Effect of Flour Particle Size on the Glycemic Index of Muffins Made from Whole Sorghum, Whole Corn, Brown Rice, Whole Wheat, or Refined Wheat Flours

The unique properties of sorghum are increasingly being studied for potential health benefits, with one area of emphasis being the impact of sorghum consumption on mitigating type 2 diabetes. The glycemic index (GI) of muffins made from whole grain sorghum flour ground to three different particle sizes (fine, intermediate, coarse) was tested on eight healthy volunteers (ages 18-40) and compared to the glycemic index of whole grain corn, wheat, and rice flours produced using a similar product formula. Sorghum flour ground through a 0.5 mm screen ("fine") had an overall similar particle size to that of the brown rice flour ground using a 0.5 mm screen. The range of GI values was 32 to 56, with only the GI of intermediate milled sorghum flour being lower than that of corn, rice, or wheat (p < 0.05). The lowest glycemic index (32 +/- 17) was found when using sorghum flour with an intermediate particle size (167 +/- 4 μm). Muffins made using brown rice had the next lowest glycemic index at 37 +/- 17. All GI values calculated had large standard deviations, which is common for these types of studies. These results can assist in the product development process to advance the quality of healthy, gluten-free sorghum-based foods for consumers. Further research should investigate if these results can be duplicated and the possible reason for the lower GI of intermediate particle size sorghum flour.

Dry fractionation process operations in the production of protein concentrates: A review

The market for plant proteins is expanding rapidly as the negative impacts of animal agriculture on the environment and resources become more evident. Plant proteins offer competitive advantages in production costs, energy requirements, and sustainability. Conventional plant-protein extraction is water and chemical-intensive, posing environmental concerns. Dry fractionation is an energy-efficient and environmentally friendly process for protein separation, preserving protein's native functionality. Cereals and pulses are excellent sources of plant proteins as they are widely grown worldwide. This paper provides a comprehensive review of the dry fractionation process utilized for different seeds to obtain protein-rich fractions with high purity and functionality. Pretreatments, such as dehulling and defatting, are known to enhance the protein separation efficiency. Factors, such as milling speed, mill classifier speed, feed rate, seed type, and hardness, were crucial for obtaining parent flour of desired particle size distribution during milling. The air classification or electrostatic separation settings are crucial in determining the quality of the separated protein. The cut point in air classification is targeted based on the starch granule size of the seed material. Optimization of these operations, applied to different pulses and seeds, led to higher yields of proteins with higher purity. Dual techniques, such as air classification and electrostatic separation, enhance protein purity. The yield of the protein concentrates can be increased by recycling the coarse fractions. Further research is necessary to improve the quality, purity, and yield of protein concentrates to enable more efficient use of plant proteins to meet global protein demands.

Performance of a Handheld MicroNIR Instrument for Determining Protein Levels in Sorghum Grain Samples

Near infrared (NIR) spectroscopy is widely used for evaluating quality traits of cereal grains. For evaluating protein content of intact sorghum grains, parallel NIR calibrations were developed using an established benchtop instrumentation (Perten DA-7250) as a baseline to test the efficacy of an adaptive handheld instrument (VIAVI MicroNIR OnSite-W). Spectra were collected from 59 grain samples using both instruments at the same time. Cross-validated calibration models were validated with 33 test samples. The selected calibration model for DA-7250 with a coefficient of determination (R2) = 0.98 and a root mean square error of cross validation (RMSECV) = 0.41% predicted the protein content of a test set with R2 = 0.94, root mean square error of prediction (RMSEP) = 0.52% with a ratio of performance to deviation (RPD) of 4.13. The selected model for the MicroNIR with R2 = 0.95 and RMSECV = 0.62% predicted the protein content of the test set with R2 = 0.87, RMSEP = 0.76% with an RPD of 2.74. In comparison, the performance of the DA-7250 was better than the MicroNIR, however, the performance of the MicroNIR was also acceptable for screening intact sorghum grain protein levels. Therefore, the MicroNIR instrument may be used as a potential tool for screening sorghum samples where benchtop instruments are not appropriate such as for screening samples in the field or as a less expensive option compared with benchtop instruments.

Variations in Total Protein and Amino Acids in the Sequenced Sorghum Mutant Library

Sorghum (Sorghum bicolor) is the fifth most important cereal crop worldwide; however, its utilization in food products can be limited due to reduced nutritional quality related to amino acid composition and protein digestibility in cooked products. Low essential amino acid levels and digestibility are influenced by the composition of the sorghum seed storage proteins, kafirins. In this study, we report a core collection of 206 sorghum mutant lines with altered seed storage proteins. Wet lab chemistry analysis was conducted to evaluate the total protein content and 23 amino acids, including 19 protein-bound and 4 non-protein amino acids. We identified mutant lines with diverse compositions of essential and non-essential amino acids. The highest total protein content in these lines was almost double that of the wild-type (BTx623). The mutants identified in this study can be used as a genetic resource to improve the sorghum grain quality and determine the molecular mechanisms underlying the biosynthesis of storage protein and starch in sorghum seeds.

