These fresh-keeping "black technologies" escort the taste of the year

With the Spring Festival approaching, various online and offline New Year festivals have kicked off one after another, and people have bought melons, fruits, meat, seafood and other New Year goods to prepare for the festival
.

From the place of origin to the refrigerator at home, the food has gone through thousands of mountains and rivers, but it is still fresh; The fruits and vegetables that are hoarded early are still delicious when they are taken out during the Spring Festival.
.
.
These all depend on the continuous iterative upgrading of food cold chain preservation technology
.

Li Xihong, a professor at the School of Food Science and Engineering of Tianjin University of Science and Technology, said in an interview with Science and Technology Daily that temperature control, moisturizing, atmosphere and green antiseptics are the four major elements of food preservation, and almost all preservation technologies revolve
around these four aspects.
New preservation technology can not only maintain the freshness of food, so that more food can go out of the place of origin and onto our table, but also be safer, energy-saving and environmentally friendly
.

Modified atmosphere preservation technology:

Change the environment inside food packaging with gas

This year, when many consumers buy fresh products on e-commerce platforms, they will find that the words "modified atmosphere preservation box" are printed on the packaging box
.
So, what exactly is modified atmosphere preservation?

In this regard, Li Xihong introduced that modified atmosphere preservation technology is to use "fresh-keeping gas" to change the environment inside food packaging, so as to achieve the purpose
of slowing down the speed of food spoilage and prolonging the freshness of food.

"The so-called 'fresh-keeping gas' is generally made of carbon dioxide, oxygen and nitrogen mixed according to the characteristics of the food, which is filled into the closed package where the food is located and replaced with the original air
inside.
In general, this can extend the shelf life of food by more than
10%.
Li Xihong said
.

In the "fresh-keeping gas", carbon dioxide has the effect
of inhibiting the growth and reproduction of most spoilage bacteria and fungi.
The higher the concentration of carbon dioxide, the less perishable
the food is.
However, the concentration of carbon dioxide in the package for a long time is too high, which will also affect the quality of
the food.

"If there is too little or no oxygen in the confined space where the food is located, the food will ferment and its taste will become sour
.
" Li Xihong said that filling food packaging bags with a small amount of oxygen can maintain the color and taste
of fresh meat and fresh fruits and vegetables.
In addition, oxygen can inhibit the respiration of organisms, and also has a certain inhibitory effect
on the breeding of spoilage bacteria and fungi.

Nitrogen is an inert gas that generally does not react chemically with food and is not absorbed
by food.
In addition, the price of nitrogen is relatively cheap and the cost of use is low
.
Therefore, in the "fresh-keeping gas", nitrogen is generally used as a filling gas
.
Nitrogen can form a protective film on the surface of food to achieve the purpose of bacteriostatic and fresh-keeping, which can not only maintain the taste and color of food, but also play a certain anti-extrusion effect
.

"Depending on the type of food, the 'fresh-keeping gas' recipe is adjusted
.
" Li Xihong explained
.

The reporter learned that some e-commerce platforms sell marinated cooked food, the use of modified atmosphere packaging is to mix carbon dioxide and nitrogen in a ratio of 3:7, while cold fresh meat is to mix carbon dioxide and oxygen in a ratio of 2:8, if the gas mixing ratio changes, the preservation cycle may be unstable, resulting in a shortened
shelf life.

"The use of modified atmosphere preservation packaging is very wide, not only for the preservation of livestock and poultry meat, fish, etc.
, but also for the preservation of fruits, vegetables, grain and oil, flowers, coffee, cheese, pastries and other foods, even cooked food can use this preservation method
.
" Li Xihong added
.

Active packaging film technology:

Upgrade the fresh-keeping function of plastic wrap

In daily life, we often use plastic wrap, and now with the advancement and development of science and technology, people add active ingredients to the plastic wrap or attach a coating to the plastic wrap, and adjust the packaging environment inside the food through the active components, so that the fresh-keeping ability of the plastic wrap is improved
.
This type of technology is called active packaging film technology, and the packaging that applies this technology is called active packaging
.

