Sorghum for human food – A review

A brief review of literature on sorghum for human foods and on the relationship among some kernel characteristics and food quality is presented. The chief foods prepared with sorghum, such as tortilla, porridge, couscous and baked goods are described. Tortillas, prepared with 75% of whole sorghum and 25% of yellow maize, are better than those prepared with whole sorghum alone. A porridge formulation with a 30:40:30 mix of sorghum, maize and cassava respectively, has been shown to be the most acceptable combination. The cooked porridge Aceda has lower protein digestibility and higher biological value than the uncooked porridge Aceda. Sorghum is not considered breadmaking flour but the addition of 30% sorghum flour to wheat flour of 72% extraction rate produces a bread, evaluated as good to excellent.     

Acceptability of wheat-sorghum composite flour products: An assessment

The acceptability of sorghum as human food has been a problem in Tanzania even in regions showing promising potential for its production and utilization. Reasons given for low acceptability of sorghum products as human foods include unpleasant colour, aroma, mouthfeel, taste, unpleasant aftertaste and stomachfeel. An acceptability test of selected sorghum products was, therefore, conducted in the Department of Food Science and Technology, Sokoine University of Agriculture, Morogoro, Tanzania. The objective of the test was to determine consumers' preference for the following wheat-sorghum composite flour products: bread and buns or maandazi. The products were prepared using sorghum flour composited with wheat flour in the following proportions: 100% brown sorghum flour (standard products); and 80:20%; 60:40%; 40:60% and 20:80% for wheat/sorghum (white and brown) composite flours. Results indicated that in the case of composite flour bread, preference for the product improved as the amount of sorghum flour decreased. In the case of buns or maandazi the 100% sorghum flour products of both white and brown were equally preferred. Buns prepared from 100% sorghum flour of white and brown varieties showed promising potential in the improvement of the acceptability of sorghum products. Taking advantage of such products, especially in villages, could enhance sorghum utilization in rural communities.     

Important Sensory Attributes Affecting Consumer Acceptance of Sorghum Porridge in West Africa as Related to Quality Tests

Studies were conducted in Niger, West Africa to determine the most important sorghum porridge quality parameters that affect consumer acceptance. Consumer sensory evaluation was carried out on 14 sorghum cultivars varying in pericarp colour and endosperm hardness. Laboratory analyses were then conducted to determine the physical and chemical properties of the grain responsible for porridge quality. Porridge texture was evaluated using three different techniques and porridge colour was measured using the Hunter Lab colorimeter. Results were compared with consumer ratings. The textural characteristics of stickiness in the mouth and cohesiveness were found to be the most important sensory attributes, followed by the taste and aroma of the product. Instron slope measurement was the most reliable objective method for predicting consumer response to texture followed by the penetrometer method. The gel consistency test showed some association with consumer rating for porridge texture but had no significant relationship with consumer ratings of porridge texture intensity. A wide range of porridge colour was acceptable to consumers with only brown or dark-coloured porridge being rejected. Consumer rating for porridge colour correlated significantly with Hunter L and ΔE values. Porridge quality was affected by grain hardness, but none of the proximate components (ash, fat, and protein) of the decorticated grains correlated with the texture of the product.     

Effects of endosperm texture and cooking conditions on the in vitro starch digestibility of sorghum and maize flours

The effects of endosperm vitreousness, cooking time and temperature on sorghum and maize starch digestion in vitro were studied using floury and vitreous endosperm flours. Starch digestion was significantly higher in floury sorghum endosperm than vitreous endosperm, but similar floury and vitreous endosperm of maize. Cooking with 2-mercaptoethanol increased starch digestion in both sorghum and maize, but more with sorghum, and more with vitreous endosperm flours. Increasing cooking time progressively reduced starch digestion in vitreous sorghum endosperm but improved digestibility in the other flours. Pressure-cooking increased starch digestion in all flours, but markedly more in vitreous sorghum flour; probably through physical disruption of the protein matrix enveloping the starch. Irrespective of vitreousness or cooking condition, the alpha-amylase kinetic constant (k) for both sorghum and maize flours remained similar, indicating that differences in their starch digestion were due to factors extrinsic to the starches. SDS-PAGE indicated that the higher proportion of disulphide bond-cross-linked prolamin proteins and more extensive polymerisation of the prolamins on cooking, resulting in polymers of M_r>100k, were responsible for the lower starch digestibility of the vitreous sorghum endosperm flour.     

