1. Reduce respiration and extend storage period

An effective method to reduce the respiration of stored vegetables is the controlled atmosphere preservation method. This method is based on mechanical refrigeration to adjust the gas concentration in the storage environment, mainly reducing the concentration of oxygen and increasing the concentration of carbon dioxide, thereby suppressing the respiratory metabolism intensity of postharvest vegetables and reducing the consumption of nutrients. .

The most commonly used controlled atmosphere preservation technologies in our country are plastic bag small packaging controlled atmosphere, plastic large tent controlled atmosphere and silicone rubber window controlled atmosphere. In addition, there is a decompression storage method, which is to reduce the air pressure in the storage place, usually to 1/10 of the atmospheric pressure, to create a certain degree of vacuum, thereby achieving the purpose of reducing oxygen. This is a new technology for preserving vegetables and many other foods. , is a further development of controlled atmosphere refrigeration.

Decompression storage has a wide range of adaptability. Spinach, lettuce, green beans, green onions, radish, mushrooms, tomatoes and other types have better effects under reduced pressure storage. The best storage effect of this method is tomatoes. , the shelf life can reach more than 3 months.

The respiration intensity of vegetables should be reduced as much as possible during storage. The stronger the respiration, the faster the changes in various physiological processes and the earlier the end of life, which is not conducive to storage. The difference in the respiration intensity of vegetables varies depending on the type, variety and age. Generally, leafy vegetables have the highest respiration intensity, followed by fruit vegetables, and taproot, tuber, and bulb vegetables have the smallest intensity; late-maturing varieties have stronger respiration intensity, and early-maturing varieties have weaker intensity;

The respiration intensity is stronger in the young stage, The mature stage is weak. In addition, temperature, atmospheric composition, mechanical damage, pests and diseases, etc. also have a great impact on vegetable respiration. When the temperature is high, the breathing intensity is strong. Between 5 and 35°C, for every 10°C rise, the breathing intensity increases by 1-1.5 times. When it exceeds 35°C, the breathing intensity drops significantly;

When the temperature is low, the breathing intensity It is weak and consumes less nutrients, but it cannot be considered that the lower the storage temperature, the better. Reducing the oxygen concentration in the air will inhibit breathing. Usually the oxygen concentration is reduced to about 5%, which is effective. Vegetables that are mechanically damaged and damaged by pests and diseases will increase respiration and should be eliminated when selecting samples for storage.

2. Reduce the transpiration of stored vegetables

The water content of fresh vegetables is as high as 65-95%. They are prone to transpiration and dehydration during storage. If not supplemented, it will cause tissue wilting, Shrinkage and fading of luster make vegetables lose weight and freshness, and reduce eating quality.

So it is very important to reduce the transpiration and wilting of stored vegetables. The environmental conditions during storage should be controlled according to the characteristics of different vegetables. For example, the leaf surface area of ??leafy vegetables is larger, and the stomata of growing leaves and young leaves are They are relatively large in number, have severe transpiration, and are most susceptible to dehydration and wilting during storage.

Therefore, it is necessary to increase the air humidity in the storage room (library), reduce air flow, and keep the stored vegetables in a high-humidity environment to minimize transpiration. In addition, the selection of appropriate packaging materials is also an effective measure to improve preservation technology.

Vegetables that evaporate violently such as water should use anti-turbid packaging materials. This type of film is hydrophobic. To improve the hydrophilicity, surfactants can be applied to form a thin water film on the surface of the film. This not only It can prevent turbidity and can also prevent moisture condensation in the packaging. Moisture evaporation inhibitors, ethylene adsorbents, bactericides, cold storage agents, etc. can also be placed in the packaging to help preserve freshness.

3. Inhibit postharvest ripening and senescence

Vegetables enter the senescence stage from the beginning of harvest, which is manifested in the decrease in the number of ribosomes in cells, the collapse of chloroplasts, and the reduction of mitochondria. The cells are aging, not resistant to storage, and perishable. Senescence is closely related to the content of ethylene, gibberellin or other hormones in vegetables and their changes during storage, the growth and development status of vegetables and storage conditions.

To delay the aging of vegetables and extend the storage period, firstly, choose robust and well-growing vegetables for storage; secondly, strictly control the content of ethylene and other hormones during the storage process of vegetables to delay vegetable aging. ; The third is to create optimal storage conditions, such as controlling temperature and humidity, gas composition and ratio, etc.

Fruits, vegetables, bulbs, root vegetables, etc. have a post-ripening effect during storage. During the post-ripening process, a series of physiological and biochemical changes often occur, such as starch hydrolyzing into sugar, organic acid content decreasing, tannins beginning to solidify and oxidize, protopectin decomposing into water-soluble pectin, chlorophyll decomposing, and the flavor improving. Produce aromatic components, the texture changes from hard to soft, etc.

Therefore, by taking advantage of this post-ripening effect, vegetables can be harvested early and suitable conditions can be created during storage to maintain their post-ripening power.