Sorghum Flour Application in Bread: Technological Challenges and Opportunities

Sorghum has a long history of use in the production of different types of bread. This review paper discusses different types of bread and factors that affect the physicochemical, technological, rheological, sensorial, and nutritional properties of different types of sorghum bread. The main types of bread are unleavened (roti and tortilla), flatbread with a pre-ferment (injera and kisra), gluten-free and sorghum bread with wheat. The quality of sorghum flour, dough, and bread can be improved by the addition of different ingredients and using novel and traditional methods. Furthermore, extrusion, high-pressure treatment, heat treatment, and ozonation, in combination with techniques such as fermentation, have been reported for increasing sorghum functionality.

Modification of zein dough functionality using kafirin as a coprotein

Kafirin, sorghum prolamin, was investigated as a coprotein for zein as visco-elastic masses and in starch-based model doughs. Regular kafirin and kafirins from waxy and high protein digestibility (HD) sorghum crosses were studied. HPLC revealed that waxy-HD kafirin was of smaller molecular size and low in β-kafirin. It also had greater surface hydrophobicity. Kafirin addition to zein increased visco-elastic mass elasticity up to ≈50% stress-recovery, similar to wheat gluten. Waxy-HD kafirin gave the highest elasticity, possibly due to its hydrophobicity. Kafirin inclusion at 2:8 parts zein increased the tensile strength of model doughs. Maximum strength was, however, only 60% that of gluten-based dough. Kafirin from regular sorghum gave the highest strength, possibly because of greater disulphide-bonded polymerisation. Confocal laser scanning microscopy showed that zein-kafirin copolymers formed fairly linear fibrils in stretched doughs, indicating excellent compatibility between the proteins. Future research should establish how kafirin-zein copolymer performs in non-wheat flour products.

Chemical Composition, Fatty Acid and Mineral Content of Food-Grade White, Red and Black Sorghum Varieties Grown in the Mediterranean Environment

Grain sorghum (Sorghum bicolor) is a gluten-free cereal grown around the world and is a food staple in semi-arid and subtropical regions. Sorghum is a diverse crop with a range of pericarp colour including white, various shades of red, and black, all of which show health-promoting properties as they are rich sources of antioxidants such as polyphenols, carotenoids, as well as micro- and macro-nutrients. This work examined the grain composition of three sorghum varieties possessing a range of pericarp colours (white, red, and black) grown in the Mediterranean region. To determine the nutritional quality independent of the contributions of phenolics, mineral and fatty acid content and composition were measured. Minor differences in both protein and carbohydrate were observed among varieties, and a higher fibre content was found in both the red and black varieties. A higher amount of total saturated fats was found in the white variety, while the black variety had a lower amount of total unsaturated and polyunsaturated fats than either the white or red varieties. Oleic, linoleic, and palmitic were the primary fatty acids in all three analysed sorghum varieties. Significant differences in mineral content were found among the samples with a greater amount of Mg, K, Al, Mn, Fe, Ni, Zn, Pb and U in both red and black than the white sorghum variety. The results show that sorghum whole grain flour made from grain with varying pericarp colours contains unique nutritional properties.

Genetic control of source-sink relationships in grain sorghum

QTL hotspots identified for selected source-sink-related traits provide the opportunity for pyramiding favorable alleles for improving sorghum productivity under diverse environments. A sorghum bi-parental mapping population was evaluated under six different environments at Hays and Manhattan, Kansas, USA, in 2016 and 2017, to identify genomic regions controlling source-sink relationships. The population consisted of 210 recombinant inbred lines developed from US elite post-flowering drought susceptible (RTx430) and a known post-flowering drought tolerant cultivar (SC35). Selected physiological traits related to source (effective quantum yield of photosystem II and chlorophyll index), sink (grain yield per panicle) and panicle neck diameter were recorded during grain filling. The results showed strong phenotypic and genotypic association between panicle neck diameter and grain yield per panicle during mid-grain filling and at maturity. Multiple QTL model revealed 5-12 including 2-5 major QTL for each trait. Among them 3, 7 and 8 QTL for quantum yield, panicle neck diameter and chlorophyll index, respectively, have not been identified previously in sorghum. Phenotypic variation explained by QTL identified across target traits ranged between 5.5 and 25.4%. Panicle neck diameter and grain yield per panicle were positively associated, indicating the possibility of targeting common co-localized QTL to improve both traits simultaneously through marker-assisted selection. Three major QTL hotspots, controlling multiple traits were identified on chromosome 1 (52.23-61.18 Mb), 2 (2.52-11.43 Mb) and 3 (1.32-3.95 Mb). The identified genomic regions and underlying candidate genes can be utilized in pyramiding favorable alleles for improving source-sink relationships in sorghum under diverse environments.

