Physiological changes and preservation of the hott

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Physiological changes and preservation of vegetables after harvest (Part 1)

vegetables are still living organisms in storage. It needs to resist the invasion of adverse environment and pathogenic microorganisms, maintain quality, reduce consumption, and extend storage period. Therefore, the normal life process of fresh vegetables must be maintained during storage, and the changes of appearance, color, weight, hardness, taste, aroma and so on must be minimized to achieve the purpose of fresh preservation. Therefore, it is necessary to adopt the corresponding fresh-keeping technology according to the physiological changes of vegetables after harvest to promote the healthy development of China's vegetable industry

first, reduce respiration and prolong storage period

during storage, the respiratory intensity should be reduced as much as possible. The stronger the respiration, 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 age. Generally, leafy vegetables have the highest respiratory intensity, followed by fruit vegetables, and taproot, tuber and bulb vegetables have the lowest respiratory intensity; The respiratory intensity of late maturing species was stronger, while that of early maturing species was weaker; The respiratory intensity is strong in childhood, and the cooperation with parts manufacturers and automobile engine manufacturers is getting closer and closer. The mature period is weak. In addition, temperature, atmospheric composition, mechanical injury, pests and diseases also have a great impact on the respiration of vegetables. The temperature is high and the respiratory intensity is high. The respiratory intensity increases every 10 ℃ between ℃ 5 times, more than 35 ℃, respiratory intensity decreased significantly; The temperature is low, the respiratory intensity is weak, and the nutrients consumed are also less, but it cannot be considered that the lower the storage temperature, the better. If you reduce the oxygen concentration in the air, your breathing will be inhibited. Usually, the oxygen concentration will be reduced to about 5%, and the effect is good. Vegetables affected by mechanical damage and diseases and insect pests will strengthen respiration, so they should be removed when selecting storage samples

an effective method to reduce the respiration of stored vegetables is controlled atmosphere preservation. On the basis of mechanical refrigeration, this method adjusts the gas concentration in the storage environment, mainly reducing the concentration of oxygen and increasing the concentration of carbon dioxide, so as to inhibit the respiratory and metabolic intensity of post harvest vegetables and reduce the consumption of nutrients. At present, the most widely used modified atmosphere preservation technologies in China are plastic bag small package modified atmosphere, plastic large tent modified atmosphere and silicone rubber window modified atmosphere. In addition, there is decompression storage method, which is to reduce the air pressure in the storage place, generally to 1/10 of the atmospheric pressure, resulting in a certain vacuum, so as to achieve the purpose of reducing oxygen. This is a new technology for the preservation of vegetables and many other foods, and a further development of modified atmosphere refrigeration. Decompression storage has a wide range of adaptability. Spinach, lettuce, green beans, shallots, radish, mushrooms, tomatoes and other species have a better effect under decompression storage. Tomatoes have the best storage effect by using this method, and the fresh-keeping period can reach more than 3 months

second, reduce the transpiration of stored vegetables

the water content of fresh vegetables is as high as%, which is easy to transpiration and dehydration during storage. If it is not supplemented, it will cause tissue wilting, shrinkage, gloss fading, loss of weight and freshness of vegetables, and reduce the eating quality. Therefore, it is very important to reduce the transpiration and wilting of stored vegetables. According to the characteristics of different vegetables, the environmental conditions during storage should be controlled, such as the leaf surface area of leafy vegetables is large, the stomata of growing leaves and young leaves are more and larger, the transpiration is serious, and they are most prone to dehydration and wilting during storage. Therefore, it is necessary to increase the air humidity of the storage room (storehouse), reduce the air flow, make the stored vegetables in a high humidity environment, and minimize the transpiration. In addition, the selection of appropriate packaging materials is also an effective measure to improve the preservation technology. Vegetables with severe evaporation of water and other vegetables should use anti turbidity packaging materials. This kind of film is hydrophobic. In order to improve the hydrophilicity, surfactant can be coated to form a thin water film on the surface of the film, which can not only prevent turbidity, but also prevent moisture condensation in the package. Water evaporation inhibitor, ethylene adsorbent, bactericide, refrigerant storage agent, etc. can also be put in the package to help keep fresh

III. inhibit Post Harvest Ripening and aging

fruits and vegetables, nodulation, root vegetables, etc. have post ripening effect during storage. A series of physiological and biochemical changes often occur in the post ripening process, such as the hydrolysis of starch into sugar, the reduction of organic acid content, the solidification and oxidation of tannins, the decomposition of original pectin into pectin dissolved in water, the decomposition of chlorophyll, the improvement of flavor, the production of aromatic components, and the change of texture from hard to soft. Therefore, using this post ripening effect, vegetables can be harvested early and suitable conditions can be created during storage to maintain post ripening ability. The commonly used method is to reduce the temperature of the storage room, maintain high humidity, timely ventilate, eliminate the accumulated ethylene and other gases, inhibit the activity of hydrolases, delay the hydrolysis rate, and prevent the consumption of nutrients, so as to achieve the purpose of inhibiting post ripening and extending the storage period

vegetables enter the aging stage from the beginning of harvest, which is manifested in the reduction of the number of sugar bodies in the cell core, the collapse of chloroplasts, the reduction of mitochondria, cell aging, intolerance to storage, and perishable. Aging is closely related to the content of ethylene, gibberellin or other hormones in vegetables and their changes during storage, as well as the growth and development of vegetables and storage conditions. To delay the aging of vegetables and extend the storage period, first, choose vegetables that are more and more difficult to live and grow well for storage; Second, strictly control the content of ethylene and other hormones in vegetables during storage, so as to delay the aging of vegetables; The third is to create the best storage conditions, such as controlling temperature and humidity, gas composition and proportion, etc

(to be continued)

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