Use of peanut and cowpea in wheat-based products containing composite flours

Cowpeas and peanuts are legumes of major dietary and economic importance. They are favored worldwide because of their palatability, contribution to nutritional status, and low cost as a protein source compared to animal protein. Flours processed from cowpeas and peanuts have unique physico-chemical and sensory properties when used in composite flour mixtures. Appropriate blends of cowpea and peanut flours to replace wheat flour in Chinese-type noodles, muffins, and tortillas were determined using modelling and optimization procedures. For noodles, 15% peanut flour and 8% cowpea flour supplementation produced an acceptable product with high protein content (21%). For wheat flour replacement in muffins, up to 43% cowpea and up to 44% peanut flours may be used. However, when wheat flour replacement is 50% or greater, cassava flour should comprise 56 to 72% of the blend with a few exceptions. In tortillas, 24% cowpea and 46% peanut flours produced products similar in quality characteristics to those made from 100% wheat flour. The systematic approach used in these studies is more efficient than the traditional substitution method to optimize sensory qualities of wheat-based products containing composite flours.     

Nutritional Evaluation and Shelf Life Studies of Papads Prepared from Wheat–Legume Composite Flours

The present study was carried out to develop papads from wheat and legume blends and to analyze them for organoleptic acceptability, nutritional quality, and keeping quality. Papad is a dehydrated product prepared from dhals or rice. A firm but pliable dough is made from the flours of dhals or rice with addition of suitable seasoning. It is shaped into balls, rolled out thin, dried and toasted over open fire so as to give a light, crisp product. Mung flour papads were kept as control and wheat flour, chickpea flour, and pea flour were used to supplement mung flour papads. Three different proportions (10, 20, 30%) of each flour were used to supplement Mung flour. Papads with wheat flour (10%), chickpea flour (20%), and pea flour (10%) level of supplementation were found to be most acceptable and these papads were subjected to nutritional evaluation. Protein content significantly increased on supplementation with legume flours at all levels. Fat content was significantly higher in chickpea flour supplemented papads. Ash content varied significantly from 10.17 to 10.78% in papads. Total carbohydrates decreased significantly on supplementation with chickpea flour. Copper content increased significantly on supplementation. A significant decrease in phytic acid and trypsin inhibitor of supplemented papads was found. In vitro protein digestibility significantly increased on supplementation but a significant decrease in in vitro starch digestibility was found in supplemented papads. Storage studies showed that chickpea flour and pea flour supplemented papads can be stored safely for 60 days and wheat flour supplemented papads for 30 days both at room and refrigeration temperatures.     

Physical properties of wheat flour composites dry-coated with microparticulated soybean hulls and rice flour and their use for low-fat doughnut preparation

Air-classified wheat flour was dry-coated with microparticulated rice flour (30%, db) and/or microparticulated soybean hulls (up to 10%, db) using a hybridization system, and the physical properties of the dry-coated wheat flour were examined. The composite wheat flours exhibited the higher water-holding capacity but lower swelling power and oil-holding capacity than their counterpart mixtures. In pasting viscosity, the composites of wheat and rice flours had substantially lower values for peak viscosity and breakdown than did pure wheat flour. The incorporation of soybean hulls to the composites of wheat and rice flours further reduced the peak viscosity. The composites with rice flour and soybean hulls showed slightly higher melting (gelatinization) temperatures but lower melting enthalpy compared to the counterpart mixtures. By using the composite flours for the deep-fat fried doughnut preparation, the oil uptake could be substantially reduced by approximately 30%, in comparison to pure wheat flour or the mixture samples. The composite wheat flours with microparticulated rice flour and soybean hulls produced dough matrices with improved compactness and cell structure, which were attributed to the reduced fat uptake during frying.     

Physical properties of wheat flour composites dry-coated with microparticulated soybean hulls and rice flour and their use for low-fat doughnut preparation

Air-classified wheat flour was dry-coated with microparticulated rice flour (30%, db) and/or microparticulated soybean hulls (up to 10%, db) using a hybridization system, and the physical properties of the dry-coated wheat flour were examined. The composite wheat flours exhibited the higher water-holding capacity but lower swelling power and oil-holding capacity than their counterpart mixtures. In pasting viscosity, the composites of wheat and rice flours had substantially lower values for peak viscosity and breakdown than did pure wheat flour. The incorporation of soybean hulls to the composites of wheat and rice flours further reduced the peak viscosity. The composites with rice flour and soybean hulls showed slightly higher melting (gelatinization) temperatures but lower melting enthalpy compared to the counterpart mixtures. By using the composite flours for the deep-fat fried doughnut preparation, the oil uptake could be substantially reduced by approximately 30%, in comparison to pure wheat flour or the mixture samples. The composite wheat flours with microparticulated rice flour and soybean hulls produced dough matrices with improved compactness and cell structure, which were attributed to the reduced fat uptake during frying.     

