Wheat bran is the outer structure of wheat grain, accounting for about 20% of the weight of wheat grain.As shown in Fig.1，from outside to inside, wheat bran is composed of exocarp, endocarp, episperm, nucellar layer and aleurone layer. Among them, the aleurone layer accounts for the largest proportion, accounting for 7-9% of the weight of wheat grain.
In 2010, the American Academy of Cereal Chemistry (AACC) has set up a special international aleurone task force, which defines aleurone as:”Cereal aleurone tissue comprises the outermost layer(s) of the endosperm in cereal grains, and surrounds the starchy endosperm and part of the embryo. Cereal aleurone tissue is separated from the germ and starchy endosperm by standard milling practices, starting with the grain kernel or starting with the bran, followed by further extraction processes. Microscopic evaluation reveals that aleurone cells are morphologically distinct from other grain tissues because they contain a high concentration of niacin bodies. Each aleurone cell is enclosed within a fibrous cell wall that is thicker than endosperm cell walls and that is composed mainly of arabinoxylans and beta glucans in various ratios. Isolated aleurone tissue should contain low levels of starch and pericarp and represents a major portion of the grain’s physiologically beneficial substances for human nutrition.”