Optimisation of Solar Drying Parameters for Quality Preservation of Selected Nigerian Food Products

This study develops and validates an optimised solar drying model for preserving quality characteristics in selected high-value Nigerian food products including ginger, chilli pepper, and leafy vegetables. Solar drying is widely promoted as a low-cost, energy-efficient alternative to fossil fuel-powered dryers for agricultural produce drying in Nigeria, but product quality outcomes are highly sensitive to drying temperature, air velocity, humidity, and product layer thickness. Current solar dryer designs used in Nigeria are not optimised for the quality parameters most important for export market requirements. This study applies Response Surface Methodology using a central composite design to simultaneously optimise drying parameters including collector temperature, air flow rate, and product layer thickness for minimum drying time and maximum retention of targeted quality indices including capsaicin content in pepper, gingerol content in ginger, and chlorophyll content in leafy vegetables. A specially instrumented indirect solar dryer with variable fan speed and adjustable collector tilt is used for experimental trials at Bayero University Kano research facilities. Regression models and contour plots are developed for each product-quality combination. Findings reveal significant interactions between drying parameters, with optimal conditions differing by product type. Ginger achieves maximum gingerol retention at 55 degrees Celsius, 1.2 metres per second air velocity, and 10 millimetre layer thickness, reducing gingerol loss to below 8 percent. The study contributes original optimisation models for Nigerian food product solar drying and recommends product-specific solar dryer design guidelines for export-quality production.

Keywords: solar drying optimisation, food quality, Nigeria, response surface methodology, ginger.