Chemical and sensory evaluation of vegetable milks from African yam bean Sphenostylis stenocarpa (Hochst ex A Rich) Harms and maize (Zea mays L.)

Vegetable milks were developed from fermented and unfermented African yam bean (AYB) flours and their maize blends. AYB was cleaned, dehulled, milled and fermented for 24 hours by the natural microflora present in the legume flour. Maize was fermented for 48 hours. A ratio of 70:30 (protein basis) of AYB: maize was used to formulate the blends. Vegetable milks were prepared from the AYB flours and their maize blends. Standard assay techniques were used to evaluate the milks for proximate, mineral, ascorbate and antinutrient composition. The protein contents of the milks (1.47–2.06 percent) was comparable to soymilk (2.04 percent) and bambara groundnut milk (2.00 percent). The milks contained appreciable quantities of carbohydrate and minerals tested. The milk blends had traces of ascorbate and contained higher phosphorus than the milks from the AYB flours. The fermented milk blend had higher protein, ash and sugar levels and lower phytate and stachyose levels compared to non-fermented blend. Raffinose was reduced to trace levels in the fermented milks. The milks were appetizing. The fermented milk blend was more acceptable than others and was preferred in terms of flavor and color. It had greater advantages over the other vegetable milks evaluated in terms of zinc, phosphorus and stachyose levels.     

Chemical,sensory and rheological properties of porridges from processed sorghum (Sorghum bicolor,bambara groundnut (Vigna subterranea L. Verdc) and sweet potato (Ipomoea batatas) flours

The chemical, sensory and rheological properties of porridges made from blends of sprouted sorghum, bambara groundnuts and fermented sweet potatoes were examined. Sorghum and bambara groundnuts were sprouted for 48 h while sweet potatoes were fermented for the same period. Blends were formulated from the processed ingredients in the ratio of 60:40:0, 57:42:1, 55:44:1 and 52:46:2 (protein basis) of sorghum, bambara groundnuts and sweet potatoes. Porridges were prepared from the composite flours and the traditional sorghum complementary food. Standard assay methods were used to evaluate the flours for nutrient composition. The porridges were also tested for sensory properties and viscosity. Processing increased the levels of most of the nutrients evaluated. Relative to the sorghum traditional complementary food, thecomposite flours had higher levels of lipids, protein, ash, crude fiber and minerals (p<0.05). The porridges from the composite flours were generally liked slightly by the panelists and were about seven times less viscous than the porridge from the traditional sorghum complementary food. Use of the composite flours, particularly the 52:46:2 blend, as a traditional complementary food should be encouraged in Nigeria especially with the increasing cost of commercial complementary foods.     

Physico-chemical properties and acceptability of yam flour substituted with soy flour

Yam flour was substituted 10, 20 and 40% with defatted and full fat soy flour. The effect of the substitution on the proximate composition, swelling power, solubility, water binding capacity and Brabender visco amylograph cooking properties of the yam flour and acceptability of the cooked paste (amala), were evaluated. Protein contents of the mixtures were 23.0 and 25.5% on substituting 40% full-and defated soy flours for yam flour; ash and crude fibre contents increased while carbohydrate content, swelling power, Brabender paste viscosities decreased with increase in soy flour substitution of yam flour. Colour, texture, taste and overall acceptability of pastes (amala) from the mixed flours were rated lower than that of yam flour. Up to 10% defated and 20% full fat soy flour substitution for yam flour was acceptable for amala.     

Studies on the development of high-protein biscuits from composite flours

Composite flours prepared from wheat, greengram, bengalgram and blackgram flours were studied for the preparation of biscuits. Protein content of biscuits increased as the level of the pulse flours increased. Wheat flour containing bengalgram and blackgram flours adversely affected the top grain, texture and colour of biscuits. Biscuits made with higher levels of bengalgram (more than 15%) were tough and difficult to break and required higher compression force. Addition of greengram flour did not significantly affect top grain, texture and colour of biscuits. The biscuits made from 15% greengram supplemented wheat flour scored the highest for flavour characteristics. Thickness, diameter and spread ratio of biscuits containing different levels of pulse flours were significantly different from control sample. Sensory evaluation scores showed that acceptable biscuits can be prepared from wheat flour supplemented with these pulse flours at a level of 15 percent.     

