Will slow-cooking meat for several hours or even more than ten hours produce more amino acids or purines?

A few friends have been asking me about slow cookers lately.

A said: Several elderly people in the hospital watched a health program and bought the electric stew pot promoted in the program, which said that stewing meat for 12 hours can produce amino acids. My father is over 90 years old and I also want to buy one. The elderly usually have a very poor stomach and can only eat fish, but cannot digest red meat. I would like to ask you, can slowly stewing meat for a long time really produce amino acids? Is it really beneficial to eat it?

B Question: After chemotherapy for cancer, my relative couldn't even digest soft-boiled chicken. Someone suggested using an electric stew pot to stew beef with tendons overnight, saying that it can replenish the patient's body. But won't the nutrients be lost if it is stewed for such a long time?

C Question: My mother likes to use the electric soup cooker that can be used for several hours to stew fish and meat. She says that the soup is delicious. But if the soup is cooked for a long time, will there be more purine in the soup?

Let me summarize the questions first. There are roughly 5 questions:

1 Is meat easier to digest after slow cooking? Why?

2 Will the amino acids be released after slow-cooking meat?

3 Is the broth cooked in a slow cooker really delicious? Does it contain higher levels of purine?

4 If meat is stewed for a long time, will the nutrients be lost due to heat?

5 Who is suitable for using meat cooked in a slow cooker to increase nutrition?

Then let’s talk about the reasons one by one.

For those who are not interested in reading the explanation, please read the answer at the end of the article.

Question 1

Is meat easier to digest after slow cooking?

The major difference between a slow cooker and an ordinary pot is that it heats up very slowly. Not only does it take a long time to heat from 20°C to above 60°C, but it also stays at 60°C to 90°C for a long time before finally reaching a temperature close to boiling. During this slow heating process, the various enzymes inside the meat have ample time to become active .

Although meat has been separated from animals, it still has "live" tissues in which various enzymes can act. At temperatures below 60°C, the activity of enzymes increases as the temperature rises.

Enzyme is a kind of protein. Most proteins will "denature" at around 60°C. Denaturation means the loss of natural active structure, and the enzyme will gradually become inactive.

The protease in meat tissue will slightly hydrolyze the protein in muscle fibers (this is the basic principle of using papain to make meat tenderizer). At the same time, slowly heating the temperature can reduce the problem of hardening and water loss during the cooking process of the meat, making the meat appear more tender.

The human body cannot directly absorb large molecular proteins. The process of human digestion of protein is to first chew the meat, then use digestive enzymes to cut the food protein into pieces, and finally cut it into individual amino acids, as well as small peptides composed of two or three amino acids, which are then absorbed into the blood and used to assemble the body's own proteins.

Muscle tissue is usually covered with a thin layer of collagen. Many people have heard that collagen cannot be digested by the human body, which is true. However, the "gelatin" decomposed from collagen can be digested.

Heating the meat to 70-90℃ for a long time will have a wonderful effect. Although this temperature can kill the enzyme activity, it can also unwind the helical structure of collagen and turn it into gelatin. At this time, the meat will no longer have the problem of "getting stuck in the teeth" because the tendons inside are all soft. Part of the gelatin dissolves in the soup, and the soup can become jelly after cooling.

At the same time, if less water is added, the protein that is slowly cooked at a lower temperature can better retain moisture and will not shrink together, so the meat tastes more tender. Studies have shown that braised pork protein that is stewed at high temperature will aggregate excessively, and the digestibility after in vitro simulated digestion treatment is low, while meat that is slowly stewed at 65°C for 8 hours has the highest digestibility and is more easily broken down into small peptides under the action of proteases [1]. However, further extending the heating time will not produce better results.

Mr. Dongpo said that stewing meat should be done with "slow fire and less water, and it will be delicious when the fire is enough". The first secret is to "slow fire". Slower heating is conducive to tenderizing meat, softening tendons, and producing umami components. If the fire is too strong and the temperature is raised too quickly when stewing meat, these benefits will be lost.

In short, if the protein in the meat is gently cut with protease first, and the texture becomes softer and easier to chew, the meat will of course become easier to digest.

Question 2

Will the amino acids be released when meat is slow-cooked?

Meat already has a small amount of free amino acids, peptides, and soluble proteins that can be dissolved. It doesn't take 12 hours, just one or two hours of stewing time, and basically all that can be dissolved will come out . However, if the temperature is raised slowly, the amount of amino acids that can be dissolved will really increase.

This is because if the temperature rises very slowly, the protease in the meat tissue will work for a long enough time, and after the muscle protein is chopped up, more amino acids and small peptides will be released. They are all water-soluble and will run into the soup.

This is the origin of the claim that some slow cookers "cook out amino acids." Although it is not very accurate, it is not completely wrong.

