Riche : adj. (word coming from Frankish °riki“ powerful ").
In its first meaning, the adjective "rich" qualifies someone whou have some fortune, owns property, et specially money in abundance.
En Food, "rich" describes something that contains many elements, or important elements in abundance.
Un food rich (feeding, nutrient).
Too rich food (oily).
Un food rich in vitamins.
Rich in (and substitute).
A subsoil rich in minerals.
See as well Riche under the Wine and Vine Dictionary.