Tofu Gel Research Articles

Application of two-stage ohmic heating to tofu processing

Thermal denaturation of soybean proteins is a prerequisite for tofu gel formation. Soymilk is conventionally heated with a one-stage steam heating. Two-stage ohmic heating was applied to soymilk in this study. Optimizing the two-stage heating condition for making filled-tofu and the effect of the two-stage heating on soft-tofu were investigated. Our results show that the combination of 70 °C for 10 min and 100 °C for 5 min was the best condition of the two-stage heating for preparing filled-tofu. Compared to the one-stage heating, the two-stage heating increased the soft-tofu's apparent breaking strength by 12.2% and apparent Young's modulus by 16.2%, reduced the syneresis rate by 21.8%, and increased the yield and the solid recovery by 4.5% and 5.4%, respectively. Two-stage ohmic heating is a potential method for heating soymilk in tofu manufactures.

Effect of Salts on Tofu Gel Hardness

Effect of Salts on Tofu Gel Hardness

The viscoelastic properties of soybean curd (tofu) as affected by soymilk concentration and type of coagulant

SummaryThe viscoelastic properties of different types of tofu were investigated. Soymilk concentrations were 5, 6, 7, 8 and 9%. Coagulants used were 30 mm CaSO4 or 30 mm glucono‐delta‐lactone (GDL). As the concentration of soymilk was increased viscosity and handling difficulties increased. A high concentration of soymilk in tofu gave a high break stress and produced hard tofu. The four‐element Burgers model fitted the creep behaviour and both viscous and elastic parameters could be acquired from model analysis, reflecting changes in elasticity and viscosity of tofu. The constant viscous parameter in the model increased with increasing soymilk concentration. The viscous parameters of viscoelastic materials like tofu gel, obtained from small deformation tests, seemed to correlate, to some extent, with the break stress obtained from large deformation tests. For hard tofu production increasing the soymilk concentration within a certain range and the partial replacement of calcium sulphate coagulant by GDL could be effective options.

High-pressure treatment effects on proteins in soy milk

Effects of high-pressure treatment on the modifications of soy protein in soy milk were studied using various analytical techniques. Blue shifts of λ max could be observed in the fluorescence spectra. Spectrofluorimetry revealed that the soy protein exhibited more hydrophobic regions after high-pressure treatment. Electrophoretic analysis showed the change of soy protein clearly and indicated that soy proteins were dissociated by high pressure into subunits, some of which associated to aggregate and became insoluble. High-pressure denaturation occurred at 300 MPa for β-conglycinin (7S) and at 400 MPa for glycinin (11S) in soy milk. High pressure-induced tofu gels could be formed that had gel strength and a cross-linked network microstructure. This provided a new way to process soy milk for making tofu gels.

High-pressure treatment effects on proteins in soy milk

Effects of high-pressure treatment on the modifications of soy protein in soy milk were studied using various analytical techniques. Blue shifts of λ max could be observed in the fluorescence spectra. Spectrofluorimetry revealed that the soy protein exhibited more hydrophobic regions after high-pressure treatment. Electrophoretic analysis showed the change of soy protein clearly and indicated that soy proteins were dissociated by high pressure into subunits, some of which associated to aggregate and became insoluble. High-pressure denaturation occurred at 300 MPa for β-conglycinin (7S) and at 400 MPa for glycinin (11S) in soy milk. High pressure-induced tofu gels could be formed that had gel strength and a cross-linked network microstructure. This provided a new way to process soy milk for making tofu gels.

Effect of calcium sulfate concentration in soymilk on the microstructure of firm tofu and the protein constitutions in tofu whey.

The effects of calcium sulfate concentration in soymilk on the microstructure of tofu and the constitutions of protein in tofu whey were investigated. The firm tofu made with 0.4% CaSO(4).2H(2)O was found to be most uniform and continuous in the microstructure. This tofu gave the maximal tofu yield, maximal solid and protein recoveries, and the best water retention ability. The results of gel electrophoresis and the ratio of amino nitrogen to total organic nitrogen indicated that the low molecular weight proteins in tofu whey were at their lowest when the tofu was made with 0.4% CaSO(4).2H(2)O. The SEM observations suggested that the tofu made with 0.4% CaSO(4).2H(2)O has the most uniform and homogeneous microstructure and, consequently, can most efficiently retain soybean proteins and water in the tofu gel.

Potential Improvement of Soymilk Gelation Properties by Using Soybeans with Modified Protein Subunit Compositions.

