What's in the eggshell?

Eggshell is mainly composed of calcium carbonate, containing 9 1.96 ~ 95.76%. In addition, it also contains magnesium carbonate, calcium phosphate and colloid. The content of organic matter is about 3.55 ~ 6.45%, and there are several kinds of "pigments" in eggshells, mainly? ? ? (porphyrin) and so on.

Nutrients in eggs

All poultry eggs (including eggs) are acidic foods. An egg is covered with a thick layer of egg white, egg white or egg white after the shell and "inner membrane" are removed (called "phoenix coat" in Chinese medicine). Egg white consists of three layers, the outer layer and the inner layer are relatively thin, and the middle layer is relatively thick because it contains 0.3% mucin (accounting for 65% of the total weight of egg white). Every 100g contains about 10g of protein, 0. 1g of fat and 0. 3g of carbohydrate (see table 1 for details). According to the ratio of water and solid, the water content is 88% and the solid is 12%. About 90% of the solids are protein, including ovalbumin (75%), ovomucin (15%) and ovomucin (7%).

Ovalbumin is a phosphorus-containing protein containing 1.7% mannose. The sugar in ovomucin is a kind of "mixed sugar", accounting for about 9.2%, which consists of three parts of mannose and one part of galactose. Ovmucin also contains 14.9% mixed sugar, including mannose and galactose. Whole egg white also contains about 0.4% free glucose.

Egg mucin is also a mixture containing lysozyme, egg inhibitor, egg glycoprotein, vitellin and egg mucin.

Egg white contains little fat, but it also contains trace amounts of fat, such as lecithin, cholesterol and fat-soluble pigment lutein. Chicken protein has excellent nutrition, because it contains all the "essential amino acids", namely leucine (1 175 mg 100 g, the same below), isoleucine (639), methionine (433) and lysine (765438).

Chicken or egg yolk is wrapped inside. Water content per 100g is 53.3g, protein 13.6g, lipid 30g and carbohydrate1.3g. The protein contained in it is vitellin and vitellin, and the content ratio is about 3.6:. In addition, it also contains at least five saliva glycoproteins.

Black-bone chicken contains a lot of fatty substances, of which about 10% is phospholipid, and lecithin is the main component. The above-mentioned "egg yolk phosphoprotein" exists in egg yolk by combining with lecithin. Fatty acids in fatty substances are mainly oleic acid (46.7%), linoleic acid (19%), linolenic acid (2.9%) and saturated acid (3 1.4%). In addition, it also contains lipochrome and its isomers, free and bound glucose (about 0.3%), and a small amount of carotene (no more than 0.02 mg/ 100 g). Although the whole egg (together with egg white and yolk) contains 450~680 mg of cholesterol per 100 g, it is 65438+.

The main component of "egg shell" is calcium carbonate, containing 9 1.96 ~ 95.76%, in addition to magnesium carbonate, calcium phosphate and colloid. The content of organic matter is about 3.55 ~ 6.45%, and there are several kinds of "pigments" in eggshells, mainly? ? ? (porphyrin) and so on.

Basic nutritional components of eggs

I asked a nutrition expert, and he said that "it is basically calculated according to" every100g "of eggs, and it is rarely calculated according to" one "; Even if it is counted as "one", each one does not exceed 40 grams or 45 grams, and foreign nutritionists also measure it according to this standard. " I was curious, so I brought back a lot of eggs from other places. Actually, I have a lot of details in my heart. Fortunately, I was shocked by a test. The minimum weight of each egg is about 34.9 grams, and the maximum weight is 78.6 grams, especially for "egg-type" chickens (generally speaking, chickens are divided into egg type, meat type, egg meat type and ornamental type; Egg types are nested). One kilogram of eggs is only about 18~20, and the big one is about 12~ 14. Take the largest 78.6 grams. After removing 8.3 grams of eggshell and inner membrane, there are still 49. 1 gram of protein and 2 1.2 grams of egg yolk (both of them). It seems that this is not the case!