A study compared the effects of cooking chicken soup using a four-stage heating method [2], and studied the effects of different heating rates and holding times. The study found that the best heating rate was 0.43°C/min, and the best time was to lower the temperature to 95°C and hold it for 40 minutes after boiling. Slow heating can prevent the outer layer of protein from coagulating quickly, allowing more time for the soluble components and umami substances inside the meat to fully dissolve .

The question is, for people who are healthy and have normal digestive abilities, they can digest protein in their gastrointestinal tract, so why only eat amino acids?

It's like a person with normal chewing ability. Why should he use a blender to grind all his food into a "easy to digest" paste to drink every day? Therefore, not everyone needs a slow cooker, let alone a 12-hour electric cooker that "stews out a lot of amino acids".

On the other hand, if you want to eat meat, the longer the stewing time, the better the delicious effect. You should also use less water when stewing the meat. Generally speaking, the meat will be soft and rotten after stewing for two or three hours. If the temperature rises too slowly and the softening takes too long, more amino acids will be released, but the meat will lose its taste. After the umami substances and gelatin are dissolved into the soup, the meat will become tasteless dregs and the aroma will also dissipate.

Question 3

Is broth better in a slow cooker? Is it higher in purines?

Many people have heard that adding chicken essence will increase the purine content in the soup. However, "pure natural" stewed soup is still high in purine.

Some of the amino acids and small peptides dissolved during the stewing process have umami taste. During the slow heating process, nucleases will also decompose the genetic material in the cells to produce umami nucleotides. However, the products of nucleic acid decomposition include purines. Moreover, inosinic acid and guanylic acid, two purine-containing compounds, have umami taste. Therefore, in theory, the broth cooked slowly will taste better.

Fish, meat, poultry, and mushrooms can all be slow-cooked with water. However, the optimal slow-cooking time for each ingredient is different , and fish requires a shorter time than meat[3]. Studies have shown that the appropriate heating conditions for pork shank bone soup are: a heating rate of 2.4℃/min, a constant temperature time of 20 min, and finally a heat preservation at 80℃ for 50 min[3]. Heating for too long will also deteriorate the flavor, especially if the boiling time is too long, the aroma will be lost, and the fat oxidation reaction will increase, generating oxidation products with bad smells.

A study used HPLC to measure the nucleotides in chicken soup cooked in different ways [4]. The results showed that the inosinic acid content of the chicken soup samples was between 21.57 and 28.04 mg/100g, the adenylic acid content was between 6.62 and 9.13 mg/100g, and the guanylic acid content was between 2.38 and 3.14 mg/100g. As the cooking time increased, the inosinic acid and adenylic acid content in the electric stew pot chicken soup showed a trend of first decreasing and then increasing. The inosinic acid content in the chicken soup cooked in a pressure cooker was lower than that in the electric stew pot, and there was no significant difference in other nucleotides. The analysis of flavor substances confirmed that the flavor of slow-cooked chicken soup was better than that of chicken soup cooked in a pressure cooker .

It can be seen that slow-cooked soups do contain more purine. The thicker and more delicious the soup, the higher the purine content may be.

However, on the other hand, purine is also a normal component of human cells, and healthy people do not need to limit their purine intake . Some infant formula even specifically adds these components that build nucleic acids. Only when there is a problem with uric acid metabolism, do we need to consider the purine content in the broth.

Question 4

If you stew meat for a long time, will the nutrients be lost due to heat?

Meat contains 8 kinds of B vitamins. They are water-soluble and will dissolve into the soup, so it is not a loss. Just drink the soup.

Some vitamins are not afraid of heat, such as niacin, which is very stable. Vitamin B2 and biotin do not lose much at normal heating temperatures. However, some B vitamins are afraid of heat, and the most delicate ones are folic acid and vitamin B1 . Long-term stewing will cause a significant loss of these two vitamins.

However, even if some vitamins are lost, proteins, heat-resistant vitamins and various minerals are still there. If the elderly and patients with bad teeth and weak gastrointestinal tract can eat more protein, this approach is still meaningful. Vitamins can be supplemented from small tablets.

B vitamins, as a byproduct of microbial fermentation, can actually be obtained cheaply. For example, yeast tablets and complex B vitamin tablets only cost a few cents each. Swallowing them while eating is enough to make up for the loss caused by cooking.

Many people don't know that lean meat is rich in potassium, because potassium is the ion with the highest content in human intracellular fluid. Therefore, drinking broth, milk, and fruit and vegetable juice can supplement potassium for the elderly.

When using a slow cooker to stew chicken wings, even the bones can be stewed until they are soft, and the red bone marrow can be chewed and eaten. Some cartilage can also be stewed until soft and eaten. This increases the intake of minerals such as calcium and iron .

Question 5

Who is suitable for using slow cooker stewed meat to increase nutrition?