Effect of Tempering Conditions on White Sorghum Milling, Flour, and Bread Properties

The effects of room temperature water, hot water, and steam tempering methods were investigated on sorghum kernel physical properties, milling, flour, and bread-making properties. Overall tempering condition and tempering moisture content were found to have a significant effect on the physical properties. Milling properties were evaluated using a laboratory-scale roller milling flowsheet consisting of four break rolls and eight reduction rolls. Room temperature tempering (18% moisture for 24 h) led to better separation of bran and endosperm without negatively impacting flour quality characteristics i.e., particle size distribution, flour yield, protein, ash, damaged starch, and moisture content. Bread produced from the flour obtained from milling sorghum kernels tempered with room temperature water (18% m.c for 24 h) and hot water (16% m.c at 60 °C for 18 h) displayed better bread-making properties i.e., high firmness, resilience, volume index, higher number of cells, and thinner cell walls when compared to other tempering conditions. Room temperature water tempering treatment (18% m.c for 24 h) could be a better pretreatment process for milling white sorghum kernels without negatively impacting the flour and bread-making quality characteristics.

Analysis of corn and sorghum flour mixtures using laser-induced breakdown spectroscopy

BACKGROUND

In a world constantly challenged by climate change, corn and sorghum are two important grains because of their high productivity and adaptability, and their multifunctional use for different purposes such as human food, animal feed, and feedstock for many industrial products and biofuels. Corn and sorghum can be utilized interchangeably in certain applications; one grain may be preferred over the other for several reasons. The determination of the composition corn and sorghum flour mixtures may be necessary for economic, regulatory, environmental, functional, or nutritional reasons.

RESULTS

Laser-induced breakdown spectroscopy (LIBS) in combination with chemometrics, was used for the classification of flour samples based on the LIBS spectra of flour types and mixtures using partial least squares discriminant analysis (PLS-DA) and the determination of the sorghum ratio in sorghum / corn flour mixture based on their elemental composition using partial least squares (PLS) regression. Laser-induced breakdown spectroscopy with PLS-DA successfully identified the samples as either pure corn, pure sorghum, or corn-sorghum mixtures. Moreover, the addition of various levels of sorghum flour to mixtures of corn-sorghum flour were used for PLS analysis. The coefficient of determination values of calibration and validation PLS models are 0.979 and 0.965, respectively. The limit of detection of the PLS models is 4.36%.

CONCLUSION

This study offers a rapid method for the determination of the sorghum level in corn-sorghum flour mixtures and the classification of flour samples with high accuracy, a short analysis time, and no requirement for time-consuming sample preparation procedures. © 2020 Society of Chemical Industry.

Advancing provitamin A biofortification in sorghum: Genome-wide association studies of grain carotenoids in global germplasm

Vitamin A deficiency is one of the most prevalent nutritional deficiencies worldwide. Sorghum [Sorghum bicolor L. (Moench)] is a major cereal crop consumed by millions of people in regions with high vitamin A deficiency. We quantified carotenoid concentrations in a diverse sorghum panel using high-performance liquid chromatography and conducted a genome-wide association study (GWAS) of grain carotenoids to identify genes underlying carotenoid variation. There was moderate variation for β-carotene (00.8 μg g^-1 ), lutein (0.3-9.4 μg g^-1 ), and zeaxanthin (0.2-9.1 μg g^-1 ), but β-cryptoxanthin and α-carotene were nearly undetectable. Genotype had the largest effect size, at 81% for zeaxanthin, 62% for β-carotene, and 53% for lutein. Using multiple models, GWAS identified several significant associations between carotenoids and single nucleotide polymorphisms (SNPs), some of which colocalized with known carotenoid genes that have not been previously implicated in carotenoid variation. Several of the candidate genes identified have also been identified in maize (Zea mays L.) and Arabidopsis (Arabidopsis thaliana) carotenoid GWAS studies. Notably, an SNP inside the putative ortholog of maize zeaxanthin epoxidase (ZEP) had the most significant association with zeaxanthin and with the ratio between lutein and zeaxanthin, suggesting that ZEP is a major gene controlling sorghum carotenoid variation. Overall findings suggest there is oligogenic inheritance for sorghum carotenoids and suitable variation for marker-assisted selection. The high carotenoid germplasm and significant associations identified in this study can be used in biofortification efforts to improve the nutritional quality of sorghum.