In addition to the difference in weight, the nutrients contained in "laying eggs" are naturally different, because chickens eat different things in different places. For example, eggs produced in Fujian contain 64 mg of calcium per100g, and eggs produced in Beijing contain 55 mg of calcium. What's more, the average calcium content of eggs produced in Hubei is only 3 1 mg. Another example is that the eggs laid by chickens in "non-goiter endemic areas" contain 97 micrograms (micrograms)/kg of iodine, while those in "goiter endemic areas" contain 63 micrograms/kg, with a minimum of 0.2 micrograms/kg; So are other metal elements and trace elements (such as iron, zinc, manganese, selenium, etc.). ). Even protein, fat and its heat energy are different (see Table 2 and Table 3 for details).

Contents of inorganic salts and trace elements in eggs.

Inorganic salts are mineral nutrients existing in the body and food, which are composed of organic substances (such as C) and inorganic substances. More than twenty kinds of essential inorganic salts have been found in human body, accounting for about 4 ~ 5% of human body weight. Among them, seven inorganic salts (> 5g) are sodium, potassium, chlorine, calcium, phosphorus, magnesium and sulfur, and their daily dietary requirements are all above 65,438+μ g ~ mg, which are called "macro elements", while others are low. With the development of modern analytical technology, iron, zinc and sulfur have been discovered by atomic absorption spectrometry and neutron activated plasma emission spectrometry. Among them, sodium and potassium are the most important cations in intracellular fluid, which can maintain water balance, osmotic pressure and acid-base balance in the body and strengthen muscle excitability; Calcium and phosphorus are not only the skeleton of human body, but also responsible for nerve conduction, the composition of some enzymes in the body, the changes of cell membrane and the main components of nuclear protein. Magnesium can maintain the stability of nucleic acid structure, activate various enzymes in the body and inhibit the excitability of nerves; Iron is the main component of hemoglobin, myoglobin, cytochrome and other enzyme systems, which can help oxygen transport. Without it, anemia will occur. Zinc can participate in the metabolism of nucleic acid and protein, and is a component of metal osprey containing zinc. Iodine is an important component of thyroxine. Without it, you can get simple goiter. If the mother lacks iodine, it will cause cretinism); Among children. Manganese can participate in normal osteogenesis and activate the ebony system of chondroitin sulfate synthesis. How many inorganic salts and trace elements can an "egg" get (average amount)? See Table 4 for details.

If "egg white" is simply extracted, it contains 19 mg of calcium, 16 mg of phosphorus and 0.3 mg of iron per 100 g; If "yolk" is simply extracted, it contains 134 mg of calcium, 533 mg of phosphorus and 7 mg of iron per 100 g.

Vitamin content in eggs.

Vitamins are low molecular weight organic compounds that maintain the normal function of human body. They can't be synthesized in vivo or in insufficient quantities. Although the demand is small, they must be supplied by food. Vitamins can be divided into fat-soluble and water-soluble. The former contains vitamins A, D, E and K (except vitamin K in eggs, others are found). Fat-soluble vitamins are insoluble in water, but soluble in fat. They coexist with lipids in eggs and are closely related to lipid absorption when absorbed in the intestine. When suffering from lipid malabsorption (such as biliary obstruction or long-term diarrhea), their absorption is greatly reduced. Water-soluble vitamins include B vitamins and vitamin C (unfortunately, there is no vitamin C in eggs), but there are many B vitamins, which can form various "coenzymes". For example, vitamin B 1, also called thiamine, can form thiamine pyrophosphate; Vitamin B2, also called riboflavin (riboflavin or riboflavin), can form flavin mononuclear cells? Acid (flavin mononucleotide) and flavin adenine dinuclear? Acid (flavin adenine dinucleotide); Vitamin B6, also called pyridoxine, can form pyridoxal phosphate; Vitamin B 12, also called cyanocobalamin, can form cobalamin coenzyme, etc.

: 1) vitamin e refers to α -tocopherol

2) "dry protein powder" contains 0.055 mg of p-aminobenzoic acid (PABA) per 100 g, while "dry egg yolk powder" contains 0.8mg； of the above substances per 100 g; It is a part of vitamin B complex, also known as vitamin Bx. Without it, it will cause premature gray hair.

