I’ve you have ever visited a laboratory or museum & admired a pristine eyeball or a small deceased critter floating in glass jar, you’ve seen the preservation power of alcohol. The formal name of this method is fluid preservation. Scientists are counting on it since the 1600s to preserve their curious specimens. And, if done correctly, it can sustain a sample for many hundred of years, consistent with the American Museum of explanation .
But, how does it work?
“The long & short of it’s that it’s toxic to the sorts of microorganisms that might cause decay,” Bill Carroll, an adjunct professor of chemistry at Indiana University Bloomington. He used wine as an example. It’s made as yeast eats sugar from grapes then excretes alcohol. But the yeast excrete such a lot alcohol that the concentration becomes toxic & kills the yeast, he said. which alcohol content — around 14% — helps delay growth of bacteria for years (many wines also contain additional preservatives like sulfur), consistent with the California wine Advisor.
Preserving other organic material — like DNA, tissues or maybe entire animals — requires a better alcohol concentration, said Katherine Maslenikov, the fish collections manager at the Burke Museum in Seattle. Maslenikov typically relies on alcohol, specifically ethanol, for long-term storage.
For example, Maslenikov might take a fish specimen, remove some tissue samples for DNA analysis & inject the fish with formalin (a solution of formaldehyde gas dissolved in water) to prevent the interior biological processes, like enzymatic reactions & tissue degradation. Then, she might immerse the fish specimen in jar of 70% alcohol, 30% water. For long-term storage, “70% seems to be that magic-number ,” Maslenikov said. There’s enough water within the solution that the tissues will stay hydrated, which helps the animal or specimen hold its shape, and there is enough alcohol to stop mold & bacterial growth, she said.
Alcohol at even higher concentrations, as an example 95% ethanol, works as a dehydrant, meaning it removes & replaces the water within the cell, tissue or whole-body specimen with alcohol. the shortage of water causes changes to water-sensitive proteins; they unfold, or denature, and harden in place-next to at least one another, fixing the specimen’s shape, consistent with Ask a Biologist, a series run by Arkansas State University. This method may be a common way of preserving DNA, consistent with a 2013 study within the journal PLOS One.
It are often tricky deciding what percentage of alcohol to use. Using an excessive amount of or insufficient can affect the sample’s shape & flexibility , or maybe lower its ability to preserve the sample within the solution. High concentrations of alcohol wont to dehydrate a specimen will preserve it. But Maslenikov said this process also can leave a specimen shriveled (from the loss of water) & brittle (from the hardened proteins). Sometimes that’s OK; it all depends on what you’re trying to preserve.
Meanwhile, a specimen might deteriorate quickly if it retains an excessive amount of water.
“If an organism has enough water in its tissues, it can dilute the alcohol,” Christopher Rogers, an associate research professor at Kansas Biological Survey & Center for Ecological Research at the University of Kansas. If this happens, the alcohol concentration won’t be potent enough to kill lurking microorganisms which may be harbored deeper within the specimen, somewhere just like the gut of a whole-animal specimen. Those missed bacteria can decompose the specimen. “This is why it’s important to-change alcohol about 24 hours after pickling the critter,” because it boosts the solution’s alcohol concentration, Rogers said.
When it involves using alcohol as a preservative, Carrol said you are looking for concentration sweet spot: “A concentration such that inhibit microorganisms, but not destroy the cell structure of what you are looking at.”