A family of dicotyledonous plants, subclass Rosa. The fruits are pods with various shapes, and the roots often have nodules that can fix nitrogen. The leaves are alternate, rarely opposite, and usually have one or two pinnate leaves. There are about 650 genera and 18,000 species, widely distributed all over the world. Woody species are mainly distributed in the tropics and subtropics, while temperate areas are mostly herbs and dwarf shrubs. China produces about 1,500 species in 172 genera, which are distributed in all provinces and regions. Among them, Alpine Bean and Winter Bean are endemic to China.

Nutritional value of beans and bean products

Beans include the edible seeds of various leguminous plants, among which soybeans are the most important, including red beans, mung beans, and peas , broad beans and other miscellaneous beans. The structure of beans and cereal seeds is different. Their nutrients are mainly in the cotyledons inside the seeds. Therefore, removing the seed coat during processing does not affect the nutritional value.

1 Nutritional characteristics of soybeans

Soybeans include soybeans, green soybeans, black soybeans, white soybeans and other varieties, among which soybeans are more common. The protein content of soybeans reaches 35% to 45%, making it one of the crops with the best protein quality and quantity among plants. Soy protein is high in lysine, but methionine is its limiting amino acid.

The lysine content of soybean protein is more than twice that of cereal protein. If eaten together with cereals lacking lysine, the complementary effect of protein can be achieved, so that the biological value of the mixed protein reaches that of meat. Proteinoid levels. This feature is particularly important for people who cannot consume enough animal foods for various reasons. Therefore, the consumption of legumes should be strongly promoted in my country, where cereals are the staple food.

The fat content of soybeans is 15% to 20%, and they are traditionally used to produce soybean oil. The unsaturated fatty acid content in soybean oil is as high as 85%, the linoleic acid content is more than 50%, the oleic acid content is more than 30%, and the vitamin E content is also very high. It is an excellent edible oil. Its yellow color comes from carotenoids. The linolenic acid content in soybean oil varies according to different varieties, mostly between 2% and 10%. Varieties with low linolenic acid, high oleic acid and linoleic acid are popular because soybean oil with high linolenic acid is prone to oil oxidation and is unfavorable for processing and storage. Soybeans contain more phospholipids, accounting for 2% to 3% of the fat content. During the refining of soybean oil, most of the phospholipids are separated and become the main source of phospholipids in food processing.

Soybeans contain 25% to 30% carbohydrates, of which about 50% are raffinose and stachyose that cannot be digested by the human body. In addition, there are polysaccharides composed of arabinose and galactose. They can be fermented by microorganisms in the large intestine to produce gas, causing abdominal distension. But it is also a growth-promoting factor for bifidobacteria in the intestine, so it does not harm health. During the processing of soy products, these sugars are dissolved in water and essentially removed, so eating soy products will not cause severe bloating.

Various B vitamins in soybeans are relatively high. For example, the content of vitamin B1 and vitamin B2 is more than twice that of flour. Soybeans contain a small amount of carotene. However, dry soybeans do not contain vitamin C and vitamin D.

Soybeans are rich in minerals, with a total content of 4.5% to 5.0%. The content of calcium is higher than that of ordinary cereals, and the content of trace elements such as iron, manganese, zinc, copper, and selenium is also higher. In addition, beans are a type of alkaline food with high potassium, high magnesium, and low sodium, which is beneficial to maintaining the acid-base balance of body fluids. It should be noted that the bioavailability of minerals in soybeans is low, such as iron, which is only about 3%.

In addition to nutrients, soybeans also contain a variety of health-promoting substances, such as soysaponins, daidzein, soybean sterols, soybean oligosaccharides, etc.

2 Nutritional value of other legumes

In addition to soybeans, other legumes also have high nutritional value, including red beans, mung beans, broad beans, peas, cowpeas, and kidney beans , lentils, etc. They are low in fat and high in starch and are called starchy dry beans.

Starchy beans have a starch content of 55% to 60% and a fat content of less than 2%, so they are often incorporated into grains.

Their protein content is generally above 20%, and their protein quality is good and rich in lysine, but not enough in methionine, so they can also play a nutritional complementary role with cereal foods. The content of B vitamins and minerals in starchy dry beans is also relatively high, which is equivalent to that of soybeans.

In addition to being rich in protein and minerals, fresh beans and bean sprouts also have high levels of vitamin B1 and vitamin C; they are often included in vegetables.

3 Anti-nutritional factors in beans

Various beans contain some anti-nutrients, which are not conducive to the absorption and utilization of nutrients in beans, and are even harmful to human health. . These substances are collectively called antinutritional factors.

A variety of beans contain protease inhibitors, which can inhibit the activity of trypsin, pepsin, chymotrypsin and other proteases in the human body. Among them, soybean trypsin inhibitors are the most studied. Due to the presence of these substances, the protein digestion and absorption rate of raw soybeans is very low. Heat treatment in water deactivates this substance. Hemagglutinin is also found in many legumes. It is a type of glycoprotein that can specifically bind to the red blood cells of the human body, causing red blood cells to agglomerate, and has certain toxicity to the human body. Appropriate moist heat treatment can inactivate this protein, and protease treatment can also break it down.

The large amounts of phytic acid contained in beans can hinder the absorption of calcium and iron; soybeans are also rich in lipoxygenase, which is not only one of the causes of the beany smell, but also causes It is easy to cause oxidative rancidity of unsaturated fatty acids and loss of carotene.

The oligosaccharides contained in beans are fermented by large intestinal bacteria and produce carbon dioxide, methane, hydrogen, etc., which can cause abdominal distension and discomfort. In the past, they were also treated as anti-nutritional factors. In fact, they are harmful to nutrient absorption. There is no hindrance to collecting.

4 Nutritional Value of Soybean Products

Soybeans are widely used in food processing. In addition to being traditionally used to make various soy products, they can also be added to a variety of foods. , improve its nutrition or quality.

Traditional soy products are represented by tofu, which retains most of the advantages of soybeans. It is not only easier to digest than whole soybeans, but also removes various anti-nutritional factors that are harmful to humans. It has always been a favorite food of our people. .

Soy products are rich in protein, and their content is equivalent to that of animal foods. For example, the protein content of dried tofu is equivalent to beef, reaching about 20%; the protein content of soy milk and soy milk is close to cow's milk, between 2% and 3%; the protein content of water tofu is between 5% and 8%, which is equivalent to that of pig. pork belly; the protein content of yuba reaches 45% to 50%, which is equivalent to beef jerky.

At the same time, soy products contain a certain amount of fat, but these fats are high-quality vegetable oils, which are rich in essential fatty acids and phospholipids, do not contain cholesterol, and are beneficial to human health.

The water-soluble vitamins in soybeans are greatly lost during the production of tofu, which is manifested in the decrease in the contents of thiamine, riboflavin and niacin.

Soy products are a good source of minerals. Soybeans themselves contain a lot of calcium, and tofu uses calcium salt as a coagulant. Therefore, tofu has a high calcium content and is an important source of calcium in the diet. The trace elements in soybeans are basically retained in soy products.

Vegetarians often use soy products to replace animal foods. What needs to be noted is that these foods are rich in protein, unsaturated fatty acids and B vitamins, but compared with animal foods, soy products It does not contain vitamin B12, and the iron content and bioavailability are not as good as meat, which can be improved through nutritional fortification.