I remember seeing that topic discussed on here before and will post more about it shortly. here are a few links that may help.. I said may help so read them with an open mind.

https://www.cesarsway.com/dog-behavior/food-aggressive/food-aggression-and-what-to-do-about-it  This one by Caesar is probably the best of the three.  Now I go to search the forum on here where much have been written about this issue.

http://www.dog-obedience-training-review.com/dog-food-aggression.html

http://veterinarymedicine.dvm360.com/how-i-treat-food-related-aggression-dogs