By: Maria Janine L. Juachon
Sometimes, having more of something isn’t always the best choice.
Ethanol, also commonly known as ethyl alcohol, is a compound with a structural formula of CH3CH2OH, often written as C2H5OH, C2H6O. Commonly abbreviated as EtOH, it is an essential part of our daily lives seeing as it is used in antiseptics, in post-mercury thermometers, and in alcoholic beverages. In addition to this, it is also commonly used in microbiology laboratories as a prerequisite before any experiments can be conducted; however, it is to be noted that specifically 70% ethanol is the best concentration to be used – not 50% and not 100%. This article will attempt to explain the reason for the said case.
As stated, ethanol is used to kill microorganisms. It works by denaturing their proteins and dissolving their lipids of their cellular membrane. The water in the ethanol solution is the portion that actually does the denaturing. Using higher concentration makes the ethanol less effective because there cells cannot be denatured by the water; meanwhile, lower concentrations do not allow the ethanol to be as effective because it cannot break down the all lipids or allow the water to get into the cells.
To explain further, using higher concentration, say 100%, of alcohol will only most likely lead to coagulation of protein. If pure alcohol is poured over the bacterial cell, the alcohol will go through the cell wall of the bacteria in all directions, coagulating the protein just inside the cell wall; this coagulated protein would then stop the alcohol from penetrating farther from the cell, and no more coagulation would take place. This would result to the cell would getting sealed and become merely inactive and not dead. (Under favourable conditions the cell may revert to its active state).
Seventy percent is considered the optimum concentration because it was found that it coagulates protein at a relatively slower rate. This allows penetration all the way through the cell before coagulation can block it. Then the entire cell is coagulated and the organism dies.