1. Introduction
Herbal medicines are important tools in the management of health from the ancient days; traditional medicines and folk medicinal systems utilized these plants and plant products [
1]. Among the various plants, the predominant ones include the spices that are the part of the daily diet [
2]. Several such spices are widely utilized in Ayurvedic and Chinese traditional medicines as dietary agents in the management of infectious and chronic illness [
3,
4]. Bioactive compounds and extracts from various aromatic plants are known for their biological activities, including antimicrobial properties [
5,
6]. Members of Zingiberaceae, Apiaceae, Lamiaceae, and Myrtaceae are well-known spices with potential health benefits. The predominant spices include turmeric, ginger, clove, cinnamon, and ajwain; these spices are used in flood and medicines. Among these, the predominant ones belong to the Zingiberaceae; the different spices, including
Curcuma and
Zingiber genus, are widely studied ones.
Curcuma spp. are well described for their phytochemistry, pharmacological, and biological properties. Different species including
C. longa,
C. aromatica,
C. aeruginosa,
C. amada, and
C. xanthorrhiza are utilized in pharmaceutics, cosmetics, and other industries. The cosmetic uses of the
Curcuma spp. are well explored; the extract of the
C. longa extract indicated the potential of improving skin color [
7]. Likewise,
Curcuma mangga extracts are shown to protect against the oxidative stress-associated ageing in fibroblast cells [
8]. Likewise, the extracts of
C. aromatica and
C. comosa prevented the ultraviolet-induced oxidative damage and matrix mellatoproteinase expression in skin cells [
9]. The pharmacological properties of the different species of
Curcuma spp. are also evaluated in different disease models. In Parkinson’s disease, the
Curcuma longa was found to be effective by preventing the apoptotic death of dopamine producing cells in substantia nigra [
10]. The oral consumption of curcumin has been found to improve the cognitive aspects of Alzheimer’s patients [
11,
12]. Apart from these, the
Curcuma spp. is also effective against metabolic disease including non-alcoholic fatty liver disease. The turmeric has been effective in regulating the hepatic hyperlipidemia and reducing NAFLD complications [
13]. Clinical studies also confirmed the potential of
Curcuma spp. and their isolated bioactive compounds [
14,
15].
The essential oils are other important compounds that are produced from the
Curcuma rhizomes and leaves. The predominant compounds present in the rhizome essential oils of different species of
Curcuma include Curzerenone and 14-hydroxy-δ-cadinene [
16]. Further, the essential oils derived from the
Curcuma and
Zingiber are widely utilized for pest repellence and medicinal purpose. The essential oil of
C. longa and
C. aromatica are found to be biologically active in preventing the growth of bacterial communities and cancer cells [
17]. In addition, the essential oils of
C. longa was found to inhibit the mutagenesis and subsequently prevent the carcinogenesis in murine models [
18,
19]. Apart from these, the
C. aromatica has been demonstrated to exert antioxidant effects by scavenging reactive radicals [
20].
Primarily, the rhizomes of these plants are utilized in medicine and food; however, the leaves of the plants are usually considered and left alone as an agrowaste. Agro-wastes are the emerging concerns in the agriculture sector, which often increase the concern of pollution and other issues. The agricultural waste products include the residues of grains and crops, litter from leaf and plant parts, and the excretory material from livestock or poultry [
21,
22]. The decaying and burning of these wastes will cause serious pollution issues in water, soil, and air [
23]. Hence, the management of these agro-wastes is emerging as an important concern. Recent developments in the area have indicated that the conversion of these products to value-added components makes an economically beneficial and environmentally friendly method for waste management. Among the various value-added products, the essential oils are predominant ones that are mainly isolated from the agrowastes [
24,
25]. Hence, the present study aims to analyze the chemical composition and pharmacological activities of essential oils derived from three species of
Curcuma viz.,
C. longa,
C. aromatica, and
C. augustifolia. It is expected that, by virtue of the bioactive compounds present, these essential oils may control the population of microbial communities and cancer cell survival.
