Seed Protein Content and Consistency of Tofu Prepared with Different Magnesium Chloride Concentrations in Six Japanese Soybean Varieties

Abstract

The relationship between the protein content of soybean seeds and the consistency of tofu was examined for six Japanese soybean varieties, Enrei, Fukuyutaka, Sachiyutaka, Ayakogane, Hatayutaka and Tachinagaha. The seed protein content was estimated by determining the nitrogen content using the Dumas method. Tofu was prepared from a raw homogenate of water-soaked soybeans by heating and by the addition of MgCl 2 as a coagulant. The tofu consistency was evaluated by measuring the breaking stress of tofu curd using a Creep meter. The breaking stress of tofu increased when the concentrations of MgCl 2 in soymilk increased above 0.20 %. The breaking stress reached a maximum value at concentrations of around 0.40 %, with differences among soybean varieties and cultivation conditions of the soybeans. There was a significant positive correlation (r = 0.87) between the maximum breaking stress of tofu and the seed protein content for the six varieties. In contrast, the breaking stress of tofu prepared with 0.25 % MgCl 2 did not show a significant correlation (r = 0.27) with the seed protein content for the six varieties but was significantly correlated (r = 0.52), when the data of Sachiyutaka were excluded. Fukuyutaka and Ayakogane required a lower MgCl 2 concentration for the maximum breaking stress of tofu than Sachiyutaka, Enrei, Tachinagaha and Hatayutaka, which required a MgCl 2 concentration above 0.40 % for the maximum breaking stress of tofu. Especially, Sachiyutaka required the highest MgCl 2 concentration, 0.45 % on the average, for the maximum breaking stress of tofu among the six varieties. Sachiyutaka-tofu showed the lowest breaking stress on the average at a concentration of 0.25 % MgCl 2 , which is the concentration generally used by manufacturers, in spite of its high content in seed protein. In contrast, Fukuyutaka required the lowest MgCl 2 concentration, 0.34 % on the average, for the maximum breaking stress and the highest breaking stress of tofu prepared with 0.25 % MgCl 2 . That is one of reasons why manufacturers prefer to use Fukuyutaka for producing tofu. Concentration of a coagulant for the maximum breaking stress as well as seed protein content could become criteria for quality evaluation of soybeans for tofu processing.

Homogeneity and Microstructure of Tofu Depends on 11S/7S Globulin Ratio in Soymilk and Coagulant Concentration

“…The tofu network even for filled tofu forms some cracks using CaSO 4 but forms few cracks using GDL. Toda et al (2003) found that each soybean variety requires a particular coagulant concentration to achieve the maximum tofu firmness. Fukuyutaka variety reaches maximum tofu firmness at a lower coagulant concentration than Sachiyutaka variety.…”

“…Technol. Res., 15 (3), 265 -274, 2009 11S content (Cai and Chang, 1999;Yagasaki et al, 2000;Cai et al, 2002;Tay and Perera, 2004;Kim and Wicker, 2005).Tofu firmness is also dependent on coagulant concentration, which is correlated with both protein concentration and protein composition at low concentrations, and each soybean has a particular coagulant concentration to obtain maximum tofu firmness (Toda et al, 2003). Protein particles in soymilk aggregate at lower coagulant concentration than soluble protein (Ono et al, 1993).…”

Components in Soybean Seeds Affecting the Consistency of Tofu

“…When MgCl 2 concentration was changed, Sachiyutaka showed the highest MgCl 2 concentration for the maximum breaking stress of tofu and the lowest breaking stress of tofu made with 0.25% MgCl 2 among six soybean cultivars 15 . In contrast, Fukuyutaka showed the lowest MgCl 2 concentration for the maximum breaking stress of tofu and the highest breaking stress of tofu made with 0.25% MgCl 2 15 .…”

Contribution of Disulfide Bonding to Viscoelastic Properties and Microstructures of 11S Globulin Gels from Soybeans: Magnesium Chloride-Induced Gels

“…A protein concentration of less than 3.4% was preferable to compare gel structures of 11S and SPI gels. In addition, manufacturers prefer to use a concentration of 0.25% MgCl 2 as the coagulant in tofu production (Toda et al, 2003). Therefore, for this study, 11S or SPI gels containing 3.3% (w/w) protein and 0.25% (w/ v) MgCl 2 were used to determine the effects of NaCl concentration on viscoelastic properties of the gels.…”

“…Magnesium chloride (MgCl 2 ), calcium sulfate (CaSO 4 ), and glucono-δ-lactone (GDL) are common coagulants used on an industrial scale for the preparation of tofu (deMan et al, 1986). Although MgCl 2 is the most commonly used coagulant for tofu production in Japan (Toda et al, 2003), there is little information concerning MgCl 2 -induced gels of soybean proteins. Most studies on tofu formation and properties have used GDL or CaSO 4 as the coagulant because the rates of gel formation are relatively slow and more homogeneous gels are formed (Saio et al, 1969;Nishinari et al, 1991;Kohyama and Nishinari, 1993;Kohyama et al, 1995;Liu et al, 2004;Tay and Perera, 2004;Guo and Ono, 2005;Ono, 2008).…”