132 TECHNOLOGY OF CEREALS is also present. The spaces among closely packed pherical or near spherical starch granules are wedge shaped and where protein occupies these spaces It is compressed into shape. It has thus been called wedge protein Clearly the size of starch granules determines the sizes of the interstitial wedges. In the case of the Triticeae cereals the wedges among the larger population of starch granules generally have granules of the smaller population(see p. 57) embedded in them Microns When wheat endosperm is fragmented by grinding it is usually reduced to a mixture of particles, differing in size and composition( Greer 1951). These may be classified into three main fractions ○○ 1. Whole endosperm cells(singly or in clumps) segments of endosperm cells, and clusters of starch granules and protein(upwards of 35 2\ Hm in diameter). This fraction has a protein content similar to that of the parent flour. 2. Large and medium sized starch granules FIG 6.3 Above: the two main types of endosperm cell rismatic(lef), polyhedral (right)-showing large and sma some with protein attached (15-35 um in starch granules(white)embedded in protein matrix(black) diameter). This fraction has a protein content Below: exposed endosp of further breakdown (night): 1. detached large starch granules 3 one half to two thirds that of the parent flour (about 25 Hum diameter ); 2. 'clustersof small starch granules Small chips (wedges)of protein, and detached and protein matrix(about 20 um diameter);3. detached sma small starch granules (less than 15 um in starch granules (about 7 um diameter); 4. fragments of free diameter). This fraction has a protein content wedge protein(less n eh aperture width of a typic approximately twice that of the parent flour flour bolting cloth (Redrawn from C.R. Jones et al., y (Fig.6.3) Biochem MicrobioL. Technol. Engng. 1959, 1: 77 and repro- duced by courtesy of Interscience Publishers. The proportion of medium-sized and small particles(below 35 um) in flour milled conven- The reduction in particle size due to fine tionally from soft wheat is about 50% by weight, grinding further separates the components, as but in hard wheat flours it is only 10%. The previously described, allowing increased propor proportion of smaller particles can be increased tions of starch and protein to be concentrated into at the expense of larger ones by further grinding different fractions n, for example, a pinned disc grinder, which Particles below about 80 um are considered to consists of two steel discs mounted on a vertical be in the sub-sieve range, and for making separa axis, each disc being studded on the inward- tions at 15 um and 35 um, the four as ground facing surface with projecting steel pins arranged or after fine-grinding, is fractionated by air in concentric rings that intermesh. One disc, the classification. This process involves air elutria stator, remains stationary while the other rotates tion, a process in which particles are subjected at high speed. Feedstock enters the chamber to the opposing effects of centrifugal force and between the discs at the centre, and it is propelled air drag Smaller particles are infuenced more by centifugally by the air current created. The the air drag than by centrifugal force, while the particles impact against the pins and against each reverse is true of the larger particles. The size at other, as a result of which, they are fragmented. which a separation is made is controlled by132 TECHNOLOGY OF CEREALS is also present. The spaces among closely packed spherical or near spherical starch granules are wedge shaped, and where protein occupies these spaces it is compressed into the same wedge shape. It has thus been called wedge protein. Clearly the size of starch granules determines the sizes of the interstitial wedges. In the case of the Triticeae cereals the wedges among the larger population of starch granules generally have granules of the smaller population (see p. 57) When wheat endosperm is fragmented by particles, differing in size and composition (Greer et al., 1951). These may be classified into three main fractions: embedded in them. Microns grinding it is usually reduced to a mixture of 12 xx -I 0 OI 1. Whole endosperm cells (singly or in clumps), 9 03,~ segments of endosperm cells, and clusters of 2 starch pm in diameter). granules and protein (upwards This fraction has a protein of 35 * 4 content similar to that of the parent flour. 2* Large and medium sized starch granules, some with protein attached (15-35 pm in diameter). This fraction has a protein content One ha1f to two thirds that Of the parent flour* 3. Small chips (wedges) of protein, and detached small starch granules (less than 15 pm in diameter)* This fraction has a protein content approximately twice that of the parent flour (Fig. 6.3). The proportion of medium-sized and small particles (below 35 pm) in flour milled conven￾tionally from soft wheat is about 50% by weight, but in hard wheat flours it is only 10%. The proportion of smaller particles can be increased at the expense of larger ones by further grinding on, for example, a pinned disc grinder, which consists of two steel discs mounted on a vertical axis, each disc being studded on the inward￾facing surface with projecting steel pins arranged in concentric rings that intermesh. One disc, the stator, remains stationary while the other rotates at high speed. Feedstock enters the chamber between the discs at the centre, and it is propelled centifugally by the air current created. The particles impact against the pins and against each other, as a result of which, they are fragmented. FIG 6.3 Above: the two main types of endosperm cell - prismatic (left), polyhedral (right) - showing large and small starch granules (white) embedded in protein matrix (black). Below: exposed endosperm cell contents (left) and products of further breakdown (right): 1. detached large starch granules (about 25 pm diameter); 2. ‘clusters’ of small starch granules and protein matrix (about 20 pm diameter); 3. detached small starch granules (about 7 pm diameter); 4. fragments of free wedge protein (less than 20 pm diameter). 12xx is the representation to scale of the mesh aperture width of a typical flour bolting cloth. (Redrawn from C.R. Jones et al., J. Biochem Microbiol. Technol. Engng. 1959, 1:77 and repro￾duced by courtesy of Interscience Publishers.) The reduction in particle size due to fine grinding further separates the components, as previously described, allowing increased propor￾tions of starch and protein to be concentrated into different fractions. Particles below about 80 pm are considered to be in the sub-sieve range, and for making separa￾tions at 15 pm and 35 pm, the flour as ground, or after fine-grinding, is fractionated by air￾classification. This process involves air elutria￾tion, a process in which particles are subjected to the opposing effects of centrifugal force and air drag. Smaller particles are influenced more by the air drag than by centrifugal force, while the reverse is true of the larger particles. The size at which a separation is made is controlled by