Whole Grains from a Mechanistic View

Wheat, rice, and corn are the most widely eaten whole grains, followed by oats, rye, and barley. A wheat kernel consists of 80–85% endosperm, 10–14% bran, and 2.5–3% germ (Figure 1). Whole grains contain a high amount of bioactive substances such as fiber, vitamins, minerals, antioxidants, and other phytochemicals such as betaine, choline, sulfur amino acids, and melatonin, which account for at least 15% of the whole grain by weight. Most bioactive substances are in the bran (about 52% by weight) and the germ (at least 24% by weight) fractions. In refined cereals, the levels of bioactive compounds are substantially reduced due to the complete or partial removal of the germ and bran fractions.