Influence of drying methods on the curcuminoid content of Curcuma longa L.

Curcuminoids are bioactive compounds naturally present in turmeric (Curcuma longa L.) rhizomes and are sensitive to processing conditions, particularly prolonged thermal exposure and light. Turmeric is commonly marketed as fresh rhizomes or dried powder; therefore, selecting a drying method that minimizes curcuminoid losses is important for obtaining a dry raw material with high bioactive content. Freeze-drying removes water under low-temperature and reduced-pressure conditions and may limit thermal degradation compared with conventional hot-air drying. This study evaluated the influence of drying methods on curcuminoid content to select the most suitable method for subsequent formulation development. Fresh turmeric rhizomes were divided into two treatments: convective oven-dried samples (65 °C for 16 h) and freeze-dried samples (72 h), unprocessed fresh samples, were used as a control. Curcumin (CUR), demethoxycurcumin (DMC), and bisdemethoxycurcumin (BDMC) were quantified by HPLC-DAD. Moisture was determined, and curcuminoid contents were expressed on a dry-weight basis. Freeze-dried samples showed the highest total curcuminoid content (912.57 ± 20.32 mg/100 g), followed by oven-dried (632.71 ± 28.87 mg/100 g) and fresh samples (310.48 ± 25.11 mg/100 g), with significant differences among treatments (p < 0.05). Compared with the fresh control, freeze-drying yielded 194% higher total curcuminoid content and 141% higher CUR content; compared with oven drying, the increases were 44% and 36%, respectively. CUR remained the predominant curcuminoid in all samples. The results were normalized to dry matter, the higher contents observed after freeze-drying cannot be attributed solely to water removal. They are consistent with reduced thermal stress during low-temperature dehydration and may also reflect processing-induced changes in the plant matrix that favored curcuminoid recovery during analysis. Among the evaluated conditions, freeze-drying was the most favorable treatment resulting in the highest curcuminoid content and was therefore selected as the raw material preparation method for subsequent curcuminoid-based formulations. Acknowledgments to: CAPES e FAPERJ.