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OPTIMIZATION OF EXTRUSION PROCESSING PARAMETERS FOR READY-TO-EAT SNACKS FROM SORGHUM-COWPEA BLENDS  KADUNA STATE.

CHAPTER ONE

INTRODUCTION
1.1 Background of the Study
There has been a tremendous growth in the demand for pre-cooked (ready-to-eat, RTE) snacks worldwide as a result of increasing urbanization, shifting dietary patterns, and an increased desire for convenient and nutritious snacks. This is especially true in Nigeria, where a growing middle class, increasingly demands affordable, long shelf-life and nutritious cereal-based snacks. Of the wide range of food processing technologies that can be used for snack processing, extrusion cooking is one of the most versatile, energy-efficient and cost-effective ways to convert a variety of raw materials into value-added snack products (Ojo et al., 2021).
Sorghum (Sorghum bicolor L. Moench) is a major sub-Saharan African cereal crop, mostly grown in the semi-arid areas of northern Nigeria. Kaduna State, located in Nigeria’s North-West geopolitical zone, ranks high in sorghum production, and there are thousands of smallholder farmers who rely on sorghum production for food security and income generation (FAO, 2022). Sorghum, which is high in complex carbohydrates, B vitamins and phenolic antioxidants, is duly nutritious and is also very tolerant to drought, but its value-added food processing potential is unmet compared with maize and wheat (Bello et al., 2020).
Cowpea (Vigna unguiculata L. Walp), another crop of significant importance to Nigeria’s food security, is a nutritious grain legume containing high-quality protein (22-25%) with essential amino acids, dietary fibre, iron and zinc (Arise et al., 2021). Its high protein quality and amino acid complementarity to sorghum (which is lysine deficient) allows cowpea to be suitably blended with sorghum for protein nutritional enhancement. Combining the two in certain ratios provides the amino acid complementarity required to enhance the amino acid profile and protein quality of the extruded product.
Extrusion conditions – such as the barrel temperature, feed moisture content, screw speed and die shape – are key factors that influence the physical, functional, and sensory attributes of extruded products. The combination of these parameters, using response surface methodology (RSM) or other statistical techniques, has been reported to yield improved expansion ratio, bulk density, water absorption index (WAI) and texture in extruded cereal-legume blends (Meng et al., 2020). Yet, there is limited literature on the extrusion processing parameters, particularly for sorghum-cowpea blends, in the Nigerian processing environment, particularly in the kaduna state’s agro-industry.
This research is thus driven by the objective of valorizing the farming resources of sorghum and cowpea in Kaduna State, create nutritionally fortified “healthier” and marketable RTE snacks, and add to the sparse literature on food extrusion technologies in the Nigerian agro-processing industry.

1.2 Statement of the Problem

While sorghum and cowpea are widely available in Kaduna State and the northern part of Nigeria, their incorporation in modern value-added processing (especially for the production of extruded RTE snacks) is widely underexploited. The majority of these commercially available snacks in Nigeria are imported or produced using refined wheat flour, which results in products that are less nutritious, expensive to produce and consumes a large amount of foreign exchange (Nwosu et al., 2022).
The existing extruded snacks that are locally manufactured are largely derived solely from maize grits without inclusion of protein-rich legume; hence, they are energy-dense but low in protein content. In addition, there has been no systematic research to optimize the extrusion processing parameters particularly barrel temperature, moisture level and screw speed during the processing of sorghum-cowpea composite snacks in Kaduna State. Failure to optimise the processing conditions may result in products with poor texture, expansion, hard or undercooked products, which would eventually affect the market acceptance and commercialisation of the products (Ojo et al., 2021).
The absence of such knowledge calls for a thorough study on the optimum extrusion parameters that will give high quality, nutritionally balanced, and commercial acceptable RTE snacks from sorghum-cowpea blends, based on the raw material and processing facilities available in Kaduna State.

1.3 Objectives of the Study

Aim: The general aim of this study is to optimize extrusion processing parameters for the production of ready-to-eat snacks from sorghum-cowpea blends in Kaduna State.

Specific Objectives:

1. To determine the proximate composition of sorghum-cowpea composite flour blends at varying ratios (100:0, 80:20, 70:30, 60:40, and 50:50).
2. To evaluate the effect of varying extrusion parameters (barrel temperature: 120–160°C, feed moisture: 14–20%, screw speed: 150–250 rpm) on the physical properties (expansion ratio, bulk density, water absorption index) of the extruded snacks.
3. To assess the functional and sensory properties of the optimized extruded sorghum-cowpea snacks.
4. To determine the optimal combination of extrusion parameters using Response Surface Methodology (RSM) for producing snacks with the most desirable quality attributes.

