These food additives, disodium insonate and disodium guaynalate, seem to be made from various protein sources such as fish or soybeans. I would expect them to be made from corn also. In the near future, I am sure they will also be made from protein rich green algae cake.
They are said to be expensive and are often used sparingly with MSG as they enhance the effects of MSG.
They and MSG are often found occurring in complex ingredients and are often not listed on labels even when they are found there.
also see;
http://www.associatepublisher.com/e/d/di/disodium_guanylate.htm
http://www.associatepublisher.com/e/d/di/disodium_inosinate.htm