Nutritional Evaluation of Wheat–Fenugreek Blends for Product Making

Wheat flour was separately substituted with fenugreek flour (raw, soaked, and germinated) at 5–20% levels for product making. Nutrient analysis of the blends, product development, and their acceptability were carried out. Replacement of wheat flour with fenugreek flour increased the protein, fat, lysine, minerals, and dietary fibre contents proportionately to the level of substitution. Among the composite flours, the blends containing germinated fenugreek flour were found superior in nutritional quality compared to others. However, products, viz., bread, biscuits, noodles, and macaroni prepared from the wheat–fenugreek blends at 10, 15, and 20% levels, were found organoleptically acceptable.     

Development and quality evaluation of pawpaw-ogi

Pawpaw-ogi was evaluated for proximate and chemical composition, amylograph pasting viscosity, colour and acceptability. The addition of pawpaw to maize ogi slurry had no significant effect on protein and fat contents nor on amylograph pasting characteristics but resulted in significant increases in ash, ascorbic acid, sugars and mineral contents. The Munsell colour notations indicated that the addition of pawpaw improved the colour of ogi. Taste panel evaluation showed that both the powder and porridge of pawpaw-ogi were acceptable.     

Effect of extrusion cooking of sorghum flour on rheology,morphology and heating rate of sorghum–wheat composite dough

Addition of a gluten-free flour such as sorghum has negative impact on the quality of wheat dough for bread making. One of the methods which can be used to promote the quality of sorghum-wheat composite dough is to extrude the sorghum flour before incorporation. In this regard, to produce a dough with appropriate bakery properties sorghum flour was extruded at 110 °C and 160 °C die temperature with 10%, 14% and 18% feed moisture. The effect of extruded sorghum flour incorporation (10%) on rheological (farinography and stress relaxation behavior), morphological and temperature profile of sorghum-wheat composite dough were evaluated. Extrusion cooking altered the sorghum-wheat composite dough properties through partial gelatinization of starch granules. Addition of extruded sorghum flour increased the water absorption and dough development time but it decreased the dough stability. Native sorghum-wheat composite dough showed viscoelastic liquid-like behavior whereas addition of sorghum flour extrudate changed dough to a more viscoelastic solid-like structure. Maxwell model was more appropriate than Peleg model to describe the viscoelasticity of the sorghum-wheat composite dough. Extrusion cooking decreased composite dough elasticity and viscosity. Sorghum extrudate increased the heating rate of composite dough crumb during baking. Addition of extruded sorghum flour formed a non-uniform and less compact dough structure. As a result, dough containing extruded sorghum flour had a good potential for producing a high-yielding bread in a short time of baking.     

Effect of Grain Structure and Cooking on Sorghum and Maize in vitro Protein Digestibility

Uncooked and cooked sorghum showed improvement in in vitro protein digestibility as the structural complexity of the sample reduced from whole grain flour through endosperm flour to protein body-enriched samples. This was not the case for maize. Cooking reduced protein digestibility of sorghum but not maize. Treating cooked sorghum and maize whole grain and endosperm flours with alpha -amylase to reduce sample complexity before in vitro pepsin digestion slightly improved protein digestibility. The reduction in sorghum protein digestibility on cooking was not related to the total polyphenol content of samples. Pericarp components, germ, endosperm cell walls, and gelatinised starch were identified as possible factors limiting sorghum protein digestibility. Electrophoresis of uncooked and cooked protein-body-enriched samples of sorghum and maize, and prolamin fractions of sorghum under non-reducing conditions showed oligomeric proteins with molecular weights (M_r) 45, 66 and >66 kDa and monomeric kafirins and zeins. Protein-body-enriched samples of sorghum had more 45–50 kDa oligomers than those of maize. In cooked sorghum, some of these were resistant to reduction. Pepsin-indigestible residues from protein-body-enriched samples consisted mainly of α-zein (uncooked and cooked maize) or α-kafirin (uncooked sorghum), whilst cooked sorghum had in addition, β- and γ-kafirin and reduction-resistant 45–50 kDa oligomers. Cooking appears to lead to formation of disulphide-bonded oligomeric proteins that occurs to a greater extent in sorghum than in maize. This may explain the poorer protein digestibility of cooked sorghum.     

