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 μg/mL) compared to open sun drying (101.88 and 158.20 μg/mL). A quality assessment was performed on dried Adulsa and Durva leaf samples, and they exhibited appropriateness for pharmaceutical industry drug production.

Practical applications

Greenhouse solar dryer is an eco-friendly, sustainable, clean, and hygienic way to dry herbs and medicinal plants. The greenhouse solar dryer can shorten the drying time by 50%–60% compared to natural stand in the sun (open sun drying) and improve the quality of the dried herbs, medicinal plants, and reduce the decay rate of the dried products. These leaves can be best suited for Ayurveda medicine industries for herbal powder (Churna). Being an economically advantageous greenhouse solar dryer improves the shelf life of the dried leaves, reduces their density, and lower transportation costs, leading to boost farmers' income in herbal farming and nutritional security.