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Name: Errol
Status: other
Grade: 9-12
Location: N/A
Date: July 2008

Question:
Lemon added to fish removes the smell from the fish why?



Replies:
I don't think lemon removes the fish smell, I think it just covers the fish smell. (lemon on fish tastes good too)

Burr


Most of the "fishy" of fish smell comes from low-molecular-weight amines, which are alkaline molecules that are volatile enough to enter the air in enough concentration to smell. When acidic lemon juice is qdded to the fish, the amine becomes an ammonium salt, which is not volatile and thus does not enter the air and your nose.

Richard Barrans, ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming


Any good fish monger will tell you that fish should have very little smell to start with - a fresh fish should smell of the sea. If it smells 'fishy' it is probably not fresh.

Why does lemon get rid of the smell? There are a couple of possibilities I will offer -

- the smell of the lemon is strong and 'masks' the other smell. In fact some smells are capable of 'turning the volume down' on your ability to smell things. Hydrogen Sulphide (rotten egg gas) is one, perhaps lemon is another (which would explain why it is so popular in room air fresheners, fabric sprays, etc)

- another possibility is that the acid quality of the lemon is reacting to destroy some of the chemicals which are causing the smell.

- third, is the lemon combining with the oils in the fish to prevent the release of molecules which are contributing to the smell?

What is the correct answer - I cannot say, but interesting to think on

Nigel
Tennant Creek High School
AUSTRALIA


There are probably more than one contributing factor, but one factor is the reduction in the pH. "Fishy" odor is caused by amines, which are bases, and fairly low in molecular weight. Otherwise their vapor pressure would be too low to make them volatile. The addition of lemon juice does two things (at least). First, the odor of lemon juice and oil masks the unpleasant odor of the "fishy-smelling" amines. Second, the acidic lemon juice reduces the pH converting the amine(s) from their more volatile neutral form [R3--N] to their much less volatile salt form [R3--NH]+1.

Vince Calder



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