送交者: 桂铭 于 2006-2-26, 10:26:57:
回答: 我只是讲了一点常识，很奇怪你会不懂。 由 方舟子 于 2006-2-26, 01:28:31:
III. PRESERVATION AND STORAGE. Liquid N2 is used to preserve tissue culture cells, either in the liquid phase (-196°C) or in the vapor phase (-156°C). Freezing can be lethal to cells due to the effects of damage by ice crystals, alterations in the concentration of electrolytes, dehydration, and changes in pH. To minimize the effects of freezing, several precautions are taken. First, a cryoprotective agent which lowers the freezing point, such as glycerol or DMSO, is added. A typical freezing medium is 90% serum, 10% DMSO. In addition, it is best to use healthy cells that are growing in log phase and to replace the medium 24 hours before freezing. Also, the cells are slowly cooled from room temperature to -80°C to allow the water to move out of the cells before it freezes. The optimal rate of cooling is 1°-3°C per minute. Some labs have fancy freezing chambers to regulate the freezing at the optimal rate by periodically pulsing in liquid nitrogen. We use a low tech device called a Mr. Frosty (C#1562 -Nalgene, available from Sigma). The Mr. Frosty is filled with 200 ml of isopropanol at room temperature and the freezing vials containing the cells are placed in the container and the container is placed in the -80°C freezer. The effect of the isopropanol is to allow the tubes to come to the temperature of the freezer slowly, at about 1°C per minute. Once the container has reached -80°C (about 4 hours or, more conveniently, overnight) the vials are removed from the Mr. Frosty and immediately placed in the liquid nitrogen storage tank. Cells are stored at liquid nitrogen temperatures because the growth of ice crystals is retarded below -130°C. To maximize recovery of the cells when thawing, the cells are warmed very quickly by placing the tube directly from the liquid nitrogen container into a 37°C water bath with moderate shaking. As soon as the last ice crystal is melted, the cells are immediately diluted into prewarmed medium.
http://www.research.umbc.edu/~jwolf/method5.htm
食物保鲜与细胞冷冻以复苏细胞的目的不一样。食物，尤其是肉类，快速冷冻可以阻止细胞内容物渗出，保持口味。
Freezing
The general rule of thumb is freeze fast at low temperature. Processing plants rapidly freeze product in blast freezers or cryogenically with condensed liquid nitrogen. The faster meat is frozen, the smaller the ice crystals are that form within the cells. Smaller ice crystals keep the natural cell structure of meat intact and lead to less moisture loss.
http://72.14.207.104/search?q=cache:ALwj-P7fchoJ:www.beefinfo.org/fs_foodsafety.cfm+beef,+freeze+fast+at+low+temperature&hl=en&gl=us&ct=clnk&cd=1