**2.2. Lipid**

Soybeans have 20% lipids. The lipid concentration varies among harvested regions. Soybeans harvested in the United States have more lipids than those in China [1]. A main reason is that soybeans there have long been bred and modified to contain high oil concentrations as oilseed.


*Source*: Yamauchi and Ookubo (1992).

**Table 3.** Components of fatty acids in foods (%)

Components of fatty acids in foods shows Table 3. Soy oil comprises a small amount of saturated fatty acids, such as palmitic acid and stearic acid, and large amount of unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid. Polyunsaturated fatty acids (PUFAs) containing more than unsaturated bonds are important nutrition as necessary lipids for humans. Soybeans have over 60% PUFA. In particular, one kind of PUFA as linoleic acid contained approximately 54.5%.

Actually, PUFAs in animal lipids have low concentration. Therefore, they are insufficient nutritionally. Saturated fats and unsaturated fats are ideally in the following ratio: saturated– unsaturated (1:2) [1]. Soybean lipids were well known to be much stable against oxidation because they are covered as oil body particle by oleosin and other proteins.

## **2.3. Isoflavone**

Isoflavone is one kind of flavonoid (Fig. 1). Fabaceae sp. contain high concentrations (Fig. 1).

Generally, soybeans have totally 12 isoflavones in 3 aglycones, and they have three types of glycosides as glucoside, acetyl-glycoside and malonyl-glycosides: genistein, daidzein, glystein, genistin, daidzin, glycitin, acetyl-genistin, acetyl-daidzin, acetyl-glycitin, malonylgenistin, malonyl-daidzin and malonyl-glycitin [7]. After soybean consumption, glycoside isoflavone, which is contained in food as soy milk or *Tofu*, hydrolyzes aglycon and glycoside by bacteria in intestines. Their aglycon are absorbed by the body. Genistein and daidzein have estrogenic effects and hormone-like activity. The isoflavone binding with estrogen receptor

**Figure 1.** Isoflavone structure.

**2.2. Lipid**

84 Food Production and Industry

*Source*: Yamauchi and Ookubo (1992).

**Table 3.** Components of fatty acids in foods (%)

contained approximately 54.5%.

**2.3. Isoflavone**

Soybeans have 20% lipids. The lipid concentration varies among harvested regions. Soybeans harvested in the United States have more lipids than those in China [1]. A main reason is that soybeans there have long been bred and modified to contain high oil concentrations as oilseed.

Pork fat 26.2 13.5 42.9 9 0.3 Beef fat 38.7 3.8 42.1 2.3 2.4 Milk lipid 31.1 9.2 21.7 1.6 0.4 Soybean oil 10.5 3.2 22.3 54.5 8.3 Sunflower oil trace 4 27.6 58.3 trace Cotton oil 27.3 3.1 16.7 50.4 trace Safflower oil 6 3.4 12.2 77 0.3

Components of fatty acids in foods shows Table 3. Soy oil comprises a small amount of saturated fatty acids, such as palmitic acid and stearic acid, and large amount of unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid. Polyunsaturated fatty acids (PUFAs) containing more than unsaturated bonds are important nutrition as necessary lipids for humans. Soybeans have over 60% PUFA. In particular, one kind of PUFA as linoleic acid

Actually, PUFAs in animal lipids have low concentration. Therefore, they are insufficient nutritionally. Saturated fats and unsaturated fats are ideally in the following ratio: saturated– unsaturated (1:2) [1]. Soybean lipids were well known to be much stable against oxidation

Isoflavone is one kind of flavonoid (Fig. 1). Fabaceae sp. contain high concentrations (Fig. 1).

Generally, soybeans have totally 12 isoflavones in 3 aglycones, and they have three types of glycosides as glucoside, acetyl-glycoside and malonyl-glycosides: genistein, daidzein, glystein, genistin, daidzin, glycitin, acetyl-genistin, acetyl-daidzin, acetyl-glycitin, malonylgenistin, malonyl-daidzin and malonyl-glycitin [7]. After soybean consumption, glycoside isoflavone, which is contained in food as soy milk or *Tofu*, hydrolyzes aglycon and glycoside by bacteria in intestines. Their aglycon are absorbed by the body. Genistein and daidzein have estrogenic effects and hormone-like activity. The isoflavone binding with estrogen receptor

because they are covered as oil body particle by oleosin and other proteins.

**Palmitic acid Stearic acid Oleic acid Linoleic acid Linolenic acid**

reacts as an estrogen agonist in the human body. Their substances from plants having estrogenic effects are called "plant estrogen." *Miso* paste has a high level of isoflavone because glucosyl isoflavone is hydrolyzed to their related aglycons.