To examine the effects of protein subunit compositions on tofu gel formation, we prepared soymilk from a low-β-conglycinin soybean line lacking two β-conglycinin subunits and from a low-glycinin soybean line lacking three glycinin subunit groups, the proportion of glycinin to β-conglycinin (11S/7S ratio) of which was 3.76 and 0.12, respectively. The two kinds of soymilk were mixed to give various 11S/7S ratio, and heated at 80°C with 0.4% glucono-δ-lactone (GDL) in a water bath to make tofu gel or in a cell for measuring dynamic viscoelasticity. The breaking stress of the GDL-induced tofu gel made from the low-β-conglycinin soymilk was nearly four times higher than that made from the low-glycinin soymilk. The tofu breaking stress and the soymilk storage modulus both increased with increase of 11S/7S ratio. The storage modulus correlated well with the tofu gel breaking stress (r=0.932**). The decrease of glycinin content by lacking the subunit(s) resulted in decrease of 11S/7S ratio. The heated soymilk made from soybean seeds having different glycinin subunit compositions showed a close association between 11S/7S ratio and storage modulus (r=0.946**). Therefore, 11S/7S ratio is considered to have an important effect on the physical properties of tofu gel. The soymilk from low-β-conglycinin soybean and low-glycinin soybean showed a similar pH change after the addition of MgCl2. Soymilk from the low-β-conglycinin soybean coagulated immediately after addition of 0.3% MgCl2 was added. Soymilk from the low-glycinin soybean, in contrast, remained liquid even at 1°C. These results suggest that soymilk gelation properties can be improved by using soybeans with modified protein subunit compositions.

Effect of carrageenan on yield and properties of tofu

The effects of the polysaccharide carrageenan and three types of coagulants namely, glucono-δ-lactone (GDL), calcium sulphate (CS) and calcium acetate (CA) on yield and physical properties of tofu (soybean curd), were investigated. Moisture content and yield of GDL-coagulated tofu were higher than that coagulated with CS and CA. Addition of carrageenan did not increase yield of GDL-tofu significantly but increased yield of CS-tofu and CA-tofu by 33 and 46.7%, respectively. Texture of CS-tofu was harder than CA- and GDL-tofu. Carrageenan brought about a significant decrease in hardness of CS- and CA-tofu which was more pronounced at the higher gum concentration. Hardness of GDL-tofu was not significantly altered. The tofu gels exhibited syneresis on storage at 4°C for 24 h in the order: CS-tofu<CA-tofu<GDL-tofu. Addition of carrageenan increased the syneresis, which was higher in CA-tofu than CS-tofu. On the other hand, GDL-tofu showed a decrease in syneresis in the presence of carrageenan. ©

Rheological study on the effect of the A5 subunit on the gelation characteristics of soybean proteins.

In order to clarify the effect of acidic subunit A5 of 11S globulin in soybean protein on gelation characteristics, the gelation process for soymilk was studied by dynamic viscoelastic measurements. It was found that tofu gels prepared from cultivars without the A5 subunit were harder and more solid-like than those prepared from cultivars with the A5 subunit.

DIFFERENCES IN FUNCTIONAL PROPERTIES OF 7S AND 11S SOYBEAN PROTEINS

ABSTRACTThis paper summarizes the work done by the authors (most of it published in Japan) and other researchers. The 11S protein is different from the 7S protein in that it makes much harder Tofu gels which are more sensitive to the softening effect of phytic acid and in which the S—S bonds appear to predominate. The US protein precipitates faster and forms larger aggregates. Its gelation characteristics suggest suitability as fish and meat extender. 11S gels have a higher water holding capacity than 7S gels, higher tensile values, higher hardness and expand more on heating. Similarly, 11S films are more elastic and have higher tensile values. It is pointed out that the functional properties of proteins may be controlled by regulating the binding forces through pH and additives.

Observation of Soybean Foods under Electron Microscope

Of the electron microscopic pictures taken in the investigation on protein bodies and the protein in soybean seeds, some were presented to elucidate fine structures of them and their changes in processing. No change in protein bodies and spherosomes in intact cells of soybean cotyledon occurred by soaking in water overnight, while remarkable changes, such as bursting of protein bodies, curdling of their protein in mass without dissolving, and converting of spherosomes into rather large oil droplets, were observed after successive heat-steaming and fermentation with Bacillus natto. In tofu gel, a network is formed with protein microgranules, and oil droplets located in groups along it. The meshy structure of fresh tofu for kori-tofu is denser than that of ordinary tofu. During freezing, protein microgranules are localized and denatured by growth of ice crystals.