MadSci Network: Biochemistry
Query:

Re: What chemicals in a tomato cause an 'off-flavor' when NaOH and HCl are add?

Date: Thu Jul 27 12:40:58 2000
Posted By: Robert LaBudde, Staff, Food science, Least Cost Formulations, Ltd.
Area of science: Biochemistry
ID: 958657329.Bc
Message:

This is a very violent treatment of tomatoes!

When you raise the pH to 11, you will be denaturing all proteins present, 
and the open configurations may allow rapid reactions that were impossible 
at normal pHs (~ 4.5). Reducing the pH back to 4 with HCl is simply a 
restoration of the normal pH. Most likely some irreversible reactions or 
conformational changes have occurred. Heat would only accelerate the 
effects.

The particular chemicals used to change pH are irrelevant, although 
getting to pH 11 wouldn't be easy with weaker bases. 

You mention "burnt" smell and taste, so I'd suspect a Maillard-reaction 
between the tomato proteins and the sugars present. This type of reaction 
is responsible for the broiled flavors of meat and fish and caramels. Most 
flavors and odors are developed from aldehydes and ketones generated from 
oxidation or reduction products.

pH 11 or higher is a very harsh treatment. In food with fats, you'd 
saponify the fats and make soap of them. I doubt if any food would have 
its flavor profile survive intact from such a treatment.





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