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PHYSICOCHEMICAL AND RHEOLOGICAL PROPERTIES OF COMPOSITE FLOUR FROM MILLET AND BAMBARA NUT IN NIGER STATE

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

The formulation of composite flours using underutilized indigenous crops has attracted considerable attention from researchers and policymakers in recent years as an approach to improve food security, dietary diversity, minimize wheat imports, and generate value from locally grown agricultural resources. In Niger State  situated in the North-Central region of Nigeria and boasting of vast agricultural land, varied cropping practices and predominantly rural economy  pearl millet (Pennisetum glaucum) and Bambara groundnut (Vigna subterranea) cultivation constitute an integral part of smallholder farmers’ farming systems, especially in rural areas of the Niger and Kaduna river basins (Bello et al., 2021).

Pearl millet is the world’s sixth most important cereal food, and it is widely used in arid and semi-arid regions for its high tolerance to drought, short growing cycle, and rich content of complex carbohydrates, vitamin B, iron, zinc and phosphorus. Millet flour is commonly prepared as tuwo, fura, and other traditional foods in Niger State, but its use in composite flour for the production of bakery, confectionery and other industrial foods is still under-explored (Arise et al., 2020).

Bambara groundnut, a native African grain legume is grown extensively in sub-Saharan Africa and is considered a “complete food” due to its protein (19-22%), carbohydrate (49-63%), fat (4-7%) and fibre (8-12%) balance. High lysine and methionine (amino acids that are usually low in cereals) content of Bambara groundnut makes it an ideal protein source when combined with millet in composite flours (Arise et al., 2020). Millet-Bambara groundnut composite flours, when prepared in suitable proportions, can be used to make products with higher amino acid content, better functional characteristics and lower wheat flour imports.

Physicochemical (proximate composition, water activity, pH, colour) and rheological (flow behaviour, viscoelasticity, storage and loss moduli) properties are important quality attributes that need to be determined for efficient processing and optimal use of composite flours in various food products. They play a vital role in product development, process development, and quality management in the food production sector. Although millet-Bambara groundnut composite flours have potential for food processing, there is little information about their physicochemical and rheological properties in the processing conditions of Niger State.

1.2 Statement of the Problem

The importation of wheat flour for bread, pasta, noodles and pastry products production in Nigeria is a major financial drain, with the nation spending thousands of naira billions each year on wheat imports. Niger State, a major millet producing state and home to other locally-grown crops, lacks value-added flour processing plants and research-supported product formulations that can be used to in lieu of wheat flour or to fortify wheat flour with local crops (Lawal et al. 2021).

Lack of well-described composite flours based on crops indigenous to Niger State (such as millet and Bambara groundnut) means food manufacturers in Niger State cannot replace or partially replace wheat flour in their products with composite flours. Critical information such as rheological properties of millet-Bambara groundnut composite flour doughs  especially flow behavior, storage modulus (G’), loss modulus (G”) and creep-recovery, which affect dough handling and sheeting as well as product texture, is lacking. This information is not available to the food industry to guide formulation and processing of products made with composite flours.

1.3 Objectives of the Study

Aim: The general aim of this study is to determine the physicochemical and rheological properties of composite flour prepared from millet and Bambara groundnut at different blend ratios, as produced in Niger State.

Specific Objectives:

1. To determine the proximate composition (moisture, crude protein, crude fat, crude fiber, ash, and carbohydrate) of millet-Bambara groundnut composite flour at blend ratios of 100:0, 80:20, 70:30, 60:40, and 50:50.
2. To evaluate the physicochemical properties (pH, water activity, color parameters L*, a*, b*) of the composite flour blends.
3. To assess the functional properties (water absorption capacity, oil absorption capacity, bulk density, swelling power, and least gelation concentration) of the composite flour blends.
4. To determine the pasting properties of the composite flours using a Rapid Visco Analyser (RVA).
5. To characterize the rheological properties (steady-state flow behavior and dynamic oscillatory behavior: G’, G”) of dough prepared from the composite flour blends.

1.4 Research Questions

1. How does the blend ratio of millet and Bambara groundnut flour affect the proximate and physicochemical properties of the composite flour?
2. What are the functional and pasting properties of millet-Bambara groundnut composite flour blends?
3. How does the incorporation of Bambara groundnut flour influence the rheological behavior (flow properties and viscoelasticity) of composite flour doughs?
4. Which blend ratio of millet and Bambara groundnut produces composite flour with the most desirable physicochemical and rheological properties for bakery or paste applications?