1.4 Research Questions

1. What is the proximate composition of sorghum-cowpea composite flour at different blend ratios?
2. How do barrel temperature, feed moisture content, and screw speed affect the physical and textural properties of extruded sorghum-cowpea snacks?
3. What are the functional and sensory characteristics of the optimized extruded snacks?
4. What combination of extrusion parameters yields sorghum-cowpea snacks with optimal expansion, texture, and consumer acceptability?

1.5 Significance of the Study

This research is of great importance for several reasons. Nutritionally, the inclusion of protein fortified RTE snacks based on locally sourced composites of sorghum-cowpea blend will help tackle the issue of protein-energy malnutrition, especially in children and poverty-stricken households in the state of Kaduna and northern Nigeria. For the economy, this research will support small and medium-scale processors to develop marketable extruded snacks from locally-available raw materials, thereby supporting local production in lieu of imported wheat-based extruded snacks and relatively boosting the local agro-processing value chain (FAO, 2022).
In terms of academic contribution, this study will contribute to the expanding knowledge on packaging cereal-legume composites in sub-Saharan Africa, providing a validated set of optimal processing conditions that can be used as a starting point by other researchers and industry players. Government policy makers and agencies such as NAFDAC (National Agency for Food and Drug Administration and Control) and Kaduna State Ministry of Agriculture will also have “scientific evidence” that will guide the commercialization of locally grown crop-based snacks.

1.6 Scope of the Study
This research focuses on the optimization of extrusion processing conditions of sorghum-cowpea composite blends using a twin-screw extruder. The types of sorghum and cowpea will be those readily available in the market of Kaduna State. The extrusion variables will be limited to barrel temperature (120-160°C), feed moisture content (14-20%) and screw speed (150-250 rpm). The research will be limited to the physical, proximate, functional and sensory characteristics of the extruded snacks. The microbiology, shelf-life, and industrial production of the products are not within the objectives of this study.

1.7 Definition of Terms

Extrusion: A high-temperature, short-time (HTST) food processing technique in which moistened starchy or proteinaceous material is plasticized and forced through a die under pressure to form shaped products.

Ready-to-eat (RTE) snacks: Food products that require no further cooking or preparation before consumption.

Sorghum-cowpea blend: A composite mixture of sorghum flour and cowpea flour combined at defined ratios.

Expansion ratio: The ratio of the cross-sectional area of the extrudate to the cross-sectional area of the die opening, indicating the degree of puffing.

Response Surface Methodology (RSM): A collection of statistical and mathematical techniques useful for developing, improving, and optimizing processes.

Screw speed: The rotational speed of the extruder screw, expressed in revolutions per minute (rpm), influencing shear rate and residence time of the material in the barrel.

Barrel temperature: The temperature applied along the extruder barrel that determines the degree of starch gelatinization and protein denaturation.

References

Arise, A. K., Arise, R. O., Sanusi, M. O., Esan, O. T., & Oyeyinka, S. A. (2021). Effect of cowpea protein concentrate on the chemical, functional, and pasting properties of maize flour. Food Science & Nutrition, 9(4), 2139–2148. https://doi.org/10.1002/fsn3.2180

Bello, F. A., Badifu, G. I. O., & Mgbemere, V. N. (2020). Nutritional and functional properties of sorghum flour and its potential for food product development in Nigeria. Journal of Food Science and Technology, 57(2), 412–421. https://doi.org/10.1007/s13197-019-04085-5

Food and Agriculture Organization of the United Nations. (2022). Crops and livestock products. FAOSTAT. https://www.fao.org/faostat/en/#data/QCL

Meng, X., Threinen, D., Hansen, M., & Driedger, D. (2020). Effects of extrusion conditions on system parameters and physical properties of a chickpea flour-based snack. LWT – Food Science and Technology, 129, 109591. https://doi.org/10.1016/j.lwt.2020.109591

Nwosu, J. N., Owuamanam, C. I., Omeire, G. C., & Eke, C. C. (2022). Quality parameters of biscuit produced from substitution of wheat with cassava flour. American Journal of Research Communication, 10(2), 1–14.

Ojo, M. O., Ariahu, C. C., & Chinma, E. C. (2021). Proximate, functional, and pasting properties of cassava starch and mushroom (Pleurotus ostreatus) flour blends. American Journal of Food Science and Technology, 9(1), 9–15. https://doi.org/10.12691/ajfst-9-1-2