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  If you need a Chinese Frozen Fruits and vegetables, you need to understand the problem

1. The frozen effects on fruit and vegetable organizational structure
In general, plant cell tissue in the freezing process can result in changes of cell membrane, increase permeability, reduce pressure, that is cold treatment to increase the permeability of the cell membrane or cell wall of water and ions, it might cause tissue damage. , in the process of frozen fruits and vegetables were too cold limited to its several degrees below freezing temperature, and time is short, within a few seconds of mostly, under the special situation also has a long time and lower super-cooling temperature cold. During the freezing, the moisture of intercellular frozen before the moisture in cell protoplast, even as low as a 15 ℃ under the freezing temperature of protoplast can still maintain its too cold. Too cold water in the cell than outside the cell has high vapor pressure of ice crystals and the free energy, thus the moisture inside the cell by cell to extracellular, cause extracellular ice crystal growing, the inside of the cell solution concentration increasing, the situation until intracellular water freezes. Tissue freezing temperature and freezing rate of fruit and vegetable is its internal soluble solids, such as salt, sugar and acid concentration control.

In the case of slow freezing, ice crystals are mainly formed in the intercellular space, intracellular water being drained, the protoplast of inorganic salt concentration increasing, sufficient to precipitate protein, make its degeneration or irreversible coagulation, causing cell death and disintegration of organization, the quality of a material softening. In the case of quick-frozen is different. Such as quick-frozen tomatoes, the organization of parenchyma cells under a microscope, reveal the inside cells and cell wall of ice crystals are very tiny, intercellular space not enlarge 3 v, the protoplasm against the cell wall, prevent the outward flow of water, the tiny ice crystals will have little impact on the organization structure. Observed in the rapidly thawing damage to the protoplasm is extremely small, plastid relatively intact, tonoplast sometimes not compromised. Maintain the structural integrity of cell membrane, such as to maintain static pressure inside the cell is very, can prevent Browning.
Important, can prevent flow softening juice and organization. Frozen fruit and vegetable storage purpose is to keep its characteristic of fresh fruits and vegetables as much as possible, but during the freezing and thawing, texture and appearance of the product compared with fresh fruits and vegetables, there are differences. Organization's collapse, the degree of softening, flow juice varies because of the product types and conditions, such as rhubarb fleshy tissue cells although have rigid cell walls, but frozen in the organization form of ice crystals, cell wall separation in the cells, many cells near the frozen crystal was crooked and collapse, content of logistics in the intercellular space to the cell, the juice loss after thawing. Asparagus with temperatures in not frozen, it is difficult to restore to its original freshness but thawing.
A thought, frozen fruit and vegetable tissue destruction caused by the cause of softening, flow juice, etc., the direct impact is not due to low temperature, but by the crystal) caused by mechanical damage. At the same time, the intercellular space of frozen cells caused by dehydration, higher concentration of salt solution, destroy protoplasm colloid properties, causing cell death and losing the control ability of fresh features.

2. Caused by chemical changes during freezing and frozen fruits and vegetables raw material during cooling and freezing, frozen storage and thawing is likely to make its flavor, texture and color, nourishment composition change, thus affecting the quality of the products.
(1) the stale During the freezing and storage, accumulates carbonyl compounds in fruit and vegetable group and ethanol, etc., to produce volatile odor. Raw material contains lipid content more, due to the oxidation also can produce peculiar smell. Have been reported, peas, green beans and sweet corn in the frozen storage changing lipid, free fatty acids in their lipid, etc have been increased significantly.
(2) the quality of a material soft frozen and thawed soften fruit and vegetable group, one of the reasons is due to the existence of pectinase, make the original pectin hydrolysate soluble pectin, causing separation of organization structure, quality of a material softening. In addition, frozen cells in the inland waters especially permeability, thawed cannot recover all absorbed by the plasma, Jdz easy to soften fruits and vegetables.
(3) discoloration Freezing storage period, the colour and lustre of fruits and vegetables also have varying degrees of change, the main is changed from green to celadon. This is due to the chlorophyll into magnesium chlorophyll off, affect the appearance, the lower the value of commodities. In the aspect of color change, fruits, vegetables, Browning in freezing and storage, especially after thawing changes in brown as serious. This is because the phenolics under the action of enzyme, the result of oxidation, such as apples, pears of chlorogenic acid, catechin, etc is the main component of the role of polyphenol oxidase, the enzymatic Browning reaction is rapid, change color quickly, affect the quality.
For the enzymatic Browning to take some prevent measures, such as raw material for heat treatment, combined with inhibitor (so) and Ascorbic Acid (4) the change of the nutrient Frozen itself has the protection of nutrients, the lower the temperature, the more protection. Because the organic material is closely relative to chemical reaction speed and temperature. But a series of processing of raw materials before freezing, such as washing, peeling, segmentation process, the raw materials exposed to air, vitamin c because of oxidation and reduction. These chemical changes in the frozen continue thermal fluid activity, but much more slowly. Vitamin B. Are heat sensitive, but rarely in cold storage loss. Vitamin B before freezing process is reduced, but the loss is not much in the frozen storage. Frozen products of color change, flavor many was conducted under the participation of enzyme. The activity of enzyme is affected by temperature is very large, but also affected by pH value of the matrix. Enzyme activity in 93.3 ℃ or so, the destruction, and the temperature dropped to 73.3 oC, there are some active exists, but greatly reduced the rate of enzymatic reactions. Frozen food make only inhibition of enzyme activity, reduce its activity, but the enzyme activity did not disappear. Instead, enzyme in extreme cold conditions, its activity is often inspire. Therefore, in order to keep frozen fruits and vegetables of good quality, general requirements frozen storage temperature is not higher than a l8 ℃, some countries have adopted the lower frozen storage temperature. 3. The frozen effects on microbial microbial growth, reproduction and the activities of hazard has its appropriate temperature, more than or less than optimum temperature, microbial fertility and activities is gradually weakened until stopped or killed. Most microbes grow in the fall under the temperature of 0 oc activities will be suppressed. Fruit and vegetable raw materials before freezing, vulnerable to bacterial infection. And the longer the time dragged the heavy infection. Sometimes raw material after heat packing frozen immediately, due to the packaging materials hinder the heat conduction, slow cooling, especially packaging center temperature drop slowly, there is still a microbial spoilage occurred during freezing. Therefore, best before packaging materials cooled to near freezing temperatures, and then to packing frozen safer. Pathogenic bacteria in food freeze survival rate after falling rapidly, the frozen on the thermal fluid activity inhibition and killing effect is very slow. The experiment proved that spore mold can grow under the condition of a 2 ℃. Spore powder can mould and yeast in _4 ℃ under the condition of growth, some sex psychrophilic bacteria can survive in a 10 oc ~ 20 oc. As a result, the temperature of frozen fruit and vegetable storage is a temperature 18 ℃ or lower. Freezing can kill many bacteria, but not all bacteria. Some mold, yeast and bacteria can survive for several years in frozen food. Frozen fruits and vegetables once thawed, suitable temperature and humidity, residual microbial activity, causing rot, so food should be eaten as soon as possible after thawing.

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