Various factors, including starch granule channels, have been suggested to contribute to the control of sorghum starch digestibility for animal feed. Isolated starch from two normal sorghum lines (P721N, IS6986) and one high protein digestibility (HPD) mutant line (111) that differed in starch granule morphology were selected to study the influence of these factors on starch digestibility. Scanning electron micrographs were taken of raw and digested starches. Microscopy results confirmed that in all three sorghum lines channels in starch granules are the main route of enzyme penetration and the central cavity area is the starting point of enzyme digestion. Channel density was more pronounced in the HPD sorghum mutant line than in normal lines, which may have been responsible for its relatively high digestibility. Micrographs of IS6986 showed unique starch granule morphology with a collapsed "doughnut-shaped" structure in a portion of the granules. These unusual granules were rapidly digested and, unlike normal spherical granules, totally disappeared after 30 min of digestion. Amylases appeared to have fast access to the collapsed-appearing starch granules. Digestion profiles, following incubation with pepsin and a-amylase, showed that IS6986 and the HPD mutant (111) had the highest initial rate of starch digestion, followed by P721N. These findings provide insight as to how new sorghum cultivars might be developed with high starch digestibility for animal feed use.

Starch was isolated from kernels of 27 rice samples consisting of nine U.S. long grain rice cultivars grown in three different locations (Missouri, Arkansas, Texas). Amylose (AM) content of the starches and the fine structure of the respective amylopectin (AP) were determined and used to explain differences observed in gelatinization properties. The AM content of rice cultivars grown at the lower temperature Missouri location increased 0.4–3% and 0.5–4% when compared with the same rices grown in Arkansas and Texas, respectively. AP values of the rice samples were isolated, debranched, and separated by low‐pressure size‐exclusion chromatography. The eluted AP linear chains were divided into three fractions to represent extra long (FrI), long (FrII), and short chains (FrIII). The corresponding average degree of polymerization (DPn) at the peaks of fractions FrI, FrII, and FrIII were 100, 39, and 16, respectively. Total carbohydrate analysis of the fractions indicated that cultivars grown in Missouri had a consistently higher proportion of FrIII and lower proportion of FrII as the same cultivars grown in Arkansas and Texas. Furthermore, the Missouri samples showed a shift toward shorter DPn in FrII and FrIII and had more of the shortest chain components (DPn < 6) of AP. The proportion of FrI did not follow a trend and varied depending on the cultivar and across location. Thermal analysis indicated that the higher temperature growth environments (Arkansas and Texas) resulted in higher onset, peak, and heat of gelatinization for the starches, suggesting longer cooking time and higher heat requirement. Overall, the data support the nonfield findings of other researchers that higher growing temperature results in AP with more DPn short chains that are within a range of DP >10 to form consistent crystallites, and thus results in higher gelatinization temperatures and enthalpies.

Cereal Chem. 78(2): [160][161][162][163][164][165] Protein digestibility in sorghum (Sorghum bicolor (L.) Moench) lines was determined using two standard procedures (pepsin digestibility and pH-stat) and compared with a newly developed, rapid electrophoresisbased screening assay. The new assay was based on the rate of α-kafirin disappearance after pepsin digestion. α-Kafirin, the major sorghum storage protein, makes up ≈60-70% of the total protein in the grain. In the new assay, samples were first digested with pepsin for 1 hr, and undigested proteins were then analyzed by SDS-PAGE. The intensities of the undigested α-kafirin bands were measured. Higher band intensity indicated lower protein digestibility. The new assay was significantly correlated with the standard pepsin digestibility assay (r = -0.96, n = 16) after which it was patterned. The same was true of the pH-stat procedure (r = -0.85, n = 16). This implies that the new assay is comparable to existing procedures and can be used for screening sorghum lines for protein digestibility. Two groups consisting of high-protein digestibility and wild-type sorghum lines were identified when the new assay was tested on 48 sorghum lines derived from crosses of wild-type and mutant high protein digestibility lines, indicating that the new assay was efficient in differentiating between the two groups. Advantages of the new assay over the standard procedures include considerable reduction in analysis time and sample size required for the analysis. For example, analysis time was reduced by 20% and sample size by 10% when the new assay was used as compared with the pH-stat procedure. We estimate that ≈60 sorghum lines can be screened in a day by a single operator using the new assay.Sorghum (Sorghum bicolor (L.) Moench) grain ranks fifth among the world cereal grains. It is a major staple food in many parts of Africa and India. In the United States, it is mainly used as an animal feed grain. A significant problem with sorghum is its comparably poor nutritional quality. Protein digestibility in cooked sorghum was considerably lower when compared with other cereals (MacLean et al 1981; Hamaker et al 1986). The cooking process as used for human consumption reduces protein digestibility of sorghum due to rearrangement and formation of disulfide bonds (Hamaker et al 1987;Oria et al 1995b). This was demonstrated by the significant increase in protein digestibility observed when sorghum was cooked in the presence of 2-mercaptoethanol and other reducing agents that cleave disulfide bonds. Increasing protein digestibility in sorghum would benefit the undernourished poor. who rely heavily on sorghum as their main source of protein and energy. Proteins in sorghum grain used for animal feed are also somewhat less available than other grain proteins, and may further inhibit starch digestibility (Bramel-Cox et al 1995).The main proteins in sorghum are the aqueous alcohol-soluble storage prolamins known as kafirins. Sorghum prolamins are classified as α-, β-, and γ-kafirins based on m...

Cereal Chem. 76(2):308-313Flours from eight sorghum cultivars were evaluated for their couscousmaking ability with the objective of finding predictive relationships between flour physicochemical properties and couscous quality. Chemical composition, physical characteristics, and pasting and gelatinization properties of the flours were determined. A laboratory procedure was used to prepare couscous. Couscous properties were evaluated and compared to a laboratoryprepared and a commercial durum wheat couscous. Hard grain produced flours containing a high proportion of coarse particles with low ash and high damaged starch content and yielded a higher proportion of desirable sorghum couscous granules. A variety of colors ranging from brown to yellow were obtained when flours were processed into couscous. Cooked sorghum couscous stickiness was positively correlated (r = 0.89, P < 0.01) with the amount of damaged starch in flour. Cooked couscous hardness correlated positively (r = 0.79, P < 0.05) with apparent amylose content of flour and correlated negatively (r = -0.75, P < 0.05) with flour peak viscosity. Durum wheat couscous was lighter and had more yellow color than sorghum couscous. Sorghum couscous was stickier and harder than durum wheat couscous. Addition of 2% oil to the cooking water considerably improved the texture of some sorghum couscous to a level comparable to that of durum wheat couscous.

Sorghum grain was decorticated to remove 10%, 20%, 30% and 40% of the kernel for the purpose of improving flour colour, couscous colour and yield, and porridge texture. Flour lightness increased while yellow colour decreased with increased extent of decortication. Processing of the flours into couscous caused a considerable drop in lightness and increased yellow colour in couscous at all levels of decortication. As decortication level increased, couscous colour became lighter. Yellow colour progressively increased up to 30% kernel removal and dropped at 40%. Couscous yield, as measured by the proportion of particles of 1-2 mm size, also increased up to 30% kernel removal. This improvement in yield was attributed to decreased proportion of bran as indicated by ash content. However, the yield dropped at 40% kernel removal due to formation of large chunks of agglomerated flour particles. Thick porridge became harder as decortication level increased and this was strongly associated with the concomitant increase in starch concentration. Overall, this study defined the decortication levels necessary to improve the couscous colour and yield, and texture of porridge made from different sorghum cultivars.