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Whole Grains and Health


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of the original starting grain, and displays a total β‐glucan content of at least 5.5% (dry weight basis) and a total dietary fibre content of at least 16.0% (dry weight basis) such as at least one‐third of the total dietary fibre corresponds to soluble fibre.

Schematic illustration of the tissue composition of different bran issues obtained from different processes, and for similar process but with different grain cultivars.

      Until recently, bran has mostly been used in the animal feed industry. However, considering its richness in compounds of high nutritional value mainly located in the aleurone layer, the food industry has begun to use it as a food ingredient, especially in cereal products. Bran fraction is commonly added in a fixed proportion to white flours to obtain whole‐meal flour from wheat, barley, rye, oat and maize (van der Kamp et al. 2014). The addition of bran generally impacts technological properties (e.g., bread volume, color), but also the shelf‐life and sensory attributes (texture, bitter taste) of the food product. Various available processes can overcome such problems but also impact nutritional properties (Katina et al. 2007). Bran consumption has also increased for non‐food uses such as bioethanol production (Friedman 2013; Apprich et al. 2014; Pruckler et al. 2014). It has also been used as a raw material to produce ingredients by wet extraction, for example, proteins (Youngs 1974), oil (Friedman 2013) or dietary fibres such as β‐glucans from oat or barley (Knuckles et al. 1992).

      Due to the aleurone’s richness in compounds with large nutritional potential, different strategies to increase the amount of this tissue in fractions have been developed during the last years. This has been possible due to the improvement of fractionation methods and tissue monitoring with the measurement of specific molecules. These methods have also opened the way to molecular fractionation in order to particularly isolate molecules with specific end‐uses in dry conditions, that is, starch, storage proteins, dietary fibres such as β‐glucans.

       3.6.1 The aleurone fraction – richest in micronutrients and phytochemicals

      Aleurone develops from surface endosperm cells and is therefore located in the outer part of the cereal grain starchy endosperm. A unicellular layer made from block‐shaped cells in wheat (37–65 x 25–75 micrometre; Evers and Bechtel 1988), the aleurone layer is multi‐layered in other cereals such as barley (2–3 parallel cell layers), rice and oat (Stone 1985). Aleurone represents 7–9% (w/w) of the wheat kernel (Buri et al. 2004). In wheat, the cell‐wall of its constitutive cells are larger and thicker than in other cereals (Xiong et al. 2013).

      The biochemical composition of the wheat aleurone fraction has been recently reviewed in Rosa‐Sibakov et al. (2015) and Brouns et al. (2012). Even if this fine composition depends on the wheat sample and the fractionation processes used, the aleurone fraction is always particularly rich in fibres (44–50% dm, Amrein et al. (2003)), mainly arabinoxylans (65%) and β‐glucans (30%) coming from the non‐lignified cell‐walls (Bacic and Stone 1981; Saulnier et al. 2007). The main part of these arabinoxylans (95%) are water unextractable (Saulnier et al. 2007; Rosa et al. 2013b) and esterified with ferulic acid that is the main phenolic acid compound found in the aleurone layer (constitutes 95%). Ferulic acid is mainly bound to arabinoxylans and only minor amounts of ferulic acid are under free or