Comparative GC-MS Analysis of Fresh and Dried Curcuma Essential Oils with Insights into Their Antioxidant and Enzyme Inhibitory Activities

Abstract

Species belonging to the Zingiberaceae family are of high nutritional, industrial, and medicinal values. In this study, we investigated the effect of processing steps (fresh vs. dried milled rhizomes) and extraction methodologies (hydrodistillation vs. hexane extraction) of curcuma essential oil on its chemical content (using GC-MS analysis), its antioxidant behavior (using in vitro assays such as DPPH, ABTS, CUPRAC, FRAP, phosphomolybdenum, and metal chelation), and its enzyme inhibitory activities (on tyrosinase, acetylcholinesterase, butylcholinesterase, α-amylase, and α-glucosidase) supported by multivariate analysis, in silico studies, and molecular dynamics. The GC-MS investigations revealed a high degree of similarity in the chemical profile of fresh hydrodistilled and hexane-extracted essential oils with tumerone and curlone being the major metabolites. The extraction techniques affected the concentrations of other minor constituents such as terpinolene, caryophylla-4(12), 8(13)-dien-5α-ol, and neo-intermedeol, which were almost exclusively detected in the hydrodistilled fresh essential oil; however, zingiberene and β-sesquiphellandrene were predominant in the hexane-extracted fresh essential oil. In the dried curcuma rhizomes, tumerone and curlone contents were significantly reduced, with the former being detected only in the hydrodistilled essential oil while the latter was doubly concentrated in the hexane-derived oil. Constituents such as D-limonene and caryophyllene oxide represented ca. 29% of the dried hydrodistilled essential oil, while ar-turmerone was detected only in the dried hydrodistilled and hexane-extracted essential oils, representing ca. 16% and 26% of the essential oil composition, respectively. These variations in the essential oil chemical content have subsequently affected its antioxidant properties and enzyme inhibitory activities. In silico investigations showed that hydrophobic interactions and hydrogen bonding were the characteristic binding modes of the bioactive metabolites to their respective targets. Molecular dynamics revealed the stability of the ligand-target complex over time. From the current study we conclude that fresh hexane-extracted essential oil showed the best radical scavenging properties, and fresh rhizomes in general display better enzyme inhibitory activity regardless of the extraction technique.

Keywords: GC-MS; antioxidant; docking; enzyme inhibition; fresh vs. dried; molecular dynamics; multivariate analysis; turmeric essential oil.

Figure 1

Components that are detected exclusively in the fresh hydrodistilled essential oil (pink), fresh essential oil extracted by n-hexane (green), hydrodistilled essential oil from dried turmeric rhizomes (turquoise), and essential oil from dried sample extracted by n-hexane (orange).

Figure 2

(A) Partial least square discriminant analysis (PLS-DA) analysis between the tested samples based on their chemical profiles and biological activities, (B) hierarchical cluster analysis between the tested samples, and (C) biplot distribution from PLS-DA analysis between the tested solvents based on chemical profiles and biological activities.

Figure 3

Binding energies (docking scores) of bioactive metabolites in turmeric essential oil samples.

Figure 4

Protein–ligand interactions of (A) ar-turmerone with AChE, and (B) curlone with BChE.

Figure 5

Protein–ligand interactions between (A) tyrosinase and neo-intermedeol, (B) α-amylase and curlone, and (C) α-glucosidase and caryophyllene oxide.

Figure 6

Molecular dynamics (MD) simulations. Root-mean-square displacement (RMSD) profiles of (A) AChE and ar-turmerone, (B) BchE and curlone, (C) tyrosinase and neo-intermedeol, (D) α-amylase and curlone, and (E) α-glucosidase and caryophyllene oxide. The RMSD variations indicate the stability of the ligand binding mode over time. The complexes displayed higher structural stability over time.