A Novel Modified Endosperm Texture in a Mutant High‐Protein Digestibility/High‐Lysine Grain Sorghum (Sorghum bicolor (L.) Moench)

Development of high‐protein digestibility (HPD)/high‐lysine (hl) sorghum mutant germplasm with good grain quality (i.e., hard endosperm texture) has been a major research objective at Purdue University. Progress toward achieving this objective, however, has been slow due to challenges posed by a combination of genetic and environmental factors. In this article, we report on the identification of a sorghum grain phenotype with a unique modified endosperm texture that has near‐normal hardness and possesses superior nutritional quality traits of high digestibility and enhanced lysine content. These modified endosperm lines were identified among F₆ families developed from crosses between hard endosperm, normal nutritional quality sorghum lines, and improved HPD/hl sorghum mutant P721Q‐derived lines. A novel vitreous endosperm formation originated in the central portion of the kernel endosperm with opaque portions appearing both centrally and peripherally surrounding the vitreous portion. Kernels exhibiting modification showed a range of vitreous content from a slight interior section to one that filled out to the kernel periphery. Microstructure of the vitreous endosperm fraction was dramatically different from that of vitreous normal kernels in sorghum and in other cereals, in that polygonal starch granules were densely packed but without the typically associated continuous protein matrix. We speculate that, due to the lack of protein matrix, such vitreous endosperm may have more available starch for animal nutrition, and possibly have improved wet‐milling and dry‐grind ethanol processing properties. The new modified endosperm selections produce a range that approaches the density of the vitreous parent, and have lysine content and protein digestibility comparable to the HPD/hl opaque mutant parent.     

Hardness Changes and Endosperm Modification During Sorghum Malting in Grains of Varying Hardness and Malt Quality

This study examined the interaction between sorghum grain hardness and sorghum malt quality in terms of diastatic power and free amino nitrogen with endosperm modification during malting. The changes in kernel hardness during malting of four commercial sorghum cultivars of differing quality in terms of endosperm texture and potential malt quality were measured using tests for hardness and density, and endosperm modification was followed by scanning electron microscopy. The general pattern of modification during sorghum malting was confirmed to start at the endosperm–scutellum interface and then continue into the floury endosperm toward the kernel distal end. Significantly, a cultivar of intermediate hardness and low malting quality remained harder and modified more slowly than a harder cultivar of high malting quality. It appeared that intrinsic grain hardness and malt amylase and protease activity both affected malt hardness and endosperm modification, but amylase and protease activity had a greater effect because of their degradation of endosperm starch and protein. Of the hardness and density tests studied, the tangential abrasive dehulling device (TADD) gave the best measure of hardness throughout malting; maximum range was 24–100% kernel removed over five days of malting. Also, the data agreed with the observed malt modification rates. Thus, the TADD may have application as a simple and rapid test for estimating sorghum malt quality.     

A Rapid Protein Digestibility Assay for Identifying Highly Digestible Sorghum Lines

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 electrophoresis‐based 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 intensitizes 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.     

Protein Quality and Physical Characteristics of Kisra (Fermented Sorghum Pancake‐like Flatbread) Made from Tannin and Non‐Tannin Sorghum Cultivars

Kisra is a naturally lactic acid bacteria‐ and yeast‐fermented sorghum thin pancake‐like flatbread produced in Sudan. Kisra has considerable potential as the basis for development of a gluten‐free sandwich wrap. To help direct cultivar selection for commercial production of these products, two white, tan plant non‐tannin Type I, one white Type II tannin, and one red Type III tannin sorghum cultivars were evaluated with respect to kisra protein quality and physical characteristics. Kisra from the non‐tannin sorghums were flexible and had an open‐textured structure with many regular gas cells, whereas those from the tannin sorghums were more brittle, denser in structure, and contained far fewer and smaller gas cells. Kisra from the tannin sorghums had the lowest reactive lysine content, in vitro protein digestibility, and Protein Digestibility Corrected Amino Score (PDCAAS), with values being lowest for the Type III sorghum. PDCAAS of kisra from the Type III sorghum was only 0.12, less than half of that from the Type I sorghums. As the tannins in tannin sorghums adversely affect kisra protein quality and physical characteristics, white tan plant, non‐tannin sorghum cultivars are most suitable for kisra production and for development of wrap‐type sorghum‐based baked goods.     

