Drying Kinetics and Efficiency of Vacuum-assisted Drying of Phyllanthus emblica (Amla) Slices at Moderate Temperature

This study investigated the drying behaviour and efficiency of vacuum-assisted drying of Phyllanthus emblica (amla) slices under controlled pressure and temperature conditions. Fresh amla slices (1-2 mm thick) were pre-dried at 60 °C for 90 min and subsequently vacuum-dried at '-600 mm Hg' and 60, 65, 70, and 75 °C. The effects of temperature on moisture reduction, drying rate, moisture ratio, and energy efficiency were evaluated. Drying curves exhibited a continuous decline typical of the falling rate period without a constant rate period, confirming that internal diffusion dominated moisture migration. Increasing the drying temperature significantly reduced total drying time from 5.5 h at 60 °C to 4 h at 75 °C, achieving final moisture contents of 11.47-12.41 ą (d.b.). The drying rate peaked within the first 0.5 h (0.530-0.926 g g⁻¹ h⁻¹) and decreased progressively as moisture content decreased. Moisture ratio curves demonstrate a faster approach to equilibrium at higher temperatures, demonstrating enhanced diffusivity under vacuum. Drying efficiency improved from 13.97 ą at 60 °C to 19.63 ą at 75 °C, indicating better utilisation of thermal energy at elevated temperatures. Among packaging materials, polypropylene exhibited superior moisture barrier properties compared with low-density polyethylene during storage. Overall, vacuum-assisted drying produced shelf-stable amla slices with minimal thermal degradation, offering strong potential for the development of high-quality, functional, and nutraceutical food products.