Aromatic Profiling and Bioactive Potentials of Thai Edible Flowers from the Curcuma spp. (Zingiberaceae)

Abstract

This study investigated the aroma profiles, nutritional composition, and bioactive potential of three edible Curcuma species, namely Curcuma candida, C. singularis, and C. petiolata, traditionally consumed in Northern Thailand. An aroma analysis revealed distinct volatile profiles for each species. C. petiolata was qualitatively characterized by high sabinene levels, while β-pinene, limonene, caryophyllene, and humulene were prominent markers for C. candida, and C. singularis exhibited the highest abundance of camphor. A nutritional analysis showed the edible floral tissue of C. petiolata to possess the highest carbohydrate (83.47 g/100 g DW), protein (18.04 g/100 g DW), and energy content (342.83 g/100 g DW). The mineral composition of the edible flowers revealed high levels of macronutrients, including phosphorus (0.36 g/100 g DW), potassium (1.82 g/100 g DW), sodium (0.33 g/100 g DW), and calcium (1.30 g/100 g DW). Palmitic acid (31,098 mg/100 g DW) was the predominant saturated fatty acid, while linoleic acid (45,356 mg/100 g DW) was the most abundant unsaturated fatty acid from these edible flora species. The ethanolic extracts of floral tissues of C. singularis exhibited the highest total phenolic content (0.26 mg GAE/g DW), followed by C. petiolata. Conversely, C. petiolata demonstrated the highest total flavonoid content (0.20 mg QE/g sample), followed by C. singularis (0.11 mg QE/g sample). Antioxidant potential exhibited a significant positive correlation with the quantified total flavonoid content. This research contributes to a deeper understanding of the nutritional and bioactive properties of edible Curcuma flowers, providing valuable information for the development of novel functional foods with unique flavor profiles and potential health benefits.

1. Introduction

Neglected or underutilized edible flowers, despite their potential to bolster food security and sustainability, remain marginalized in contemporary agricultural systems. These species often exhibit inherent resilience and elevated nutritional profiles, rendering them critical resources for mitigating food insecurity, especially within vulnerable populations [1]. Furthermore, their distinct organoleptic properties contribute to culinary diversification, satisfying consumer demand for novel food experiences. The revitalization of these species supports biodiversity preservation and can generate economic benefits for rural communities [2]. As scientific investigation into their nutritional and medicinal properties advances and innovative food product development accelerates, the integration of these underutilized species into contemporary diets is anticipated to exhibit sustained growth, presenting a promising avenue for sustainable and nutritionally rich food systems. The genus Curcuma, belonging to the Zingiberaceae family, comprises a diverse array of species with significant cultural and culinary importance in Thailand [3,4,5]. The rhizomes of C. aeruginosa, C. amada, C. aromatica, C. longa, C. pierreana, C. pseudomontana, C. purpurascens, C. xanthorrhiza, and C. zedoaria are widely employed in culinary applications, contributing distinctive aromas, flavors, and colors to various dishes, and are also utilized as sources for dyes and spices. Specifically, Rajkumari and Sanatombi [4] reported that C. angustifolia, C. caulina, C. leucorrhiza, and C. xanthorrhiza are known for their substantial starch content and utilized as nutritional supplements and arrowroot powder substitutes. Apart from the rhizomes, other plant parts, including inflorescences, tuberous roots, and shoots, have been documented as valuable sources for nutritional and medicinal compositions [6,7,8]. These species, and many others within the genus, have been deeply integrated into Thai cuisine and cultural practices, reflecting the nation’s rich botanical heritage and its longstanding relationship with the natural world. Curcuma flowers often hold profound cultural significance, functioning as symbolic decorative elements in traditional ceremonies and celebrations. Within the diverse genus Curcuma, certain species produce edible flowers that offer unique culinary and cultural value [7]. Notably, the vibrant blooms of Ao (C. plicata) are frequently incorporated into salads or side dishes, imparting a distinctive bitter–peppery flavor and adding a striking visual element. The flowers of C. longa are generally also consumed as vegetables in many Asian cultures [9]. Beyond their culinary applications, these flowers possess significant ornamental value, serving as visual embellishments for dishes and enhancing the overall aesthetic appeal of culinary presentations.

