Investigating drying behavior and quality of Neem leaves using a novel biomass gasification-powered climate control unit with built-in humidity control

Abstract

Traditional food drying methods, such as open sun drying (OSD) and hot air convective drying (HAC), are widely employed due to their simplicity. However, these methods are inefficient and often yield lower-quality and contaminated products. To address these limitations, we utilize a novel Climate Control Unit (CCU) powered by biomass gasification. The CCU allows independent control of temperature ranging from 0−70°C as well as humidity 10−90%. Our primary objective was to investigate the various drying methods to preserve essential nutrients, reduce power-consumption, and promote environmental-sustainability. In this study, we focused on Neem leaves, a valuable medicinal ingredient, and investigated their drying behaviour and quality using the CCU as a dryer. We implemented diverse control strategies, including temperature control, humidity control, and combined temperature and humidity control. The drying experiments were conducted across different temperature ranges: moderate 45−55°C15−30%, low 25−35°C15−30%, and high 65−75°C15−30%. For comparison, we evaluated the results against OSD and HAC. Next, we assessed various thin-layer drying models to describe the optimal drying kinetics of Neem leaves. Furthermore, we focus on quality aspects, including chlorophyll, phenolic, and tannin content and the thermal performance of the system. Overall, our study elucidates the need to balance drying time and product quality while selecting drying methods. Moderate temperature with humidity control drying appeared to be optimal with a slight compromise on drying time (final moisture content ≈13%drybasisin7hours, and preserving chlorophyll (≈95%) and phenolic content (≈55%)); however, high-temperature drying seemed optimal with a slight compromise on product quality (final moisture content ≈6%in3hours, and preserving chlorophyll (≈70%) and phenolic content (≈45%)). The peak drying efficiency of ≈21%, ≈28%, and ≈38% was obtained during temperature, humidity, and combined temperature and humidity control at moderate temperature drying respectively. The drying cost (≈0.29 $/kg) was observed minimal in case of combined temperature and humidity control. We believe the diverse control strategies reported in this study are expected to find viable applications in drying technology for various perishables, such as wood, tea seasoning, and processing in leather industries, among others.