**5.1 Tofu**

*Legume Crops - Prospects, Production and Uses*

**4.4 Vitamins and minerals**

**4.5 Functional components**

22% monounsaturated fatty acid, oleic acid (18:1). Monounsaturated fatty acids are healthy and have good oil stability [42]. Soybean oil possesses the two polyunsaturated fatty acids: linoleic acid (18:2), an omega-6 fatty acid, and linolenic acid (18:3), an omega-3 fatty acid [26]. They can be found in average concentrations of 53 and 8% of the oil, for linoleic and linolenic acid, respectively. Low (reduced) linolenic soybeans have half the linolenic acid level of standard soybeans, which reduces the need for hydrogenation, a process used in converting vegetable oils to

Soybean crude oil is also shown to consist of phospholipids, unsaponifiable material, free fatty acids, and metals. Unsaponifiable material consists of tocopherols, phytosterols, and hydrocarbons [27]. Tocopherols and phytosterols are considered as functional components. Soybean oil provides an additional benefit due to presence of enriched amounts of α-tocopherol or natural vitamin E. Oils containing low contents of linolenic acid (18:3) have been shown to contain high amount of

Soybeans contain water-soluble and oil-soluble vitamins. The water-soluble vitamins such as vitamin B1 (thiamin), vitamin B2 (riboflavin), vitamin B5 (pantothenic acid), and vitamin B6 (niacin) and the oil-soluble vitamins vitamin A and vitamin E (tocopherols) are present in soybean. Vitamin A mainly exists in the form of β-carotene in immature and germinated seeds, whereas it is present in negligible amount in mature seeds [27]. Most of the minerals are found in the meal fraction rather than in the soybean oil fraction. Dry soybean seeds contain on an average concentration ranging from 0.2 to 2.1% major minerals such as potassium, which is present in the highest concentration followed by phosphorus, magnesium, sulfur, calcium, chloride, and sodium [27]. Minor minerals found in soybeans include silicon, iron, zinc, manganese, copper, molybdenum, fluorine, chromium, selenium,

Functional components of soybeans include isoflavones, saponins, lecithin, trypsin inhibitors, lectins, oligosaccharides, tocopherols, and phytosterols [27]. Presence of such biological ingredient creates interest to consider soybean food products as functional foods, i.e., foods that contain biological components that deliver special health benefits, e.g., anticancer, hypocholesteromic, and antioxidative effects to the consumer [26]. Isoflavones are phytoestrogens and are known to have positive health effects such as the reduction of the risks for coronary heart disease, osteoporosis, certain types of cancer, and the moderation of postmenopausal symptoms in women [43]. Soybean possesses 0.1–0.4% of isoflavones on a dry weight basis; hence, soybean possesses the highest amount of isoflavones compared to all other crops [27]. The isoflavone concentration varies considerably depending upon the genotype and environmental conditions. It is thought that isoflavones are mainly responsible for most of the health benefits from soybean-based foods. Therefore, they gained more and more attention from the scientific world [27], and research on breeding for enhanced isoflavone content is increasing. Refined soybean oil possesses about 1000–2000 mg/kg. Tocopherol exists in four isomers, three of them being α-, ϒ-, and δ-isomers that are present in soybean oil. α-tocopherol (natural vitamin E) in soybean is the leading commercial source of this vitamin. Tocopherols protect the polyunsaturated fatty acids from oxidation; hence, they are

margarine that results in the production of unhealthy trans fatty acids.

α-tocopherol and results in lowered amount of ϒ-tocopherol [5].

cobalt, cadmium, lead, arsenic, mercury, and iodine [27].

antioxidants and used in pharmaceutical applications [42].

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Soybeans with large seed size and high protein levels are primarily used for soymilk and tofu production. Other traditional food from soybean includes tempeh, miso, soy sauce, okara, soynuts, soy milk, yoghurt, meat, and cheese alternatives. Tofu is perhaps the most widely consumed soy food in the world. Tofu is naturally processed and it retains a good amount of nutrients and phytochemicals such as the isoflavones [5]. Tofu typically contains 7.8% protein and 4.2% lipid on a wet basis [5]. It has a relatively low carbohydrate and fiber content, making it easier to digest. There are two main types of tofu: silken, or soft tofu and hard tofu. They are made by soaking whole soybeans and grinding them into a slurry with water. The slurry is cooked to form soymilk and a coagulant is added. The most commonly used coagulants are magnesium chloride, calcium sulfate, or glucono-D-lactone; the coagulants can be used purely or in combinations to achieve different flavor or textural characteristics. Heating is also usually applied in order to facilitate the coagulation. The result of the coagulation is that after a few minutes, the soymilk begins to curdle and large white clouds of tofu curd are formed. The water in the curds are then removed and placing the tofu curd in cloth-lined forming boxes where pressure is applied from the top results in the formation of hard tofu. Silken tofu in comparison to hard tofu is not pressed and is often coagulated in the container in which it is to be sold. [2].
