Simple extraction method of non-allergenic intact soybean oil bodies that are thermally stable in an aqueous medium.

This study supplied a simple extraction method for intact soybean oil body (ISOB) and examined the heating effect on ISOB. ISOB, which just contained its intrinsic protein (oleosin), could be obtained by pH 11 extraction (50000g, 45 min). ISOB suspension was dialyzed to deionized water (1:3600) and named DISOB. DISOB aggregated at pH 5.7, but NaCl pre-addition (5-500 mM) made ISOB disperse well at pH 5.7. The heating (30, 40, 50, 60, 70, 80, and 90 degrees C and boiling water baths, 30 min) did not affect the particle size distributions of ISOB. The pH and CaCl(2) effects on DISOB and its surface hydrophobicity were also not affected by heating (>95 degrees C, 5 min). Both unheated and heated ISOB were bound to native soybean protein but were not bound to the heat-denatured one. Thus, it was suggested that ISOB changed little by heating. This study was meaningful in two aspects: (1) pH 11 extraction removed beta-conglycinin, glycinin, and allergenic proteins (such as Gly m Bd 30K), and the obtained ISOB had good stability in an aqueous medium. (2) Heating could denature the contamination allergenic proteins.

The mechanisms for Yuba formation and its stable lipid.

Yuba is a protein-lipid film formed on soymilk surface by heating. It is characteristic of textured structure and long shelf life (3-6 months) in the dry state at room temperature. It was known that soymilk contained oil bodies, protein particles and soluble protein as main components. In this study their roles on Yuba formation were examined. Film was formed by heating an oil body suspension, but it was dispersed again by mixing; Tosan 205 soluble protein (mainly alpha' and alpha subunits of beta-conglycinin) formed film after a long time heating; Yumeminori soluble protein (mainly acidic peptides of glycinin) did not form a film even after all water was evaporated; Tosan 205 and Yumeminori non-lipid soymilks (containing protein particles and soluble protein) formed films by heating. Thus, it was concluded that protein particles were the most important for Yuba formation. In addition, Yuba was treated by liquid nitrogen, vacuum freeze-drying and observed by field emission scanning electron microscope (FESEM). The FESEM pictures showed that oil bodies, protein particles and soluble protein themselves were the "blocks" for Yuba network formation; the Yuba network was formed from protein, but oil bodies were incorporated in the network.

Mechanism of the chemical composition changes of yuba prepared by a laboratory processing method.

Yuba is a filmlike soybean food made from heated soymilk that contains oil bodies (average diameter, 270 nm), particulate protein (>40 nm; average diameter, 70 nm), soluble protein (<40 nm), and carbohydrate (molecular size). Three varieties of soybean were used to make yuba. The carbohydrate in the remaining soymilk increased sharply while lipid increased a little. The particle size distributions of oil body showed the trend that smaller oil bodies were concentrated in the remaining soymilk, and the percentage of soluble protein in whole protein increased in the remaining soymilk. These results could be explained well with diffusion theory. The temperature gradient and concentration gradient originating from the heat treatment were considered to cause the net particle diffusion from the surface to the bottom soymilk. Lipids, which mainly exist as oil bodies, are easily incorporated into yuba films because a few of these less dense droplets diffuse downward, causing the lipid concentration in the soymilk to change a little. Carbohydrate at the surface quickly diffuses downward, causing the carbohydrate concentration increase in the soymilk beneath the developing yuba. Protein (particulate and soluble) in the soymilk was intermediate between lipid and carbohydrate.

Effect of components extracted from okara on the physicochemical properties of soymilk and tofu texture.

The physicochemical properties of soymilk and the texture of tofu were compared with regard to 2 kinds of soymilk, one of which was prepared by squeezing homogenates before heating and the other was prepared by squeezing after heating raw soymilk with okara, residue of soymilk production. Relative particulate protein content and viscosity were higher and pH was lower in the soymilk prepared by the latter method, in which liberated lipid bodies were decreased and more lipids were precipitated with protein after centrifugation, suggesting a change in the interaction between proteins and lipids. A difference in the distribution of proteins and lipids was also implied by analysis with a laser particle size analyzer. The breaking stress of tofu made with 0.30% glucono-delta-lactone increased in accordance with an increase in particulate protein. The calcium and magnesium contents increased in soymilk prepared by squeezing after heating with okara. Viscosity was slightly increased and pH decreased by adding calcium to the soymilk, but the particulate protein content and breaking stress of tofu did not increase significantly. To examine the effect of macromolecules, okara was extracted by boiling and dialyzed. Viscosity and particulate protein content in soymilk increased as the dialyzed extracts of the okara were added. The breaking stress of tofu was increased by adding the dialyzed extracts but excessive amounts of the extracts resulted in softer tofu. Spectra of Fourier-transform infrared spectroscopy and electrophoresis-separated patterns of proteins indicated that the dialyzed extracts contained mainly polysaccharides and the Basic 7S globulin protein.

A novel ornithine-containing tripeptide isolated from the extract of the brackish-water bivalve Corbicula japonica.