Allelochemicals targeted to balance competing selections in African agroecosystems

Among major cereals domesticated as staple food, only sorghum has a high proportion of cultivars with condensed tannins in grain, which can trigger bitter taste perception in animals by binding to type 2 taste receptors (TAS2Rs). Here, we report the completion of uncovering of a pair of duplicate recessive genes (Tannin1 and Tannin2) underlying tannin presence. Three loss-of-function alleles from each gene were identified in non-tannin sorghum desired as palatable food. Condensed tannins effectively prevented sparrows from consuming sorghum grain. Parallel geographic distributions between tannin sorghum and Quelea quelea supported the role of tannins in fighting against this major herbivore threat. Association between geographic distributions of human TAS2R variants and tannin sorghum across Africa suggested that different causes had probably driven this bidirectional selection according to varied local herbivore threats and human taste sensitivity. Our investigation uncovered coevolution among humans, plants and environments linked by allelochemicals.

Factors Influencing Zein-Whole Sorghum Flour Dough Formation and Bread Quality

Zein is known to able to form viscoelastic dough with wheat-like properties under certain conditions. Several studies have been conducted to explain the mechanism behind this ability and to improve the functionality and end-use quality of zein-based dough systems. However, most of this research has been conducted using zein in combination with isolated starches or high-starch flours. To investigate the production of additional zein-whole sorghum flour breads, experiments were conducted to determine factors impacting zein-whole sorghum flour dough and bread quality. Optimizing water levels, using defatted zein and/or sorghum flour, and increasing zein content in dough formulas were investigated as initial formulation steps. Of these factors, increasing zein content from 20% to 30% (flour weight basis) had the greatest impact, resulting in stronger zein-based dough and improved bread quality. Additives and zein treatments shown to impact zein functionality were then investigated for their effect of zein-whole sorghum flour breads. Mixing zein and whole sorghum flour with 0.5% hydrogen peroxide, 5% ethanol, or 3% hydroxypropyl methylcellulose resulted in improved dough strength and bread quality. Breads made from whole white sorghum flour had improved quality compared to zein-based breads made with black or high-tannin whole sorghum flour. PRACTICAL APPLICATION: Zein is known to be able to form wheat-like dough when mixed under the right conditions. Most of the research on zein-based dough and food products has used high-starch flours. This project investigated optimizing the production of zein-whole sorghum flour dough and bread as an alternative. Increasing the zein content in the formula and using additives including ethanol and HPMC produced breads from zein-whole sorghum flour that were like those made with zein and pure starch.

The effect of genotype and traditional food processing methods on in-vitro protein digestibility and micronutrient profile of sorghum cooked products

Sorghum (Sorghum bicolor (L.) Moench) is one of the principal staple for millions of people in sub-Saharan Africa serving as the main sources of protein. However, protein digestibility is low in sorghum and this may be affected by processing methods. In this study 15 sorghum cultivars and one variety each of maize (Zea maize) and tef (Eragrostis tef) all of Ethiopian origin were investigated for in-vitro protein digestibility (IVPD), activity and concentration of anti-nutritional factors and micro nutrient profile in raw flour and various cooked food samples. Kafirin composition content and composition was also determined from raw flour samples of the sorghum cultivars. IVPD was significantly different between genotypes with both maize and tef superior to sorghum both in cooked and uncooked state except for the high lysine genotype Wetet Be-gunchie. Cooking significantly reduced IVPD in all crops but had only minor effect in maize. Results revealed a highly significant interaction between genotype and food processing methods where, occasionally, genotypes with highest IVPD under one processing method ended up to be the lowest under another. Trypsin inhibitor levels had a significant and negative correlation with IVPD (r2 = 0.1), while changes in phytic acid concentration and intrinsic phytase levels during processing followed opposite trends to each other. Processing increased mineral levels by 20-44% for iron and 4-29% for zinc perhaps due to degradation of phytic acid. Results demonstrated that protein digestibility and the concentration of anti- nutritional factors varied widely depending on the food type. Identification of specific genotypes for a specific food product may help improve the nutritional quality of sorghum based foods.

Impacts of Fungal Stalk Rot Pathogens on Physicochemical Properties of Sorghum Grain

