Physiological Changes and Preservation of Postharvest Vegetables

Vegetables are still living organisms in storage. They need to resist the adverse environment and pathogenic microorganisms, maintain quality, reduce losses, and prolong the storage period. Therefore, the normal life process of fresh vegetables must be maintained during storage to minimize changes in appearance, color, weight, hardness, taste, flavor, etc., in order to achieve the purpose of preservation. For this reason, it is necessary to adopt appropriate preservation techniques for the physiological changes of vegetables after harvest to promote the healthy development of the vegetable industry in China.

First, reduce the respiration, extend the storage period

In the storage of fruits and vegetables, the respiratory intensity should be reduced as much as possible, the more vigorous the respiration, the faster the change of various physiological processes, the sooner the life is terminated, and it is not conducive to storage. The difference in the respiratory intensity of vegetables depends on the species, breed, and age. Leaf vegetables usually have the highest respiratory intensity, fruit and vegetable are the second, and roots, tubers and bulbs are the least. Late maturation has stronger respiratory intensity and early maturing species are weaker; younger stage has stronger respiratory intensity and weaker mature stage. In addition, temperature, atmospheric composition, mechanical injury, pests and diseases also have a great influence on the respiration of vegetables. High temperature, high respiratory intensity, between 5-35°C, every 10°C increase, respiratory intensity increases 1-1.5 times, exceeds 35°C, respiratory intensity decreases greatly; temperature is low, respiratory intensity is weak, and nutrient consumption is also lower Less, but do not think that the lower the storage temperature, the better. Reducing the concentration of oxygen in the air, breathing will be suppressed, usually the oxygen concentration is reduced to about 5%, and the effect is good. Vegetables that are damaged by machinery and pests will increase their breathing and should be removed when selecting storage samples.

An effective method to reduce the respiration of stored vegetables is air fresh-keeping. This method is based on the mechanical refrigeration, adjust the gas concentration in the storage environment, mainly to reduce the concentration of oxygen, increase the concentration of carbon dioxide, in order to inhibit the respiratory metabolism of post-harvest vegetables, reduce the consumption of nutrients . At present, China's application of more air-conditioning fresh-keeping technology is a small plastic bags, air conditioning, plastic large account of the atmosphere and the atmosphere of silicone rubber window. In addition, there is a vacuum storage method, which is to reduce the pressure of the storage place, generally to 1/10 of the atmospheric pressure, resulting in a certain degree of vacuum, so as to achieve the purpose of reducing oxygen, which is a new technology for the preservation of vegetables and many other foods , is the further development of modified atmosphere refrigeration. The scope of decompression storage is wider, spinach, lettuce, green beans, shallots, radishes, mushrooms, tomatoes and other species have better storage under reduced pressure. The best storage effect using this method is tomato, and the fresh-keeping period can reach 3 More than month.

Second, reduce the transpiration of storage

The moisture content of fresh vegetables is as high as 65-95%. It is easy to evaporate and dehydrate in storage. If it is not supplemented, it will cause wilting, wrinkling, and fade of luster, which will cause loss of weight and freshness of vegetables and reduce food quality. Therefore, it is very important to reduce the transpiration and wilting of storage vegetables. According to the characteristics of different vegetables, the environmental conditions during storage should be controlled. For example, the leaf surface area of ​​leafy vegetables is larger, the stomata of the growing leaves and young leaves are larger, and the transpiration is serious. , Dehydration and wilting most easily during storage. Therefore, it is necessary to increase the air humidity of the storage room (library) and reduce the air flow, so that the storage dish is in a high-humidity environment and the transpiration is minimized. In addition, the use of appropriate packaging materials is also an effective measure to improve preservation technology. For vegetables with strong evaporation of moisture, etc., it is better to use anti-turbid packaging materials. Such films are hydrophobic. To increase the hydrophilicity, surfactants can be applied to make the surface of the film produce a thin film of water. This can not only prevent turbidity, but also prevent Water condensation in the package. In the package, moisture evaporation inhibitors, ethylene adsorbents, bactericides, coolants, etc. can also be added to help preserve freshness.

Third, post-harvest post-harvest and aging inhibition

Fruit vegetables, knots, root vegetables, etc., have a ripening effect during storage. In the process of ripening, a series of physiological and biochemical changes often occur. For example, the starch is hydrolyzed into sugar, the content of organic acid is reduced, the tannins begin to solidify and oxidize, the protopectin is decomposed into pectin dissolved in water, chlorophyll decomposes, and the flavor is improved. Produces aroma ingredients, texture from hard to soft. Therefore, by utilizing this post-maturation, vegetables can be harvested earlier and suitable conditions can be created during storage to maintain the subsequent ripening power. Commonly used methods are to reduce the temperature of the storage room, maintain high humidity, timely ventilation, eliminate accumulated ethylene and other gases, inhibit the activity of hydrolytic enzymes, delay the hydrolysis rate, prevent the consumption of nutrients, can inhibit the post-maturation, extend storage The purpose of the period.

From the beginning of harvest, vegetables will enter the aging stage, showing a decrease in the number of ribosomes in the cell's inner core, the collapse of the chloroplasts, the reduction of mitochondria, the aging of cells, the impatience of storage, and the perishability. Aging is closely related to the content of ethylene, gibberellin or other hormones in vegetables and changes in storage, the growth and development of vegetables, and storage conditions. To delay the aging of vegetables and prolong the storage period, one is to select healthy and well-growing vegetables for storage; the other is to strictly control the content of ethylene and other hormones during storage in order to delay the aging of vegetables; third is to create optimal storage. Conditions, such as control of temperature and humidity, gas composition and proportioning.

