Fond memories of my grandmother’s larder, strike me as I tuck into my plate of curd rice, pickles accompanied by crunchy pappads (fryums or sun-dried snacks made of lentils which are fried before consumption). A quick fix lunch after a hectic morning – thanks to the traditionally preserved food in my store. As my taste buds get contented thus, my mind linked this to methods used in my research laboratory to preserve cells. What is done at home is done in the laboratory as well with much more fanfare. The principles remain the same though and that is what this article is going to be all about.
Before we delve into the principles, let us first look into why this may be needed. Some cells including umbilical cord blood cells are preserved for years and years using freezing techniques. Not just the regular freezer but in a kind of deep freezer. What happens when u take a lemon or grape or tomato and store it in the freezer. They stay without rotting no doubt but what happens when you remove them out of the freezer. They just break down into a mush (try doing that by yourself). This is what happens when one freezes cells in the laboratory too. Why does this happen?
As you all know cells are mostly composed of water. When one freezes cells as such, the water in the cytoplasm of the cell freezes as does the water in its external medium. These ice crystals are like sharp icicles or spears which can rupture the cell by punching holes in the membrane. This is why some special techniques are needed to reduce the water inside the cell and this is where some special agents like glycerol, Dimethyl Sulfoxide etc are used. They dehydrate the cell to some extent and also mediate the formation of blunt-edged ice instead of the sharp ones thereby minimizing injury to the cells during ice crystal formation. Preserving cells in the laboratory thus is called Cryopreservation (Cryo: frost) and the agents used (glycerol etc) are called Cryoprotectants. Solid carbondioxide (dry ice), Liquid Nitrogen, deep freezing are the methods used to cryopreserve cells.
Dehydration has been a method of choice during food preservation as well. Right from pappads to sun-dried vegetables or using brine (salt) to suck out the water from cells, all these methods rely on the principle of dehydration to reduce the water content and thus also enhance the storage life of the food being preserved.
Other than food preservation, even mummification uses methods involving salts to suck out the moisture from the body to be preserved.
Water, while is the elixir of life is also what needs to be kept on hold while trying to preserve things in its most natural form.
Fun exercise: Place a grape, and a raisin (dry grape) inside the freezer for 24 hours. Observe their texture, firmness before doing so. Remove it from the freezer and keep it at room temperature for some time. Observe the texture, firmness now. Share your observations in the comment box below or write to us with pictures of your mini-experiment.
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