Optimization of ultrasound-assisted extraction and characterization of curcuminoids from yellow turmeric rhizomes

This study aimed to optimize ultrasound-assisted extraction (UAE) conditions of the turmeric rhizome (Curcuma longa L.) for the curcuminoid yield using response surface methodology (RSM) and characterize purified curcuminoids. Box–Behnken design was employed to assess the effect of ethanol concentration, solvent-to-material ratio, extraction temperature, and extraction time on the total curcuminoid content (TCC). The results showed that RSM was an accurate and reliable method for predicting TCC. UAE was found to be more efficient in comparison to conventional extraction, with a shorter time for extraction and a higher TCC level. The optimal UAE conditions for the maximal value of TCC were ethanol concentration (81.4%), extraction temperature (60°C), solvent-to-material ratio (60/1; v/w), and extraction time (60 min). The thin layer chromatography (TLC) was applied with solvents for elution (chloroform: methanol, 95:5 (v/v) that revealed the Rf values of curcumin (CUR), demethoxycurcumin (DMC), and bisdemethoxycurcumin (BDMC) 0.83; 0.59; 0.39, respectively. Column chromatography (CC) was performed by using the mixture of chloroform: methanol (95:5; v/v) as the elution solution for separating the components. CUR is the major component (approximately 63.29%), followed by DMC (27.44%), and then BDMC (9.27%). The purity of CUR, DMC, and BDMC fractions was determined by HPLC were 100, 95.63, and 98.45%, respectively. In the FTIR spectrum of purified curcuminoids, the presence of major functional groups in the keto and enol structures of curcuminoids was shown by the appearance of characteristic peaks. XRD spectrum of purified curcuminoids had characteristic signals of curcuminoid crystals. Ultrasonic-assisted extraction using RSM was effective for the extraction of TCC from the rhizome of turmeric, and purified curcuminoids were further applied for various purposes.