The fact that dogs can be protective of their food is ultimately a matter of distrust of their surroundings and of their owners. You can try sitting next to your dog when he eats and slowly try to feed him by putting the food directly in your hand, so that he understands that you are the one sharing the food. Next time, feed the dog with the bowl in your hand so that the dog understands that the bowl is yours and that you are the provider of the food. At the same time pet him with your other hand and if he resists, take the bowl away immediately and stop him at the same time, repeating until he does not resist.
