Effects of heat pump drying conditions on saponin content in hydroponic Centella asiatica (L.) URB tuber powder

Addressing the global food crisis, climate change, and environmental pollution necessitates the immediate and long-term development of sustainable food systems. Hydroponics is a soil-free cultivation method that offers a promising solution to global food demands and used to grow vegetables such as Centella asiatica (L.) Urban. Centella asiatica (L.) Urban is commonly known as one of the traditional herbal medicines widely used in Southeast Asia. Centella asiatica contains bioactive compounds like triterpenoids, flavonoids, and alkaloids, which offer antimicrobial, antioxidant, wound-healing, and memory-enhancing properties. They also aid in treating cardiovascular diseases, diabetes, cancer, and gynecological disorders. Centella asiatica contains a significant amount of triterpenoid saponins, primarily asiaticoside, madecassoside, centelloside, and sceffoleoside, collectively known as centelloids. Among them, the biological activity of saponins is believed to be attributed to these characteristics, making them a valuable raw material with significant and unique medicinal properties. Utilizing by-products from the production of hydroponic Centella asiatica in products with valuable biological properties will contribute to the sustainable development of food systems worldwide. Heat pump drying, a highly efficient and eco-friendly technology, operates based on thermodynamic principles with transferring heat between environments and enabling precise temperature control. Heat pump drying ensures minimal alteration of bioactive compounds, retains nutritional quality, and maintains desirable characteristics such as color and flavor. Additionally, it offers low energy consumption and enhanced storage stability of the dried product. Despite these benefits, initial investment and maintenance costs of this technology are high. Moreover, the operating temperature ranges were restricted to specifical initial materials, et cetera. In this study, Centella asiatica tubers cultivated hydroponically were harvested six months post-planting, achieving a peak saponin content of 3.17%. These tubers were processed into powder using heat pump drying, fine grinding and sieving. The drying conditions, set at 60°C for 420 minutes, collected Centella asiatica tuber powder with a high saponin concentration of 6.30% and notable antioxidant activity, demonstrated by an IC50 value of 8.13 mg/mL. Key words: Centella asiatica, tuber powder, heat pump drying, hydroponics, saponin, polyphenol, antioxidant, biological activity