Commonly used methods are to lower the temperature of the storage room, maintain high humidity, ventilate in time, eliminate accumulated ethylene and other gases, inhibit hydrolase activity, delay the hydrolysis rate, and prevent large consumption of nutrients, thereby inhibiting the after-ripening effect and prolonging storage. period purpose.

4. Pay attention to pre-cooling and low-temperature storage in the place of origin to reduce storage loss

Since various vegetables have different responses to temperature, the storage temperature of vegetables must be determined based on the characteristics of the vegetables themselves. Depends on low temperature adaptability. For example, the storage temperature of green ripe tomatoes is 10-12°C, bell pepper is 7-9°C, cucumber is 10-13°C, radish is 1-3°C, carrot is 0-1°C, potato is 3-5°C, and spinach. The temperature is -6 to 0℃, the temperature of cauliflower is 0 to 0.5℃, the temperature of onion is -3 to 0℃, the temperature of garlic is -1 to 0℃, etc.

It can be seen that the suitable low temperature for storage of most vegetables is around 0℃. If the temperature is lower than this, vegetables will also be frozen. After vegetables are frozen, tissues and cells are damaged by mechanical force, resulting in dehydration. After some vegetables are frozen, their cells are damaged and die; after thawing, the juice flows out and loses their commercial and edible value. However, some vegetables have strong cold tolerance, such as spinach, which can remain fresh at -9°C and is suitable for frozen storage.

5. Delay material transformation and consumption, and maintain the quality of stored vegetables

Pre-cooling of the production area is a key part of post-harvest preservation of vegetables. With the development of vegetable exports, pre-cooling of vegetable production areas is becoming increasingly important. Be taken seriously. The function of pre-cooling is to quickly remove field heat, effectively reduce the metabolism of vegetables, reduce nutrient consumption, delay aging, and extend the shelf life of vegetables. Under high temperatures, extending the time from harvest to pre-cooling will promote vegetable aging and greatly shorten the shelf life of vegetables.

Low temperature can effectively inhibit the growth and activity of rot pathogens and reduce losses. It is also a key factor in storing vegetables. After the vegetables are pre-cooled at the place of production, they are transported into circulation by refrigerated containers. After arriving at the place of sale, they enter circulation cold storage or sales freezers, which can maintain the quality of vegetables to the maximum extent and reduce circulation losses.

After vegetables are harvested, substance accumulation stops and dry matter no longer increases. Various substances that have been accumulated are gradually consumed or, under the catalysis of enzymes, transformed, transferred, decomposed and recombined in the tissue. and a series of changes in cell morphology, structure, characteristics, etc.

For example, after storage, the taste of Chinese cabbage becomes sweeter, the texture is softer, and the green color fades. Green ripe tomatoes are hard and green in color. During storage, they gradually lose their green color and appear red or yellow. The pulp softens and the acidity decreases, which causes major changes in the vegetable's flavor, texture, nutritional value, commercial properties, storability, and disease resistance. .

The change in color of vegetables is often a sign of post-ripening and aging. At the same time, vitamin C in vegetables gradually decreases at different rates during storage. For this reason, delaying the transformation and consumption of vegetable nutrients is one of the keys to maintaining the quality of stored vegetables. Commercially, reducing respiration, inhibiting after-ripening and aging, and creating optimal storage conditions and gas composition can all achieve satisfactory results. result.

During the storage process of vegetables, the dynamic balance between the synthesis and hydrolysis of various substances is constantly changing. During storage, the synthesis process of most vegetables gradually weakens, and the hydrolysis process continues to strengthen, accumulating simple hydrolyzate products, thereby stimulating respiration and conducive to microbial infection. The transformation of pectic substances reduces the mechanical resistance of vegetables.

6. Improve storage tolerance and disease resistance

The storage tolerance of vegetables means that after a period of storage, the edible value and flavor characteristics are not significantly reduced, and the weight loss is small; Disease resistance refers to the ability to resist attack by rot pathogens. The two are closely related and interdependent. Vegetables with strong storage tolerance have strong immunity to rot pathogens, and vice versa.

In terms of the characteristics of vegetables, vegetables whose vegetative organs are the edible parts, such as greens, spinach, celery, mustard, chrysanthemum, amaranth, water spinach, alfalfa, etc., have high water content and many types and quantities of enzymes. , strong respiratory metabolism, rapid decomposition of substances, most of which are intolerant to storage and have poor disease resistance. Young cucumbers, sponge gourds, kidney beans, peppers, and eggplants are not resistant to storage, while mature winter melons and pumpkins are more resistant to storage.

Vegetables with nutrient accumulation organs as their edible parts - tubers, roots, leaf bulbs and bulbs - are also more resistant to storage. Among them, late-maturing varieties are more storage-resistant and have stronger disease resistance than early-maturing varieties. People need to know that this knowledge.

Baidu Encyclopedia-Vegetables