What aspects can be used to evaluate the quality of frozen vegetables?

Frozen vegetables are small packaged foods made by processing fresh vegetables and then quickly freezing, packaging, refrigeration and other processing methods. Therefore, it has the same advantages as other frozen foods, which are manifested in the following aspects.

1. It can be stored for a long time.

Since the flash freezing of vegetables is carried out at a low temperature of -18. Uniform and fine ice crystals are formed inside the tissue, which will not destroy the cells of vegetables and effectively avoid the chemical reaction of vegetable cells.

and inhibit the growth of microorganisms, so it can achieve the purpose of long-term storage and preservation. Under normal circumstances, quick-frozen vegetables produced in the summer can be stored for sale in the winter or spring. If the warehouse refrigeration temperature is lower than -18, the storage period is longer.

2. Quality 1) The original color, nutrients and flavor of fresh vegetables have been well guaranteed.

2) Less juice loss after thawing.

3) After cooking, it can maintain the shape of the dish, the taste is good, and there is no frozen vegetable taste.

3. Packing, easy to transport.

Because quick-frozen vegetables are loose in a single form, they are very convenient to weigh, package and seal compared with fresh vegetables. In the case of outer packaging, refrigeration and transportation are simpler.

4. Pay attention to hygiene and easy to eat.

Because quick-frozen vegetables have been sorted, cleaned and blanched before freezing and processing, and the hygienic conditions of these processing processes are very strict, therefore, quick-frozen vegetables generally meet the food hygiene standards. In addition, because quick-frozen vegetables do not require any processing during cooking and can be used as they are needed, it has the advantage of saving time.

Of course, quick-frozen vegetables also have their limitations, the main being that their quality is lower than that of fresh vegetables. That is, after a few months of refrigeration of quick-frozen vegetables, their nutrients are slightly lost. But it still has a high edible value. The nutritional content of quick-frozen vegetables is mainly based on vitamin C

Generally speaking, the loss rate of vitamin C does not exceed 40, which is considered normal. The data showed that the loss rate of vitamin C of fresh vegetables reached about 40 when they were stored at L0 for 4-6 days.

To evaluate the quality of refrigerated vegetables, it can be evaluated by the following aspects:

Clause. 1. Most of the current fruit and vegetable storage is low-temperature storage. The use of low-temperature storage of fruits and vegetables is mainly to weaken the respiration and water evaporation of fruits and vegetables, delay metabolic activities, minimize the consumption of nutrients, and better maintain the integrity of fruit pulp cells and the nutritional quality of fruits, so as to achieve the purpose of storage and preservation.

Clause. 2. Through the study of the changes in the appearance and main nutrients of fruits, experts have found the most suitable temperature for the storage of various fruits and vegetables, so as to provide scientific methods for people to reasonably store fruits and obtain fresh and nutritious fruits and vegetables.

Clause. 3. The appearance and taste of fruits and vegetables. This is the first threshold to test the quality of fruits and vegetables. For example, if the color of the skin is pure, how soft and hard the texture is, what the taste is, whether there is an ethanol taste, etc.

Clause. Fourth, different storage temperatures have a significant impact on the sensory quality of fruits and vegetables, especially low temperature can significantly inhibit the growth of microorganisms, delay browning, and in the high temperature environment is easy to be infected by microorganisms, browning, and easy to lose water and age, affecting the taste of food, some studies believe that the ethanol content of storable varieties is low, with the extension of fruit storage time, ethanol content increases.

Clause. 5. The sensory quality of fruits and vegetables has a great impact on their commodity value. Therefore, it is necessary to study the effect of storage temperature on it.

From production to trading, quick-frozen vegetables are not good, mainly based on the initial quality and the final quality. The initial quality is determined by how the ingredients are processed and packed before they are frozen. The final quality is determined by the relationship between the time and temperature that the frozen food can withstand when it is held.

The initial quality of quick-frozen vegetables is good, but the final quality changes after each distribution process reaches people's hands. The quality of the product also changes when it is frozen, and the degree of change mainly comes from the temperature and the length of time it has been frozen. The lower the temperature, the less the change in mass and the longer the freezing time; At a consistent temperature, the longer the refrigeration, the greater the change in quality and the worse the final quality.

From 48 to 58 years, after many experiments in the United States, it was concluded that there is a relationship between the quality of frozen food and the temperature of freezing, and called this relationship. The quality of quick-frozen vegetables comes from the problems in each link of this project, and high-quality products cannot be obtained. Therefore, only by using good raw materials and scientific methods for refrigeration, but also with good materials for packaging, can you get good quick-frozen vegetables.

