Maize kernels. Close-up of numerous kernels (grains) of the maize plant, Zea mays. Maize can be used in cooking as corn-on-the-cob", kernels (sweetcorn), corn oil, corn starch and corn meal. "Popcorn" is made from a maize variety which has small kernels of great hardness. When heated, the moisture in the kernels expands, causing the kernels to pop open. Maize is a good source of protein, fibre, vitamin A and potassium."