TECHNOLOGY OF CEREALS Size distributions less than half the total starch present. Some 70% The literature contains many tables of granule all the amylose bu size ranges and size distributions of granules from must also include much of the amylopectin. The different botanical sources While such tables evidence of biochemical studies and electron microscopy has pointed to the existence of struc useful guides they do not all accord in detail and tures with a periodicity of 5-10 nm,reflecting the some fail to indicate the nature of the distribution. alternating crystalline and amorphous zones of For example the bimodal distribution of the Triticeae is not always indicated although this is amylopectin an important characteristic by which the source of a starch may be recognized. In wheats the Granule surface and minor components proportional relationship between large biconvex The distribution of amylose and amylopectin and small spherical granules is fairly constant molecules in one starch granule was estimated by (approx 70% large granules w/w), and this is the same for rye and triticale French (1984): for one spherical granule 15 um G In barley there is a wider variation, in part due in diameter, with a mass of 2.65 x 10 g there to the existence of more mutant types( Goering would be about 2.5 x 10% molecules of amylose et al., 1973). Among 29 cultivars, small granules (D P=1000, 25% of total starch)and 7.4 x 10 counted for between 6% and 30%of the total molecules of amylopectin(D P.= 100,000,75% of starch). If the molecular chains are perpend- icular to the surface of the granule there would be about 14 x 10 molecular chains terminating Granule organization at the surface. Of these 3.5 x 10 would be amylose molecules and the rest would be Under crossed polarizers starch granules amylopectin chains exhibit birefringence in the form of a maltese Surface characteristics of granules are also cross. This indicates a high degree of order affected by the minor components of starches within the structure. The positive sign of the Bowler et al.(1985) reviewed developments in birefringence suggests that molecules are organized work on these although they point out that this in a radial direction(French, 1984). Amylomaize is an under-researched area. Non-starch materials starch exhibits only weak birefringence of an present in commercial starch granules can arise unusual type(Gallant and Bouchet, 1986) from two sources. They may be inherent com Starch granules exhibit X-ray patterns, indicat- ponents of the granules in their natural condition ing a degree of crystallinity. Cereal starches or they may arise as deposits of material solubilized give an a pattern, tuber, stem and amylomaize or dispersed during the process by which the starches give a B pattern and bean and root starch is separated arches a c pattern the c pattern is considered The main non-starch components of starch to be a mixture of A and B. It is accepted that granules are protein and lipid amounts vary with the crystallinity is due to the amylopectin as it is starch type: in maize 0. 35% of protein (n X 6.25) shown by waxy granules. Furthermore, amylose is present on average Slightly more is present can be leached from normal granules without in wheat starch(0.4%). The most significant ffecting the X-ray pattern. The a and B patterns proteins in terms of their recognized effects or are thought to indicate crystals formed by double starch behaviour are amylolytic enzymes bound helices in amylopectin. The double helices occur to the surface Even traces of alpha-amylase can in the outer chains of amylopectin molecules, have drastic effects on pasting properties through where they form regions or clusters. The crystal- hydrolyzing starch polymers at temperatures up line parts of starch granules are responsible for to the enzymes inactivation temperatures many of the physical characteristics of the granules' SDS PAGE(sodium dodecyl sulphate, poly- structure and behaviour. Nevertheless they involve acrylamide gel elecrophoresis) showed surface60 TECHNOLOGY OF CEREALS Size distributions less than half the total starch present. Some 70% is amorphous; this comprises all the amylose but must also include much of the amylopectin. The evidence of biochemical studies and electron microscopy has pointed to the existence of struc￾tures with a periodicity of 5-10 nm, reflecting the alternating crystalline and amorphous zones of amylopectin. Granule surface and minor components The distribution of amylose and amylopectin molecules in one starch granule was estimated by French (1984): for one spherical granule 15 pm in diameter, with a mass of 2.65 x lO-9 g there would be about 2.5 x lo9 molecules of amylose (D.P = 1000, 25% of total starch) and 7.4 x lo7 molecules of amylopectin (D.P. = 100,000, 75% of starch). If the molecular chains are perpend￾icular to the surface of the granule there would be about 14 x 10' molecular chains terminating at the surface. Of these, 3.5 x 10' would be amylose molecules and the rest would be Surface characteristics of granules are also affected by the minor components of starches. Bowler et al. (1985) reviewed developments in work on these although they point out that this is an under-researched area. Non-starch materials present in commercial starch granules can arise from two sources. They may be inherent com￾ponents of the granules in their natural condition or they may arise as deposits of material solubilized or dispersed during the process by which the starch is separated. The main non-starch components of starch granules are protein and lipid. Amounts vary with starch type: in maize 0.35% of protein (N x 6.25) is present on average. Slightly more is present in wheat starch (0.4%). The most significant proteins in terms of their recognized effects on starch behaviour are amylolytic enzymes bound to the surface. Even traces of alpha-amylase can have drastic effects on pasting properties through hydrolyzing starch polymers at temperatures up to the enzymes' inactivation temperatures. SDS PAGE (sodium dodecyl sulphate, poly￾acrylamide gel elecrophoresis) showed surface The literature contains many tables of granule size ranges and size distributions of granules from different botanical sources. While such tables are useful guides they do not all accord in detail and some fail to indicate the nature of the distribution. For example the bimodal distribution of the Triticeae is not always indicated although this is an important characteristic by which the source of a starch may be recognized. In wheats the proportional relationship between large biconvex and small spherical granules is fairly constant (approx 70% large granules w/w), and this is the same for rye and triticale. In barley there is a wider variation, in part due to the existence of more mutant types (Goering et al., 1973). Among 29 cultivars, small granules accounted for between 6% and 30% of the total starch mass. Granule organization exhibit birefringence in the form of a maltese cross. This indicates a high degree of order within the structure. The positive sign of the birefringence suggests that molecules are organized in a radial direction (French, 1984). Amylomaize starch exhibits only weak birefringence of an unusual type (Gallant and Bouchet, 1986). Starch granules exhibit X-ray patterns, indicat￾ing a degree of crystallinity. Cereal starches give an A pattern, tuber, stem and amylomaize starches give a B pattern and bean and root starches a C pattern. The C pattern is considered to be a mixture of A and B. It is accepted that the crystallinity is due to the amylopectin as it is shown by waxy granules. Furthermore, amylose can be leached from normal granules without affecting the X-ray pattern. The A and B patterns are thought to indicate crystals formed by double helices in amylopectin. The double helices occur in the outer chains of amylopectin molecules, where they form regions or clusters. The crystal￾line parts of starch granules are responsible for many of the physical characteristics of the granules' structure and behaviour. Nevertheless they involve Under crossed polarizers starch granules amylopectin chains