Rheological and pasting properties of composite flour from wheat, sorghum and finger millet

Introduction

Cereal technologists broadly agree that partial replacement of wheat with locally grown millets can strengthen food security, boost micro-nutrient intake, and reduce foreignexchange expenditure on wheat imports [2] . Sorghum (Sorghum bicolor) contributes slowly digestible starch, phenolic antioxidants, and iron, while finger millet (Eleusine coracana) is among the richest cereal sources of calcium (344 mg 100 g⁻¹), dietary fibre, and essential amino acids [3,4] . Yet, incorporating these grains into wheat-based products is not straightforward neither sorghum nor finger millet contains gluten-forming proteins, and their starch granules differ in size, shape, and gelatinisation temperature [5] . Rheological measurements such as farinograph and extensograph parameters predict dough machinability, while RVA pasting profiles predict cooking behaviour and shelf life. Prior work has examined wheat-sorghum or wheat-millet binary blends individually [6,7] , but ternary composites that combine both millets with wheat are less well characterised. This research systematically mapped the rheological and pasting landscape of five wheat: sorghum: finger millet ratios to identify formulations suited for flatbread and biscuit manufacture.

Reagents and chemicals

Wheat grain (cv. Kakaba), sorghum grain (cv. Melkam), and finger millet grain (cv. Tadesse) were procured from the university research farm. All grains were cleaned, tempered, and milled on a Brabender Quadrumat Junior laboratory mill. Composite flours were prepared by dry-blending at specified ratios and sieving through a 60-mesh screen. Analytical-grade chemicals for proximate analysis were from Sigma-Aldrich, Addis Ababa [8] .

Instrumentation

Farinograph and extensograph tests were conducted on a Brabender Farinograph-E and Extensograph-E (Brabender GmbH, Germany) following AACC methods 54-21 and 54-10, International Journal of Agriculture and Food Science https://www.agriculturaljournals.com respectively [9] . Pasting properties were measured on a Rapid Visco Analyser (RVA 4500, Perten Instruments) using the Standard 1 profile (13 minutes). A TA.XTplus Texture Analyser was used for dough extensibility measurements.

Material and Methods Material

The research was conducted from March to September 2023 at the Cereal Processing Laboratory of the Rift Valley College of Food Technology, Hawassa (7.06°N, 38.48°E), SNNPR, Ethiopia. Five flour blends were prepared: F1 (wheat 100%), F2 (80:10:10), F3 (70:20:10), F4 (60:25:15), and F5 (50:30:20 wheat: sorghum: finger millet by weight). Each blend was prepared in three independent batches. Proximate composition (moisture, protein, fat, fibre, ash) was determined by AOAC methods [10] .

Methods

For farinograph analysis, 300 g flour was mixed with water at 30 ± 0.2 °C until the consistency reached 500 Brabender Units (BU); water absorption, development time, stability, and mixing tolerance index were recorded [9] . Extensograph dough was prepared with 2% salt, rested for 45, 90, and 135 minutes, and stretched to obtain resistance to extension and extensibility. RVA parameters peak viscosity, trough viscosity, breakdown, final viscosity, setback, pasting temperature, and peak time were recorded from triplicate runs. Data were analysed by one-way ANOVA in SPSS 26; means separated by Tukey's HSD at p≤0.05 [11] .

Results

Protein content decreased from 11.8% in F1 to 9.4% in F5 as wheat proportion fell, while dietary fibre rose from 2.7% to 5.1% and calcium increased from 28 to 167 mg 100 g⁻¹. These compositional shifts drove the rheological changes described below.

Discussion

The progressive decline in dough stability with increasing millet and sorghum content reflects the dilution of wheat gluten the main structural protein responsible for viscoelastic dough behaviour [5] . At the 70:20:10 ratio, the gluten network retained enough connectivity to produce handleable dough, matching the threshold described by Rao et al. [6] for acceptable roti making (stability > 5.5 min). Beyond 30% substitution, however, stability fell below 4 min and mixing tolerance index exceeded 80 BU, values associated with slack, difficult-to-sheet dough.

The lower setback viscosity in millet-containing blends stems from the smaller amylose fraction in sorghum and finger millet starch, which retrogrades more slowly than wheat amylose [12] . This aligns with the findings of Shobha et al. [7] who observed reduced staling in roti made from wheat-finger millet blends at 25% substitution. The elevated pasting temperature of F5 (73.6 °C vs. 65.3 °C for wheat) indicates that composite flour requires slightly more cooking energy a consideration for energy-efficient flatgriddle baking [13] .

Conclusion

Replacing part of the wheat flour with sorghum and finger millet alters rheological and pasting behaviour in predictable ways governed by gluten dilution and starch composition differences. Among the blends tested, the 70:20:10 wheat: sorghum: finger millet ratio delivered a workable dough with acceptable farinograph stability, the lowest staling tendency, and a substantial nutritional uplift. Flatbread and biscuit manufacturers in millet-growing regions are encouraged to trial this ratio at pilot scale. Extending this work to include hydrocolloid additions (guar gum, xanthan) and sensory-panel evaluation of finished products would help bridge the gap between laboratory characterisation and commercial adoption [14] .

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