenomenon of rice cooked with SSPS. We assumed that the phenomenon resulted from the interaction between SSPS and starch during cooking, and studied the effects of SSPS on the gelatinizing behavior of rice starch by using a Rapid-Visco-Analyzer. The addition of SSPS reduced the viscosity of the gelatinized starch. This lower final viscosity of the rice starch was more distinct from than that of potato starch. These results imply that the properties of SSPS in forming a non-sticky condition might result from a decrease in the viscosity of the gelatinized starch.