3. Discussion
Spices are important dietary components with potential biological and pharmacological activities [
26]. Spices are highly utilized in food industries and therefore it is an important source of biologically active molecules that are referred to as nutraceuticals [
27]. Among the various spices used, the Turmeric (
Curcuma longa) is considered to be the most accepted one [
28,
29]. Apart from the
C. longa, there are several other species that exist in the genus. In the present study, we evaluated the chemical composition of the leaf essential oils of different
Curcuma spp., which is considered to be the important agrowaste. Apart from these, the antibacterial and cytotoxic activities were also evaluated.
Our results indicated a yield between 0.37 to 1.62% for the different
Curcuma spp. essential oils. However, previous studies by Kutti Gounderand and Lingamallu [
30] and Hong, et al. [
31] indicated a yield of 3.05 to 4.45% from rhizomes. However, considering that the present study used leaves as the source of essential oil, a yield of 1.62% may not be considered low.
The three essential oil contains entirely different chemical composition; In LEO, α-phellandrene, 2-carene, and eucalyptol predominated the chemical contents; whereas, the REO was predominated by camphor, 2-bornanone, and curdione. The main components detected in NEO were eucalyptol, curzerenone, α-lemenone, longiverbenone, and α-curcumene. Previous studies by Jena, Ray, Banerjee, Sahoo, Nasim, Sahoo, Kar, Patnaik, Panda, and Nayak [
16] indicated the presence of curzerenone (33.2%), 14-hydroxy-δ-cadinene (18.6%) and γ-eudesmol acetate (7.3%) in the
C. angustifolia leaf essential oil. Chemical analysis of
C. longa leaf essential oil in the studies of Sindhu, et al. [
32] and Sharma, et al. [
33] indicated the presence of phellandrene, eucalyptol, p-cymene, terpinolene, and β-pinene. According to the previous reports, in
C. aromatica leaf essentila oil, the main components are eucalyptol (20.0%), camphor (18.0%) germacrone (11.8%), camphene (9.4%), limonene (8.6%), and isoborneol (6.4%) [
20]. Hence, previous reports are also in line with our study; however, the percentage composition shows a significant variation.
Besides the chemical constituent analysis, the results also indicated strong free radical quenching potential. The previous reports by Avanço, et al. [
34] and Jena, Ray, Banerjee, Sahoo, Nasim, Sahoo, Kar, Patnaik, Panda, and Nayak [
16] indicated the antioxidant properties of the rhizome essential oils of different
Curcuma spp. Likewise, the radical quenching properties are also attributed to the
Curcuma leaf essential oils [
17,
35]. Furthermore, the bioactive compounds including eucalyptol, α-lemenone, α-phellandrene, 2-carene and α-curcumene are also reported to act as chain breaking antioxidants [
36,
37]. Since the role of antioxidants in alleviating chronic diseases and preventing infectious disease are evident [
38,
39], the leaf essential oils from different
Curcuma spp. may also have significant health promoting effects.
The present results also indicated strong cytotoxic properties against breast cancer cells. Cytotoxic activity of the essential oil of
C. aromatica has also been evident in multiple cancer cells by stimulating apoptotic cell death [
40,
41]. Previous studies have also been reported that the essential oils of
Curcuma rhizome and leaves induce apoptotic cell death in lung and liver cancer cells [
42,
43]. The cytotoxicity is attributed to the specific compounds such as α-phellandrene [
44,
45], camphor [
46], curdione [
47,
48], eucalyptol [
49,
50], terpinolene [
51], and α-pinene [
52,
53], which are already known to induce apoptosis and signaling interruption in cancer cell. The cytotoxic effect was mediated through cell cycle inhibition at the G
2/S checkpoint [
54].
Results also indicated strong antimicrobial properties to the leaf essential oils of different
Curcuma spp. against bacterial strains such as
E. coli,
S. aureus, and
S. enterica. These pathogenic microbes are known to cause various health issues in humans and animals [
55,
56]. The antibacterial activity was also attributed to the different
Curcuma essential oils; previous studies have indicated the antibacterial properties of
C. longa [
57,
58],
C. aromatica [
59,
60],
C. angustifolia [
61]. The antibacterial activity of
C. longa rhizome essential oil is also evident against
Bacillus subtilis,
Staphylococcus aureus,
Salmonella typhimurium, and
Escherichia coli [
34,
57]. Likewise, the rhizome essential oil of
C. aromatica is also found to be effective against various microorganisms [
60]. In addition, the essential oils were also capable of inhibiting the biofilm forming properties of bacteria, including
Streptococcus mutans [
62]. A recent study by Septama, et al. [
63] has also indicated the antibacterial and anti-biofilm formation activities of the
C. xanthorrhiza. To support this information, there are bioactive constituents, such as α-phellandrene [
64,
65], camphor [
66,
67,
68], eucalyptol [
69], terpinolene [
70], and α-pinene [
52,
71].
