Doughnuts preseratives
I have experience with a few natural options such as Bred-Mate, Bro-Lite and MoisturLok, but I doubt that any of those will get you as much shelf life as calpro will. MoisturLok and Brolite both have formulations for sweet goods, and I did have luck getting yeast breads to have a 7+-day shelf life with Bro-Lite. 
If you have access to it, I'd recommend just getting halal calpro, as that's going to have the longest shelf-life by far.