Drying Kinetics, Characteristics, and Quality Assessment of Hot-Air Dried Semi-Dried Biser Stage Dates Using Computer Vision

Abstract

Drying dates to a semi-dried, soft, preferred by most consumers, remains a challenge for small-scale processors due to limited control, longer drying time, quality degradation, and other inefficiencies of traditional methods such as open-sun drying. This study investigated the mechanical hot-air drying kinetics and characteristics and evaluated quality changes after drying of Biser dates from 57% to 30% moisture content (wet basis) at various temperatures using a state-of-the-art computer vision system (CVS). This study findings revealed that drying time decreased with increasing temperature, with the shortest drying time observed at 70°C (14.5 h) and the drying occurred predominantly in the falling rate period. Additionally, among the three thin-layer drying models investigated in this study, Page model stands out as the best fitting model to describe the mechanical hot-air drying behavior of Biser dates, having an uppermost coefficient of determinations (R²) of (0.9899–0.9984) and least standard error (SE). The effective moisture diffusivity (D_eff) followed second Fick's diffusivity model and fall between a range from 3.50 × 10⁻¹⁰ to 5.84 × 10⁻¹⁰ m²/s across the temperatures studied (50°C, 60°C, and 70°C). Higher temperatures led to greater shrinkage but helped prevent surface cracking. Notably, CVS measurements showed significant differences (p < 0.05) in shrinkage across samples, with 60°C and 70°C yielding higher volumetric shrinkage. Rehydration capacity was highest at 60°C (45.47%), followed by 70°C (34.21%) and 50°C (20.99%). Overall, drying at 70°C provided the most efficient balance between drying time and product quality, making it the optimal condition for small-scale processors already transitioning to mechanical hot-air drying. It also reduced drying period, minimized quality losses, improved operational consistency, and product standard in the shift away from traditional methods. Future research should focus on sensory evaluation to assess consumer acceptance of semi-dried Biser dates processed under these conditions.