Lloyd W. Rooney

Interaction of tannins and other sorghum phenolic compounds with starch and effects on in vitro starch digestibility.

This study investigated interactions of sorghum proanthocyanidins (PAs) with starch molecules and the effect on in vitro starch digestibility. High tannin (predominant in PA), black (monomeric polyphenols), and white (low in polyphenols) sorghum phenolic extracts were mixed and cooked with starches varying in amylose content. Starch pasting properties, polyphenol profile, and resistant starch (RS) were determined. PAs decreased setback of normal starch and were least extractable after cooking with all starches. Pure amylose interacted more strongly with oligomeric and polymeric PA compared to amylopectin. The PA extract increased the net RS in normal starch by about 2 times more than the monomeric polyphenol extract; debranching amylopectin increased the difference by 4.3 times. Only treatments with PA increased RS in high amylose starch (52% higher than the control). Sorghum PAs interact strongly with starch, decreasing starch digestibility. The interactions appear to be specific to amylose and linear fragments of amylopectin, suggesting hydrophobic interactions are involved.

Sorghum and millets

Sorghum and millets constitute a major source of calories and protein for millions of people in Africa and Asia. These cereals are mainly considered as subsistence crops because of their unique tolerance to drought and adaptation to dry tropical and subtropical ecosystems throughout the world. They rank fifth and sixth in terms of total production.

Starch properties as affected by sorghum grain chemistry

To determine the relationship between sorghum grain polyphenol content, grain structure, and starch properties, starch was isolated from 10 sorghum varieties using an alkali steep and wet-milling procedure. SV2, a tannin-free variety with white pericarp, gave a white starch. Varieties having red or white pericarp and higher polyphenol levels gave pink starches. Hunter colour values (L, a, b) of starches were not correlated with grain polyphenol content. Grain appearance in terms of pericarp colour, or presence or absence of pigmented testa, did not relate to the intense pink colouration of sorghum starches. Starch amylose content was significantly negatively correlated (r  = −0.88, p < 0.001) to grain floury endosperm texture. Sorghum starches had higher peak viscosity (PV) in pasting than commercial maize starch. The time taken to reach peak viscosity from the initial viscosity rise was less for sorghum starches than maize starch. However, sorghum starches had a higher rate of shear thinning (Rst) than maize starch. There was a significant positive correlation between grain polyphenol content and starch PV (r  = 0.75, p < 0.05). Starch gel hardness was negatively correlated to pasting properties of Rst and paste breakdown (r  = −0.78 and −0.77 respectively) at p < 0.01. Peak gelatinisation temperature (Tp) occurred over a narrow range from 66 to 69 °C. Tp was negatively correlated to the floury endosperm portion of the grain (r  = −0.77) at p < 0.01. It is concluded that sorghum grain polyphenol content and grain characteristics influence its starch properties. © 2000 Society of Chemical Industry

Phenolic compounds and kernel characteristics of Zimbabwean sorghums

Sixteen sorghum varieties widely cultivated in Zimbabwe were examined for levels of phenolic compounds and kernel characteristics, to help identify those with desirable properties and develop suitable processing methods. Assays for polyphenols included the chlorox test, the vanillin- HCl, the ferric ammonium citrate and the butanol-HCl methods. Free phenolic acids were analysed using reverse-phase high performance liquid chromatography. Varieties DC-75, Mutode and Chirmaugute had the highest levels of condensed tannins. The polyphenols in Chibonda were mostly unextractable in methanol. No significant levels of polyphenols were found in 13 varieties. Phenolic acid content was related to pericarp colour. Endosperm texture and pericarp thickness were evaluated using video image analysis. Katandanzara and SV1 had relatively corneous endosperms ( 0.060 mm). Endosperm texture was not correlated with phenolic compounds. A positive correlation, however, was observed between pericarp thickness and polyphenol content (r> 0.64). Zimbabwean sorghums lack ideal agronomic and processing physico-chemical characteristics defined in terms of high polyphenols, plus hard endosperm and thin pericarp. Research is required to develop effective methods to process the available polyphenol-rich sorghums. # 1999 Society of Chemical Industry

Cooking Characteristics and Quality of Noodles from Food Sorghum

ABSTRACT Three white food sorghums, ATx631*RTx436, ATxARG*RTx436, and SC283-14, were decorticated, milled into flour and processed into 100% sorghum noodles. Flour, water, and salt (1%) were preheated using a hotplate or a microwave oven. The mixtures were put through a forming extruder to produce noodles. Extruded noodles were dried by three methods: air-dry method (23°C, 48 hr); one-stage (60°C, 30% rh, 3 hr), or two-stage (60°C, 100% rh for 2 hr followed by 60°C, 30% rh for 2 hr). Noodles were evaluated dry and after cooking. Sorghum flours with smaller particle sizes yielded better noodles. The microwave preheating method yielded better noodles than the hot-plate method. Stronger and firmer noodles, dry or cooked, were prepared using two-stage drying compared with the other drying methods. Fine flour that was preheated using a microwave oven and dried using the two-stage method gave the best noodles with moderate (10%) dry matter loss. Optimized processing conditions yielded sorghum noodles with good ...

