you can join n-butanol to the mixture and u will get the MDA-TBA  in butanol. 

but even like this u will not solve the problem.

u can use one tube in wich u dont (lipid) for each concentration on the sample, and u subtract this absorbencn from the absorbance of rection having (lipid).

Did you test if cinamaldehyde is actually reacting with TBA? If yes, did you check absorption maxima of cinamaldehyde-TBA abduct (if any) ? If you are evaluating antioxidant potential of cinamaldehyde, then try to use an alternate method.