Whole grain chemistry and nutrition from a health perspective: Understanding the fibre-phenolic-starch ménage à trois

Increasing regular consumption of products made of cereal whole grains (including the bran and germ of cereal grains) is associated with lower occurrence on non-communicable chronic diseases. These health benefits are strongly linked to the bioactivity of dietary fibres and phenolic compounds, via their physicochemical and biochemical properties. Whereas the properties of these classes of nutrients individually are well understood, they can be affected by molecular interactions among them and with starch, the main component of grains. This review summarises the state of the art with respect to two-way interactions between starch, fibres, and phenolic compounds, considering the effects of these interactions on these nutrients' physicochemical and biochemical properties in relation with their nutritional properties. The studies reported and critically appraised in this review are limited to those relevant to whole grains products, possibly formulated with other sources of phenolics and fibres, such as fruits. In vitro studies show that phenolics and polysaccharides (starch and fibres) form complexes that alter their respective properties: polysaccharides can sequester phenolics and limit their ability to inhibit digestive enzymes and intestinal transporters; phenolics can limit viscosity build-up from soluble dietary fibres; phenolics can alter the supramolecular organisation of starch and modify its digestibility. However, these observations are poorly reflected in clinical studies, suggesting that these two-way interactions don't explain the nutritional properties of fibres, phenolics and starch in whole grains, and warranting elucidation of their three-way interactions.