Associations of Starch Gel Hardness,Granule Size,Waxy Allelic Expression,Thermal Pasting,Milling Quality,and Kernel Texture of 12 Soft Wheat Cultivars

Starches were isolated from 12 soft wheat (Triticum aestivum L.) cultivars and were characterized for waxy (Wx) allelic expression, thermal pasting characteristics, and starch granule size. Gels were produced from the thermally degraded starches and were evaluated using large deformation rheological measurements. Data were compared with cultivar kernel texture, milling characteristics, starch chemical analyses, and flour pasting characteristics. Larger flour yields were produced from cultivars that had larger starch granules. Flour yield also was correlated with lower amylose content and greater starch content. Harder starch gels were correlated with higher levels of amylose content and softer kernel texture. The cultivar Fillmore, which had a partial waxy mutation at the B locus, produced the highest peak pasting viscosity and the lowest gel hardness. Softer textured wheats had greater lipid‐complexed amylose and starch phosphorus contents and had less total starch content. Among these wheats of the soft market class, softer textured wheats had larger starch granules and harder textured wheats had smaller starch granules. In part, this may explain why soft wheats vary in texture. The smaller granules have larger surface area available for noncovalent bonding with the endosperm protein matrix and they also may pack more efficiently, producing harder endosperm.     

Qualitative Zymographic Studies of Major Proteinases from Malted Sorghum (Sorghum bicolor L.) and Effects of Cultivar

Proteolysis during cereal germination is vital both to seedling growth and the success of commercial malting and brewing. In this study, proteinases in proteolytic extracts from seeds and germinated grains of 11 Botswana sorghum cultivars were analyzed and partially characterized by one‐dimensional electrophoresis on SDS‐PAGE gels containing incorporated gelatin. Proteinase polymorphism was detected in both germinated and ungerminated sorghum grains. Fifteen distinct proteinase bands, with M_r values of 27,000–100,000 were detected in sorghum malt extract, while ungerminated sorghum displayed a maximum of four bands (M_r ≈ 78,000–100,000). Band numbers and identity varied markedly according to cultivar. More proteinase bands were detected at pH 4.6, than at pH 6.2 and 7.0, suggesting pH optima considerably below neutrality. Cysteine‐proteinases constituted a higher proportion (9 of 15) of the detected sorghum malt proteinases and were most detectable at pH 4.6. Multiple representatives were also detected for both serine‐ and metallo‐proteinases, although these were more active at pH 6.2 and 7.0. 1‐10 Phenanthroline inhibited malt metallo‐proteinase more strongly than EDTA, suggesting that these enzymes were most probably zinc‐dependent. Aspartyl‐proteinases were not detected, probably because of the substrate employed. Results indicate that the sorghum proteinase system is complex.     

Steam Flaking Characteristics of Sorghum Hybrids and Lines with Differing Endosperm Characteristics

Commercial and food-type sorghum hybrids with differing kernel and endosperm characteristics were grown under comparable conditions and steam flaked in each of three years. The raw-grain kernel characteristics and proximate analyses were homogenous over the three-year period. The waxy hybrid produced large, translucent, durable flakes that had significantly higher enzyme-susceptible starch values for all years compared to the other varieties. Flakes with lower amylose contents (waxy endosperm) were positively correlated with percent whole flakes (r² = 0.509), flake diameter (r² = 0.846), and enzyme-susceptible starches (r² = 0.564) and negatively correlated with higher flake fragility (r² = -0.647), test weight (r² = -0.626), and flake breakage (r² = -0.560). The heterowaxy flakes had a good appearance and were generally comparable in quality to the nonwaxy commercial and experimental hybrids. Heterowaxy sorghum hybrids with good grain yields can provide improved quality grain and flakes without sacrificing agronomic performance and yields. No difference in flaking performance was detectable among the kernels with different pericarp colors; flakes from the white food-type sorghums had excellent appearance. Nontempered control samples were inferior in quality to all conditioned treatments.     

