Читать книгу Whole Grains and Health - Группа авторов - Страница 65

While arabinoxylan and β‐glucan are the major non‐starch polysaccharides in whole cereal grains, pectin and xyloglucan are mainly present in whole grain pseudocereals (amaranth, quinoa) (Lamothe et al. 2015). A low amount of xyloglucan was found in rice (Choct 1997). Also, glucomannans comprised of β‐(1→4)‐linked glucose and mannose is in cereal grains and galactomannan in low amounts is found in amaranth and quinoa (Gartaula et al. 2018; Lamothe et al. 2015). Arabinogalactan, a polymer of β‐(1→4) galactan (comprised of (1→4)‐β‐D‐galactose) substituted with arabinose side chains was found in wheat flour. Although RS does not belong to the non‐starch polysaccharides, it is regarded as dietary fibre (Phillips and Cui 2011). Depending on the origin of RS, different types are recognized. RS1is physically inaccessible starch; RS2 refers to raw starch granule types that are resistant to digestion such as potato and banana; RS3 is retrograded starch, namely, of amylose after cooking to gelatinization; and RS4 is a chemically‐modified resistant starch. Although they are all termed resistant starch, processing can affect their resistance to digestion as RS1, RS2 and RS3 can disappear during some types of thermal and shear‐induced processing, while RS4 is generally not sensitive to such treatments.

Cellulose is a linear polymer of β‐(1→4)‐linked D‐glucopyranosyl residues with a dimer of anhydrocellobiose as the repeating unit (Brown et al. 1996). The strongly associated cellulose molecules into crystalline structures are one component of water‐insoluble dietary fibre in whole grains. The cellulose content of cereal grain cell walls varies among cereal species and location in the grain. In endosperm cell walls of wheat and barley, cellulose accounts for only a few percent of the total cell wall material, while in the outer, lignified layers it may comprise up to 20% of the cell wall weight (Fincher and Stone 1986). Lignin is a polymer of phenyl‐propanoides deposited in secondary thickened cells walls (Vanholme et al. 2010). As it is an intrinsic component of cell wall, it is considered as another component of dietary fibre.