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Name: Diane P.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 2001


Question:
How does a cucumber turn into a pickle? Is it due to osmosis (which would explain why the water leaves the cucumber in a brine solution and becomes shriveled)? If so, what happens to the semipermeable membrane of the cucumber after the "shriveling" (osmotic forces); is it altered to then allow the passage of salt molecules back into the cucumber for the flavor, which would be diffusion? I am interested in identifying the processes by which a cucumber is made into a pickle!


Replies:
Dear Diane,

You're correct that the salty brine used in the pickling process would cause the cucumber to lose water through osmosis. The cell membranes do not require alteration to allow for the passage of either water or salt molecules. The primary event would be the movement of water out of the cucumber to compensate for the osmotic differential. Then, the passive transfer of salts across the cell membranes from the brine would also still occur, but by diffusion or facilitated diffusion, as you suggest, which occurs at a slower rate. This cellular response is actually an another mechanism for equalizing intracellular osmotic pressure in hypertonic environments. As for the cell membranes themselves, they are not really harmed much by the osmotic "shriveling". Note how plant leaves that lose their turgor and shrivel in dry conditions can recover once water is provided, as long as the dry period is not long enough to cause permanent cellular damage. Cell membranes can rupture if too much water enters a cell by osmosis, but plant cells are actually somewhat protected against that problem by their rigid cell walls. The cell walls might also help prevent severe damage during hypertonic membrane shrinkage, as well, by providing some degree of structural support.

Thanks very much for the interesting question,

Jeff Buzby, Ph.D.


This is more complex than one might think but there are two main processes I would consider involved: the preservation by the acetic acid (vinegar) which will invade the cucumber by diffusion and the preservation by the salt..which will invade the cucumber by diffusion. Initially there will be some osmosis going on leading to a large loss of water from the cuke but since the cuke is at least 80% water and there is no where near that amount of loss in total cuke weight the water is replaced by the vinegar/brine solution which preserves (pickles) the cuke.

Peter Faletra Ph.D.
Assistant Director
Science Education
Office of Science
Department of Energy



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