Like the rest of the folks said, one should worry about these substances in the long run. Of course if you have a year worth of MREs that you are planning to consume when all hell breaks loose, then maybe you should worry about them. <img src="/images/graemlins/smirk.gif" alt="" /> Otherwise, probably not a big concern.

p.s. After reading labels on some MREs, I realized that they do not have any preservatives in them, just flavor enhancers, so people with allergies to preservatives will probably be able to consume them without too much trouble.