Nutritional value of preserved eggs
The nutritional components of preserved eggs are quite similar to those of ordinary eggs, and the curing process has experienced the action of strong alkali, so protein and lipids are decomposed, which is easier to digest and absorb, and cholesterol is reduced. It is cured with iron agent, so the iron content is also high. However, vitamin B and essential amino acids were destroyed.
Are preserved eggs more nutritious?
Songhua preserved eggs are characterized by white needle-like crystals in protein, which some people think are particularly nutritious. This is because iron phosphate is added in the processing. Therefore, compared with ordinary preserved eggs, only the iron content is higher, and there is no difference in other nutrients.
How to buy preserved eggs?
At present, preserved eggs on the market are duck eggs or preserved eggs, which can be selected according to personal preferences. When buying preserved eggs, you can pay attention to whether there is a quality certification mark. In addition, preserved eggs with high lead and copper content will have more spots on the eggshell surface, and after hulling, you can also see that the protein is dark green or occasionally has black spots, which is not suitable for purchase. Some preserved eggs made by traditional methods will be covered with red soil and straw, which is unsanitary and inconvenient to judge the lead content by appearance, and is not suitable for purchase. It is recommended to buy products with complete packaging and clear labels. Pay attention to the date of production when buying, and pay attention to the way and period of preservation when going home to save.
Does preserved egg contain lead?
In the traditional preserved egg making process, heavy metals such as lead or copper are often added to the dipping solution to solidify protein. According to the regulations of Taiwan Province Provincial Health Department, the lead content of preserved eggs should not exceed 2ppm, and the copper content should not exceed 8ppm. Moreover, agricultural administrative units also help manufacturers to produce excellent preserved eggs, so that the lead content does not exceed 0.3ppm and the copper content does not exceed 5ppm. Therefore, most of the soaking solutions of qualified manufacturers do not add heavy metals or have little content.
Now that there are lead-free preserved eggs, let's introduce them again:
Many people know that preserved eggs contain lead, so people buy lead-free preserved eggs and think they can eat them safely. In fact, lead-free preserved eggs also contain lead, which is ok for adults, but children should eat less.
When processing preserved eggs, soda ash, lime, salt and yellow lead powder should be mixed in a certain proportion, and mud and bran should be wrapped outside the duck eggs. Two weeks later, the delicious preserved eggs are ready. Plumbum preparatium powder is lead oxide, which can make eggs produce beautiful patterns, but with Plumbum preparatium powder, preserved eggs will be polluted by lead. According to the national regulations, the lead content of preserved eggs per1000g should not exceed 3mg, and preserved eggs that meet this standard are also called lead-free preserved eggs. Therefore, "lead-free preserved eggs" are not lead-free, but lead content is lower than the national standard.
Chinese medicine believes that children's bodies are "young yin and young yang" and their metabolism is extremely vigorous. Trace lead in "lead-free" eggs will remain in tissues such as liver, lung, kidney, brain and red blood cells after being absorbed by children, and will also cause calcium loss in bones and teeth. Regular consumption of "lead-free preserved eggs" will cause bone and tooth dysplasia, loss of appetite, gastroenteritis and so on. In children, it will also affect intellectual development. Lead-free preserved eggs are delicious and nutritious, but children are in a stage of vigorous physical development and have obvious reactions to the harm of lead, so it is better to eat less.
Supplement:
Harm of lead to human body;
1. Extreme neurotoxicity: Lead can damage the brain and nerves, making people mentally retarded, unresponsive, hyperactive, inattentive, hearing impaired, learning difficulties and dyskinesia.
2, cause anemia
3. Suppress immunity
4. Loss of appetite, unexplained abdominal pain, vomiting, diarrhea or defecation.
5, affect the absorption and utilization of minerals and vitamins. Lead to calcium deficiency, zinc deficiency, iron deficiency and so on.
But eating preserved eggs can also be toxic.
Summer is hot, and most people like to entertain themselves with preserved eggs when drinking beer, or treat the whole family with cold preserved eggs. It may never occur to them that preserved eggs may also cause food poisoning.
