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The nutritional loss of frozen meat and frozen vegetables is not large, in fact, fresh vegetables after 5 days of refrigeration may not be as nutritious as quick-frozen vegetables (see the text for data)
"Quick freezing" is the key to ensuring quality, and commercial quick-freezing temperature is lower, which is better than its own freezing effect.
The recommended thawing method of frozen meat is to put it in the refrigerator refrigerator to thaw overnight, and the frozen vegetables do not need to be thawed, and can be steamed, grilled and microwaved directly.
Whether it is ordinary life or epidemic hoarding, frozen food is a kind of convenient and durable good thing. Is it better to prepare frozen meat and frozen vegetables at home or to buy ready-made vegetables? Is it raw or cooked? Let's talk about it today
Frozen meat
First ask the question, if you want to hoard meat, or buy meat that you are not sure if you are about to eat it, will you choose to buy cold fresh meat or frozen meat?
1. Buy frozen meat directly
2, buy cold fresh meat, and then freeze yourself (do not put, buy back to freeze)
3, first buy cold fresh meat in the refrigerator, if you can't finish eating, then freeze it
4, buy cold fresh meat, cooked first and then frozen
From a nutritional safety point of view, 1>2>3 is recommended, and from a taste point of view, 4 is not recommended
Is frozen meat nutritious?
Protein, fat, iron and other minerals in the meat will not be greatly affected by freezing, at most the juice lost during thawing may take away a little B vitamins, and the nutritional value of frozen meat is not much worse than fresh meat.
Why is it more recommended to buy ready-made than to freeze yourself?
Because the conditions of commercial quick-freezing are better than their own home, they can make meat "quick-frozen".
Why freeze?
When frozen, all parts of the food quickly pass through the temperature zone formed by ice crystals (0 ° C to -5 ° C), the juice "too late to react" is frozen in place, and the whole food appears evenly with many and small ice crystals, without damaging tissues and cells. In this way, the frozen food can not see any large pieces of ice ballast, and when it is thawed, the juice can be absorbed back in situ.
And slow freezing, food for a long time to stay in the temperature zone formed by ice crystals, some places are cold enough to freeze out of the ice crystals first, resulting in the remaining juice in the vicinity is concentrated, in order to "balance", the water of other parts will continue to penetrate over, so that the ice crystals continue to grow, and finally slowly form a small and large ice crystal, these large ice crystals will squeeze the tissue, puncture the cells, destroy the muscle fibers, resulting in thawing when the juice can not be absorbed back, reflected on the meat is poor taste.
[1]
Simply put, the lower the temperature, the faster it freezes.
Therefore, the industry mostly uses extremely low temperatures to freeze, such as -30 ° C or less, or use some special techniques to make food freeze instantly. But the usual family does not have this condition, the freezer of the refrigerator is only -18 ° C.
But it also depends on storage and transport conditions
In theory, commercial quick-frozen meat is better, but if the supermarket is not well preserved, or the cold chain conditions during transportation are not good, it may be that the frozen meat you bought has undergone repeated freeze-thawing, and the nutrition and safety will be greatly reduced.
An easy way is to see if the meat is still not a fine and uniform Xiaoice crystal, if there is a large ice ballast locally, it is not very good.
What do you pay attention to when you freeze yourself?
Buy back to freeze yourself can also be, but pay attention to cold fresh meat to buy home, directly start freezing, do not put, try to reduce the initial number of microorganisms, shelf life is longer.
Another important thing is to freeze them in small pieces, ideally cut into thinner pieces, bagged separately and frozen.
In this way, not only can all parts be quickly cooled together when freezing, but also achieve the purpose of quick freezing. When eating, it is also convenient to take the amount on demand to avoid repeated freezing, and the thin slices of frozen meat can be cut even if it is not thawed, which is more convenient.
Is it better to freeze raw or cooked?
Some people also asked if it was good to freeze the meat when it was cooked.
If you can ensure that the cooked frozen meat is fully heated again before eating, then there is no problem with the frozen.
But in terms of taste, the cooked frozen meat is heated and then eaten, and it is basically impossible to be tender and juicy. After heating, the meat protein degenerates, itself can not absorb water, freezing, thawing, reheating the process will further lose water, and finally the meat will become hard and woody. The taste is far less than that of raw frozen meat after thawing and cooking.
What to watch out for thawing?
Earlier said that when freezing, it should be "quick-frozen", and when it is thawed, it is the opposite, to "slow down", that is, to give the juice enough time to absorb back into the tissue, and try to restore the food to the rich and elastic state of the juice before it was frozen.
However, "slowing" takes a long time, and the food in the thawing process faces problems such as microbial reproduction, protein and fat oxidation, discoloration under the action of enzymes, etc., so we must keep the food at a temperature where ice crystals can melt but the oxidation reaction and microbial reproduction are inhibited. This temperature is about 3 °C-5 °C.