A Study of Puroindoline b Gene Involvement in the Milling Behavior of Hard‐Type Common Wheats

Differences in milling behavior among hard‐type common wheat (Triticum aestivum) cultivars are well known to millers. Among them, the French cultivar Soissons, which contains the Pinb‐D1d allelic form of the puroindoline b gene, is particularly distinguished for its high milling value. Near‐isogenic lines (NILs) differing by the allelic forms of the puroindoline b gene, Pinb‐D1d or Pinb‐D1b (one of the most frequent alleles found in the European wheat population), were constructed. Grain characteristics obtained after wheat cultivation in distinct environmental conditions were compared between NILs and the cultivar Soissons, as was their fractionation behavior. Results showed that NILs containing the Pinb‐D1d allele displayed lower values of grain hardness and vitreousness than did the corresponding lines containing the Pinb‐D1b allelic form under the same cultivation conditions. Both genetic background and environmental conditions appeared to affect grain texture. Measured single‐kernel characterization system hardness index values of the samples under study were found to be correlated with the vitreousness values. Studies of the milling behavior helped to point out that grain vitreousness is an important factor acting on endosperm breakage ability, whatever the genetic background of the wheat. Our results also demonstrated that, at similar levels of vitreousness, the endosperm of Soissons could more easily be reduced than that of other wheat lines.     

Physicochemical Properties of Flours that Relate to Sorghum Couscous Quality

Flours from eight sorghum cultivars were evaluated for their couscous-making 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 laboratory-prepared 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.     

Nifedipine influence on calcium and aluminum absorption in roots of three sorghum cultivars

A 1,4‐dihydroxypyridine type of ion channel blocker, nifedipine [1,4‐dihydro‐2,6‐dimethyl‐4‐(2‐nitrophenyl)‐3,5‐pyridinedicarboxylate dimethyl ester], was tested on the root absorption of Al³⁺ and Ca²⁺ by sorghum [Sorghum bicolor (L.) Moench] cultivars with varying acid stress tolerance. In an acid stress sensitive cultivar, Funk G522DR, nifedipine (1 μM) influenced Ca²⁺ but not Al³⁺ absorption. In one acid stress tolerant cultivar, SC574, nifedipine (1 μM) influenced both Ca²⁺ and Al³⁺ absorption. In a second acid stress tolerant cultivar, SC283, nifedipine (1 μM) did not influence Ca²⁺ but did influence Al³⁺ absorption. Considerable genetic diversity is present in Ca²⁺ and Al³⁺ absorption between sorghum cultivars.     

Nifedipine influence on mineral nutrient uptake by sorghum primary root tips

Seedling sorghum [Sorghum bicolor (L.) Moench. cv GP‐10, SC283, SC574, and Funk G522DR] primary root tips (1‐cm) content of calcium (Ca), phosphorus (P), zinc (Zn), boron (B), manganese (Mn), iron (Fe), magnesium (Mg), and copper (Cu) in response to a Ca²⁺‐channel blocker (nifedipine 0, 0.01, 0.1, or 1 μM) was measured after a 1‐hr exposure to Hoagland and Arnon complete mineral nutrient solution. Content of ions was significantly different among the cultivars. Responses to nifedipine were element‐cultivar‐blocker concentration dependent.     

Genetic Diversity in Properties of Starch from Zimbabwean Sorghum Landraces

Starch was isolated from 95 sorghum landraces from Zimbabwe using an alkali steep and wet‐milling procedure. The physicochemical properties of sorghum starch were examined for potential use in Southern Africa. All the landraces evaluated had a normal endosperm indicated by the amylose content of the starches. Starch properties were not correlated to most of the physical grain quality traits evaluated. Grain hardness was weakly correlated to starch gel adhesiveness (r = 0.36) and amylose content (r = 0.38) (P < 0.001). The mean peak viscosity (PV) of the sorghum starches was 324 Rapid Visco Analyser units (RVU) compared with 238 RVU in a commercial corn starch sample; PV was 244–377 RVU. Some landraces had low shear‐thinning starches, implying good paste stability under hot conditions. Pasting properties were highly correlated among the sorghum starches. The starch gel hardness showed considerable variation (44–71 g) among the landraces. Gelatinization peak temperatures were 66–70°C. The thermal properties of starches were not correlated with starch swelling and pasting properties. Genotype grouping by highest and lowest values in each category would allow selection of sorghums based on a specific attribute depending on the desired end use.     

