Res. Agr. Eng., 2026, 72(3):167-180 | DOI: 10.17221/54/2026-RAE

Effect of the probe diameter, cultivar and post-harvest storage on the cocoa pod firmness and deformation energyOriginal Paper

Randy Amuaku¹, Francis Kumi², Godwin Kwasi Amanor¹, Enoch Asante³, Gladys Pepertual Awudi¹

¹ Department of Mechanical Engineering, Koforidua Technical University, Koforidua, Ghana

² Department of Agricultural and Mechanical, School of Sustainable Engineering, University of Cape coast, Cape coast, Ghana

³ Department of Renewable Energy Engineering, Koforidua Technical University, Koforidua, Ghana

The mechanical characterisation of cocoa pods is essential for improving the post-harvest handling, mechanised processing, and objective quality assessment. This study investigated the effects of the probe diameter, cultivar, and post-harvest storage duration on the cocoa pod firmness, deformation energy, and yield stress using penetration testing. Three cultivars (Amazonia, Forastero and Amelonado) were evaluated under controlled conditions (27 ± 2 °C; 70 ± 5% RH) over 8 days using probe diameters of 3.5, 8 and 11 mm. The results showed that the probe diameter significantly influenced the measured firmness, with smaller probes producing higher values due to stress concentration effects. The firmness and deformation energy decreased significantly during storage, particularly within the first 2–4 days, indicating rapid structural degradation. Cultivar-specific responses were observed, with Forastero exhibiting the highest mechanical strength and slowest softening, while Amazonia showed the fastest degradation, losing approximately 60% of firmness by Day 6. A strong positive correlation between the firmness and deformation energy (r = 0.9478–0.9999; P < 0.05) confirms the deformation energy as a reliable substitute for the mechanical integrity. The Partial Least Squares Regression models improved with the increasing probe diameter, with optimal performance observed in Forastero (R² = 0.8118; RMSE = 1.4036 MPa).

Keywords: mechanical modelling; penetration resistance; pod mechanics; texture analysis; yield stress

Received: March 10, 2026; Accepted: May 14, 2026; Published: September 24, 2026  Show citation