Carotenoid bioaccessibility from whole grain and decorticated yellow endosperm sorghum porridge

Sorghum is a staple crop and a potential dietary source of carotenoids in semi-arid regions of Africa, but information on the bioavailability of these pigments is limited. This study aimed at exploring the effects of agronomic manipulation on sorghum carotenoid contents at selected stages of kernel development and maturation and assessing carotenoid bioaccessibility from matured yellow-endosperm sorghum varieties (P88 and P1222), by comparing porridge made from sorghum whole and decorticated milled grains. Carotenoid content of sorghum milled fractions ranged from 2.90 to 7.22 mg/kg in P88 unbagged decorticated flour, at 50 and 30 days after half bloom (DAHB) respectively, to 9.87-13.69 mg/kg in bagged decorticated bran fractions in P88, at 50 and 30 DAHB respectively. Maize milled fractions were significantly (P < 0.05) higher in carotenoid content than all sorghum products. Bagging increased sorghum carotenoid content by 8-184% vs. unbagged panicles. Carotenoid bioaccessibility was generally higher from sorghum (63-81%) compared to maize (45-47%). Micellarization of xanthophylls (75%) was more efficient than carotenes (52%) in sorghum, while they were similar in maize (40-49%). These results suggest that the higher bioaccessibility of sorghum carotenoids combined with efforts to enhance sorghum carotenoid content may allow for sorghum to provide similar levels of bioaccessible carotenoid pigments as common yellow maize.     

Proximate composition and selected functional properties of African Breadfruit and sweet potato flour blends

Full-fat African breadfruit flour was used to replace 30, 40, 50, 60 and 70% of sweet potato flour. The chemical composition and functional properties of composite flours showed that they contains more protein, fat, and ash and less carbohydrate than sweet potato flour. With increasing level of supplementation of breadfruit, ash, protein and fat contents increased while carbohydrate decreased. The composite flours possessed higher water absorption than sweet potato flour. The water absorption capacity increased from 20% for sweet potato flour to the range of 85–120% for composite flours. The oil absorption capacities for some composite flours were higher than that for sweet potato but less than that of breadfruit. Composite flours had good foaming capacity but lacked foaming stability. The bulk density of the composite flours was found to be low which will be an advantage in the preparation of weaning food formulations.     

Grain of high digestible,high lysine (HDHL) sorghum contains kafirins which enhance the protein network of composite dough and bread

The aim of this study was to determine whether protein body-free kafirins in high digestibility, high-lysine (HDHL) sorghum flour can participate as viscoelastic proteins in sorghum-wheat composite dough and bread. Dough extensibility tests revealed that maximum resistance to extension (g) and time to dough breakage (sec) at 35 °C for HDHL sorghum-wheat composite doughs were substantially greater (p < 0.01) than for normal sorghum-wheat composite doughs at 30 and 60% substitution levels. Functional changes in HDHL kafirin occurred upon exceeding its T_g. Normal sorghum showed a clear decrease in strain hardening at 60% substitution, whereas HDHL sorghum maintained a level similar to wheat dough. Significantly higher loaf volumes resulted for HDHL sorghum-wheat composites compared to normal sorghum-wheat composites at substitution levels above 30% and up to 56%, with the largest difference at 42%. HDHL sorghum-wheat composite bread exhibited lower hardness values, lower compressibility and higher springiness than normal sorghum-wheat composite bread. Finally, HDHL sorghum flour mixed with 18% vital wheat gluten produced viscoelastic dough while normal sorghum did not. These results clearly show that kafirin in HDHL sorghum flour contributes to the formation of an improved protein network with viscoelastic properties that leads to better quality composite doughs and breads.     

Selected nutritional,physical and sensory characteristics of pan and flat breads prepared from composite flours containing fababean

Composite flour blends containing wheat (W), fababean (F), cottonseed and sesame flours were formulated to provide the FAO/WHO/UNU protein requirements for the 2–5 year old child, and evaluated in pan and flat bread applications. Water absorption of composite flour doughs was up to 35% greater than the control but gluten strength and slurry viscosities were markedly reduced. Loaf volume and specific volume of pan breads prepared from composite flours were 25–60% less than that of the control bread but flat breads tolerated the protein supplements extremely well. The W/F flat bread, containing 27% of fababean flour, received acceptable taste, texture and colour scores and was only slightly inferior to the control in puffing and layer separation. Additions of cottonseed or sesame flours to the W/F blend failed to improve sensory properties of the flat breads.