Shrinkage and drying kinetics effects of process variables of Bitter leaf (Vernonia amygdalina): An investigative study

This study explores the drying characteristics of Vernonia amygdalina (bitter leaf) through the use of an electric cabinet dryer, focusing on the effects of air temperature (40–60°C), air velocity (2.6–4.6 m/s), and leaf size on drying kinetics and shrinkage. Leafy vegetables need carefully controlled drying conditions because of their high moisture content (80–90% w.b.) in order to maintain their nutritional value and their marketability. The Box-Behnken Design (BBD), a response surface methodology, was employed to evaluate the effects and interactions of process variables on moisture ratio (MR), drying rate, and shrinkage. The BBD technique enables efficient development of quadratic models with minimal experimental runs. The findings demonstrated that air temperature had a significant impact on drying rate (F = 418.11, p < 0.0001) and that shrinkage was affected by both linear and quadratic temperature terms (F = 272.86, p < 0.0001; F = 55.75, p = 0.0001). R² = 0.9869 for drying rate and R² = 0.9864 for shrinkage indicated high model accuracy. Optimal drying conditions were 52.36 °C, 2.6 m/s airflow, and a leaf area of 0.0028 m² and these yielded a drying rate of 3.53 g/h and shrinkage of 30.62%. Model reliability was confirmed by validation assessments that revealed small errors (1.40% and 3.38%). This study emphasizes how important temperature is for maximizing convective drying while preserving product quality. Further studies on the microstructural behaviour of different species using image analysis under varied pre-treatments and drying conditions are recommended. Adopted ASTM Standard: Modified ASTM D4442 for moisture content determination.