Eggs, whether scrambled or boiled, will not lose too much vitamins. Suppose that a raw egg originally contained 0. 10 mg of thiamine, 0.27 mg of riboflavin and 0. 10 mg of nicotinic acid, and after frying (that is, shelling, beating, adding appropriate amount of salt, frying in oil for 1~ 1.5 minutes), it still kept 0. 5%. After boiling (boiling the whole egg in water for 10 min), the difference with the original content was limited, and the preservation rates reached 93%, 97% and 96%, with 0.09 mg, 0.27 mg and 0. 1 mg reserved.

Relationship between eggs and diseases

Generally speaking, "eggs" are of great help to our human nutrition. They can provide us with protein, metal elements and vitamins, and the heat generated can do all kinds of work. For example, an egg weighing 50 grams generates 3 18 kilojoules of heat energy, which can be used for walking for 32 minutes, cycling for 23 minutes or running for 15 minutes. If you say that once you get sick, you will increase your nutrition, which is inevitable, so you have an idea: it seems that "the more eggs you eat, the better"; In fact, this is not entirely correct.

For example, every100g of egg yolk contains nearly 2000 mg of cholesterol, and protein also contains about 650 mg. Obviously, patients with severe hyperlipidemia should eat something with low cholesterol, at most one egg, or only eat protein without egg yolk, such as liver failure and hepatic coma (hepatic coma; Patients with hepatic encephalopathy should never eat eggs, because each 100 g of egg white can produce 0.744 g of amine, and each 100 g of egg yolk can produce 2.560 g of amine, both of which can aggravate the disease (for example, an egg weighing about 55 g can produce approximately the following amounts of amine: histamine acid 169 mg, glycine. Patients with chronic renal failure, diabetic renal insufficiency and uremia should eat a "high-cost, low-protein diet", so they can only eat one egg or 40 grams of protein at most every day. When doctors tell patients that they need a "special diet" (such as a low-calcium diet, a low-phosphorus diet, a low-protein diet without creatinine, a calcium, phosphorus and sodium diet, etc.). ), they can only eat one or two eggs at most, instead of "the more eggs they eat, the better."

Gout is a disease caused by hereditary disorder of purine metabolism. In order to avoid ingesting foods with high exogenous purine content, such as lean meat, fish and poultry, 65,438+000 ~ 65,438+0000 mg of purine is contained in every 65,438+000 g of food, in addition to dried beans, lentils, spinach and reeds? Mushrooms and asparagus also contain 90 ~ 100 mg per 100 g, while an egg contains only 0.4 mg, so you can eat more.

If you don't eat eggs, you can use meat instead For example, an egg weighing about 50 grams can be replaced by 9 grams of lean meat and 5 grams of fat. Or use 25 grams of fat cattle, sheep and pork. 20g of sausage, 50g of shredded tofu, 20g of south tofu125g (20g of north tofu100g) and so on.

An egg a day is the most moderate nutrition.

Eggs are a very nutritious food. But there are some misunderstandings in eating eggs: some people think that "egg yolk contains high cholesterol, so I don't eat egg yolk, only eat protein"; Others think that you should not eat more than two eggs a day. How to eat eggs is the most scientific? Please listen to Dr. Chen Chaogang, head of the Nutrition Center of the Second Affiliated Hospital of Sun Yat-sen University.

One egg a day is enough.

Chen Chaogang said that eating an egg every day can help to supplement vitamins A, D and protein needed by human body and cholesterol and lecithin needed by brain, and can effectively prevent the lack of these nutrients. The China Residents' Balanced Diet Pagoda recommended by China Nutrition Society also suggests that everyone should eat half an egg (about 25-50g) every day.

Everyone eats more than one egg every day. For some people, such as pregnant women, wet nurses, young people with strong growth and development, or people with a large amount of labor, the impact is not too great, because these people need more energy and consume more, so they can consume this part of energy. But for the elderly and people with little activity, if you eat a few eggs every day for a long time, you will need less energy every day. If you add high fat, you can't consume this part of energy, which will eventually lead to excessive body load and more fat deposition, which will lead to hyperlipidemia.

People with mild hyperlipidemia, people who need to lose weight and control their food intake, the elderly can eat less eggs, but they have to eat 2-3 eggs a week.

It is enough to eat half an egg a day.

