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Process Optimization of Oil Extraction from African Walnut (Tetracarpidium Conophorum) Seeds for Bio-Based Coating Applications

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Abstract:

African walnut (Tetracarpidium conophorum) is an underutilized oilseed with potential application as a feedstock for alkyd resin and bio-based coating production. However, efficient extraction of high-quality oil remains a major challenge. This study investigated the optimization of walnut oil extraction using a semi-automated mechanical expeller integrated with microwave pre-treatment. A Box–Behnken design within the framework of Response Surface Methodology (RSM) was employed to evaluate the effects of moisture content (4–12%), microwave exposure time (3–5 min), feed rate (10–20 kg h⁻¹), and screw speed (20–60 rpm) on oil yield and selected quality parameters over 29 experimental runs. The developed quadratic models were statistically significant (p < 0.01), with coefficients of determination (R²) ranging from 0.9714 to 0.9898 and non-significant lack-of-fit values, indicating satisfactory model performance. The optimum extraction conditions were 8.2% moisture content, 4.2 min microwave exposure, 14.2 kg h⁻¹ feed rate, and 23.6 rpm screw speed. Under these conditions, the predicted oil yield was 45.4%, representing an improvement of more than 15% compared with the unoptimized process. The extracted oil exhibited an acid value below 2 mg KOH g⁻¹, an iodine value of approximately 141 g I₂ 100 g⁻¹, and a peroxide value below 2 meq O₂ kg⁻¹, indicating good oxidative quality and suitability for drying-oil applications. These values were within acceptable limits reported for oils used in alkyd resin production. The results demonstrate that microwave-assisted mechanical pressing can improve walnut oil recovery while maintaining desirable physicochemical properties. The developed models provide useful information for process optimization and may support further utilization of African walnut oil in coating and polymer-related applications.

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International Journal of Engineering Research in Africa Vol. 80 View Preview

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Periodical:

International Journal of Engineering Research in Africa (Volume 80)

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15-42

DOI:

https://doi.org/10.4028/p-1nPz4t

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Online since:

July 2026

Authors:

Abdulqadir Tosho Opobiyi*, Rasheed Amao Busari

Keywords:

African Walnut Oil, Bio-Based Materials, Physicochemical Properties, Process Optimization, Response Surface Methodology, Semi-Automated Expeller, Sustainable Coatings

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© 2026 Trans Tech Publications Ltd. All Rights Reserved

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