Stalk rot diseases are among the most ubiquitous and damaging fungal diseases of sorghum (Sorghum bicolor (L.) Moench) worldwide. Although reports of quantitative yield losses to stalk rots are available, the impact of stalk rot on grain quality attributes is unknown. This study was conducted to test whether stalk rot diseases could affect grain mineral (N, P, K; Ca, Mg, Cu, Fe, Mn, and Zn) and macronutrient (protein, fat, and starch) content, ash content, and physical traits (unit grain weight, hardness, and diameter). A field experiment was conducted in 2013 and 2014 with four sorghum genotypes (two hybrids and two lines). Plants from each genotype were inoculated with four stalk rot pathogens (Fusarium andiyazi, F. proliferatum, F. thapsinum, and Macrophomina phaseolina) and mock-inoculated with phosphate-buffered saline (control). Grains collected from infected and control plants were analyzed for macronutrient and ash content using near-infrared reflectance spectroscopy, grain hardness and diameter using the single-kernel characterization system, and mineral content using the Rapid Flow Analyzer (Model RFA-300 for N) and inductively coupled plasma spectrometer (for P, K, Ca, Mg, Cu, Fe, Mn, and Zn). Although stalk rot pathogens significantly reduced unit grain weight, they did not significantly affect grain hardness and diameter and, therefore, may not affect milling quality. Pathogens significantly reduced all macronutrient and most mineral contents across genotypes and environments on a per-unit-grain basis, except N and Mg, which were affected in a genotype- and environment-specific manner, and Fe, which was not significantly affected. Most minerals tested were significantly and negatively correlated with disease severity (lesion length) and total grain weight per panicle. The hybrid tested (Pioneer 84G62) exhibited reduced mineral and macronutritional changes after stalk rot infection, providing insights into the possibility of producing high-yielding, nutritionally stable hybrids under stalk rot disease pressure through dedicated breeding efforts.

Interaction mechanisms of condensed tannins (proanthocyanidins) with wheat gluten proteins

Proanthocyanidins (PA) crosslink wheat gluten, increasing its polymer size and strength. However, mechanisms behind these interactions are unknown. This study used PA of different MW profiles (mean degree of polymerization 8.3 and 19.5) to investigate how PA polymerize gluten. The higher MW PA had greater binding affinity for both glutenins and gliadins than lower MW PA, whereas both PA precipitated glutenins more efficiently than gliadins. The PA preferentially bound the largest of the protein fractions available: high MW glutenin subunits (HMW-GS) over low MW-GS, and ω-gliadins over α- and γ-gliadins. Furthermore, within the HMW-GS, PA bound more of the larger x-type than the smaller y-type. Proanthocyanidins reduced gluten solubility in urea and decreased surface hydrophobicity of glutenins, but not gliadins. The PA appear to preferentially crosslink HMW-GS via hydrophobic interactions and hydrogen bonding, whereas their interaction with gliadins is dominated by hydrogen bonding and is relatively weaker.

Effect of Condensed Tannin Profile on Wheat Flour Dough Rheology

Proanthocyanidins (PA) cross-link proteins and could expand wheat gluten functionality; however, how the PA MW or gluten profile affect these interactions is unknown. Effect of PA MW profile (sorghum versus grape seed PA) on dough rheology of high versus low insoluble polymeric protein (IPP) wheat flour was evaluated using mixograph, large (TA.XT2i) and small (HAAKE Rheostress 6000) deformation rheometry. Sorghum PA (93% polymeric) more effectively (p < 0.05) strengthened both glutens than grape seed PA (45% polymeric), without reducing gluten extensibility. These effects were higher in low IPP (weak gluten) flour, e.g., sorghum PA doubled IPP, increased mix time by 75%, dough elasticity by 82%, and peak angle by 17° versus control. Grape seed PA increased IPP by 75% and elasticity by 36%, but reduced peak angle by 15°, indicating reduced mixing tolerance. Sorghum PA, but not grape seed PA, increased (p < 0.05) all above parameters in high IPP dough. Polymeric PA more effectively strengthened gluten than oligomeric PA, likely via more efficient protein cross-linking to overcome strong antioxidant effect of PA. High MW PA may be useful natural gluten strengtheners for diverse applications.

Grain sorghum proteomics: integrated approach toward characterization of endosperm storage proteins in kafirin allelic variants

Grain protein composition determines quality traits, such as value for food, feedstock, and biomaterials uses. The major storage proteins in sorghum are the prolamins, known as kafirins. Located primarily on the periphery of the protein bodies surrounding starch, cysteine-rich β- and γ-kafirins may limit enzymatic access to internally positioned α-kafirins and starch. An integrated approach was used to characterize sorghum with allelic variation at the kafirin loci to determine the effects of this genetic diversity on protein expression. Reversed-phase high performance liquid chromatography and lab-on-a-chip analysis showed reductions in alcohol-soluble protein in β-kafirin null lines. Gel-based separation and liquid chromatography-tandem mass spectrometry identified a range of redox active proteins affecting storage protein biochemistry. Thioredoxin, involved in the processing of proteins at germination, has reported impacts on grain digestibility and was differentially expressed across genotypes. Thus, redox states of endosperm proteins, of which kafirins are a subset, could affect quality traits in addition to the expression of proteins.