The characterization of bioactive aromatic compounds from indigenous edible plants is crucial for developing functional foods and beverages that enhance consumer well-being. The unique aromatic profile of a species serves as a chemical fingerprint, enabling authentication and quality control [3,10,11]. Furthermore, numerous aromatic compounds, including terpenes, exhibit documented bioactivity, such as antioxidant, anti-inflammatory, and anticarcinogenic effects [12,13,14]. Therefore, a comprehensive analysis of these plants’ aromatic profiles is essential for the food industry. Building upon the established importance of aromatic compound characterization in developing functional foods, this research aims to comprehensively analyze the aroma profiles, nutritional composition, and bioactive potential of inflorescences from three underutilized Curcuma species (C. candida, C. singularis, and C. petiolata). By elucidating these properties, we seek to expand the inventory of edible Curcuma flowers, identify novel food sources with enhanced flavor and health benefits, and contribute to food security and dietary diversification. Furthermore, this study will support the preservation of the cultural heritage through the revitalization of traditional culinary practices and foster sustainable economic opportunities via the cultivation and commercialization of these valuable botanical resources.

2. Materials and Methods

2.1. Plant Material and Sample Preparation

The flowers of the three Curcuma species, namely C. candida (Wall.) Techapr. and Škorničk., C. singularis Gagnep. and C. petiolata Roxb., were either from the living collections at Queen Sirikit Botanic Garden (QSBG) or collected locally by our botanists in Chiang Mai, Thailand. Voucher specimens were taxonomically identified by QSBG botanists and verified using the relevant literature [3,15] (Figure 1). These plant specimens were then deposited in the Queen Sirikit Botanic Garden (QBG) herbarium with the following voucher specimen numbers: QBG 89559 for C. candida, QBG 93482 for C. singularis, and QBG 66915 for C. petiolata. For volatile compound analysis, fresh samples were either processed immediately or stored at 4 °C and analyzed within 24 h. A separate petal of the flowers was dried to a constant moisture content (3–5%) using a hot air oven (Memmert, UF 705, Schwabach, Germany) set at 45 °C.

2.2. Analysis of the Chemical Composition of Aroma Compounds

Fresh flowers at different young inflorescences were analyzed to determine their volatile compounds using Solid-Phase Microextraction (SPME) with Restek PAL SPME Polydimethylsiloxane (PDMS) Fibers (Restek, Böckten, Switzerland), similar to a previously published method with some adjustments [16]. Briefly, a small amount of fresh flowers (600 mg) was placed in SPME screw cap vials (1.5 mL). A fiber was inserted to capture the volatile compounds, and the vial was heated in an oven at 40 °C for 10 min. The fiber was then removed and inserted into a gas chromatography–mass spectrometer (GC-MS) (Restek, Bad Homburg, Germany) equipped with an Rtx-5MS capillary column (diphenyl dimethyl polysiloxane, 30 m × 0.25 mm, fused silica 0.25 µm) and (Scion 456-GC, Stanleyweg 4, Rotterdam, The Netherlands) mass spectrometer. The temperatures of the interface, injector, and oven accordingly used a gradient temperature program. Helium (99.999%) was utilized as the carrier gas at a total flow rate of 1 mL/min, using the spitless injection mode. The quadruple mass spectrometer was operated in electron impact ionization (EI) mode at 70 eV, and the scan range was set at 30–550 m/z. The identification of volatile compositions was conducted through comparison with mass spectra available in the NIST 2017 library.

2.3. Nutritional Composition

2.3.1. Proximate Composition

The analysis included measurements of key components like moisture, protein, fat, fiber, and ash [7,17].

The amount of protein in the dried samples was determined using the Kjeldahl method. This method measures the nitrogen content in the sample, which is then converted to protein content using a standard conversion factor of 6.25, following this equation:

Protein% = [(A − B) × N × 1.4 × 6.25]/W

(1)

where A = volume of HCl (0.01 N) used in sample titration;

B = volume of HCl (0.01 N) used in blank titration;

N = normality of HCl;

W = weight of sample (g).

