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The relationship between the coagulant concentration and soybean protein composition for the finer structure of tofu was investigated using its textural and microstructure data. The textural property of tofu with different ratios of 11S/7S globulin was measured at various concentrations of coagulant, and the tofu structure was observed by scanning electron microscopy. The tofu microstructure had the finest network near its change point of breaking stress (CaSO 4 ) or breaking strain (glucono-δ-lactone). Thus, the coagulant concentration for obtaining a finer tofu network is important for tofu preparation. At concentrations below and above the optimal coagulant concentration, the tofu network consisted of large cell-like units, while at the optimal concentration it consisted of small, uniform units. The structural change point of tofu rich in 11S globulin was at lower coagulant concentrations (0.15~0.2%) and that rich in 7S was at higher coagulant concentrations (0.3~0.4%) Keywords: tofu, soymilk, microstructure, tofu, coagulant, SEM *To whom correspondence should be addressed. E-mail: tomon@iwate-u.ac.jp IntroductionSoybean contains 30-40% protein and 20-30% lipid, making them an important dietary source of these components. The major soybean products are soymilk and tofu, which are used in many Asian countries as milk and cheese are used in western countries.Tofu, a traditional curd-like food prepared from soymilk by the addition of a coagulant, has mild taste. Therefore, its sensory evaluation, especially of its physical property, is important for quality control. Many studies indicate that the factors that influence the physical properties of tofu depend on the differences in components of the soybean varieties and on cultivation conditions (Skurray et al., 1980; Wang and Hesseltine, 1983;Taira, 1990). The use of soybean varieties with high protein content produces tofu with a firmer and springier texture (Wang and Hesseltine, 1983;Shen et al., 1991). Tofu manufacturers in Japan have commonly used soybean varieties, such as Fukuyutaka and Enrei, containing high protein content. The gel hardness from purified soy proteins is reported to be positively correlated with the 11S (glycinin) content (Saio et al., 1969;Saio, 1979;Kang et al., 1991). In the preparation of tofu curd, a coagulant is added to soymilk, which is comprised of many components including protein, lipid, and sugar. Therefore, the factors that influence curd firmness remain to be clarified (Skurray et al., 1980;Taira, 1990;Murphy et al., 1997). The main components involved in the formation of tofu curd were found to be particle and soluble proteins and lipid globules in the soymilk (Ono et al., 1993;Guo et al., 1999). Curd formation is able to explain a 2 step process: (1) conjugation of protein particles on the surface of lipid globules following the addition of the coagulant and (2) formation of a network of non-repulsive lipid globules covered with protein particles (Ono, 2000). Soybeans with different subunits, including 11S (glycinin) an...
The relationship between the coagulant concentration and soybean protein composition for the finer structure of tofu was investigated using its textural and microstructure data. The textural property of tofu with different ratios of 11S/7S globulin was measured at various concentrations of coagulant, and the tofu structure was observed by scanning electron microscopy. The tofu microstructure had the finest network near its change point of breaking stress (CaSO 4 ) or breaking strain (glucono-δ-lactone). Thus, the coagulant concentration for obtaining a finer tofu network is important for tofu preparation. At concentrations below and above the optimal coagulant concentration, the tofu network consisted of large cell-like units, while at the optimal concentration it consisted of small, uniform units. The structural change point of tofu rich in 11S globulin was at lower coagulant concentrations (0.15~0.2%) and that rich in 7S was at higher coagulant concentrations (0.3~0.4%) Keywords: tofu, soymilk, microstructure, tofu, coagulant, SEM *To whom correspondence should be addressed. E-mail: tomon@iwate-u.ac.jp IntroductionSoybean contains 30-40% protein and 20-30% lipid, making them an important dietary source of these components. The major soybean products are soymilk and tofu, which are used in many Asian countries as milk and cheese are used in western countries.Tofu, a traditional curd-like food prepared from soymilk by the addition of a coagulant, has mild taste. Therefore, its sensory evaluation, especially of its physical property, is important for quality control. Many studies indicate that the factors that influence the physical properties of tofu depend on the differences in components of the soybean varieties and on cultivation conditions (Skurray et al., 1980; Wang and Hesseltine, 1983;Taira, 1990). The use of soybean varieties with high protein content produces tofu with a firmer and springier texture (Wang and Hesseltine, 1983;Shen et al., 1991). Tofu manufacturers in Japan have commonly used soybean varieties, such as Fukuyutaka and Enrei, containing high protein content. The gel hardness from purified soy proteins is reported to be positively correlated with the 11S (glycinin) content (Saio et al., 1969;Saio, 1979;Kang et al., 1991). In the preparation of tofu curd, a coagulant is added to soymilk, which is comprised of many components including protein, lipid, and sugar. Therefore, the factors that influence curd firmness remain to be clarified (Skurray et al., 1980;Taira, 1990;Murphy et al., 1997). The main components involved in the formation of tofu curd were found to be particle and soluble proteins and lipid globules in the soymilk (Ono et al., 1993;Guo et al., 1999). Curd formation is able to explain a 2 step process: (1) conjugation of protein particles on the surface of lipid globules following the addition of the coagulant and (2) formation of a network of non-repulsive lipid globules covered with protein particles (Ono, 2000). Soybeans with different subunits, including 11S (glycinin) an...
