An effective way to reduce the respiration of stored vegetables is modified atmosphere preservation. On the basis of mechanical refrigeration, this method adjusts the gas concentration in the storage environment, mainly reducing the oxygen concentration and increasing the carbon dioxide concentration, thus inhibiting the respiratory metabolism intensity of postharvest vegetables and reducing the consumption of nutrients.
Modified atmosphere preservation technology widely used in China includes small plastic bag modified atmosphere, large plastic tent modified atmosphere and silicone rubber window modified atmosphere. There is also a decompression storage method, that is, the air pressure in the storage place is reduced to110 of atmospheric pressure, resulting in a certain degree of vacuum, thus achieving the purpose of reducing oxygen. This is a new technology to keep vegetables and many other foods fresh, and it is the further development of modified atmosphere refrigeration.
Decompression storage has a wide range of applications. Spinach, lettuce, string beans, shallots, radishes, mushrooms, tomatoes and other varieties have better effects under reduced pressure storage. This method is the best for storing tomatoes, and the preservation period can reach more than 3 months.
The respiratory intensity of vegetables should be reduced as much as possible during storage. The more vigorous the respiratory function, the faster the changes of various physiological processes and the earlier the end of life, which is not conducive to storage. The difference of respiration intensity of vegetables varies with species, varieties and ages. Generally, leafy vegetables have the highest respiratory intensity, followed by fruits and vegetables, while taproot, tuber and bulbous vegetables have the lowest respiratory intensity. The respiratory intensity of late-maturing varieties is strong, while that of early-maturing varieties is weak;
Breathing intensity is strong in youth and weak in old age. In addition, temperature, atmospheric composition, mechanical injury, pests and diseases also have great influence on the respiration of vegetables. When the temperature is high, the breathing intensity is high. When the temperature is between 5℃ and 35℃, the respiratory intensity increases by 10℃ for every increase of 1 ~ 1.5 times. When it exceeds 35℃, the respiratory intensity is greatly reduced.
Low temperature, weak respiratory intensity and less nutrition consumption, but it cannot be considered that the lower the storage temperature, the better. When the oxygen concentration in the air is reduced, breathing will be inhibited. Usually, the oxygen concentration is reduced to about 5%, and the effect is good. Vegetables with mechanical damage and diseases and insect pests will enhance respiration, so they should be removed when selecting storage samples.
2. Reduce the transpiration of stored vegetables
The water content of fresh vegetables is as high as 65-95%, which is easy to evaporate and dehydrate during storage. If it is not supplemented, it will cause tissue wilting, atrophy, luster fading, make vegetables lose weight and freshness, and reduce edible quality.
Therefore, it is very important to reduce the transpiration and wilting of stored vegetables, and the environmental conditions during storage should be controlled according to the characteristics of different vegetables. For example, leafy vegetables have a large surface area, many stomata in the growing leaves and young leaves, and serious transpiration, so they are most prone to dehydration and wilting during storage.
Therefore, it is necessary to increase the air humidity in the storage room (warehouse) and reduce the air flow, so that vegetables can be stored in a high humidity environment and transpiration can be minimized. In addition, selecting suitable packaging materials is also an effective measure to improve the preservation technology.
Vegetables with serious water evaporation should use anti-turbidity packaging materials, which are hydrophobic. In order to improve hydrophilicity, surfactant can be coated to form a thin water film on the surface of the film, which can prevent turbidity and condensation of water vapor in the package. Water evaporation inhibitor, ethylene adsorbent, bactericide, cold storage agent, etc. You can also put it in a bag to help keep it fresh.
3. Inhibition of postharvest maturity and senescence.
Vegetables enter the aging stage from the beginning of harvesting, which is characterized by the decrease of ribosomes in cells, the disintegration of chloroplasts, the decrease of mitochondria, cell aging, storage resistance 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 of vegetables and storage conditions.
Delaying the senescence of vegetables and prolonging the storage period, firstly, selecting robust and well-growing vegetables for storage; Secondly, strictly control the content of ethylene and other hormones in vegetables during storage to delay the senescence of vegetables; The third is to create the best storage conditions, such as controlling temperature and humidity, gas composition and proportion.
Fruits and vegetables, meatballs, root vegetables, etc. It has after-ripening effect during storage. In the process of post-ripening, a series of physiological and biochemical changes often occur, such as starch hydrolysis into sugar, reduction of organic acid content, solidification and oxidation of tannin, decomposition of original pectin into pectin soluble in water, chlorophyll decomposition, flavor improvement, generation of aromatic components, and texture change from hard to soft.
