Hot Air vs. Vacuum Microwave Drying of Lemon Slices: Effects on Drying Kinetics and Quality Attributes at Different Temperatures

The demand for high-quality dried fruit products with preserved nutritional and sensory attributes has increased significantly in recent years. However, conventional drying methods often result in prolonged processing times and quality degradation. This study compared hot air drying and vacuum microwave drying at different temperatures (50, 60, and 70 °C) in terms of drying kinetics and quality attributes of lemon slices. Drying behavior, moisture content, pH, total titratable acidity, bulk density, total phenolic content, ascorbic acid, and color parameters were evaluated. The drying times for vacuum microwave drying were 144, 108, and 81 min at 50, 60, and 70 °C, respectively, which were substantially shorter than those for hot air drying (360, 204, and 156 min). In addition, vacuum microwave drying resulted in higher drying rates and effective moisture diffusivity. The Page and logarithmic models provided the best fit for the drying kinetics, with higher R2 and lower RMSE and χ2 values. Furthermore, vacuum microwave drying better preserved quality attributes, with total phenolic content ranging from 120.90 to 174.62 mg GAE/100 g DM and ascorbic acid from 59.87 to 186 mg/100 g DM, consistently higher than in hot air-dried samples. Total titratable acidity was also better retained (3.54–4.63 g citric acid/100 g DM), and lower total color change (ΔE: 14.57–23.23) indicated improved color preservation compared to conventional hot air drying. Overall, vacuum microwave drying offers a promising alternative for producing high-quality dried lemon slices with improved process efficiency.