Re: why does vitamin c in lemons degenerate quicker than broccoli after boiling

Lemon juice loses about 50% of its vitamin C during heat treatment, while 
broccoli loses about 25% of its vitamin C during heat treatment.  There are 
several factors that help explain this.  The biggest factor is surface 
area.  The vitamin C in lemon juice is in the solution and more exposed to 
the heat than the vitamin C in the broccoli, which is still in the cells of 
the broccoli and not exposed to the same intensity of heat for the same 
period of time.  Other factors include the severity of the heat treatment 
and the type of container used.  In general, the more severe the heat 
treatment, the more vitamin C that is lost.  



References:

USDA Food Composition Tables  (www.usda.gov)
Karmas and Harris, Nutritional Evaluation of Food Processing, 3rd edition., 
1988