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Whole Grains and Health


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This network consists of highly swollen starch granules with some leaked amylose (Johansson et al. 2015 and Johansson et al 2018).

       1.8.1 Whole grain flakes

      Flaked cereals are made directly from whole grain kernels or parts of kernels. Corn flakes are made with maize endosperm. The maize grits are pressure cooked with a solution containing sugar, malt (nonenzymatic), and salt. The cooked grits are partially dried to remove stickiness and then tempered for 24 hours to allow the moisture to equilibrate. The grits are subsequently submitted to flaking and toasting, where the moisture decreases to less than 3%, and the product is browned and blistered. After cooling, the flakes are sprayed with a solution of vitamins and minerals. To make wheat or rye flakes, the whole kernel is used and each kernel makes one flake. A heating step is applied before the flaking to plasticize the kernel. Instead of cooked grains, flakes may also be made from extruded pellets in a similar way.

      Collapse of structure and formation of rubbery and crystalline states affects strongly physical properties of cereal products (Boitte et al. 2013). The mechanical and sensory properties of grain flakes are affected by water content. Crunchiness is lost upon water adsorption and it is attributed to the plasticizing effect of water. However, water adsorption has either plasticizing or antiplasticizing effect depending on the water activity (Gondek and Lewicki 2006).

      The type of grain affects the internal structure of the product. For instance, corn flakes present a porous structure with thick, continuous and homogenous air bubbles, whereas wheat bran flakes have a heterogeneous structure with many discontinuities, cracks and ruptures. These structural differences influence the behavior of the products against compression. Fragile breaking of the matrix occurs in corn flakes, while dislocations of one piece of wheat bran against the others manifest in the wheat bran flakes (Gondek and Lewicki 2006).

       1.8.2 Puffed‐grain cereals

      The ultrastructure of the grains is severely affected by puffing and is reflected in some physical properties such as bulk density and water uptake. Puffed rye and rice presents a very porous matrix made up of numerous cavities of increasing size from the center of the kernel outwards, whereas wheat and barley show a more compact and non‐homogeneous structure (Mariotti et al. 2006). The changes in the structure after compression of puffed cereals have also been studied (Roopa et al. 2009).

       1.8.3 Extruded breakfast cereals and snacks

      Extrusion cooking handles cereal flours at relatively low moisture contents (12–20%) and limited amounts of fibre and fat. It is a continuous process that uses both temperature and pressure to expand the product (Delcour and Hoseney 2010b). The dough is forced through an extruder to give it a specific shape and dried. This process causes starch gelatinization and mechanical damage in cell walls (Salmenkallio‐Marttila et al. 2004). The presence and gelatinization of starch is essential for optimal sensory properties of extruded products. Porosity is a key characteristic that determines quality properties such as crispness in this kind of products. Crispness is indeed the result of breaking behavior of complex structures at different length scales (Chanvrier et al. 2014). Extruded flours of maize or oat are usually puffed by extrusion at high temperature. In extruded whole grain rye, all starch granules are completely destroyed during processing, resulting in a continuous homogenous starch phase consisting of a mixture of amylose and amylopectin (Figure 1.2D). This also results in a very low content of resistant starch, according to Johansson et al. (2018). This recent study on rye has established a relationship between microstructure and product composition and in vitro glucose release. A later glucose peak was detected in extruded whole grain rye compared to wheat bread and fermented crisp rye bread. This was partially attributed to less degraded fibres, such as β‐glucans and arabinoxylans, in the extruded rye contributing to higher viscosity of the food digesta which would favor a slower diffusion of enzymes. Additionally, it was suggested that the extruded rye was more resistant to disintegration in the gastric compartment.

       1.8.4 Crispbread

      Crispbread is a dry cereal‐based baked and extruded product very popular in the Nordic countries. It is a light, flat and dry type of cracker with relatively long shelf life. Crispbread traditionally consists of wholemeal rye flour, salt, and water. However, different crispbread products containing wheat, other grains and spices can be found nowadays. The air cells can be introduced using leavening, mechanically or submitting the dough under pressure in an extruder. The traditional method involved rolling, sheeting and baking the dough. However, the introduction of the extrusion process has complemented and often replaced the traditional methods. Extrusion process conditions have a great influence in the porosity and texture of crispbread (Gondek et al. 2013). Furthermore, differences in insulin response between leavened and non‐leavened (whipped) whole grain rye crispbread have been recently reported (Johansson et al. 2015). Crispbread contains only about 5–8% water. However, this product is hygroscopic, depending on the process, due to its chemical composition, porosity and presence of starch