According to the inspection and analysis of relevant food experts, there are only 400-500 bacteria on clean eggshells, while there are as many as10.40-0.40 billion bacteria on dirty eggshells. If these bacteria enter the egg in large quantities through the pores of the eggshell, eating such preserved eggs will be poisoned. When buying preserved eggs, it should be noted that the protein of preserved eggs is dark brown transparent body after peeling, which has certain toughness; Contaminated preserved eggs are light green, with poor toughness and easy loosening. Such preserved eggs must not be eaten.
Salmonella is the main bacterium that pollutes preserved eggs. After it enters the human body with preserved eggs, it causes inflammation on the intestinal trace membrane. After bacterial division, it will produce highly toxic endotoxin, which will cause poisoning symptoms.
Experiments have confirmed that Salmonella will die immediately at a high temperature of 100 degrees Celsius, at 70 degrees Celsius for 5 minutes, and at 60 degrees Celsius 15-30 minutes. Therefore, when eating suspicious preserved eggs, you can steam the shelled eggs at high temperature for about 5 minutes, and then you can eat them safely after cooling. The suitable temperature for the growth of Salmonella is 20℃-37℃, and the temperature in summer and autumn is just within this range, so people should pay special attention to prevent preserved egg poisoning.
The main symptoms of preserved egg poisoning are nausea, vomiting, headache, dizziness, abdominal pain and diarrhea.
Many people like to eat preserved eggs and meat porridge, but it's okay to eat less preserved eggs, and it's not good for your health to eat too much.
Because preserved eggs are made of duck eggs wrapped in soda ash, lime, salt and lead oxide, duck eggs contain lead, which may cause lead poisoning if eaten frequently. This will lead to insomnia, inattention, anemia, joint pain, mental retardation, brain function and other symptoms. In addition, lead will replace calcium, affect calcium intake, and may also cause calcium deficiency.
How to eat preserved eggs:
1. Eating preserved eggs with ginger vinegar juice can not only neutralize the alkalinity with gingerol and acetic acid to remove the astringency of alkali, but also use the volatile oil and acetic acid contained in ginger vinegar juice to destroy a toxic substance used in the production of preserved eggs, namely, plumbum preparatium powder, and substances harmful to human body generated during the protein decomposition of preserved eggs.
Teach you three ways to distinguish preserved eggs
(1) Appearance identification.
Observe whether its appearance is complete, damaged or mildewed. You can also feel its elasticity with your hands, or shake an egg to listen to its sound. The surface of a good preserved egg is completely covered with mud, without mildew spots, and the eggshell is intact without damage after peeling off the covering; Elasticity after peeling; There is no bump when shaking. The packaging materials of inferior preserved eggs are damaged or moldy; After peeling off the wrapping material, the eggshell has spots, damage and leakage, and some contents have been polluted; After shaking, there is a sound of water swinging or a feeling of light floating.
(2) Identification by optical transmission.
After peeling off the package, the preserved eggs were identified according to the light transmission method of fresh eggs, and the color, solidification state and air chamber size of the eggs were observed. The contents of inferior rubber balls are not solidified, but watery, with a large air chamber.
(3) Have a taste.
The whole preserved egg is solidified, not sticky, clean and elastic, translucent and brown, with loose patterns and textures; When the egg is cut vertically, you can see that the yolk is light brown or light yellow with a thin center. Inferior preserved eggs have a pungent or musty smell.
Self-made health preserved eggs
Source: Publication date: 2005- 10- 15.
Health preserved eggs do not contain lead poisoning, and are rich in various amino acids and trace elements needed by human body. Rich in nutrition and delicious. The processing method of health preserved eggs is introduced as follows:
(1) Choose fresh poultry eggs (chicken, duck, goose and quail eggs) as raw materials. Cracked eggs, scattered yellow eggs, steel shell eggs and sand shell eggs are not suitable. Fresh eggs can't be washed with water, and dirty eggs can be wiped with cloth.