Value: Quick-frozen vegetables have higher nutritional value than fresh vegetables Advantages: 1. It can be stored for a long time.

2. Freeze***.

3. Packing, easy to transport.

4. Pay attention to hygiene and easy to eat.

What are the benefits of frozen vegetables: 1. It is easier to store Frozen vegetables are directly picked vegetables and put them in the freezer to freeze directly, which can extend the shelf life of vegetables by 1 or 2 months. 2. Nutrition preservation is more comprehensive Vegetables are kept fresh, the longer the time, the more nutrients will be lost, and when the vegetables are frozen, they will not affect their minerals, vitamins and dietary fiber content.

1) Before freezing, reduce the initial temperature of the food as much as possible so that it is close to the freezing point of fruits and vegetables.

2) Where possible, reduce the temperature of the cooling medium as much as possible.

3) Reduce the thickness and size of fruits and vegetables as much as possible according to your living habits.

4) Increase the flow rate of cold air and increase the convection coefficient, but it should not be too large.

5) Monomer freezing is used to increase the contact area between the frozen product and the cooling medium. Therefore, it is desirable to use a fluidized bed freezing device.

Summary. Lesions and decay often occur during the storage and transportation of fruits and vegetables, resulting in storage losses, and farmers should try to avoid them.

What are the possible adverse changes in vegetables during storage? What is the impact on the quality of vegetables? What can be done.

Lesions and decay often occur during the storage and transportation of fruits and vegetables, resulting in storage losses, and farmers should try to avoid them.

Chilling injury In order to reduce the loss of chilling injury, the storage of hail oranges at the chilling injury temperature should be avoided. If it has been affected by the chilling temperature before harvesting, it is advisable to put it in a warmer place for a short time after harvesting, or use a slow cooling method. If fruits and vegetables have been seriously affected by chilling injury, the original storage temperature should be maintained or slightly lower than the original storage temperature, and as soon as possible out of the warehouse for sale, such as a sudden increase in storage temperature, will accelerate the decay of fruits and vegetables.

In addition, the combination of pre-cooling, maintaining high humidity and controlled atmosphere storage is also an effective measure to reduce chilling damage. Rapid cooling can promote the occurrence of chilling injury, and gradual cooling can mitigate this effect. Therefore, when storing fruits and vegetables in cold storage, the temperature should not be adjusted very low as soon as they are stored, but the storage temperature should be gradually reduced.

Gas Injuries Oxygen concentrations that are too low or carbon dioxide concentrations are too high can cause physiological harm. Different fruits and vegetables can tolerate different concentrations of low oxygen and high carbon dioxide during storage, so they should choose fresh-keeping bags with different air permeability during storage to avoid injury caused by gas discomfort, which is also the main reason why different fruits and vegetables should use different varieties of fresh-keeping bags.

The causes of postharvest diseases in fruits and vegetables are complex, and the prevention and control measures of diseases are closely related to these factors. According to the survey, most postharvest diseases and field diseases are the same pathogenic bacteria. Preharvest disease prevention should adopt a variety of comprehensive cultivation measures to ensure the healthy growth of fruits and vegetables, including the selection of disease-resistant and storage-tolerant varieties for cultivation, field sanitation management, and the selection of appropriate pesticides for prevention and control (the safety interval is 7 to 14 days).

At the time of harvesting, healthy plots should be selected for harvesting, and fruits that are not diseased or injured from diseased plots should not be selected for storage. Some pathogenic bacteria in postharvest diseases of fruits and vegetables are highly parasitic, but more pathogens are weakly parasitic or saprophytic, which need to invade from wounds or occur in large quantities when the product is subjected to physiological injury (such as cold injury). For this type of disease, the following measures have a certain prevention and control effect:

1.Minimize mechanical damage; 2.During harvesting, sharp scissors are used to cut the fruit stalk into a smooth incision, so that the incision can form a callus as soon as possible; 3.

Pluck the withered petals. During the harvesting and transportation process, attention should also be paid to the cleanliness and hygiene of the packaged items used, and the vegetable baskets used for loading vegetables should be disinfected before use. The appropriate temperature should be strictly controlled during storage.

Most of the postharvest diseases of the pre-key car develop rapidly at higher temperatures, and suitable low temperatures can control their development. However, fruits and vegetables should not be stored at too low temperature to cause chilling damage, and the appropriate storage temperature should be strictly controlled to reduce rot loss. In order to prevent water loss in the storage of fruits and vegetables, plastic film is often used to package, so it is often in a high humidity state.