Development of a 96-well plate iodine binding assay for amylose content determination

Cereal starch amylose/amylopectin (AM/AP) is critical in functional properties for food and industrial applications. Conventional methods of AM/AP are time consuming and labor intensive making it difficult to screen the large sample sets necessary for evaluating breeding samples and investigating environmental impact on starch development. The objective was to adapt and optimize the iodine binding assay in a 96-well plate format for measurement at both λ 620 nm and λ 510 nm. The standard curve for amylose content was scaled to a 96-well plate format and demonstrated R(2) values of 0.999 and 0.993 for single and dual wavelengths, respectively. The plate methods were applicable over large ranges of amylose contents: high amylose maize starch at 61.7±2.3%, normal wheat starch at 29.0±0.74%, and a waxy maize starch at 1.2±0.9%. The method exhibited slightly greater amylose content values than the Concanavalin A method for normal type starches; but is consistent with cuvette scale iodine binding assays.

High-throughput micro-plate HCI-vanillin assay for screening tannin content in sorghum grain

BACKGROUND

The HCI-vanillin assay is a well-accepted method for determining tannin content in sorghum but is limited to small sample sets due to the time-consuming nature of the method. The objective was to develop an accurate and repeatable high-throughput 96-well plate assay for breeders to screen large sample sets of sorghum for tannin content. Validation of the high-throughput assay was tested on 25 sorghums suspected to contain tannin.

RESULTS

Approximately 30 measurements per day were completed using the conventional assay compared to 224 measurements using the 96-well platform. The correlation between the two tannin assays was 0.98. The coefficient of variation (CV) was 3.54% and 3.21% for the 96-well and conventional method, respectively. The 96-well assay exhibited good repeatability, with the inter-plate CV between 2.77% and 4.85%.

CONCLUSION

The high-throughput 96-well HCI-vanillin assay exhibited an eightfold increase in the number of measurements completed and was as accurate as the conventional HCI-vanillin assay.

Role of non-covalent interactions in the production of visco-elastic material from zein

The role of non-covalent interactions in the formation of visco-elastic material from zein was investigated. Hydrophobic interactions were evaluated through the addition of various salts from the Hofmeister series. Urea, ethanol, and beta mercaptoethanol (β-ME) were used to evaluate the effects of protein denaturation and disulfide bonds on zein's ability to form a visco-elastic material. The addition of NaI and NaSCN altered the properties of visco-elastic materials made from zein, making them softer and more extensible, as did urea and ethanol. The addition of NaCl and Na2SO4 negatively impacted the ability of zein to from a visco-elastic material and at higher concentrations completely disrupted the formation of visco-elastic material. These results indicate that manipulating non-covalent interactions in zein can alter and in some cases, completely disrupt the formation of a visco-elastic material. Specifically this may be due to disruption of hydrophobic interactions within individual zein proteins or interactions between proteins. The reducing agent β-ME had little effect on zein's ability to form a visco-elastic material. Therefore, the visco-elastic properties of zein arise as a result of non-covalent interactions.

Effect of nitrogen fertilization and cover cropping systems on sorghum grain characteristics

Cover crop treatments and nitrogen (N) fertilization rates were investigated for their impact on sorghum grain quality attributes. Sorghum was planted in field plots treated with differing cover cropping systems and fertilization rates. The size (weight and diameter) and hardness of the kernels were influenced by both the cover crop and N rates. The protein content increased as the N rate increased and also with the addition of cover crops to the system. The protein digestibility values and starch granule size distributions were not affected by N rate or the cover cropping treatments. Soil properties were tested to determine relationships with grain quality attributes. The utilization of cover crops appears to increase the protein content without causing a deleterious effect on protein digestibility. The end-product quality is not hampered by the use of beneficial cropping systems necessary for sustainable agriculture.

Effects of sorghum (Sorghum bicolor (L.) Moench) tannins on α-amylase activity and in vitro digestibility of starch in raw and processed flours

The purpose of this study was to investigate the effects of tannins on starch digestion in tannin-containing sorghum extracts and wholegrain flours from 12 sorghum varieties. Extracts reduced amylase activity in a tannin concentration-dependent manner when the extract was mixed with the enzyme before substrate (amylopectin) addition, with higher molecular weight tannins showing greater reduction. Conversely, when the extract and substrate were combined before enzyme addition an enhancement in amylase activity was experienced. In uncooked, cooked, and cooked and stored wholegrain sorghum flours, rapidly digestible, slowly digestible, and resistant starches were not correlated with tannin content or molecular weight distribution. Resistant starch increased from 6.5% to 22-26% when tannins were added to starch up to 50% (starch weight). Tannin extracts both reduced and enhanced amylase activity depending on conditions, and, while these trends were clear in extracts, the effects on starch digestion in wholegrain flours was more complex.

Variability in tannin content, chemistry and activity in a diverse group of tannin containing sorghum cultivars

BACKGROUND

Tannins are large polyphenolic polymers and are known to bind proteins, limiting their digestibility, but are also excellent antioxidants. Numerous studies investigating the functional properties of sorghum tannin have been conducted by comparing grain samples from different sorghum lines without considering the other intrinsic characteristics of the grain. The purpose of this study was to remove the confounding intrinsic factors present in the endosperm so the effect of the tannins could be evaluated utilizing a unique decortication/reconstitution procedure.

