Phenolic compounds in cereal grains and effects of processing on their composition and bioactivities: A review

Cereals are a staple food in the diets of many populations globally. Besides their nutritive function in food, they are also rich in various groups of bioactive compounds, especially polyphenols. Wheat, rice, barley, rye, oat, maize, millet, sorghum, and other cereal grains present a great variety of phenolic acids, flavonoids, proanthocyanidins, alkylresorcinols, and lignans, which can be affected in many ways by the post-harvest treatments and further processing of these feedstocks. This review discusses up-to-date studies about the effects of common cereal processing techniques on their phenolic composition, biological activities, and bioefficiency. Generally, mild thermal and high-pressure treatments enhance cereals’ phenolic composition by releasing the insoluble-bound fraction, which increases their bioaccessibility. On the other hand, processes involving extreme temperature conditions and removal of the grains’ outer layers may drastically reduce the phenolic content. Therefore, it is imperative to optimize the processing conditions of cereals, so their health-promoting benefits are preserved.