We all know that fruits and vegetables are demanding freshness, so the corresponding preservation technology is constantly updating and iterating. Among them, the quick-freezing technology of fruits and vegetables is rapidly developed and put into use in many places, but many people still know very little about it. Many people even hear about it. However, I will secretly doubt in my heart: Will the nutritional value of food after quick freezing be reduced? How long can I keep frozen for the longest time? What is the principle of it?
What is quick freezing?
Quick-frozen is a new technology developed rapidly in modern industry. It plays an important role in food preservation methods. It is an ideal method for maximally preserving the original flavor, fresh color and nutrients of fruits and vegetables.
What is frozen fruit and vegetables?
The so-called quick-frozen fruits and vegetables are the raw materials of the processed fruits and vegetables, which are frozen by the method of rapid freezing, and then stored at a low temperature of -18 ° C ~ -20 ° C for use.
You must know about frozen fruits and vegetables.
First, the raw materials for processing frozen fruits and vegetables should be fully mature, the color, fragrance and taste can fully emerge, the texture is crisp, the disease-free insects, no mold, no aging, yellow, no mechanical damage, the fruits and vegetables are used as processing materials, it is best to do Harvested on the same day, processed in time to ensure the quantity of products. Commonly used fruits are peach, apricot, pear, apple, plum, strawberry, raspberry, melon, cherry, mango, pineapple, kiwi and so on.
Second, pre-cooled freshly harvested fruits and vegetables, usually with atmospheric heat and released respiratory heat. To ensure fast freezing, it must be pre-cooled before quick freezing. The method has air cooling and cold water cooling, the former can be blown and cooled by a blower, and the latter is directly immersed or sprayed with cold water to cool it.
Third, the fruits and vegetables that are cleaned and harvested are usually accompanied by dust, sand and dirt. In order to ensure that the products meet the food hygiene standards, they must be cleaned before freezing. Especially for quick-frozen fruits and vegetables, because quick-frozen products are no longer cleaned when they are eaten, so this cleaning is very important, and it must not be ignored. In addition to manual washing, washing can also be carried out by washing machines (such as drum-shaped, vibrating mesh belt washing machines) or high-pressure water jet washing.
Fourth, the split frozen fruits and vegetables need to be peeled, go to the fruit handle or roots and can not be used seeds, tendons, etc., and cut the larger individual into a uniform, in order to package and freeze. The dicing can be carried out manually or mechanically, and usually the vegetables can be cut into pieces, sheets, strips, segments, silks and the like. It requires uniform thickness, uniform length and uniform specifications. The berry varieties are usually not cut, and only the whole fruit can be frozen to prevent the juice from being lost.
5. Hot blanching is mainly used for quick-frozen processing of vegetables. The goal is to inhibit the enzyme activity, soften the fibrous structure, remove the spicy scent and so on, in order to cook and process. Quick-frozen vegetables are not all varieties to be blanched, and should be treated differently according to different varieties. Generally speaking, vegetables containing more cellulose or used to cooking, stewing, etc., such as beans, cauliflower, mushrooms, etc., have a better effect after blanching. Some varieties, such as green peppers, cucumbers, spinach, tomatoes, etc., contain less fiber, and the texture is crisp and tender, so it is not suitable for blanching, otherwise the dish will soften, lose brittleness, and taste bad. Boiling 90-100 ° C, the product temperature should reach 70 ° C or more. The blanching time is usually 1-5 minutes. After blanching, it should be quickly picked up, and immediately put into cold water to cool, so that the temperature of the product drops to 10-12 ° C for use.
Sixth, the vegetables after the splitting, whether or not it has been blanched, its surface is often attached with a certain amount of water, if not removed, it is easy to form a block when frozen, which is not conducive to quick freezing, and is not conducive to post-freezing packaging. Therefore, it must be drained before quick freezing. There are many ways to drain. The vegetables can be placed in a bamboo basket on a shelf or placed flat on a single swing to allow them to dry naturally. Conditionally, they can be drained by a centrifugal dryer or a vibrating sieve.
VII. Quickly freeze and drain the vegetables after they are loaded or basketed. Strive to ensure that the body quickly passes through the ice crystal formation stage to ensure the quality of quick freezing in the shortest time. Only when the freezing is rapid, the water in the body can form small crystals without damaging the cell tissue. Usually, the peeled, cut, blanched or other solved raw materials are quickly frozen at a low temperature of -25 ° C - 35 ° C, and then packaged and stored.
8. Packaging and packaging are important conditions for storing fast-frozen fruits and vegetables. The function is to avoid monotonous situation of fruits and vegetables due to evaporation of surface moisture; avoid oxidative discoloration due to contact with air during storage; avoid air pollution (dust, slag, etc.), Maintain product hygiene; easy to transport, sell and consume. There are many packaging containers, usually tinplate cans, cardboard boxes, cellophane, plastic film bags and large barrels. Sealed after filling, it is ideal for vacuum sealing. Packing specifications can be based on the supply target, zero sales, usually 0.5 kg or 1 kg per bag, for hotels and hotels, can be loaded 5-10 kg. If it cannot be exported in time after packaging, it should be stored in a cold storage at -18 °C. The storage period varies according to the variety. For example, beans and cabbage can be refrigerated for 8 months. Cauliflower, spinach and green peas can be stored for 14-16 months. Carrots, pumpkins, etc. can be stored for 24 months.