Combined with appropriate chemicals, decay can be significantly reduced. Such as anti-mildew smoke.

What are the possible adverse changes in vegetables during storage? What is the impact on the quality of vegetables? What can be done.

The storage of vegetables and the respiration of medium rulers can reduce the respiration of vegetables and prolong the storage period of vegetables. The more vigorous 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 intensity of respiration in vegetables varies depending on the type of vegetable, the growing period, etc.

In general, leafy vegetables have the highest respiration intensity, followed by fruit vegetables, and straight-rooted, simple tubers and bulb vegetables are the smallest. The respiration intensity of late-maturing varieties was stronger, and that of early-maturing varieties was weaker. The respiratory intensity is stronger in the early age stage and weaker in the mature stage. In addition, temperature, atmospheric composition, mechanical damage, pests and diseases also have a great impact on the intensity of respiration in vegetables. At 5 35, for every 10 rises, the respiration intensity increases by 1 times; Above 35, the intensity of respiration decreases significantly.

The temperature is low, the respiration intensity is weak, and the nutrients consumed are also less, but it cannot be considered that the lower the storage temperature, the better. Reducing the concentration of oxygen in the air inhibits respiration, and usually the concentration of oxygen is reduced to about 5%, which is the best effect. Mechanical damage and pests and diseases can enhance the respiration of vegetables, which should be rejected when selecting samples for storage.

An effective way to reduce the respiration of stored vegetables is the modified atmosphere preservation method. This method is based on mechanical refrigeration, the gas concentration in the storage environment is adjusted, mainly to reduce the concentration of oxygen and increase the concentration of carbon dioxide, so as to inhibit the respiration intensity of postharvest vegetables and reduce the consumption of nutrients. At present, modified atmosphere preservation is widely used in China.

The more vigorous the respiration, the faster the changes in various physiological processes, and the earlier the termination of life, which is not conducive to storage. The respiration intensity of vegetables varies depending on the species, variety, and age. In general, leafy vegetables had the highest respiration intensity, followed by fruit and vegetables, and straight-rooted, tuber-and-bulb vegetables were the smallest. The respiration intensity of late-maturing varieties was stronger, and that of early-maturing varieties was weaker. The respiratory intensity is stronger in the early age stage and weaker in the mature stage.

In addition, temperature, atmospheric composition, mechanical injuries, pests and diseases also have a great impact on vegetable respiration. The temperature is high, the respiration intensity is large, between 5-35, every 10 rises, the respiration intensity increases by many times, more than 35, the respiration intensity decreases significantly; The temperature is low, the breathing intensity is weak, and the nutrients consumed are also less, but it cannot be considered that the lower the storage temperature, the better. Reducing the oxygen concentration in the air will inhibit respiration, usually reducing the oxygen concentration to about 5%, which is effective.

Vegetables that are subject to mechanical damage and pests and diseases can enhance respiration and should be rejected when selecting samples for storage.

An effective way to reduce the respiration of stored vegetables is the modified atmosphere preservation method. This method is based on mechanical refrigeration, the gas concentration in the storage environment is adjusted, mainly to reduce the concentration of oxygen and increase the concentration of carbon dioxide, so as to inhibit the respiratory and metabolic intensity of postharvest vegetables and reduce the consumption of nutrients. At present, the most widely used modified atmosphere preservation technologies in China are plastic bags and small packaging modified atmosphere, plastic large tent modified atmosphere and silicone rubber window modified atmosphere.

In addition, there is a decompression storage method, that is, the air pressure of the storage place is reduced, generally reduced to 1 10 of the atmospheric pressure, resulting in a certain vacuum, so as to achieve the purpose of oxygen reduction, which is a new technology for the preservation of vegetables and many other foods, and is the further development of modified atmosphere refrigeration. Spinach, lettuce, green beans, shallots, radishes, mushrooms, tomatoes and other species have a better effect under decompression storage, and the best storage effect by this method is tomatoes, and the shelf life can reach more than 3 months.

2. Reduce the transpiration of stored vegetables.

The water content of fresh vegetables is as high as 65-95%, which is easy to transpirate and dehydrate in storage, and if it is not replenished, it will cause tissue wilting, shrinkage, and luster fading, making vegetables weightless and fresh, and reducing the quality of eating. 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, such as the leaf surface area of leafy vegetables is larger, the stomata of growing leaves and young leaves are more and larger, and transpiration is serious, and it is most likely to be dehydrated and wilted in storage.