Solar drying of ginger (Zingiber officinale) and turmeric (Curcuma longa): A comprehensive review

Ginger (Zingiber officinale) and turmeric (Curcuma longa) are widely recognized for their significant medicinal value, primarily due to their bioactive compounds, gingerol and curcumin. Preserving these compounds during post-harvest processing is crucial for maintaining their therapeutic efficacy. Among various techniques, solar drying emerges as a sustainable and energy-efficient method for processing these herbs, particularly in regions with abundant solar radiation. This review explores the potential of solar drying methods in enhancing the quality and stability of dried ginger and turmeric, emphasizing the role of key parameters such as temperature, airflow, and humidity in influencing drying performance and compound retention. Different solar dryer configurations, direct, indirect, mixed-mode, and hybrid systems, are critically analyzed for their effectiveness in achieving consistent drying while minimizing nutrient degradation. The environmental and economic advantages of solar drying, such as reduced energy consumption and operational costs, are also highlighted. A major focus is placed on the importance of drying kinetics and their relationship with product quality, shelf life, and market value. Despite the growing adoption of solar drying, there remains a gap in systematically optimizing drying technologies tailored specifically to preserve bioactive compounds in medicinal herbs. The novelty of this review lies in its integrative approach to correlating solar dryer design with compound stability, offering a framework for future innovations in sustainable herb processing. It advocates for research that bridges engineering advances with phytochemical preservation, enabling a new paradigm in green, value-added post-harvest handling of medicinal plants.