Tomotada Ono

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.

Influences of Calcium and pH on Protein Solubility in Soybean Milk.

Tofu-curd is made by the flocculation of proteins in soybean milk with an addition of calcium. The proteins consist of soluble and particle fractions. The influences of calcium and pH on the protein solubility of these fractions were investigated. The protein particles precipitated at lower calcium concentrations than that of the soluble proteins. This precipitation of proteins took place at higher pH with calcium than that without calcium. Therefore, it is considered that the first step to tofu-curd is the formation of a network by the protein particles at low calcium concentration. The next step was seemed to be the binding of the soluble proteins to the network by further addition of calcium and decreasing pH.

Interaction of Protein Particles with Lipids in Soybean Milk

The protein in soybean milk exists as 11S and 7S globulins, and the particles formed from them. The lipid content and composition in the protein fractions and effects of defatting on the form of the protein particles were investigated. The size-distribution of protein particles in both raw and heated soybean milk (soymilk) was not influenced by defatting with hexane, but the number of large particles were slightly increased. The protein particles from raw and heated soymilk samples contained 60% and 3% of the total lipid, respectively. Almost all neutral lipid in the particles of raw soymilk was moved to a floating fraction by heating, but a half of the phospholipids was retained in the particles. The protein components from the hexane-defatted meal were similar to those from whole meal, but those from the C-M-de-fatted meal contained remarkably little β-conglycinin. C-M-de-fatting (Removal of polar lipids) caused a reduction in the particulate fraction, and the addition of phospholipids (lecithin) promoted the formation of protein particles.

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.

A model for the assembly of bovine casein micelles from F2 and F3 subunits

Casein micelles were reassembled from mixtures of F2 and F3 subunits, the major subunits of bovine casein micelles, in varying ratios. The average radius of the reassembled micelles was inversely proportional to the F2 content. Based on this relationship, a model for casein micelle assembly is proposed in which the F3 subunit forms the core of the micelle with F2 subunit occurring on the surface. Micelle size can subsequently be defined by the F2 content.

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 °C to −10 °C and measured the ornithine content of each extract. The ornithine content was maximized by processing at −4 °C. The increase in this ornithine content was reduced when the bivalve was stored at 5 °C or 15 °C after processing at −4 °C, this decrease being reversed when the bivalve was again processed at −4 °C after warming. Low-temperature processing of the brackish-water bivalve therefore increased the ornithine content of the extract.

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.

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.

The localization of phytate in tofu curd formation and effects of phytate on tofu texture.

The localization of phytate on tofu making and its effects on tofu texture were investigated. Thirty-eight percent and 3% of phytate in soymilk were bound to soluble protein and particulate protein, respectively, and the others were in free form. In the early stage of curd formation, phytate bound to particulate proteins and then a large part of phytate was taken into the tofu curd. Increase of phytate contents in soymilk resulted in the increase of coagulant requirement to make firm tofu. Optimal coagulant concentration (OCC) for making tofu was influenced by phytate contents. The increase of phytate in tofu caused decrease of hardness at OCC and resulted in the increase of brittleness and viscosity of tofu. We concluded that the phytate content is one important factor that contributes to tofu texture.

Molecular weights of subunit components of bovine casein micelles

Using either Sephacryl S-300 or TSK-G4000SW gel chromatography, the larger of the two major components of bovine casein micelles (F2) was eluted at the same retention time irrespective of sample concentration and column temperature. Its mol. wt was estimated to be 500K by examination of the eluate from a TSK-gel G4000SW column using a low-angle laser light-scattering photometer and a precision differential refractometer. With the second component (F3), retention time in Sephacryl gel chromatography was significantly affected by both sample concentra-tion and volume applied. Limiting retention times for F3 could be obtained by extrapolation of these two parameters to higher and lower values, and corresponded to those of water-soluble protein with mol. wt 200K and 100K respectively. Approach to sedimentation equilibrium technique at the above limiting sample concentrations gave values of F3 consistent with the above molecular weight. Sephacryl gel chromatography at either low sample concentration or low column temperature resulted in a new component being eluted at a position of mol. wt 25K