Aleurone layer cereal grains

As vitamin Bg is mainly located in the germ and aleurone layer in cereal grains polishing for the production of flour removes a substantial portion. White bread is therefore a poor source unless fortified. Some nonedible yeasts contain up to 38 mg/100 g dry weight vitamin B, the highest level of the natural sources (4,27). As a rule, these amounts are too low for cost-effective isolation. 

The caryopses of grasses and cereals are anatomically complex. The starch endosperm of the caryopsis is surrounded by the aleurone layer and pericarp, both of which can be partly or completely removed, along with the embryo, by the abrasive process known as pearling, which removes the bran. The flour obtained by milling a pearled grain consists of protein, starches, and a low proportion of endospermic hemicellulose and non-endospermic hemicellulose from the bran. 

Rice Oryza sativd) is an important cereal with an annual production of over 500-800 million tons. To produce white rice, the hull is removed and the bran layer is abraded giving 8-10% of the rice grain. The bran contains the testa, cross cells, aleurone cells, part of the aleurone layer, and the germ and includes almost all of the oil of the rice coreopsis. Gopala Krishna (45) considers that there is a potential for over 5 million tons of rice bran oil per annum, but present production is only about 0.7 million tons and not all of this is of food grade. India (0.50 million tons), China (0.12 million tons), and Japan (0.08 million tons) are the major countries producing rice bran oil. 

Phosphate is stored in the mature seed as phytic acid, which is the hexaphospho-ric ester of myo-inositol —see Chapter 2. This combines with potassium, calcium and magnesium to form the salt called phytin. Accumulation of phytin in cereals is almost exclusively in the aleurone grains of the aleurone layer where it is deposited as a discrete globoid in association with protein. The precise mechanism of phytin deposition and the enzymes involved therein have been little studied and will receive no more attention here. The importance of phytin as a phosphate reserve is discussed in Chapter 6. 

As outlined earlier (Chap. 2) reserve proteins are stored in two separate sites in the cereal grain in the aleurone grains (bodies) of the aleurone layer, and in the protein bodies (sometimes disrupted) of the endosperm. Proteolysis within... 

Cereals contain about 1% of phytate [myoinositol (1,2,3,4,5,6) hexakisphosphate], which binds about 70% of the phosphorus in the grain. Since it occurs mainly in the aleurone layer, the content of phytate in flour depends on the extent of grinding (Table 15.20). A part of it is hydrolyzed in stages to myo-inositol during dough making. 

In foods heteroxylans are mainly present in cereals, found in thin endosperm cell walls, the aleurone layer and lignified bran cells. The endosperm cell walls of most cereals contain 60-70% arabinoxylans, with 20% in barley and 40% in rice. Glumes (husks) of wheat grains contain about 64% heteroxylans. Wheat grains contain on average 1.4-2.1% of heteroxylans, of which 0.8-1.5% represent water soluble pentosans. Rice grains contain 7-8% heteroxylans. 

In the works of A. Konarev (Konarev et al. 1999 Konarev et al., 2004) shows in detail the variability of inhibitors of trypsin-like proteinases in cereals due to resistance to various grain pests. So in wheat trypsin inhibitors are represented by several genetically independent systems of proteins controlled by the genome and B chromosomes ID (endosperm), 3Dp (aleurone layer), IDS and 3Ap (leaf). Trypsin inhibitors of rye are controlled chromosome 3R and barley 3H. The most complex structure of inhibitors was wheat leaves, with the genomic formula AABBDD. In general, it is the sum of the spectra of trypsin inhibitors from several tetraploid (T. turgidum) (AABB) and (Aegilops tauschii Coss.) (DD) (Konarev, 1986 Konarev et al., 2004). 

Most phosphorus associated with cereal grains exists in the form of phytic acid (myoinositol hexaphosphate) that is stored in phytic bodies mainly loeated in the aleurone layer. These molecules bind potassium, magnesium, and other minerals. The phytases degrade these compounds to release phosphate, other minerals, and myoinositol. The myoinositol is a known precursor of sugars associated with cell wall polysaccharides and a promoter of seedling growth. The free phosphorus is critically important for synthesis of nucleic acids and phospholipids for cellular membrane proliferation, and ATP and energy production. 

Aleurone The single or multiple layers of large thick-walled cells positioned under the pericarp and outside the endosperm of cereal grains. The aleurone plays a key role during germination and malting because it produces important enzymes such as amylases. It is rich in protein, phytic acid, oil, and B-vitamins and devoid of starch granules. 

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