A comparative assessment of drying kinetics, energy consumption, mathematical modeling, and multivariate analysis of Indian borage (Plectranthus amboinicus) leaves

Abstract

In the current study, four drying methods, namely microwave (MD), vacuum (VD), hot air (HAD), and freeze drying (FD), were compared for drying of Indian borage (Plectranthus amboinicus) leaves for optimum energy consumption and bioactive compounds' retention. Effective moisture diffusivity for MD was about 100 times more than that of HAD and VD. MD at 600 W showed minimum specific energy consumption (4.04 kWh/kg), proving the most suitable drying condition. Moreover, it showed desirable energy values in terms of maximum specific moisture extraction rate (0.265 kg moisture/kWh) and maximum drying efficiency (15.85%). Bioactive compounds' retention in terms of phenols, antioxidants, and flavonoids was better in MD, followed by FD. Mathematical modeling of drying kinetics data revealed proper fitting of three drying models, namely, Aghbashlo, Modified Page‐II, and Page model, for explaining the drying behavior of Indian borage leaves. Multivariate characterization using principal component analysis revealed that FD and MD had a strong effect on bioactive compounds' retention, while VD and HAD showed least effect. Hence, based on optimum energy utilization and bioactive compounds' retention, MD at 600 W was selected for efficient drying of Indian borage leaves.Practical applicationsDrying of Indian borage leaves using microwave drying (MD) resulted in quicker drying with retention of bioactive compounds and color of dried leaves. The energy aspects were also favorable for industrial scale‐up. With due consideration to capacity enhancement in MD, it can prove to be a promising source of drying for culinary, medicinal, and aromatic plants.