Therefore, the most recommended method of thawing meat is to move directly from the freezer of the refrigerator to the refrigerator and slowly thaw it.
If you buy packaged frozen meat, you don't have to unpack it at this step, and if you are in your own plastic bag, you can also take thawing it. It is recommended to take it out the night before and thaw it in the cold room overnight. The next day, even if you can't deal with it right away, it's okay to leave it in the cold room for a while.
Hot water bubbles, cold water bubbles, microwaves, room temperature thawing have their own shortcomings, detailed understanding of poking this "frozen meat" Do not soak with water again! This 1 trick, after the end of the tender and juicy!
Frozen vegetables
Are frozen vegetables nutritious?
Everyone will naturally think that frozen vegetables are much less nutritious than fresh vegetables, but it is not so exaggerated.
First of all, fresh vegetables that you buy back and put them in the room temperature or in the refrigerator will also continue to lose nutrients. This is because vegetables still have a respiratory effect after being picked, and many enzymes in vegetables are also promoting various chemical reactions, resulting in vegetables changing color, nutrient loss, flavor changes and so on.
The commercial frozen vegetables are bleached before the blanching step, so the storage process is very stable. However, the step of blanching itself will also bring about a certain loss of nutrition.
In general, the commercial quick-freezing process has little impact on dietary fiber, minerals, carotenoids, and vitamin E in vegetables, and some polyphenol antioxidants may even increase after freezing and storage, but bleaching before freezing and thawing after water loss may take away some heat-resistant and water-soluble vitamins (vitamin C and B vitamins).
Fresh vegetables after 5 days of refrigeration may not be as nutritious as frozen vegetables
Studies have found that the vitamin C content of broccoli, corn, beans, peas, and strawberries that are refrigerated (4 ° C) for 5 days after buying home is not as good as that of frozen vegetables. Most people may buy food once a week, so it is normal to stay at home for 5 days.
[3]
However, this is also divided into vegetables, spinach after the quick-frozen treatment of vitamin C dropped from 25.2 to 14.5, a loss of nearly half. These losses are likely to occur mainly during pre-freezing blanching, and leafy vegetables such as spinach have a large surface area and no factors that can protect VC (such as acidic environments, such as starch), and the loss of vitamin C itself is very serious when heated.
What do you pay attention to when you freeze yourself?
Due to the difference in conditions, in fact, commercial quick-frozen vegetables will be better than their own frozen at home, but if you buy more vegetables one day, or want to stock up on some convenient vegetables that you like, you can try to make your frozen vegetables a little better through some skills.
Pick the right vegetables
First of all, you have to pay attention to choosing some vegetables that are suitable for freezing, and it is generally recommended to choose peas, corn, broccoli, carrots, cauliflower, which are relatively stable.
Blanch before freezing
You can change the vegetables to a shape that can be directly put into the pot, and then blanched in boiling water (ten seconds to half a minute), which is equivalent to playing a blanching role.
On the one hand, it can kill some bacteria, on the other hand, it can also make the color of vegetables better, and it can kill enzymes, so that it is not easy to produce odors during storage (especially broccoli and other special odors).
Drain
At home, you must ensure the safety of the water, and finally remember to drain the water on the vegetables, you can gently pinch out the excess water to avoid the quality of the frozen after the impact.
Dispense
Pay attention to the use of small packages, enough for the family to eat a meal, to avoid the safety risks caused by repeated thawing.
At the same time, be vigilant about whether there are plasticizers or other substances in the packaging container, and choose a safer packaging bag.
When packing, try to drain the air inside as much as possible.
Which layer?
It is generally recommended to reduce the temperature of the refrigerator freezer as much as possible, or choose the coldest layer, close to the location of the refrigerator refrigeration unit.
You can carefully check the information of the refrigerator product you bought, understand the kind of freezing technology it uses, what kind of temperature it can freeze to, and what kind of location the refrigeration device is in.
What to watch out for thawing?
Frozen vegetables are not the same as meat, in fact, they do not need to be melted and then cooked, thawing and cooking together.
Frozen vegetables can be cooked directly by steaming, microwave heating or oven, and can be fried quickly, which can minimize the loss of water-soluble vitamins and have a relatively small impact on the quality of fruits and vegetables. It is not recommended to cook, and the loss of vitamin dissolved water is relatively large.
Resources:
Feng Xianchao,Zhou Guanghong. Effect of fast freezing process on beef quality and tissue structure[J].Food Science,2016,37(19):1-7.
HU Xin. Effects of different freezing and thawing methods on pork quality[D].Nanjing Agricultural University, 201
[3] Linshan Li, et.al, Selected nutrient analyses of fresh, fresh-stored, and frozen fruits and vegetables, Journal of Food Composition and Analysis, Volume 59, 2017, Pages 8-17
Edit: Xiao Hui
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