Hence, the present study indicated significant variation in the chemical composition of the leaf essential oils of different Curcuma spp. Further, these essential oils displayed significant radical quenching potential against DPPH, ABTS, and peroxide radicals. The essential oils, especially LEO, exhibited strong antibacterial properties against Gram positive and Gram-negative strains. The cytotoxic activities of the different Curcuma essential oils were also identified against breast cancer cells.
4. Materials and Methods
4.1. Materials and Chemicals
The chemicals used for the analysis were of reagent grade and purchased from Sigma Aldrich (St. Louis, MO, USA). The chemicals were DPPH, ABTS, hydrocarbon mixture (C8–C30 n-alkanes), ethanol, and hydrogen peroxide. Cell culture reagents include Dulbecco’s Modified Eagle Media, sodium pyruvate, fetal bovine serum, non-essential amino acids, and MTT (Gibco, MA, USA). The microbial growth media included Lysogeny broth and Mueller–Hinton agar (Himedia, Mumbai, India).
The human breast cancer cell lines (MCF-7, and MDA-MB-231) were procured from National Centre for Cell Science, Pune. The bacterial strains were obtained from the Microbial Type Culture Collection and Gene Bank (MTCC), Chandigarh, India. The Gram-positive bacteria used was Staphylococcus aureus (MTCC740) and Gram-negative bacteria were Escherichia coli (MTCC1610), Pseudomonas aeruginosa (MTCC 741), and Salmonella enterica (MTCC1252) bacteria.
4.2. Collection of Curcuma Leaves and Extraction of Essential Oil
Leaves of different species of
Curcuma spp. belonging to the Zingiberaceae family were collected from Kerala Agricultural University, Thrissur, India (10.85053° N, 76.27106° E) in February 2022. Hydro-distillation was conducted to extract the essential oils from these different species of
Curcuma spp. with the help of the modified Clevenger-type apparatus for 5–6 h (100 °C). Briefly, 20 g of
Curcuma leaves alone were taken in a 2000 mL flask along with deionized water. Initially, they were heated to boil as described in
Table 1; the essential oil was then collected and dried with anhydrous Na
2SO
4 [
72]. Finally, these essential oils were stored in dark amber-colored glass bottles at 4 °C inside the refrigerator until required for experiments. The essential oil yield was determined on a dry weight basis by using the formula yield (%,
v/
w).
4.3. Chemical Component Analysis by GC-MS Analysis
The chemical composition of the essential oils were determined according to our previously published method [
73]. The chromatographic equipment used in the analysis was TSQ 8000 Evo system from the Thermo scientific (Waltham, MA, USA). The analytical system was composed of an autosampler, which was a gas chromatographic column (TG-5MS) of dimensions 30 mm × 0.25 mm × 0.25 μm. The helium gas was used as a carrier with 1.0 mL per minute flow rate. The gas chromatographic oven was maintained at 50 °C with a gradual and steady increase to 120 °C (10 °C per minute) and finally changing the temperature to 270 °C (at a rate of 5 °C per minute). The chemical composition of each essential oil was derived by matching the MS spectra of NIST library. Each run was followed by a blank run without essential oil to omit the carry over contamination. We determined the retention index (RI) values by calibrating the instrument with a homologous series of alkanes (C
7–C
30 n-alkane mixture) using the same conditions. The calculated retention indices of identified chemical components were compared with library reference retention indices in NIST and Wiley libraries [
74,
75,
76,
77].
4.4. In Vitro Antioxidant Activity as Scavenging of DPPH, Hydrogen Peroxide and ABTS Radicals of the Essential Oils of Different Curcuma spp.
