Optimization of Rice Milling Processing Efficiency Using a Fractional Factorial Design: Evidence from Local Variety in Nigeria
Nasir Sani Dauran
Sagir Badamasi
Abubakar Danbaba
Faruk Sani
Shehu Abdulazeez
Abstract
Rice processing efficiency is a critical determinant of grain quality, economic value, and food security, particularly in rice-producing regions such as Sokoto State, Nigeria, where traditional processing methods dominate. Inefficiencies in key processing parameters often result in excessive grain breakage, low milling yield, and inconsistent product quality. This study aim is to optimize rice milling efficiency using a fractional factorial design (FFD) to evaluate the combined effects of five processing factors: steaming duration, soaking duration, moisture content, re-steaming duration, and temperature. Two locally important rice varieties, Jamila and CiPi, were used for experimental analysis. A Resolution V fractional factorial design was chosen with sixteen (16) experimental runs to employed to estimate all main effects and two-factor interactions without confounding, while minimizing experimental cost and resource use. Milling yield, head rice yield, grain breakage, and whiteness were considered as response variables. Data analysis involved descriptive statistics, analysis of variance (ANOVA), regression modeling, Pareto analysis, and multi-response optimization techniques. The results showed that the processing factors had statistically significant effect on milling performance, with steaming duration and moisture content emerging as the most influential factors for the Jamila variety, while soaking duration and re-steaming duration were more influential for the CiPi variety. Milling yield increased from 50.0% to 90.0% (40 percentage point improvement) for the Jamila variety and reached up to 82.5% for CiPi. Head rice yield ranged from 54.9% to 71.9%, representing an improvement of approximately 15 – 20 percentage points compared with non-optimized processing conditions. Important interaction effects, particularly between steaming duration and moisture content, were observed in improving head rice recovery. The existing studies examine processing factors individually, but this work simultaneously evaluates main and interactive effects of multiple processing parameters in a single experimental framework. The findings indicate that optimal processing conditions are variety-specific and that improving fractional factorial design provides an efficient experimental framework for identifying critical processing parameters. The optimal processing combination consists of 30mnt steaming, 8hr soaking, 28.6% moisture content, 30mnt re-steaming, and a dry temperature of 550C, yielding maximum milling efficiency and grain quality. The study concludes that adopting optimized processing conditions can improve milling yield and rice quality, reduce post-harvest losses, and enhance the economic competitiveness of locally processed rice. The results provide practical recommendations for small- and medium-scale rice processors and contribute to evidence-based optimization of traditional rice processing systems in Nigeria.
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