Previous studies have demonstrated that frozen preparations of the brackish-water bivalve Corbicula japonica significantly increase the content of free ornithine found in its extracts. Here we report a novel ornithine-containing tripeptide commonly found in C. japonica, which is believed to be the source of increased free ornithine. The new peptide, named acorbine, was isolated from extracts of this bivalve obtained using ultra-filtration and gel permeation chromatography. Acorbine is comprised of N(2)-[N(2)-(beta-alanyl)-L-ornithyl]-L-ornithine as determined by amino acid composition analysis, N- and C-terminal amino acid analyses, proton nuclear magnetic resonance spectrometry, and chirality analysis of the ornithine residue. The total amount of beta-alanine and ornithine in the extract remained constant regardless of the temperature at which the bivalve was processed. The amount of free beta-alanine and ornithine increased significantly when the bivalve was frozen, with a corresponding decrease in peptidic beta-alanine and ornithine. The results suggest that changing the growth conditions triggers tripeptide proteolysis within the bivalve, which ultimately manifests in increased free beta-alanine and ornithine.

Changes in soybean phytate content as a result of field growing conditions and influence on tofu texture.

It is known that tofu quality tends to vary among soybeans even of the same variety. Cultivation environments can affect the contents of the soybeans. Twenty-seven soybean varieties were grown in a drained paddy field and an upland field, and then their protein and phytate contents were determined using the Fourier transfer infrared spectroscopy (FT-IR) method. The phytate contents of 12 varieties were higher in the drained paddy field than in the upland field. On the other hand, the environmental factor had little effect on the protein contents. In order to determine whether the difference in phytate content affected tofu texture, the hardness of the tofu made from phytate-added soymilk was measured. The tofu texture having more phytate became softer in the range of the common coagulant concentration. We concluded that the difference in the phytate content of the soybeans among the environmental conditions is a factor that causes fluctuation in tofu quality.

Changes of astringent sensation of soy milk during tofu curd formation.

The effect of isoflavone on soy milk and tofu astringency was investigated, and no consistency was found between an undesirable astringent taste and isoflavone contents. Isoflavone-enriched extract (approximately 39% isoflavones) showed no astringency. Soybean foods having high amounts of isoflavones showed less astringency. About 80% of isoflavones exist freely in both soy milk and tofu, but 55% of phytates (which play an important role in the formation of the tofu curd network) exist freely in the soy milk, and 6-13%, on the basis of coagulation, existed freely in the tofu curds. A 1% potassium phytate solution at pH 7 showed the very same astringency as soy milk; however, calcium phytate at the same concentration and pH showed no undesirable sensation. Thus, it is assumed that the astringent characteristics caused by phytic ions in soy milk are lost upon conversion of phytic ions to their insoluble salt forms during soy milk coagulation.

Influence of low-temperature processing of the brackish-water bivalve, Corbicula japonica, on the ornithine content of its extract.

The ornithine content of an extract of the brackish-water bivalve, Corbicula japonica, increased when the bivalve was frozen. It was not influenced by the period of freezing. This phenomenon was not apparent in the scallop, little-neck clam, or hard clam. We applied various low-temperature conditions for processing the bivalve from 4 degrees C to -10 degrees C and measured the ornithine content of each extract. The ornithine content was maximized by processing at - 4 degrees C. The increase in this ornithine content was reduced when the bivalve was stored at 5 degrees C or 15 degrees C after processing at - 4 degrees C, this decrease being reversed when the bivalve was again processed at - 4 degrees C after warming. Low-temperature processing of the brackish-water bivalve therefore increased the ornithine content of the extract.

Changes in characters of soybean glycinin groups I, IIa, and IIb caused by heating.

Soybean glycinin groups I, IIa, and IIb were purified from soybeans composed of only glycinin groups I, IIa, and IIb, respectively. When these protein solutions were heated, the amount of the particulate protein formed in these solutions was greatest in the order of groups IIa, IIb, and I. The protein solubilities decreased upon the addition of magnesium chloride in the order of groups IIa, IIb, and I. It was determined by differential scanning calorimetry analysis that the denaturation temperatures of groups I, IIa, and IIb were 92.8, 96.0, and 97.9 degrees C, and that the enthalpies of their transitions were 24.2, 27.4, and 28.1 J g(-)(1), respectively. The alpha-helix rates of groups I, IIa, and IIb in aqueous solution were analyzed by circular dichroism and were 19, 16, and 15%, respectively. The beta-sheet rates of groups I, IIa, and IIb were 44, 38, and 39%, respectively. In all group proteins, the alpha-helix rates were decreased by heating and the beta-sheet rates were increased. The surface hydrophobicity of these group proteins increased as a result of heating, and those of groups IIa and IIb were larger than that of group I. The surface hydrophobicity of these protein groups increased by heating, and those of groups IIa and IIb were larger than that of group I and beta-conglycinin. Breaking stress of curds prepared from these group proteins containing more than 1 of beta-conglycinin ration showed similar values, but the order of those containing less than 1 in strength was groups I, IIb and IIa. These results suggest that the increase of particulate contents and the curd formation are related to the increase of surface hydrophobicity by heating.

Rapid measurement of phytate in raw soymilk by mid-infrared spectroscopy.

The phytate content in soymilk is known to affect tofu curdling. A rapid measurement of phytate from a water extract of soybean (raw soymilk) in an early stage of tofu processing was investigated using mid-infrared spectroscopy (IR) with an ATR accessory. IR absorption of phytate was observed from 1200 cm-1 to 900 cm-1, and saccharide and protein in the extract also had IR absorption in the same region. In order to separate phytate from other components, the phytate was precipitated completely by the addition of calcium under alkaline condition (pH 11.5). The precipitate was dissolved in citrate buffer (pH 6.0) and then used for IR measurement. The absorbance at 1070 cm-1 correlated well with the phytate content of the soymilk. The measurement of phytate in raw soymilk can be done rapidly by FT-IR measurement with an ATR accessory and gives reproducible values, which can be used for the measurement of phytate content in various soybeans for tofu making.