Egg yolk has higher nutritional value.

When it comes to egg yolk, many people's first reaction is high cholesterol. Chen Chao just emphasized: "Eating half an egg to an egg every day is definitely a whole including egg white and yolk. If you only eat egg white and don't eat egg yolk, it is better to eat only half an egg white and egg yolk. "

In fact, protein and yolk are a perfect combination with different nutritional values. Many foods, such as soybeans, tofu, and meat, have less nutrients that are beneficial to the human body.

Some people think that hypercholesterolemia is caused by eggs. In fact, the disease of high cholesterol is not caused by eggs, but by eating too much fried, fried food and meat with more saturated fat. Chen Chaogang explained that hypercholesterolemia can also be caused by foods with high cholesterol. Although eggs are foods with high cholesterol, the human body needs 300mg of cholesterol every day, and an egg has about 2 10mg of cholesterol, so eating an egg does not exceed the required value. On the contrary, the cholesterol content of pig brain, pig liver and other animal viscera is higher than that of egg yolk. In addition, more than 70% of the cholesterol in human blood is self-synthesized, not the cholesterol in foreign food. Therefore, eating egg yolk is not directly related to hypercholesterolemia.

In addition, egg yolk is also a contradictory unity. On the one hand, it contains cholesterol, on the other hand, it contains lecithin, which can emulsify fat, inhibit cholesterol deposition and prevent arteriosclerosis. If you don't eat egg yolk, where can you get lecithin to inhibit cholesterol deposition?

Chen Chaogang said that if you pay attention to nutrition, you should eat egg white and egg yolk together. If you only eat egg white and discard egg yolk, then simply drink soy milk and skim milk instead of eggs. If you really don't like eggs, protein in eggs can be supplemented by skimmed milk, lean meat and fish, while pork liver contains vitamins A and D and cholesterol in eggs, vitamin B2 can be absorbed from meat, and lecithin can be obtained from soybeans.

It is not advisable to eat eggs raw.

Chen Chaogang also made it clear: Don't eat raw eggs. Because there is antitrypsin in raw eggs, it will affect the absorption of protein; Although the surface of eggshell looks tight, in fact, eggs contain many bacteria, such as salmonella. Eating raw eggs may cause diarrhea and even food poisoning.

Others like to eat "sunny side up" eggs, that is, half-cooked eggs. In fact, the nutritional value of this kind of egg is not high. Because the internal structure of the egg has not been completely decomposed by high temperature at this time, it will not be absorbed by the human body. At the same time, some bacteria need higher temperature to kill.

Therefore, it is best to cook eggs, which is the most nutritious and the safest to eat. Cooking methods of eggs include boiling, custard, egg drop soup and baked egg rolls.

Eating an egg every day helps to supplement vitamins A, D and protein needed by the body and cholesterol and lecithin needed by the brain, and can effectively prevent the lack of these nutrients.

How to cook eggs that are easy to shell?

There is a protective film in the eggshell of an egg. After the eggs are cooked, the film is destroyed. When boiled eggs are put into cold water, the interior of the eggs shrinks violently, and a vacuum gap is formed between the protein and the eggshell. Bacteria and viruses in water are easily absorbed into this gap of eggs by negative pressure.

To make boiled eggs easy to peel, the best way is to put a little salt when boiling eggs, and the cooked eggshells will be easy to peel off. Soak the eggs in cold water first, and then cook them in hot water. Eggs are not easy to break when cooking, and eggshells are easy to peel off.

When cooking eggs, don't burn too much, because eggs are divided into three layers: yolk, egg white and eggshell. The freezing temperature of egg yolk is 68℃ ~ 765438 0℃, and the freezing temperature of egg white is 62℃~64℃. If the fire is too big when cooking eggs, the egg white with low freezing temperature outside the yolk will solidify and harden quickly, thus preventing the heat from continuing to transfer to the yolk and affecting the solidification of the yolk with high freezing temperature. If boiled for too long, the eggshell is easy to peel, but protein can call it denaturation, and it becomes hard and unpalatable, which affects digestion and absorption.