Fourth, pay attention to the pre-cooling and low-temperature storage in the production area and reduce the loss of food storage

Precooling in production areas is the key to the preservation of vegetables after harvest. With the development of vegetable exports, pre-cooling of vegetable production areas is increasingly valued. The role of pre-cooling is to quickly remove field heat, effectively reduce the vegetable's own metabolic level, reduce nutrient consumption, delay aging, and extend the shelf life of vegetables. At high temperatures, prolonging the time it takes to receive precooling from the harvest will promote the aging of the vegetables and significantly shorten the shelf life of the vegetables. Low temperature can effectively inhibit the growth and activity of rot bacteria and reduce loss, which is also a key factor for storing vegetables. After the vegetables are pre-cooled in the production area, they are transported by the refrigerated container and entered into circulation. After being sold to the market, they enter the refrigerated warehouse or sales refrigerated cabinet, which can maximize the quality of the vegetables and reduce the circulation loss. Because various vegetables have different reactions to temperature, determining the storage temperature of vegetables must be based on the adaptability of the vegetables to low temperatures. For example, green ripe tomato storage temperature is 10-12°C, sweet 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, spinach It is -6 to 0°C, cauliflower is 0 to 0.5°C, onion is -3 to 0°C, and garlic is -1 to 0°C. It can be seen that most of the vegetables are suitable for storage at low temperatures around 0°C. If it is lower than this temperature, vegetables will also be frozen. After the vegetables are frozen, the tissues and cells are destroyed by mechanical forces and produce dehydration. Some of the vegetables were destroyed after the cells were frozen; after thawing, the juice bleeds, losing the commodity and food value. However, some vegetables are more tolerant to cold, such as spinach can be rejuvenated at -9 °C, suitable for frozen possession.

V. Delay material conversion and consumption and maintain the quality of storage

After the harvest of vegetables, the accumulation of substances ceases, the dry matter no longer increases, the various substances that have been stored gradually consume, or under the catalysis of enzymes, undergo transformation, transfer, decomposition and recombination, and the morphology, structure and characteristics of the tissues and cells A series of changes have taken place in such areas. If the cabbage is sweetened after storage, the texture is soft and the green fades. The green ripe tomato is hard and green, gradually degreening during storage and appears red or yellow, the flesh is softened, the acidity is reduced, and the vegetable flavor, texture, nutritional value, commerciality, storability, and disease resistance are all significantly changed. .

During the storage of vegetables, the dynamic equilibrium of the synthesis-hydrolysis of various substances is constantly changing. The synthesis process of most vegetables in storage is gradually weakened, the hydrolysis process is continuously strengthened, and simple hydrolysates are accumulated, thereby stimulating respiration and being conducive to microbial infection. The conversion of pectin substances reduces the mechanical resistance of vegetables.

The change in the color of vegetables is often a sign of aging. At the same time, vitamin C in vegetables gradually decreases at different speeds during storage. For this reason, delaying the transformation and consumption of nutrients in vegetables is one of the keys to maintaining the quality of the dishes. Commercial use of reducing respiration, inhibiting ripening and senescence, and creating optimal storage conditions and gas composition are satisfactory. result.

Six, improve the tolerance and disease resistance

The storage tolerance of vegetables means that after a period of storage, the food value and flavor characteristics are not significantly reduced and the weight loss is small; the disease resistance is the ability to resist the invasion of rot bacteria. The two are closely related to each other and depend on each other. Vegetables with high tolerance to Tibet have strong immunity against rot bacteria, and vice versa. In terms of the characteristics of vegetables, vegetables that use vegetative organs as edible parts, such as vegetables, spinach, celery, mustard, garland chive, leeks, spinach, wolfberry, etc., have more water content, more types and quantities of enzymes, respiratory metabolism, and substance decomposition. Fast, mostly intolerant of storage, poor disease resistance. Young cucumbers, loofahs, beans, peppers, and eggplants are not tolerant of storage, while old ripe wax gourds and pumpkins are more resistant to storage. Vegetables with nutrient-accumulating organs as edible parts - tubers, tuberous roots, leaf balls, and bulbs - are also more resistant to storage, among which late-maturing ones are more resistant to storage than early maturing ones.

We mainly export European Chinese onions, garlic and ginger.

Fresh yellow onion and red onion size 60-80mm 70-90mm 90-110mm 10kg/net bag, 20kg/net bag or 25kg/net bag (2019 new crop onion)

Peeled yellow onion and red onion size 60-80mm 70-90mm 90-110mm 10kg / box, 20kg / box, filled with nitrogen, storage time of 90 days.

Frozen onion, frozen onion cube, frozen onion ring 10kg/box or 20kg/box Save for 2 years.

We also offer garlic, ginger and peeled garlic

Our onions have been sold in the Netherlands, the UK, Poland, and Italy, and the quality is very good.

Looking forward to your response, I am very happy to quote you.


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garlic.Ginger.onion.peeled onion.peeled garlic.frozen onion pieces

henan junzhian food co., ltd ,