RESULTS

The tannin content of the 14 cultivars tested ranged from 2.3 to 67.2 catechin equivalents. The bran fractions were studied for their impact on protein binding and antioxidant capacity. Protein digestibility by pepsin ranged from 8% to 58% at the highest tannin level addition. Protein binding ranged from 3.11 to 16.33 g blue bovine serum albumin kg⁻¹ bran. Antioxidant capacity ranged from 81.33 to 1122.54 µmol Trolox equivalents g⁻¹ bran. High-performance size-exclusion chromatography detailed molecular size distributions of the tannin polymers and relationship to tannin functionality.

CONCLUSION

The tannin content and composition play a significant role in determining tannin functionality. These differences will allow for selections of high-tannin sorghums with consideration of the biological activities of the tannins.

Effect of HPMC on the quality of wheat-free bread made from carob germ flour-starch mixtures

Carob germ proteins have been shown to have functional properties similar to wheat gluten enabling formulation and production of yeast leavened gluten-free baked goods from a true dough rather than a stiff batter. The purpose of this research was to optimize the production of wheat-free bread containing carob germ flour, corn starch, NaCl, sucrose, hydroxypropyl methylcellulose (HPMC), and H₂O. A key criterion was to formulate viscoelastic dough similar to wheat dough. To that end, response surface methodology (RSM) was used to determine optimal levels of carob germ flour, H₂O, and HPMC. Components varied as follows: 4.94%-15.05% for carob germ flour, 0.05%-3.75% HPMC, and 65.25%-83.75% H₂O (percents are on a flour basis, where carob germ flour in combination with maize starch equals 100%). Sucrose, NaCl, and yeast were held constant at 2%. Bread parameters evaluated were specific volume and crumb hardness, where the largest specific volume and the lowest value for crumb hardness were considered most desirable. The optimum formula as determined by RSM consisted of 7% carob germ flour, 93% maize starch, 2% HPMC, and 80% H₂O with predicted crumb hardness of ~200 g of force and a specific volume of ~3.5 cm³/g. When proof time was optimized, a specific volume of ~5.6 ml/g and crumb hardness value of ~156 g of force was observed. Carob germ flour may be used as an alternative to wheat flour in formulating viscoelastic dough and high quality gluten-free bread.

PRACTICAL APPLICATION

Celiac disease affects approximately 1% of the world's population. Sufferers of the disease must consume a gluten-free diet. Currently, gluten-free baked products are made from batters and lack the ability to be made from dough based systems which limits the overall processability and product variety. This research is aimed at the utilization of carob germ protein and its ability to form dough to produce an optimal gluten-free bread formulation. This will help to alleviate problems in processability and product variety associated with gluten-free baked goods.

Separation of kafirins on surface porous reversed-phase high-performance liquid chromatography columns

Surface porous high-performance liquid chromatography (HPLC) columns were investigated for the separation of kafirins, storage proteins of grain sorghum. Kafirins were successfully separated using C3, C8, and C18 surface porous stationary phases in less than 17 min. Separations using a monolithic C18 stationary phase were also developed and were slightly faster than those achieved on the surface porous C18 stationary phase. However, the resolution was higher on the latter column. Using an ammonium hydroxide/acetonitrile mobile phase, separations were performed on a novel, alkaline stable surface porous C18 stationary phase. The resolution at alkaline pH was not as high, however, as with the traditional acidic acetonitrile mobile phases. In comparison to fully porous stationary phases, the surface porous phases provided higher resolution with much lower separation times (17 versus 40 min). Total peak areas were correlated to total protein content of sorghum (r(2) = 0.96; n = 10), and a method to measure in vitro pepsin digestibility using reversed-phase (RP)-HPLC peak areas showed good correlation to the traditional nitrogen combustion method (r(2) = 0.82; n = 20). Thus, the surface porous stationary phases could be used not only for more rapid separations but also to provide simultaneous information on total protein content and digestibility.

Sorghum proteins: the concentration, isolation, modification, and food applications of kafirins

Celiac disease is a serious condition affecting millions of individuals. Those afflicted with this illness are resigned to a lifelong avoidance of products containing the storage prolamin proteins found in cereal grains wheat, rye, and barley. Since many food products are based on these cereals, especially wheat, celiac patients have very limited food choices, and those that are available to them are generally poor in quality, often nutritionally deficient, and expensive. Furthermore, this condition also indirectly affects their families and friends with whom they share meals. Thus, a burgeoning need exists to develop nutritious, palatable, and affordable foods, especially staples like bread and pasta, for these individuals and their families and friends who are accustomed to wheat based products. Grain sorghum and its proteins are safe for celiac patients and individuals with varying levels of gluten intolerances. However, the main sorghum proteins, kafirins, are resistant to digestion. They are also difficult to extract and modify in an industrial-scale process and with food-compatible chemicals, thus limiting their use in foods. This review describes studies on kafirin extraction and methods for modifying sorghum proteins for improved nutrition and functionality, as well as food applications. Armed with this knowledge, scientists and technologists will be in a better position to identify opportunities that will further enhance the nutritional and functional value of sorghum proteins.