The in vitro antioxidant activities were estimated for the selected essential oils; the essential oils were initially diluted to appropriate concentrations (0–25 μg/mL) and used for the study.
4.4.1. Anti-DPPH Radical Assay
The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging was estimated according to the methods of Baliyan, Mukherjee, Priyadarshini, Vibhuti, Gupta, Pandey, and Chang [
26]. Briefly, the varying concentrations of the essential oils were mixed with DPPH (0.12 M) solution in methanol. The mixture was kept in dark at 30 °C for 20 min. The reduction in the optical densities in different essential oil doses was compared to the untreated control, and the percentage inhibition was calculated using the formula;
4.4.2. Curcuma Essential Oils and ABTS Radical Quenching Ability
The 2,2′-azino-di-(3-ethylbenzthiazoline sulfonic acid) (ABTS) radical scavenging was estimated according to the methods of Munteanu and Apetrei [
78]. Initially, the ABTS radicals were generated by incubating 8 mM ABTS and 2.5 mM potassium persulfate for 12 h at 30 °C. These radicals were diluted 1:60 to a yield working ABTS solution; 1 mL of this solution was mixed with different doses of
Curcuma essential oils and incubated at 30 °C for 10 min, and the change in absorbance was noted at 734 nm using the same formula given in
Section 4.4.1 4.4.3. Hydrogen Peroxide Neutralization Assay
The hydrogen peroxide scavenging was estimated according to the methods described by Al-Amiery, et al. [
79]. The essential oil of varying concentration (0.1 mL) was mixed with 50 mM phosphate buffer of pH 7.4 ± 0.1, containing 2 mM hydrogen peroxide solution. The mixture was mixed and incubated in the dark for 10 min at 30 °C, and the change in absorbance was noted at 234 nm.
4.5. Cytotoxic Activity of the Leaf Essential Oils of Different Curcuma spp.
Two breast cancer cell lines- MCF7 (ATCC, HTB-22™ Estrogen receptor positive) and the MDA-MB-231 (ATCC, HTB-26™ triple negative breast cancer cell) were procured from National Centre for Cell Science (Pune, Maharashtra, India). These cells were maintained in complete Dulbecco’s Modified Eagle Media (Gibco, MA, USA) with sodium pyruvate, sodium carbonate, and non-essential amino acids. The cytotoxicity analysis was conducted according to the MTT assay, as mentioned previously [
80]. The percentage of cell death was estimated by the formula;
OD means the optical density or absorbance.
4.6. Antibacterial Activity of Leaf Essential Oil of Different Curcuma spp. by Disc Diffusion Method
The bacterial strains were initially maintained in Lysogeny broth (Himedia, Mumbai, India); the bacteria were inoculated in an Mueller–Hinton agar (Himedia, Mumbai, India) plate of thickness 5 mm. The Whatman No.1 filter paper disc of 8 mm diameter was immersed with the different
Curcuma essential oils (10 μL). These filter paper discs were placed in different parts of the plates at a distance of 50 mm diameter apart in a plate. These plates were incubated at 37 °C for 24 h and the zone of inhibition was estimated for each bacterial strain [
81].
4.7. Minimum Inhibitory Concentration (MIC) of Essential Oil of Different Curcuma spp.
The MIC value was estimated by the previously described methods [
82,
83,
84]. Briefly, the bacterial inoculum density was maintained to 5 × 10
5 CFU/mL by the spectrophotometry. Further, the 50 μL of inoculum was placed in a 96-well plate and mixed with different concentrations of different
Curcuma essential oils prepared in 0.1% agar. The media was then mixed with 10 μL of 2,3,5-triphenyltetrazolium chloride (TTC), a pink dye, which loses its color in the absence of microbial growth. The lowest concentration without pink color (confirmed with control group using spectrophotometer) was estimated to be the MIC value.
4.8. Statistical Analysis
The values of antioxidant activity, cytotoxicity, and antimicrobial assays were expressed as mean ± standard deviation of six individual analyses, which are carried out in triplicate. The IC50 values were calculated using the Probit analysis method in the GraphPad prism. The statistical analysis was carried out by the analysis of variance using GraphPad prism ver. 7.0 (La Jolla, CA, USA).