Ash content was specifically determined by incinerating dried samples (1.0 g) at 550 °C for 16 h, dissolving the remaining ash in nitric acid, and filtering the solution through an ash-free, acid-washed filter paper (Albet No. 242, 9 cm diameter). Once cooled, the crucible and ash were weighed to determine the total weight. The ash content was calculated as a percentage of the original sample weight. Total lipid content was determined using the Soxhlet extraction method. Approximately 2 g of the sample was weighed and placed in a thimble. The sample was then defatted with petroleum ether in a Soxhlet apparatus for at least 4 h at high heat, seeing the solvent vaporized, condensed, and dripped back into the sample chamber at the rate 5 drops per second. The remaining ether was evaporated by drying at 80–90 °C for 2 h. The sample was then cooled in a desiccator and weighed. The fat content was calculated using the following formula:

Fat Content (%) = [Weight of fat (g)/Weight of sample (g)] × 100

(2)

Moisture content was determined by drying the sample in an oven at 105 °C until a constant weight was achieved and then reweighing the sample. The difference in weight represented the moisture content. The total carbohydrate content was calculated using the following formula:

Carbohydrate Content (%) = 100 − [Moisture Content (%) + Protein Content (%) + Ash Content (%) + Fat Content (%))

(3)

The total energy per 100 g of fresh weight was calculated according to the following formula:

Total Energy (kcal) = (Protein Content (%) × 4 kcal/g) + (Fat Content (%) × 9 kcal/g) + (Carbohydrate Content (%) × 4 kcal/g)

(4)

2.3.2. Crude Fiber

Crude fiber content was determined according to the method of the Association of Official Analytical Chemists International (AOAC) [18]. A 2 g sample, free of moisture and fat, was treated with boiling dilute sulfuric acid (0.1275 M) for 30 min. This step removes sugars, starches, and some proteins. Then sodium hydroxide (NaOH) (200 mL, 0.313 M) was added and boiled for 30 min, and then the residue was filtered and washed with hot distilled water, 1% HCl, and 95% ethanol, respectively. This removed the additional proteins and some hemicellulose. The residue remaining was filtered, washed, and dried. The dried residue was ashed in a muffle furnace at a high temperature (around 550–600 °C) to remove any remaining organic matter. The weight of the ash-free residue was determined, and the crude fiber content was calculated as a percentage of the original sample weight.

2.3.3. Elements

Concentrated hydrochloric acid (HCl) (2 mL) was added to bring the sample into a solution. The final dilution with deionized water was adjusted based on the predicted concentration of the target element, ensuring it fell within the optimal range of the analytical method. For potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) determinations [19], a 100 mL final volume generally provided sufficient concentrations above the detection limit for most plant tissues. For iron (Fe) analysis, final volumes between 10 and 50 mL were typically required. The elements were determined with an Atomic Absorption Spectrophotometer (AAS) [20]. The digestion of the dried samples was performed with HNO₃:HClO₃ (1:6). Standard preparations for the elements investigation were Na (0.3–3–ppm), K (0–10.0 ppm), Ca (1–10 ppm), Mg (0.1–0.2), and Fe (2–20 ppm).

2.3.4. Free Fatty Acid Compositions

A sample (0.5 g) was weighed into a 250 mL round-bottom flask and 5 mL of 0.5 M sodium hydroxide (NaOH) solution added in methanol. Then, the mixture was refluxed at 110–120 °C for 5 min, followed by the addition of 5 mL of 20% (w/v) boron trifluoride in methanol. The mixture was refluxed again for 5 min. After cooling, the mixture was transferred to a 50 mL test tube, and 5 mL of hexane and 10 mL of saturated salt solution was added. The mixture was shaken vigorously. Finally, the upper hexane layer was collected, filtered through a 0.45 m nylon membrane filter, and injected into the gas chromatography system coupled with an FID detector (436-GC, Bruker-SCION, Stanleyweg 4, Rotterdam, The Netherlands). Chromatograms separation was performed on the SLB^®-IL60 (30 m, 0.25 mmID, 0.2 μm diameters, Sigma-Aldrich, Bellefonte, PA, USA). The column temperature was programmed to increase from 100 °C to 240 °C, initially holding at 100 °C for 0–4 min, then increasing by 1.5 °C/min to 240 °C and remaining so for 30 min. Nitrogen gas was used as the carrier gas, with a flow rate at 1 mL/min. The injector and detector temperature were set at 225 °C and 250 °C, respectively. Samples were injected using the split injection mode (1 µL) [21,22].

