A novel turmeric drying approach based on supercritical carbon dioxide

As a widely used spice, turmeric is rich in curcuminoids, which are known for their anti-inflammatory and antioxidant properties. However, the drying process, especially at high temperatures, often leads to significant curcumin degradation, impacting its bioactivity and quality. This study investigates drying turmeric using an innovative approach based on supercritical carbon dioxide (SC-CO₂), and conventional drying methods (oven drying and freeze-drying) in terms of curcuminoid retention, color, solubility, chemical interactions, crystallinity, and morphology. The results revealed that SC-CO₂ drying preserved up to 82.3 µg curcuminoids /mg dried turmeric, which was significantly higher than the levels retained by oven drying (55.4 µg/mg) and freeze-drying (42.4 µg/mg). Moreover, SC-CO₂ drying exhibited better color retention, with higher L*, a*, and b* values compared to oven-dried samples. Further, SC-CO₂ drying improved curcuminoids' solubility (0.57 µg curcuminoids/mg turmeric) as compared to oven drying (0.29 µg/mg) and freeze-drying (0.12 µg/mg) at 60 °C, which is critical for enhancing curcumin bioavailability in food and pharmaceutical products. The morphological analysis showed that SC-CO₂ drying maintained the structural integrity of turmeric better than the other methods, making it a promising technique for preventing thermal degradation and oxidation of micronutrients during drying.