How much do you know about frozen fruits and vegetables?

Release time:

2023-04-27

Blanching is carried out with high-quality vegetables. When the vegetables are turned into dark green, they can be scooped up and cooled in cold water. The cooled vegetables are dried in a centrifuge and then frozen. The vegetables are quickly frozen in a cold air environment of minus 33 degrees Celsius to minus 40 degrees Celsius for about 45 minutes * the vegetables are formed at different times *, and then cold water is entered to form thin ice on the surface to prevent oxidation.
The purpose of blanching is to kill fungi and achieve the purpose of preservation. Water above 40 degrees Celsius can inactivate biological enzymes in vegetables, thus slowing down biological and physiological reactions. The shorter the freezing time, the better the quality of frozen fruits and vegetables.
Freezing process and its principle When the water in fruits and vegetables is reduced from the starting temperature to the freezing point below 0 ℃, it changes from liquid to solid, that is, ice. As the temperature decreases, ice crystallization increases, and fruits and vegetables harden and become frozen. The freezing point of fruits and vegetables varies according to their species (Table 1). Most vegetables begin to freeze at a temperature of about -1 ℃. When the temperature continues to drop to about -5 ℃, 70-80% of the water freezes and the fruits and vegetables harden. That is, at a temperature of -1 ~-5 ℃, a large number of ice crystals are formed, which is called the large formation stage of ice crystals. If the temperature is further reduced to -30 ~-35 ℃, the freezing process is completed. At different temperatures, the moisture in fruits and vegetables has a corresponding freezing rate (Table 2). Therefore, in order to completely freeze the water in the fruit and vegetable, it is necessary to lower the temperature to the eutectic point, that is, the temperature at which the freezing rate of the water reaches 99.99 percent.
Quick-frozen fruits and vegetables Quick-frozen processing In the quick-frozen processing of fruits and vegetables, the steps of raw material selection, cleaning, peeling, cutting and blanching are basically the same as those of vegetable drying and canning. After blanching, the fruits and vegetables should be cooled and rinsed with clear water in time, and then frozen by blast freezing or fluidized bed freezing method at a low temperature of -30 ~-35 ℃. The packaging is made of polyethylene plastic bags or plastic boxes, which are divided into two types: pre-frozen packaging and post-frozen packaging. Generally, dry packaging is adopted, but 2% salt water can also be added for wet packaging for pre-frozen packaging, such as quick-frozen processing of mushrooms.