2.4. Phytochemical Analyses

2.4.1. Total Phenolic, Flavonoid Content

The extraction method was adapted from previous studies [7,17]. Dried plant samples were powdered and extracted using an ethanol maceration method to obtain the phytochemical extract. Total phenolic content was determined using the Folin–Ciocalteu method, expressed as gallic acid equivalents (mg GAE/g sample), and measured at 765 nm using a microplate spectrophotometer. A gallic acid standard curve (0–120 ppm) was used for quantification [23]. Total flavonoid content was measured and expressed as rutin equivalents (mg RE/g extract) using a quercetin standard curve (0–2000 ppm). Flavonoid content was determined spectrophotometrically at 595 nm using a microplate reader and reported as milligrams of Quercetin equivalents per gram of extracted sample (mg QE/g sample) [24].

2.4.2. Antioxidant Activities

The DPPH (2,2-diphenyl-1-picrylhydrazyl) radical-scavenging activity of the extracts was determined using a microplate assay. Briefly, diluted plant extracts (67 μL) were mixed with 133 μL of a methanolic solution of DPPH (Sigma-Aldrich, Saint Louis, MO, USA). The mixture was incubated in the dark for 30 min at room temperature. Absorbance was measured at 517 nm using a microplate spectrophotometer. The percentage inhibition of DPPH radical was calculated. The IC₅₀ value, representing the extract concentration required to inhibit the DPPH radical by 50%, was determined [25]. The ABTS radical-scavenging activity was assessed using the ABTS⁺ assay. An ABTS⁺ working solution was prepared by reacting ABTS⁺ (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid)) with potassium persulfate. Plant extracts (1.9 μL) were mixed with the ABTS⁺ working solution, and the mixture was incubated in the dark for 5 min. Absorbance was measured at 734 nm using a microplate spectrophotometer. The results were expressed as the Trolox Equivalent Antioxidant Capacity (TEAC) in mg Trolox equivalents per gram of extract (mg TEAC/g sample), determined by comparison with a Trolox standard curve (0–5.0 mM) [26].

2.5. Statistical Analysis

Each experiment was repeated three times, and the results are illustrated as the average value and the standard deviation. In addition, Duncan’s multiple-range test was performed using SPSS statistical software version 17. A p-value of 0.05 was used to determine statistical significance, indicating a 95% confidence level. A principal component analysis was conducted using XLSTAT software version 2018.1 to comprehend the relationships between the volatile compounds and plant species.

3. Results and Discussion

3.1. Plant Utilization

Table 1. Utilization of wild edible Curcuma spp. in Thailand.

No	Collection Numbers	Local Name; Scientific Name	Plant Parts Used	Utilization
1	LC014	Dok din, Curcuma candida	Inflorescences	Young inflorescences are steamed and consumed as a vegetable, commonly paired with chili, stir-fried, or incorporated into spicy soups.
2	LC012	Krachiao khao, Curcuma singularis	Inflorescences	Young inflorescences are steamed and consumed as a vegetable
3	LC017	Queen lily ginger, Curcuma petiolata	Inflorescences	Young inflorescences are occasionally steamed, consumed as a vegetable and seasonal food source

illustrates the utilization summary of C. candida, C. singularis, and C. petiolata. While primarily recognized for their ornamental and medicinal properties, these plants also serve as valuable food sources within specific regional contexts. This study investigates the traditional culinary uses of these species, focusing on their consumption patterns, preparation methods, and cultural significance among local communities in Thailand.

C. candida is a regionally significant economic plant, particularly valued during its blooming season. Its distribution is limited to Thailand and Myanmar [27]. Locally, young inflorescences are prepared as steamed vegetables paired with Nam Prik (chili dip), stir-fried, or added to soups, especially among the Karen and Shan communities in Mae Hong Son province, Northern Thailand [28,29].

The young inflorescence of C. singularis is consumed as a vegetable, commonly served as a side dish with chili paste, particularly in Northeastern Thailand [30,31,32]. This species, a culturally significant terrestrial herb, is predominantly collected from woody areas during the rainy season [33]. It has also been observed to occasionally appear in local markets during this period.

C. petiolata is one of the Curcuma species widely cultivated as an ornamental plant and has long been used as a folk botanical in Asia [34]. Young inflorescences of C. petiolata, similar to other Curcuma species, are consumed as a seasonal food source by local people in the Lom Sak district, Phetchabun province, Thailand (based on field observations con-ducted by the authors in 2022). Harvesting occurs from natural habitats during the early flowering stage, when the inflorescences are tender. Preparation typically involves steaming or boiling, and they are often served as a side dish with condiments. This aligns with traditional consumption patterns within the Curcuma genus.

