Why do cherries survive the month it takes to arrive in China, but go bad within a few days after you bring them home?

What is the most popular fruit during the Spring Festival?

Cherries, especially those from Chile.

These cherries travel across the ocean from Chile to China, and it takes more than a month on the road. The amazing thing is that after such a long bumpy journey, the cherries we buy home can still remain quite fresh.

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A few days ago, we made a detailed analysis of "What happened to the former "premium fruit" that fell from the altar this year?" Many people in the comment area mentioned that the cherries, which were still very fresh when they were received, began to have pits on the surface after just a few days at home, and the fruit stems also turned from emerald green to brown and black. There were also many "intact on the outside, but rotten on the inside". Is it because of the use of various "technological methods"?

Image source: screenshot from Xiaohongshu

Let me start with the conclusion: the fact that cherries are still fresh after more than a month in China has a lot to do with the variety + the careful control of planting, picking and transportation . As for why cherries are still fresh when they arrive but go bad after a few days, in most cases it is because the protective magic of cherries is broken during packaging .

Today, let’s talk specifically about the “technology behind fruit and vegetable preservation.”

Apply calcium fertilizer during the fruit expansion period

Can effectively improve storage and transportation performance

As we all know, during adolescence, the body absorbs more calcium, and calcium plays a vital role in bone development. In fact, calcium supplementation is not just for animals, but is also one of the essential elements for plant growth.

In plants, calcium can effectively promote the development of fruit cell walls. When fruits are adequately supplied with calcium, they will swell to a larger size and become significantly harder. This not only helps increase yields, but also significantly improves the taste of the fruit, making it crisper and sweeter.

At the same time, as the cell wall thickens, its permeability decreases, thereby enhancing the fruit's resistance to various diseases. For the preservation and transportation of fruits, higher hardness means that the fruit has a stronger ability to resist damage, and is less likely to be damaged by bumps and squeezing during transportation. In addition, calcium can effectively inhibit the formation of ethylene in the fruit, which is a plant hormone that promotes fruit ripening.

In general, calcium plays a key role in the storage and transportation of fruits . Based on this, fruit farmers usually apply a large amount of calcium fertilizer during the fruit expansion period to improve the storage and transportation performance of the fruit.

Plants have a high demand for calcium fertilizer (photo taken by the author)

Pre-cool fruits and vegetables immediately after picking

Better maintain its freshness and quality

The fruits, vegetables and other agricultural products we eat daily are usually picked in fields with higher temperatures. After picking, if these fruits and vegetables are piled together, it is difficult for the temperature inside to drop quickly. At the same time, the fruits and vegetables will continue to "breathe". Under the dual influence of high temperature and high breathing intensity, the water content and various nutrients in the fruits and vegetables will decrease sharply, which is also the internal reason why the fruits and vegetables gradually lose their freshness.

Therefore, fruits and vegetables picked from the fields generally need to be pre-cooled first, which can not only significantly improve the overall storage and transportation time of fruits and vegetables, but also better maintain their freshness and quality.

Common precooling methods include wind precooling, cold water precooling, ice precooling and pressure difference precooling. The main purpose of these methods is to quickly eliminate the heat brought by fruits and vegetables from the field, while also effectively inhibiting the production of ethylene. A lower temperature environment also helps inhibit the growth and reproduction of microorganisms.

Kiwi fruit is precooled and stored in a cold storage (photo taken by the author)

Controlled atmosphere preservation technology

It's like putting fruits and vegetables into a hibernation capsule

In many science fiction movies, there are settings of hibernation chambers. For example, in The Wandering Earth, after the protagonist enters the hibernation chamber, he lies down and covers the cover. At this time, a special gas will be sprayed out of the chamber. This gas can significantly reduce the metabolic rate of the organism, causing it to enter a deep hibernation state, thereby stably maintaining the most basic vital signs for a long time.

The idea and principle of controlled atmosphere preservation technology for vegetables are similar to space capsule hibernation. The gases used in controlled atmosphere preservation are mainly nitrogen, oxygen and carbon dioxide. The preservation effect is achieved by adjusting the different proportions of these three gases.

Take apples as an example. When the oxygen concentration in normal air is 21%, its respiration efficiency is high. However, in a controlled atmosphere environment, when the oxygen content drops to 2%, the respiration of apples will be significantly reduced, reducing the loss of nutrients, especially sugar.

In addition, a low-oxygen and high-carbon dioxide environment can effectively inhibit the formation of ethylene and the growth of microorganisms, especially mold, thereby extending the shelf life of vegetables.

Fruit slices preserved in controlled atmosphere (photographed by the author)

Peel covered with "plastic wrap"

Can effectively extend the shelf life of fruits and vegetables

The moisture content of the fruit largely determines the freshness and quality of the fruit. Fruit wax is a natural lipid produced by the development of the fruit. It can prevent pathogens such as bacteria, viruses and other harmful substances from entering the fruit, reduce water loss, and fruit wax is hydrophobic, which can also prevent stains from accumulating on the peel.

Artificial fruit wax can also play a similar role as fruit wax. It is a liquid wax made from natural substances such as gum, beeswax, and palm wax. Compared with industrial wax, it is colorless, tasteless, non-toxic, and edible. Spraying it on the surface of the fruit can reduce water loss, hinder pathogenic microorganisms, and make the fruit bright and shiny . It is generally used for citrus fruits. For example, after applying fruit wax coating on the surface of oranges, the shelf life of oranges can be extended by 2 to 3 weeks, and the appearance of the oranges is brighter and more valuable.