Therefore, using this after-ripening effect, vegetables can be harvested early and suitable conditions can be created during storage to maintain their after-ripening ability. Common methods include lowering the temperature of the storage room, maintaining high humidity, timely ventilation, removing accumulated gases such as ethylene, inhibiting the activity of hydrolase, delaying the hydrolysis speed, and preventing a large amount of consumption of nutrients, so as to achieve the purpose of inhibiting after-ripening and prolonging the storage period.
4. Pay attention to pre-cooling and low-temperature storage in the producing area to reduce the loss of vegetable storage.
Because all kinds of vegetables have different reactions to temperature, the storage temperature of vegetables must be determined according to their adaptability to low temperature. For example, the storage temperature of green ripe tomatoes is 10- 12℃, sweet peppers are 7-9℃, cucumbers are 10- 13℃, radishes are 1-3℃ and carrots are 0-/kloc-0.
It can be seen that the storage temperature of most vegetables is around 0℃. If it is lower than this temperature, vegetables will also be frozen. After vegetables are frozen, tissues and cells are destroyed by mechanical force, resulting in dehydration. Some vegetables died of cell destruction after freezing; After thawing, the juice flows out, losing the commodity and edible value. But some vegetables have strong cold tolerance, such as spinach, which can keep fresh at -9℃ and is suitable for freezing preservation.
5. Delay the transformation and consumption of substances and maintain the quality of stored vegetables.
Pre-cooling in producing area is the key to keep vegetables fresh after harvest. With the development of vegetable export, more and more attention has been paid to precooling in vegetable producing areas. The function of precooling is to quickly remove heat in the field, effectively reduce the metabolic level of vegetables, reduce nutrient consumption, delay senescence and extend the shelf life of vegetables. At high temperature, prolonging the time from harvesting to precooling will promote the senescence of vegetables and greatly shorten the preservation period of vegetables.
Low temperature can effectively inhibit the growth and activity of rotten fungi and reduce losses, which is also a key factor in vegetable storage. Vegetables are transported into circulation by refrigerated containers after precooling in the place of origin, and then enter the rotating cold storage or the sales cold storage after sales, which can maximize the quality of vegetables and reduce the circulation loss.
After harvesting vegetables, the accumulation of substances stops, the dry matter does not increase, and the accumulated substances are gradually consumed, or a series of changes have taken place in the morphology, structure and characteristics of tissues and cells through transformation, transfer, decomposition and recombination under the catalysis of enzymes.
For example, the taste of Chinese cabbage becomes sweet, the texture becomes soft and the green becomes pale after storage. Green ripe tomatoes are hard and green in color, and gradually turn green and appear red or yellow during storage. The pulp becomes soft and the acidity decreases, which greatly changes the flavor, texture, nutritional value, commodity, storage resistance and disease resistance of vegetables.
The change of vegetable color is often a sign of maturity and aging. At the same time, vitamin C in vegetables gradually decreased at different rates during storage. Therefore, delaying the transformation and consumption of vegetable nutrients is one of the keys to maintain the quality of stored vegetables. Satisfactory results can be obtained by reducing respiration, inhibiting ripening and aging, and creating the best storage conditions and gas composition.
During the storage of vegetables, the dynamic balance of synthesis-hydrolysis of various substances is constantly changing. During the storage of most vegetables, the synthesis process is gradually weakened, the hydrolysis process is continuously strengthened, and simple hydrolysis products are accumulated, thus stimulating respiration and facilitating microbial infection. The transformation of pectin reduces the mechanical resistance of vegetables.
6. Improve the storability and disease resistance.
The storage resistance 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 the invasion of rotten bacteria. The two are closely related and interdependent. Vegetables with strong storage resistance have strong immunity to rot germs, and vice versa.
From the characteristics of vegetables, vegetables with vegetative organs as edible parts, such as green vegetables, spinach, celery, mustard, chrysanthemum, amaranth, water spinach, alfalfa and so on. High water content, many kinds and quantities of enzymes, vigorous respiratory metabolism, rapid decomposition of substances and poor disease resistance. Young cucumbers, loofah, kidney beans, peppers and eggplant are also not resistant to storage, while mature wax gourd and pumpkin are more resistant to storage.
Vegetables with nutrient accumulation organs as edible parts-tubers, tubers, bulbs and bulbs are also more resistant to storage, among which late-maturing varieties are more resistant to storage and have stronger disease resistance than early-maturing varieties, and people need to know this knowledge.
Baidu encyclopedia-vegetables