Changes in curcuminoids and chemical components of turmeric (Curcuma longa L.) under freeze-drying and low-temperature drying methods

We investigated how various drying methods affect the chemical components and microstructure of turmeric. We used freeze drying (FD), hot-air drying (HD) at 50 °C and sun drying (SD). Compared to all dried samples, fresh turmeric had greater amounts of chemical components (curcuminoids, phenolic acids, flavonoids and amino acids) and greater antioxidant activity (DPPH and FRAP) except for ABTS.+ values. SD caused a severe decline of three major curcuminoids, resulting from UV and light degradation. Curcumin was decreased the most by SD (72%), followed by HD (61%) and FD (55%), respectively. Curcumin degradation to ferulic acid and vanillin was explored by FTIR analysis. The amino acids were decreased by all drying methods. FD was considered to be most suitable for drying turmeric. Microstructure changes were least after freeze drying, but were still evident compared with fresh turmeric.