MRE’s are already probably as synthetic as Barbie dolls.
That, and if you include the wrong type spice in a food, soldiers will not eat it in a hurry.
MREs are irradiated for preservation.
There is nothing alive in the package, so they keep for years.
When I was in high school, I used to spend lots of time at the lab that developed the process. They had a peanut butter sandwich in a curio cabinet in the front office that had been treated a few years previously that looked fresh. 25 years later, the lab was shut down, and the property was sold to the city for a corporation yard. I stopped by as they were moving the furnishings out, and the sandwich was still there in that cabinet hanging on the wall, still looked fresh.