Many Japanese and throughout eastern Asia intake isoflavone from soybeans. Some research‐ ers have reported negative opinions about plant estrogen [8]. Isoflavones are produced via phenyl–propanoid pathway from phenylalanine in plants. Two intermediate substances, naringenins, are converted to genistein by two specific enzymes in soybeans: isoflavone synthetase and dehydrogenase. Chalcones are converted to daidzein by three specific enzymes in soybean: chalcone reductase, chalcone isomerase, and isoflavone synthetase. Isoflavone and a similar substance, phytoalexin, are used as antibacterial substances against phytopathogenic fungi and bacteria. In addition, they grow well as root nodule bacteria at the root for nitrogen fixation [9, 10]. 1

Other beans and peas, legumes, have isoflavones: chickpeas have biochanin A [11]; alfalfa has formononetin and coumestrol [12]; and ground peas have genistein [13].

Isoflavones in many plants store glucosyl, malonyl-glucosyl, and acetyl-glucosyl conjugate as hydrophilic substances. After invasion of phytopathogenic fungus and bacteria, the glucosyl conjugate isoflavone is transferred to infested wounds, where it hydrolyzes for phytoalexin [14]. Isoflavone has health functions against climacteric disturbances and type 2 diabetes. In Japan, soybean isoflavones are a *Tokuho* (government-approved food for specified health purpose) for the prevention of osteoporosis. The Ministry of Health, Labour and Welfare in Japan alerts consumers to avoid overdosing on isoflavones. The amount of isoflavone intake was 30 mg a day, omitting isoflavone intake from meals and by supplements.

## **3. Food processing** LVRIODYRQHLQWDNHIURPPHDOVDQGE\VXSSOHPHQWV

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Soy proteins have properties that produce curd to add specific metal ions. The property is applied for *Tofu* production. Tofu, soybean curd from soybean milk, is consumed throughout Asia. It was eaten in the tenth century in China and Japan. *Tofu* is traditionally consumed after it is produced with a combination of magnesium dichloride (MgCl2) as *Nigari* and calcium dichloride (CaCl2) as *Sumashi-ko*. More recently, glucono-δ-lactone (GDL) has been added to it for commercial production. Tofu resembles cheese or yogurt made from milk curd of cows or other mammals. It is made from soy milk. It curdles by *Nigari* or a coagulant agent [15]. The forming system of *Tofu* curdling is shown in Fig. 2. 6R\SURWHLQVKDYHSURSHUWLHVWKDWSURGXFHFXUGWRDGGVSHFLILFPHWDOLRQV7KHSURSHUW\LVDSSOLHGIRUWRIX SURGXFWLRQ 7RIXVR\EHDQFXUGIURPVR\EHDQPLONLVFRQVXPHGWKURXJKRXW\$VLD,WZDVHDWHQLQWKHWHQWKFHQWXU\LQ &KLQDDQG-DSDQ7RIXLVWUDGLWLRQDOO\FRQVXPHGDIWHULWLVSURGXFHGZLWKDFRPELQDWLRQRIPDJQHVLXPGLFKORULGH 0J&ODV*1LJDUL*DQGFDOFLXPGLFKORULGH&D&ODV*6XPDVKLNR*0RUHUHFHQWO\JOXFRQRGODFWRQH\*'/KDVEHHQ DGGHGWRLWIRUFRPPHUFLDO SURGXFWLRQ7RIXUHVHPEOHVFKHHVHRU\RJXUWPDGHIURPPLONFXUGRIFRZVRURWKHU PDPPDOV,WLVPDGHIURPVR\PLON,WFXUGOHVE\*1LJDUL*RUDFRDJXODQWDJHQW>@7KHIRUPLQJV\VWHPRIWRIX FXUGOLQJLVVKRZQLQ)LJ

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 6R\PLONLVDQHPXOVLRQFRPSRVLQJOLSLGDQGVR\SURWHLQPDLQO\JO\FLQLQDQGEFRQJO\FLQLQ\$FWXDOO\RI Soy milk is an emulsion composing lipid and soy protein, mainly glycinin and β-conglycinin. Actually, 60% of the protein in soy milk protein is composed of these two proteins, and a large size of the protein body was constructed with their proteins and others. Lipid is a triacylgly‐ ceride composed of linoleic acid, oleic acid, and phospholipids. Before treating, triacylglycer‐ ide is stored in oil bodies in soybeans. During soy milk production, and of course during *Tofu* production, oil drops are suspended, forming an emulsion after crushing of soybeans. The oil drop is formed and held stably by lecithin, phospholipid, and oleosin, all proteins forming oil bodies in soybeans. Furthermore, an outside layer is covered by soy protein. Phytic acid (*myo*inositol-1,2,3,4,5,6-hexaphosphate) and mineral and oligosaccharide are in the soluble com‐ ponent of soy milk [16]. When some bivalent ions such as calcium ion and magnesium ion are added to soy milk, the ions combine with phytic acid. As a result, decreasing the pH of the soybeans immobilizes the protein in it [17].

This phenomenon induces the charge of protein to dissipate by a combination of phytic acid and bivalent ion. Repulsion among their proteins is decreased. Moreover, the immobilized protein combines with outside layer protein easily around an oil drop [18]. Consequently, the steric network structure of soy protein is formed to gather oil drops with intermediary soy protein. Becoming low pH in soy milk, soluble soy protein becoming dissoluble is taken into the network. The curd produces a hard gel that is water retentive, such that moisture is trapped in the network.
