Gallic acid inhibits the synthesis by A. flavus of aflatoxin, a toxic carcinogen that can contaminate crops such as corn, peanuts and walnuts rendering them inedible. The present invention takes advantage of this inhibition to provide various methods and compositions useful for protecting crops from contamination. Gallic acid is also an intermediate in the production of hydrolyzable tannins, which may sequester protein in the rumen, prevent ammonia formation, and allow protein to be more efficiently absorbed in the post-ruminant digestive system. A second gene, polyphenol oxidase (PPO), also from walnut, may act to help sequester protein during ensiling, also protecting and improving nutritional value. The present invention includes non-naturally occurring plants that contain elevated levels of PPO or gallic acid as well as various methods of generating such plants. The present invention further provides methods of application of gallic acid to prevent contamination. In addition, the present invention provides certain genes and proteins that are be useful in making the non-naturally occurring plants.