For most people, including those with mild gastrointestinal diseases, it is really not necessary to stew the meat for more than ten hours. Cooking in a pressure cooker or in an electric stew pot for 2 to 4 hours will make the meat soft enough and the dissolved substances in the soup will be sufficient.

For the elderly and patients who have difficulty chewing and digesting, slow cooking for two or three hours can greatly reduce the difficulty of eating meat. It is also very friendly to people with bad teeth.

Those super slow cookers that can cook for seven or eight hours or even more than ten hours are not for eating delicious meat, but for drinking broth. Only elderly people and patients with poor digestion and absorption and serious nutritional deficiencies need this type of cooking equipment.

So, I said to A: Since the old man wants a slow cooker and he really lacks the nutrition of meat, buy him one. For a 90-year-old man with weak digestive ability and muscle loss, it is likely to be beneficial to supplement the amino acids and peptides from meat in this way. Ordinary electric cookers that stew for several hours are very cheap, and you can buy one for one or two hundred or two or three hundred yuan. For most ingredients, stewing for 2 to 4 hours is enough to make them soft.

For relatives and friends of cancer patients like B, if their digestive ability is particularly weak after chemotherapy and they cannot eat many high-protein foods, they can also consider trying the super slow cooking method. At least, eating long-cooked soft meat and broth is more delicious than using a wall-breaking machine to beat hard meat into pulp.

C is a healthy person with normal uric acid level, so there is no need to worry about purine dissolving in the broth. However, if you are a patient with hyperuricemia or gout, you should also avoid slow-cooked broth or fish soup.

A bunch of related questions:

Q: Is the electric stew pot with a long-time slow-cooking program a ceramic pot or a stainless steel pot? Will long-time stewing release harmful substances from the pot?

A: There are all kinds of inner pots, including ceramic, porcelain, and stainless steel. Food-grade ones can be used**, because ceramic, porcelain, and stainless steel are all used to hold and process food for a long time. Choose whichever you feel more assured.

Question: I don’t have an electric stew pot at home. How can I achieve the effect of long-term slow cooking at low temperature using an ordinary clay pot?

A: Heat it to a slight boil first, then turn off the heat immediately, stop heating for a while, and let the temperature slowly drop. This way the temperature inside the food is still relatively low. After half an hour to an hour, when the outside is not too hot, heat it to a slight boil again, and turn off the heat for a while. Repeat three or four times. Finally, boil it once more, and then you can serve it. This is similar to the effect of an ordinary slow cooker, but you need to turn the heat on and off manually, which is more troublesome.

Q: It is very quick to cook meat in a pressure cooker, which only takes about half an hour. What is the difference between this and a slow cooker? The meat is tender enough, but will it be less nutritious than that in a slow cooker?

A: The meat cooked in a pressure cooker is also softer. The principle is to use high temperature and high pressure to cause the protein in the meat to heat up and denature quickly. At the same time, because the pressure cooker raises the boiling point of water and is airtight, it also avoids excessive evaporation of water, so the meat will not be dry and hard. Although the final effect may not be as soft as that of a slow cooker, as long as the elderly and children can eat it, the effect is achieved.

In fact, increasing the heating temperature and shortening the heating time are more conducive to preserving the vitamins in the meat. However, from the perspective of stewing soup, the soup cooked in a pressure cooker is not as delicious as that cooked in a slow cooker or casserole, probably because the umami components are less dissolved, while the dissolution of hydrophobic amino acids with bad taste increases.

Q: If I already have an electric pressure cooker at home, do I still need a slow cooker?

Answer: Slow cookers are mainly useful for the elderly and patients with particularly poor digestion, and are not a necessity for ordinary healthy people.

A healthy person's stomach and intestines can digest the protein in food, so there is no need to eat only small peptides and amino acids that have been digested into fragments . Especially for children, being too "pampered" with the stomach and intestines is not conducive to the cultivation of digestive ability. Just as only drinking semi-fluid food and only eating food that is so soft that it does not need to be chewed is not good for children's tooth development. From the perspective of saving time, pressure cooker cooking is also more efficient, so there is no need to buy a slow cooker.

References:

1 Zhang Ze. Effects of low-temperature slow cooking on the edible quality and protein digestibility of braised pork[D]. Master's thesis of Nanjing Agricultural University, 2022

2 Li Jiaxun, Zhong Zhihao, Zhang Lu, et al. Process optimization of cooking chicken soup in electric stew pot [J]. Home Appliance Technology, 2014, 9:76-79

3 Zhang Man. Flavor formation mechanism of consommé broth and optimization of cooking process of electric stew pot[D]. Doctoral dissertation of Jiangnan University, 2019

4 Huang Funing. Analysis of flavor components of Guizhou small fragrant chicken and comparison of flavor of stewed chicken soup[D]. Master's thesis of Tianjin University of Science and Technology, 2023

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