An edible composite film prepared by Liu Kaidong's team at Lingnan Normal University using chitosan (CS) and oxidized fucoidan (CS-FU) and encapsulated cinnamaldehyde (CA) can significantly increase the shelf life of litchi (>8 days) (literature image)

For example, chitosan preservative is a natural polymer substance extracted from shrimp and crab shells. It can form a thin film on the surface of fruits and vegetables. This film has good air permeability and moisture retention, which can reduce the loss of water in fruits and vegetables and prevent the invasion of external microorganisms.

It also has certain antibacterial properties and can inhibit the growth of bacteria and mold on the surface of fruits and vegetables. For example, using chitosan preservatives in grape preservation can effectively extend the shelf life of grapes.

“Using bacteria to treat bacteria”

It’s also a great way to preserve freshness

Rot and deterioration are often the most common preservation problems of fresh food. The culprits of this problem are some microorganisms, such as Pseudomonas and Erwinia in bacteria, Penicillium and Botrytis in molds, and some yeasts. In nature, bacteria will inhibit or even "kill" each other. If the "beneficial" bacteria prevail and harmful bacteria disappear, the purpose of preservation is achieved.

Researchers have isolated strains from nature and screened out a variety of fungi that can inhibit the growth of harmful bacteria. This type of fungi is generally called biocontrol bacteria. For example, the three fungi selected by researchers, Bacillus subtilis, Bacillus amyloliquefaciens, and Bacillus wiltii, were combined to make a composite biocontrol agent, which can effectively inhibit gray mold disease in tomatoes.

The researchers found that Paenibacillus jamilae W51 has a significant inhibitory effect on fungal diseases caused by Rhizopus stolonifer. Rhizopus stolonifer is the main pathogen of peach postharvest soft rot. After peaches were inoculated with the W51 strain, the incidence rate and lesion diameter of the fruit were significantly reduced. This shows that the biocontrol bacteria W51 treatment can significantly enhance the resistance of peach fruit to soft rot and effectively improve its preservation effect.

Treatment with biocontrol bacteria W51 can significantly enhance the resistance of peach fruit to soft rot (literature image)

Why Cherry

Will it break easily in our hands?

Back to the question at the beginning of the article, why can Chilean cherries still remain fresh after 20 to 30 days of traveling across the ocean?

In addition to the characteristics of the variety itself, which has large and hard fruits, the fruits are relatively firm, the peel has a certain toughness, and is more resistant to bumps and collisions during transportation and has strong storage resistance, the key lies in the meticulous control of its planting, picking and transportation links.

During the planting stage, fruit farmers focus on the use of calcium fertilizers to make the fruit harder and more durable in storage. Within 3 to 4 hours after picking, cherries are quickly placed in ice water for precooling, and then the surface is cleaned with food-grade disinfectants. When packaging, gas conditioning gas is filled (increasing the content of carbon dioxide and nitrogen, and reducing the oxygen content), and 1-MCP (1-methylcyclopropene) ethylene adsorbent is placed to effectively inhibit the ripening effect of ethylene. Finally, with the full cold chain transportation, cherries are able to arrive in China fresh.

Cherries in modified atmosphere packaging in original boxes (photographed by the author)

The cherries we buy are generally divided into two types: imported and packaged in original boxes and original boxes.

If you buy imported cherries that have been packaged in original boxes : because the packaging has been opened, the atmosphere surrounding the cherries has been lost, and the fruit's respiration will be more vigorous, thus accelerating its decay. It is recommended to buy small boxes, put them in the refrigerator's fresh-keeping box to keep them fresh, and try to eat them within 2 to 3 days.

If you buy cherries in their original packaging : these are usually packaged in cartons and plastic film, with specifications ranging from 1.35kg to 2.5kg. It is recommended that you put them in the refrigerator immediately after you get them home to keep them fresh . Otherwise, after opening the original packaging, the shelf life will be greatly shortened due to the dissipation of the gas in the controlled atmosphere. It is also recommended that you eat the cherries as soon as possible after unpacking to prevent them from becoming stale or even spoiling.

In addition, if you purchase cherries online, the bumps and temperature changes during express delivery will greatly reduce the shelf life of the cherries.

To sum up, the preservation of fruits and vegetables is mainly based on the following principles: first, reducing the respiration of fruits and the release of endogenous ethylene; second, reducing the water loss of fruits and vegetables; third, inhibiting the growth of harmful microorganisms; and fourth, reducing the mechanical damage of fruits.

In addition to these basic measures, there are also a variety of technical means such as radiation sterilization preservation, magnetic field preservation, packaging material preservation, antioxidant preservation, nano preservation, far infrared preservation, and ultrasonic preservation.

I believe that with the widespread application of these preservation technologies, we can not only taste fresher and better quality fruits and vegetables, but also enjoy agricultural products from all over the world with confidence. All this is inseparable from the power of science and technology, not the so-called "hard work"!

References

[1] Zhu Jingfeng, Gao Yuxia, Li Xiran, et al. Study on the effect of Paenibacillus jamillaris W51 on the prevention and control of postharvest peach diseases and preservation[J]. Chinese Fruit and Vegetables, 2022, 42(11): 6-14.

[2]Liang Fengyan, Liu Chusi, Geng Jinwen, et.al Chitosan–fucoidan encapsulating cinnamaldehyde composite coating films: Preparation, pH-responsive release, antibacterial activity and preservation for litchi, Carbohydrate Polymers, Volume 333, 2024.

Planning and production

Author: Zhang Cong, a graduate student in agronomy and seed industry, majoring in vegetables

Review | Ruan Guangfeng, Deputy Director of Kexin Food and Health Information Exchange Center

Planning丨Ding Zong

Editors: Ding Zong, Lin Lin

Proofread by Xu Lai

The cover image and the images in this article are from the copyright library

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