How to cook eggs with high nutritional value

Take eggs for example. Eggs cooked for less than 10 minutes have the highest digestibility and almost no loss of nutrients. When cooking eggs, you should master the following skills to prevent nutrient loss. Boiling water must submerge the eggs. Otherwise, the protein in eggs is not easy to solidify where water is not soaked, which affects the protein digestibility; Eggs also contain avidin and antitrypsin, which are not completely destroyed. The former can cause vitamin H deficiency in human body; This affects protein's digestion.

Soak the eggs in cold water for a while before cooking to reduce the air pressure in the eggs; Then boiled in cold water, it can prevent the eggshell from breaking and avoid the loss of nutrients. After the eggs are cooked, cook for 5 minutes and soak for 5 minutes after the fire stops. In this way, the egg white in the egg is only denatured and solidified, and the digestibility is the highest, and all nutrients are basically not destroyed, so the nutritional value is high.

If the egg is boiled in boiling water for too long (more than 10 minute), a series of chemical changes will occur inside the egg. For example, protein in eggs contains more methionine. Methionine can be decomposed into sulfide after long-term heating, which reacts with iron in egg yolk to form green or gray-green iron sulfide around egg yolk, which is not easy to be absorbed and utilized by human body and reduces the nutritional value of eggs. When eggs are cooked for a long time, the structure of protein becomes more compact, which makes it difficult to contact with protein digestive enzymes in gastric juice and more difficult to digest.

Therefore, eggs can neither be boiled half-cooked nor boiled for too long. Generally, after the water is boiled, it cannot exceed 10 minutes at most.

In addition, it is not advisable to throw boiled eggs into cold water for cooling. Because there is an air chamber with a diameter of 4 ~ 1 1 mm in the egg, when the egg is cooked, the air pressure in the air chamber will also increase with the increase of temperature, and then the gas in the air chamber will be squeezed out of the egg. When boiled eggs are put into cold water, the temperature drops sharply, and the pressure in the air chamber drops accordingly, which will make cold water and microorganisms outside the eggshell enter the eggs through air holes, and the cooked eggs will be polluted again.

After the boiled egg is taken out, you should wipe the water on the surface of the eggshell with a clean rag and let it cool naturally, which is not only easy to peel, but also hygienic.

Egg instant noodles)

Stove: microwave oven [working normally]

Tools: a microwave lunch box, a knife and chopsticks.

Ingredients: a bag of instant noodles [optional], a boiled egg, a small ham sausage, a small tomato and a small garlic sprout.

Exercise: [done in the office kitchen]

1. Take out the instant noodles, add all seasonings and soak them in boiling water first;

2. Wash tomatoes and garlic seedlings, chop them with a knife and sprinkle them on instant noodles;

3. Cut the boiled eggs and ham sausage, which can be eaten quickly and covered with instant noodles; Cover and soak for 3 minutes;

4. Put it in a microwave oven and heat it for 3 minutes, then take it out;

Boiling eggs is learned.

A few years ago, I went to Germany for an internship and found that there were not only two piles of eggs, but also "3" and "5" marks on the buffet table of star-rated hotels or ordinary small hotels. The waiter in the restaurant told us that "3" means that the eggs are boiled for 3 minutes, and "5" means that the eggs are boiled for 5 minutes.

After returning home, do the experiment: wash the fresh and undamaged eggs, put them in cold water in the pot, boil them for 3 or 5 minutes, then take them out and cool them. "3-point egg", the egg white is cooked and soft, and the yolk is just cooked and slightly cooked. "5-point egg", the egg white is cooked and tender, and the yolk is cooked but not hard.

According to nutritionists, eggs cooked at different times take different time to digest in the human body. "3-minute egg" is a lightly cooked egg, which is the easiest to digest and takes about 1 hour for 30 minutes. "5 minutes" eggs are half-cooked, and the digestion time in human body is about 2 hours; Eggs boiled for too long take 3 hours to digest in the human body.

"Five-point egg" is not only soft and tender, but also rich in egg fragrance, which is beneficial to human nutrition. The American medical community published a research report. Twenty-four adults eat two half-boiled eggs every day. After six weeks, the blood lipid did not increase, but the good cholesterol (HDL) which is beneficial to human body increased by 65,438+00%.