Flavonoid composition of lemon-yellow sorghum genotypes.

Flavonoid composition of lemon-yellow sorghums grown in two locations in Texas, USA was evaluated and compared with that of white and red sorghums using high performance liquid chromatography (HPLC-PDA). Sorghums from Lubbock were brighter in colour and had minimal weathering compared to those from College Station. Sorghums with red/purple secondary plant colour had the highest levels of 3-deoxyanthocyanidins (8-187μg/g) and their levels were highest in grains from College Station (39-187μg/g). Pericarp colour did not have any effect on 3-deoxyanthocyanidin levels (p>0.05). The tan plant lemon-yellow sorghum Tx2953 had the highest levels of flavones (268-362μg/g). Among the genotypes, lemon-yellow sorghums had the highest levels of flavanones (134-1780μg/g), which are located in the pericarp and their levels were increased in the grains with a bright yellow pericarp and minimal weathering. The high flavanone levels in lemon-yellow sorghums makes this sorghum genotype a good source of those compounds.

Malted Sorghum as a Functional Ingredient in Composite Bread

ABSTRACT To alleviate the adverse effects (grittiness and high crumb firmness) caused by the inclusion of sorghum flour in composite breads, sorghum grain was malted with the aim of decreasing the gelatinization temperature and increasing the water-holding capacity of sorghum flour. Four different heat treatments were investigated: drying the malt at high temperatures (50–150°C), stewing, steaming, and boiling before drying the malt at 80°C. Malting decreased the pasting temperature of sorghum to values approaching those of wheat flour, but the paste viscosity was very low. Increasing the malt drying temperature inactivated the amylases but gave malts of darker color and bitter taste. Stewing, steaming, and boiling the malt before drying almost completely inactivated the amylases and increased the enzyme-susceptible starch content and the paste viscosity of malt flours. Bread made with boiled malt flour (30%) had an improved crumb structure, crumb softness, water-holding capacity, and resistance to stalin...

Effects of Leavening Acids and Dough Temperature in Wheat Flour Tortillas

ABSTRACT Functionality of four leavening acids (sodium aluminum phosphate [SALP], sodium aluminum sulfate [SAS], monocalcium phosphate [MCP] and sodium acid pyrophosphate [SAPP-28]) was evaluated during processing of wheat flour tortillas. Formulas were optimized to yield opaque, large-diameter tortillas with pH 5.9–6.1. Each leavening acid and sodium bicarbonate was first evaluated at 38°C and then evaluated in combination with fumaric acid at 34 and 38°C. Ionic and pH interactions of leavening salts adversely affected dough properties and resting time. Opacity and pH of tortillas prepared with MCP was lower than for other treatments. Higher dough temperature required more leavening acid and base to compensate for some of the loss of CO2 incurred during dough mixing and resting at 38°C. The addition of fumaric acid decreased the amount of leavening acid, the dough-resting time and tortilla pH, and improved storage stability. Combinations of MCP, SALP (or SAS), and fumaric acid produced dough and tortilla...

Effects of Sorghum Cultivar on Injera Quality

ABSTRACT Injera is an Ethiopian flat bread made from cereals, with tef preferred for the best quality injera. Because sorghum is less expensive in Ethiopia, there is great interest in improving the quality of sorghum injera. Effects of cultivar on injera quality were studied using 12 Ethiopian sorghum cultivars of varying kernel characteristics. White tef with good injera making quality was included as a reference. Injera quality was evaluated using two techniques: descriptive sensory analysis of fresh injera and instrumental texture analysis of injera stored over a storage period of 48 hr using a three-point bending rig. Principal component analysis (PCA) of sensory data associated fresh injera from sorghum cultivars 3443-2-op, 76TI #23, and PGRC/E #69349 of varying endosperm texture, with positive injera texture attributes of softness, rollability, and fluffiness. Across the two seasons, texture analysis showed injera prepared from AW and CR:35:5, both with soft endosperm, required the least force to be...

Microscopy of pericarp development in the caryopsis of Sorghum bicolor (L.) Moench

Abstract Five sorghum varieties typifying differences in pericarp thickness were harvested at 0–34 days post anthesis, prepared and viewed by fluorescence, bright field, polarized light, and scanning electron microscopy. The development of the pericarp at various stages is described. The pericarp reached its maximum size around 21 days post anthesis. Compound starch granules were present in the ovary wall at anthesis and disappeared at 10–14 days post anthesis; only simple granules remained. The differences in pericarp thickness among the varieties are related to the quantity of starch in the mesocarp cells; the thick pericarp varieties contain more starch. All five varieties had maximum pericarp thickness at 5–7 days post anthesis, but values varied widely among grains. Few starch granules remained in the varieties with thin pericarps at maturity. These varieties carried the dominant Z gene. At maturity starch remained in varieties with thick pericarps; the recessive zz may have blocked resorption or stimulated extra production of the granules. A large range of pericarp thickness is possible when the z gene is recessive.