"According to the mode of action of the active substances in the active packaging, active packaging can be broadly divided into two categories: release active packaging and absorbent active packaging
.
" Li Xihong introduced that one of the more common release-type active packaging is to add or apply a layer of plant essential oil to the plastic wrap or apply a layer of plant essential oil on the surface of the film; Another type of release-type active packaging is to add sulfur dioxide in the plastic wrap or apply nanomaterials to the surface of the film, and the main purpose of adding or coating these substances is to sterilize
.

Absorption type active packaging mainly includes oxygen removal type, carbon dioxide removal type, ethylene removal type, hydrophobic or hydrophilic anti-fog type, etc.
, such as by adding activated carbon in the membrane, absorbing ethylene and ethanol, acetaldehyde and other harmful gases released by food, and ethylene and ethanol have the effect
of ripening fruits and vegetables.
In addition, potassium permanganate, chitosan and other substances are often added to active packaging, and they all have bactericidal effects
.

Intelligent constant temperature preservation technology:

Reduce freezer temperature fluctuations when defrosting

The refrigerator is one of the most commonly used household appliances by the people, and it is also an important tool
for food preservation in the family.
In recent years, refrigerator preservation technology has been constantly innovating, solving many home preservation problems
.

Meat preservation is a more common problem of home preservation
.
If the meat is frozen in the freezer of the refrigerator for a long time, a thick layer of frost will appear on its surface, so that the meat is boiled without juice, and the meat quality is relatively woody
.

"The above phenomenon is caused by the temperature change of the freezer compartment of the traditional refrigerator
.
The compressor of the traditional refrigerator or freezer has a long working time, coupled with frequent opening of the door to access food, the wall of the freezer is easy to frost, if the frost is not timely, the refrigeration efficiency will be reduced, so the user needs to defrost
in time.
However, the freezer temperature rises during defrosting, at which point the meat will thaw and the meat will refreeze
after defrosting.
In this process, the cell membrane of the meat is repeatedly punctured by ice crystals, releasing cell fluid, and water is continuously lost, thus affecting the freshness
of the food.
Li Xihong explained
.

Today, refrigerators using intelligent constant temperature preservation technology can reduce temperature fluctuations through technical means during automatic frosting, so that food can be kept in better condition
.

In addition to temperature control, the freshness preservation technology of refrigerators has now penetrated deep into the cellular level - by controlling the magnetic field to affect the number of microorganisms on food and the metabolism of food cells, so as to achieve high-quality preservation of seafood, fresh meat and mushrooms
.

This technology deeply regulates the movement state of nutrient molecules in food cells by controlling the biological magnetic field, so that the nutrient molecules are closely arranged and a protective layer to prevent nutrient loss is formed in the outer layer of the cell; At the same time, it keeps nutrient molecules in a low-speed state of movement, reduces metabolic loss, and maximizes the freshness of food
.

Phase temperature library technology:

Integrate multiple freshness preservation technologies

The refrigerator is the terminal of family preservation, and before entering the terminal, fresh vegetables and fruits are inseparable from the blessing of preservation technology in the storage link
.
After the iterative development of cold storage, modified atmosphere storage and ice temperature storage, the latest generation of phase temperature storage stands out
.

"Phase temperature library, also known as mother-daughter library, the full name is mother-daughter phase coupling temperature control library, phase temperature library almost integrates all fresh-keeping technology, is the 'all-round player' in the fresh-keeping industry, it can achieve temperature control, humidity control, oxygen control and anti-corrosion, and the application of intelligent technology, more energy-saving and environmental protection
.
" Li Xihong explained
.

The phase temperature library is composed of mother warehouse, sub-library, refrigeration equipment, modified atmosphere equipment, mildew prevention equipment and intelligent control equipment, supporting corresponding temperature, humidity, gas and other sensors, the equipment can be automatically operated and can realize remote control
.

Among them, the mother warehouse is the outer storage, just like the traditional cold storage, which can be insulated and refrigerated, while the sub-warehouse is the inner storage, which is airtight but not insulated
.
The mother library and the daughter library are coupled with each other and can transfer heat to each other, but there is no exchange of water vapor, oxygen, carbon dioxide, etc.
, which can inhibit the respiration of the stored food, delay its metabolic process, and then better maintain the freshness of food, and save 30% to 50%.

(Reporter Chen Xi)