Drying kinetics (mathematical modeling) and quality evaluation of herbal leaves (Adulsa and Durva) dried in small-scale greenhouse solar dryer (GHSD): Experimental investigation and comparative analysis

The study presents the performance of a small-scale greenhouse solar dryer (GHSD) to demonstrate hygiene and superiority over traditional methods for medicinal Adulsa and Durva leaves. The GHSD dryer lowered the initial moisture of Adulsa leaves from 73.99% (w.b.) to the final 10.63% (w.b.) under natural and forced convection in 3 and 2.5 h, respectively. Similarly, the initial moisture of Durva leaves was reduced from 67.33% (w.b.) to 11.65% (w.b.) under natural and forced convection in 2.75 and 2.5 h, respectively. Furthermore, mathematical modeling with non-linear regression was implemented to characterize the drying of Adulsa and Durva leaves, which showed that Midilli-Kucuk and Modified Midilli were the most superior fits for reporting the drying of Adulsa leaves in GHSD and open sun drying, respectively, whereas Verma and Midilli-Kucuk models were superior fits for characterizing the drying of Durva leaves in GHSD and open sun, respectively. Furthermore, the quality of the dried Adulsa and Durva leaves was evaluated, where total phenolic content (TPC) and total flavonoid content (TFC) values were marked higher in the leaves dried by the GHSD as compared to open sun drying for both Adulsa and Durva leaves. Moreover, during antioxidant analysis, the IC50 values among the leaves dried in GHSD were recorded to be greater for the natural convection greenhouse solar dryer (NCGHSD) for both Adulsa and Durva (40.67 and 122.24 mu g/mL) compared to open sun drying (101.88 and 158.20 mu g/mL). A quality assessment was performed on dried Adulsa and Durva leaf samples, and they exhibited appropriateness for pharmaceutical industry drug production.