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Name: Harrison
Status: student
Grade: 4-5
Location:  ID
Country: N/A
Date: April 2006

Question:
I am working on a chemistry merit badge for Boy Scouts and I am completing an experiment on onions. I had to taste a raw onion, a partially cooked onion and a carmelized onion. I can taste and describe the differences between the three onions but I need help understanding and explaining what happened to the molecules in the onion during the cooking process



Replies:
Harrison,

This is a neat question because I really enjoy talking about food chemistry! Onion cells have sulfur-containing compounds that are released when you damage the cell wall. The cell wall can be damaged by either cutting (knife) or grinding (chewing). The sulfurous compounds are volatile, meaning that they have a high vapor pressure and you can smell them readily. In particular these compounds are lachrymators, which cause your eyes to tear up when you are cutting the onion! During the cooking process you expose the onino to heat. This heat starts to break down the sulfurous compounds and the longer you expose it to heat, the fewer sulfurous compounds will be present for you to taste. This allows your tounge to taste the sugar present in onions more than the sulfurous coumpounds.

If you are interested in the specific organic chemistry (including mechanisms) of onion chemistry a good website (as of 4 Feb 2006) is:

http://www.chm.bris.ac.uk/webprojects2001/gray/chemistry.htm

Good Luck completing the rest of your project!

Matt Voss



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