Comparative Investigation of Untargeted and Targeted Metabolomics in Turmeric Dietary Supplements and Rhizomes

In the present study, we analyzed the bioactive curcuminoids content in eight capsules (DS-1-DS-7 and DS-9), one tablet (DS-8), three ground turmeric samples (DS-10-DS-12), and three ground turmeric rhizomes (TR-1, TR-2, and TR-3). Initial screening with infrared and ultraviolet-visible spectroscopy coupled with a principal component analysis (PCA) revealed distinct differences between the samples analyzed. Hence, targeted and untargeted analyses were performed using ultra-high-performance liquid chromatography and gas chromatography coupled with mass spectrometry detections. The results show that the total curcuminoids content ranged from 1.3 to 69.8 mg/100 mg and the volatile component ranged from 0.7 to 9.1 mg/100 mg. The percentage ratio of the three prominent curcuminoids, bisdesmethoxycurcumin (BMC), desmethoxycurcumin (DMC), and curcumin (CUR), also varied remarkably compared to the expected ratio (BMC:DMC:CUR ratio of 1:2:6) described in the literature. The three prominent volatile compounds identified in most samples were ar-turmerone, turmerone, and curlone. The results demonstrated significant differences in the volatile compound levels among the DS and dried rhizome samples. The non-targeted analysis resulted in the identification of over 40 compounds, including bioactives such as piperine, phenolic acids, and amino acids. A disintegration study was performed on limited DS according to the United States Pharmacopeia protocol. The results reveal that all the selected DS samples passed the disintegration test. An analysis of curcuminoids from DS samples in neutral and acidic solutions demonstrated that all curcuminoids (BMC, DMC, and CUR) existed in the keto and enol forms and their concentrations changed with pH. This study will be of significant interest to manufacturers, consumers, and pharmacologists to accurately understand the bioactivities of three curcuminoids in different isomeric forms.