Composition and molecular weight distribution of carob germ protein fractions

Biochemical properties of carob germ proteins were analyzed using a combination of selective extraction, reversed-phase high-performance liquid chromatography (RP-HPLC), size exclusion chromatography (SEC) coupled with multiangle laser light scattering (SEC-MALS), and electrophoretic analysis. Using a modified Osborne extraction procedure, carob germ flour proteins were found to contain approximately 32% albumin and globulin and approximately 68% glutelin with no prolamins detected. The albumin and globulin fraction was found to contain low amounts of disulfide-bonded polymers with relatively low M(w) ranging up to 5 x 10(6) Da. The glutelin fraction, however, was found to contain large amounts of high molecular weight disulfide-bonded polymers with M(w) up to 8 x 10(7) Da. When extracted under nonreducing conditions and divided into soluble and insoluble proteins as typically done for wheat gluten, carob germ proteins were found to be almost entirely ( approximately 95%) in the soluble fraction with only ( approximately 5%) in the insoluble fraction. As in wheat, SEC-MALS analysis showed that the insoluble proteins had a greater M(w) than the soluble proteins and ranged up to 8 x 10(7) Da. The lower M(w) distribution of the polymeric proteins of carob germ flour may account for differences in functionality between wheat and carob germ flour.

Effects of overexpression of high molecular weight glutenin subunit 1Dy10 on wheat tortilla properties

Wheat (Triticum aestivum L.) flour properties necessary for optimal tortilla production have not been identified. Transgenic wheats (Triticum aestivum L.) overexpressing high molecular weight glutenin subunit (HMW-GS) 1Dy10 were used to make tortilla and their quality was evaluated. The level of HMW-GS 1Dy10 in flours derived from transgenic wheats was 2.5-5.8-fold greater than in controls. Polymeric proteins in the transgenic samples had a molecular weight distribution shifted toward larger polymers as indicated by increased levels of polymeric proteins present and greater M(w) averages of the largest fractions in the insoluble polymeric proteins. Dough derived from transgenic wheats had greater resistance to extension and lower extensibility than controls. Tortilla quality evaluation revealed that tortillas originated from transgenic wheats had decreased diameter, greater thickness and rupture force, and lower rollability scores and stretchability than controls. The presence of 1RS chromosomal translocations from rye (Secale cereale L.) in transgenic wheat decreased the negative effects of overexpression of HMW-GS 1Dy10, as tortillas made with this flour mostly exhibited quality properties similar to those made from control flour. Results suggested that the negative effects of overexpression of HMW-GS 1Dy10 on tortilla properties were derived from a nonideal gluten matrix formation.

Functionality of gliadin proteins in wheat flour tortillas

Gliadins are monomeric proteins that are encoded by the genes at the loci Gli 1 and Gli 2 present on the short arm of homologous wheat chromosomes 1 and 6, respectively. Studies have suggested that gliadins may play an important role in determining the functional properties of wheat flour. The main objective of this study was to understand the functionality of gliadins with respect to tortilla quality. The important tortilla quality attributes are diameter, opacity, and shelf stability, designated here as rollability or the ability to roll or fold the tortilla without cracking. In this study gliadin functionality in tortilla quality was studied using near-isogenic wheat lines that have deletions in either Gli A1, Gli D1, Gli A2, or Gli D2 gliadin loci. The deletion lines are designated by the same abbreviations. Dough and tortillas were prepared from the parent line used to derive these deletion lines, each individual deletion line, and a control commercial tortilla flour. Quantitative and qualitative evaluations were performed on the dough and tortillas derived from the flour from each of these lines. None of the deletions in the gliadin loci altered the shelf stability versus that found for the parent to the deletion lines or control tortilla flour. However, deletions in the Gli 2 loci, in particular Gli A2 reduced the relative proportion of alpha- and beta-gliadins with a greater cysteine amino acid content and gluten cross-link function versus the chain-terminating omega-gliadins in Gli 1, which were still present. As such, the dough and gluten matrix appeared to have greater extensibility, which improved the diameter and overall quality of the tortillas while not altering the rollability. Deletions in the Gli 1 loci had the opposite result with increased cross-linking of alpha- and beta-gliadins, polymeric protein content, and a stronger dough that decreased the diameter and overall quality of the tortillas. The data suggest that altering certain Gli 2 loci through null alleles could be a viable strategy to develop cultivars improved for the specific functionality requirements needed for the rapidly growing tortilla market.