Determining Weight and Moisture Properties of Sound and Fusarium‐Damaged Single Wheat Kernels by Near‐Infrared Spectroscopy

Single kernel moisture content (MC) is important in the measurement of other quality traits in single kernels because many traits are expressed on a dry weight basis. MC also affects viability, storage quality, and price. Also, if near‐infrared (NIR) spectroscopy is used to measure grain traits, the influence of water must be accounted for because water is a strong absorber throughout the NIR region. The feasibility of measurement of MC, fresh weight, dry weight, and water mass of single wheat kernels with or without Fusarium damage was investigated using two wheat cultivars with three visually selected classes of kernels with Fusarium damage and a range of MC. Calibration models were developed either from all kernel classes or from only undamaged kernels of one cultivar that were then validated using all spectra of the other cultivar. A calibration model developed for MC when using all kernels from the wheat cultivar Jagalene had a coefficient of determination (R²) of 0.77 and standard error of cross validation (SECV) of 1.03%. This model predicted the MC of the wheat cultivar 2137 with R² of 0.81 and a standard error of prediction (SEP) of 1.02% and RPD of 2.2. Calibration models developed using all kernels from both cultivars predicted MC, fresh weight, dry weight, or water mass in kernels better than models that used only undamaged kernels from both cultivars. Single kernel water mass was more accurately estimated using the actual fresh weight of kernels and MC predicted by calibrations that used all kernels or undamaged kernels. The necessity for evaluating and expressing constituent levels in single kernels on a mass/kernel basis rather than a percentage basis was elaborated. The need to overcome the effects of kernel size and water mass on single kernel spectra before using in calibration model development was also highlighted.     

Storage Stability of Flour‐Blasted Brown Rice

Brown rice was blasted with rice flour rather than sand in a sand blaster to make microperforations so that water could easily penetrate the brown rice endosperm and cook the rice in a shorter time. The flour‐blasted American Basmati brown rice, long‐grain brown rice, and parboiled long‐grain brown rice samples were stored in Ziploc storage bags under atmospheric conditions and in vacuum‐packed bags. They were periodically tested for over 10 months for changes in water absorption, free fatty acid (FFA), peroxide value (POV), viscosity changes of flour using the Rapid ViscoAnalyser (RVA), and texture of whole cooked kernel using a texture analyzer during cooking. Flour‐blasted brown rice absorbed less water but needed less cooking time than its counterpart that was not flour‐blasted. There was an increase in FFA, POV, peak viscosity (PV), final viscosity (FV), breakdown viscosity (BD), and setback viscosity (SB) during storage of flour‐blasted brown rice for 300 days, but no change was observed in texture (hardness, gumminess) and water absorption. The combined coefficient of correlation (including all types of rice) between FFA and FV is r = 0.86 and between FFA and SB is r = 0.90 at P < 0.0001.     

Reduced Amylose Effects on Bread and White Salted Noodle Quality

Amylose content in wheat endosperm is controlled by three Wx loci, and the proportion of amylose decreases with successive accumulation of Wx null alleles at the three loci. The proportion of amylose is believed to influence end‐use quality of bread and Asian noodles. The objectives of this study were to determine influence of the allelic difference at Wx‐B1 locus on bread quality, bread firmness, and white salted noodle texture in a spring wheat cross segregating for the Wx‐B1 locus and in a set of advanced spring wheat breeding lines differing in allelic state at the Wx‐ B1 locus. In addition, we examined the relationship between amylose content and flour swelling properties on bread and noodle traits. Fifty‐four recombinant inbred lines of hard white spring wheat plus parents were grown in replicated trials in two years, and 31 cultivars and breeding lines of hard spring wheat were grown in two locations. Bread and white salted noodles were processed from these trials. The presence of the Wx‐B1 null allele reduced amylose content by 2.4% in a recombinant inbred population and 4.3% in a survey of advanced breeding lines and cultivars compared with the normal. The reduced amylose was accompanied by an average increase in flour swelling power (FSP) for the Wx‐B1 null group of 0.8 g/g for the cross progeny and 2.3 g/g for the cultivar survey group. The Wx‐B1 allelic difference did not affect flour protein in cross progeny where the allelic difference was not confounded with genetic background. Bread from the Wx‐B1 null groups on average had increased loaf volume and was softer than the normal group for the cross progeny and cultivar survey group. The Wx‐B1 allelic difference altered white salted noodle texture, most notably noodle springiness and cohesiveness where the Wx‐B1 null groups was more springy and more cohesive than the normal groups for both sets of genetic materials. Flour protein was more highly related to loaf volume than were FSP or amylose. Both flour protein and FSP were positively related to noodle textural traits, but especially noodle springiness and cohesiveness.