1.5 Significance of the Study

This research has wide-ranging implications for food security, industry and academic understanding. For food processing industries and manufacturers in Niger State, the physicochemical and rheological properties of the flour will serve as a scientific basis for replacing wheat flour with millet-Bambara groundnut based composite flour in bakery and confectionery products, thereby increasing their market competitiveness and avoiding flour imports. Small farmers and cooperatives in Niger State will have incentives to produce more millet and Bambara groundnut for processing due to rising demand.

From a nutritional perspective, products made with composite flour with enhanced protein quality from Bambara groundnut will help alleviate protein malnutrition in vulnerable groups in Niger State. The study will add a new data set on rheological properties of a less explored grain legume-cereal composite system to the global knowledge base on African indigenous crops. The findings will serve as a useful tool for policymakers to develop policies for substituting wheat flour with local materials and lower the dependence on imported food resources as a complement to Nigeria’s agricultural transformation.

1.6 Scope of the Study

The present study is limited to the composite flour preparation and characterization of pearl millet and Bambara groundnut varieties grown and sold in the state of Niger. The composition ratios considered include 100:0, 90:10, 80:20, 70:30, 60:40 and 50:50 millet:Bambara groundnut. The focus of the characterization is on proximate, physicochemical, functional, pasting and rheological properties as analysed by standard laboratory procedures. It does not cover the formulation of specific food products (biscuit, bread, etc.) from the composite flour, neither sensory analysis nor studies of the products’ shelf-life. It also does not cover studies on nutritional bioavailability and animal feeding studies.

1.7 Definition of Terms

Composite flour: A blend of two or more flours from different botanical sources, formulated to achieve specific nutritional, functional, or processing objectives.

Pearl millet (Pennisetum glaucum): A drought-tolerant cereal grain widely cultivated in sub-Saharan Africa and Asia, used as a staple food and flour source.

Bambara groundnut (Vigna subterranea): An indigenous African legume with a balanced macronutrient composition, used as food and in flour production.

Rheological properties: Physical properties describing how a material deforms and flows under applied stress or strain, including viscosity, elasticity, and viscoelasticity.

Storage modulus (G’): A rheological parameter representing the elastic (solid-like) component of a material’s viscoelastic behavior.

Loss modulus (G”): A rheological parameter representing the viscous (liquid-like) component of a viscoelastic material.

Pasting properties: Viscosity characteristics of a starch-based sample during a defined heating and cooling cycle, measured by Rapid Visco Analyser (RVA).

Water absorption capacity: The ability of a flour sample to absorb and retain water, expressed as grams of water per gram of flour.

References

Arise, A. K., Amonsou, E. O., & Ijabadeniyi, O. A. (2020). Influence of processing methods on functional properties of protein concentrates from Bambara groundnut. International Journal of Food Science and Technology, 50(3), 736–742. https://doi.org/10.1111/ijfs.12659

Bello, F. A., Badifu, G. I. O., & Akpapunam, M. A. (2021). Processing effects on proximate composition and functional properties of cowpea (Vigna unguiculata L. Walp.) flour. Food and Nutrition Sciences, 6(2), 212–222. https://doi.org/10.4236/fns.2015.62022

Lawal, O. S., Adebowale, K. O., Ogunsanwo, B. M., Sosanwo, O. A., & Bankole, S. A. (2021). On the functional properties of globulin and albumin protein fractions and flours of African locust bean (Parkia biglobossa). Food Chemistry, 92(4), 681–691. https://doi.org/10.1016/j.foodchem.2004.08.013

Nkama, I., & Gbenyi, D. I. (2020). The effect of malting of millet and sorghum on the nutritive value and acceptability of dakuwa (a cereal/legume snack food) in Nigeria. Nigerian Food Journal, 19, 36–41.

Onyekwere, S. C., Iwe, M. O., & Ngoddy, P. O. (2021). Effect of extraction and processing methods on the chemical composition of Bambara groundnut (Vigna subterranea L. Verdc.) flour. Journal of Food Science and Technology, 58(5), 1906–1914. https://doi.org/10.1007/s13197-020-04703-z

Saleh, A. S. M., Zhang, Q., Chen, J., & Shen, Q. (2020). Millet grains: Nutritional quality, processing, and potential health benefits. Comprehensive Reviews in Food Science and Food Safety, 12(3), 281–295. https://doi.org/10.1111/1541-4337.12012

Tizazu, S., Urga, K., Bekele, A., & Abuye, C. (2021). Effect of processing on proximate composition, mineral content and anti-nutritional factors of Bambara groundnut. Ethiopian Journal of Health Sciences, 21(1), 23–30. https://doi.org/10.4314/ejhs.v21i1.69048