The objective is to study the microstructure, rheology, and quiescent stability of oil‐in‐water emulsions prepared with defatted soybean flour dispersions, analyzing the effects of calcium concentration and homogenization method. Dispersions are prepared without or with addition of calcium chloride at different concentrations (30, 60, and 90 mg Ca 100 g−1) and treated by heating (100 °C, 40 min) and high‐pressure homogenization (HPH) at 120 MPa. Emulsions are prepared with homogenized dispersions and sunflower oil by different homogenization methods (high‐speed homogenization, HSH; and HPH at 10 and 20 MPa). The addition of calcium produces a decrease of soluble protein in dispersions, leading to emulsions with higher oil droplet size and aggregation of particles when HSH and HPH are applied, respectively. The highest aggregation degree is observed in the systems with 30 mg Ca 100 g−1, attributed to the formation of a hydrated network of aggregated particles (oil droplets, protein aggregates, and insoluble fibers). Consequently, these emulsions also show the highest viscosity and creaming stability. The findings indicate that calcium can act as a functional ingredient in food emulsions prepared with soybean flour dispersion, because the texture and stability of the system can be controlled by the variation of calcium concentration and homogenization method. Practical Applications: In this study, the impact of calcium addition and homogenization method on the microstructure, rheological behavior, and quiescent stability of o/w emulsions prepared with soybean flour dispersions is assessed. Unlike other works, the strategy used for calcium addition is to promote the interaction of the mineral with proteins and non‐starch polysaccharides present in soybean flour and then reduce the size of aggregates by high‐pressure homogenization. The mentioned strategy can allow the obtaining of vegetable calcium‐rich emulsion‐based products with texture and consistency modulated by the amount of added calcium and the applied homogenization method. Soybean flour dispersions are heated in the presence of different calcium concentrations and then homogenized by high‐pressure homogenization. Emulsions are prepared with homogenized dispersions and sunflower oil by high‐speed or high‐pressure homogenization. The addition of calcium leads to aggregation of particles in emulsions homogenized at high pressure; and good quiescent stability is achieved in emulsions with moderate calcium content.
The objective is to study the partial coalescence process in calcium‐fortified double (W1/O/W2) and simple (O/W2) emulsions prepared with soybean flour dispersion as continuous aqueous (W2) phase and vegetable fat plus polyglycerol polyricinoleate (PGPR) as lipophilic emulsifier (at varied concentration) in lipid phase. Calcium chloride is included in the dispersed aqueous (W1) phase and the W2 phase of W1/O/W2 and O/W2 emulsions, respectively. No partial coalescence is observed in the O/W2 emulsion without PGPR and calcium, while the inclusion of the emulsifier and/or divalent cation promotes the phenomenon. The presence of PGPR in lipid phase or calcium in W2 phase can enhance capture efficiency because of the decrease of electrostatic and steric repulsions between fat globules, the modification of fat crystals, and/or the increased size of individual globules. W1/O/W2 emulsions show a lower partial coalescence degree in comparison to O/W2 emulsions prepared with the same components, attributed to the isolation of a fraction of added calcium in the W1 phase of the former systems. PGPR produces microstructural and rheological changes over time in emulsions subjected to prolonged cold storage; but its effect is reduced in the presence of calcium, probably because of the formation of stronger globule aggregates. Practical applications: This article deals with two parallel phenomena occurring in W1/O/W2 and O/W2 emulsions prepared with soybean flour dispersion as W2 phase and vegetable fat in lipid phase: the promotion of partial coalescence by the lipophilic emulsifier, PGPR; and the aggregation of proteins and fat globules due to the presence of calcium in W2 phase. In this way, the effects of PGPR and/or calcium on partial coalescence are studied in these systems, analyzing their microstructure and rheology. The encapsulation of calcium within the W1 phase of W1/O/W2 emulsions and its impact on partial coalescence is also analyzed. The results obtained in this work can be relevant for the formulation of calcium‐fortified, vegetable food emulsions, showing a texture similar to whipped dairy cream, where PGPR concentration or calcium release can be controlled to adjust the rheological characteristics of the system.
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