(2) Put quicklime, soda ash and salt into a container, add boiling water, stir for 30 minutes, after cooling, add zinc oxide, iron oxide, potassium iodide, Gynostemma pentaphyllum and selenite, and mix evenly to form powder. Put 500 grams of powder into a plastic container, add 7 kilograms of cold boiled water, stir evenly with a wooden stick, and use it after all the bubbles in the soaking agent disappear.
(3) According to the ratio of 100 duck eggs or 120 eggs prepared with 500g soaking agent, put fresh eggs into jars, cans, plastic bags and other containers. Pour the prepared soaking agent into the container, completely submerge the eggs, seal the container, and place it under the backlight, keeping the temperature above 20℃, and the eggs can be stored for about 10 day. Mature preserved eggs are washed and dried with cold boiled water, and kept in plastic bags or jars, which can be taken with you. Preserved eggs usually bloom in about 30 days, and the finished products will not deteriorate after being stored for about one year.
Homemade preserved eggs
Preserved eggs are the traditional food of our people. Because of its unique flavor, excellent taste, long shelf life and convenient carrying, it is favored by people.
The process of processing fresh eggs into preserved eggs is essentially a complex chemical reaction process. Although there are many formulas and techniques for processing preserved eggs, the main raw materials generally include: calcium oxide (CaO), soda ash (Na2CO3), plant ash (mainly K2CO3), salt, benzene leaves and so on. Based on the actual situation of students, this paper takes two preserved eggs as examples to explain how to process preserved eggs in the laboratory and the chemical principle:
Length grey material formula
The preserved eggs on the dining table are delicious, but they are covered with an ugly coat. Don't underestimate it, it is the key to making preserved eggs, and this is ash. The formula of the ash material is: 50g of quicklime, 3g of soda ash, 2g of plant ash 1 g, 2g of salt, 20g of water and trace of tea.
2. Grey material modulation
According to the requirements of ash formula, put the required ash into a container (just a big beaker) and mix it with water. Quicklime first reacts with water to produce hydrated lime, which then reacts with potassium carbonate, the main component of soda ash and peat, to produce sodium hydroxide and potassium hydroxide respectively. The chemical equation of this reaction is expressed as follows:
Calcium oxide +H2O = calcium hydroxide
Ca(OH)2+Na2CO3=CaCO3↓+2NaOH
Ca(OH)2+K2CO3= CaCO3↓+2KOH
In order to make the substances in the hair fully react, it needs to be prepared for 24 hours before use.
3. Preserved egg processing
Roll fresh eggs in the prepared ash several times, so that the surface of the eggshell is evenly coated with a layer of ash powder, and then take them out and roll them several times to form rice chaff or sawdust, so that a layer of rice chaff or sawdust is adhered to the ash. Squeeze it gently by hand to make it tight, and put it into a container prepared in advance. The second fresh egg is also treated in this way. The container is sealed and placed at ambient temperature 18 ~ 24℃. /kloc-you can eat it in 0/0 days.
On the day of 10, the inside of the egg is not as calm as a deep pool. The strong alkali (NaOH, KOH) in the ash material penetrates into the egg white and egg yolk through the eggshell, and reacts with protein in the egg white and egg yolk, so that protein decomposes, solidifies and releases a small amount of hydrogen sulfide (H2S) gas. At the same time, the infiltrated alkali will further neutralize the amino acids decomposed by protein, and the crystals of the generated salt will precipitate in the preserved egg protein of the gel peptide, resulting in a white "pine flower" (which is also the reason for the name of preserved egg). However, hydrogen sulfide gas reacts with minerals in egg white and egg yolk to generate various sulfides, so the colors of egg white and egg yolk have changed, with egg white showing a special dark brown color and egg yolk showing a dark green color. Salt can make preserved eggs shrink out of the shell and add flavor. Tannin and aromatic oil in tea can color the solidified protein and increase the flavor of preserved eggs.
And why don't preserved eggs go bad for half a month or even months? First, because there is salt in it, salt has antiseptic effect; First, alkaline substances kill bacteria in fresh eggs that may lead to protein's spoilage.
10 days later. When you sit at the table and taste this delicious preserved egg, your heart will be filled with joy, and you will think about when to cook more. But next time you are ready for mass production, don't forget to change the formula of ash in proportion.