3.2. Aroma Composition and Profiling

The volatile composition of the edible flowers from the three Curcuma species was investigated. The identified volatile compounds included aldehydes, alcohols, alkanes, terpenes, ketones, and esters, which are presented in Supplementary Table S1. A cluster analysis revealed four distinct groups among the volatile profiles (Figure 2a). The first cluster encompassed the majority of the volatile components. The remaining clusters were differentiated by the presence of specific compounds: sabinene in cluster 2 and camphor in cluster 4. The third cluster was enriched with terpenes, including β-pinene, limonene, humulene, and caryophyllene. A biplot analysis (Figure 2b) explained over 80% of the total variance, with principal components 1 (PC1) and 2 (PC2) contributing 55% and 27%, respectively.

The analysis indicated that C. petiolata was distinct due to its high concentration of sabinene, while β-pinene, limonene, caryophyllene, and humulene were markers for C. candida. C. singularis was characterized by the highest abundance of camphor. The aromatic profiles of the volatile compounds were compared to a commercial aroma database (https://foreverest.net/, accessed on 15 January 2025). β-pinene has a pine-like woody scent, limonene has an orange smell, humulene is associated with basil and spice notes, camphor is commonly found in camphor oil and ginger oil, and caryophyllene has a warm, woody, mossy, spicy, and earthy aroma, characteristic of basil and oregano. Sabinene contributes woody, spicy, citrus, and terpene notes with green, oily, and camphoraceous nuances, typically found in carrot seed oil and black pepper. As illustrated in Figure 2c, C. petiolata exhibited a distinct black pepper aroma, whereas the other Curcuma spp. shared similar characteristics with basil and citrusy notes. Dok din displayed a noticeable camphor scent, while C. singularis was marked by an even stronger camphor aroma.

While research on the volatile composition of Curcuma floral tissues has primarily focused on ornamental and medicinal species such as C. alismatifolia, C. rubescens, C. attenuate, and C. aeruginosa, terpenoids consistently emerge as the dominant volatile organic compound (VOC) group across rhizomes, leaves, and inflorescences within the genus [3,35,36]. In C. alismatifolia, a diverse array of 906 floral VOCs was identified, with caryophyllene, β-pinene, and α-pinene as the most abundant compounds. These volatiles contribute to the perceived sensory characteristics of the flowers, including woody (Wo), sweet (Sw), green (Gr), and fresh (Fr) notes [35,37]. C. longa floral oil exhibits a distinct profile, characterized by significant amounts of 1,8-cineole, α-terpinene, aphellandrene, myrcene, and zingiberene [38,39].

Other Curcuma species display a range of terpenoid constituents, including α-pinene, L-β-pinene, limonene, β-ocimene, eucalyptol, cyclofenchene, β-ionone, and (E)-labda-8(17),12-diene-15,16-dial. Additionally, significant amounts of 4-methoxy-6-phenethyl-2H-pyran-2-on and 5,6-dehydrokavain (19.34%) have been reported [35,36,37]. Given the high abundance of volatiles in the Curcuma floral tissues, essential oil extraction through distillation is feasible, typically yielding around 1% [40]. These findings suggest that floral structures may play a crucial role in the dispersal of botanical fragrances within the Curcuma genus. Furthermore, a degree of similarity has been observed between the volatile profiles of floral tissues and those of the corresponding leafy parts [38]. Previous investigations [39] have identified the essential oil constituents of the C. petiolata rhizome as camphene, (E)-β-elemenone, (E)-β-farnesene, germacrone, 1,8-cineole, and camphor. Notably, sabinene, a prominent aroma compound in the floral tissues, was absent from the rhizome. In contrast, the C. singularis rhizome [40] exhibited a distinct chemical profile, comprising camphor, germacrone, caryophyllene oxide, terpinen-4-ol, and germacrone-4,5-epoxide. This composition demonstrates a degree of similarity to the volatile compounds identified in the floral material examined in our present study.

3.3. Nutritional Composition

3.3.1. Proximate and Mineral Composition

The nutritional composition of the edible flowers from Curcuma spp. is displayed in

Table 2. Nutrition composition of edible flowers from the Curcuma spp.

Nutritional Parameters	Curcuma candida	Curcuma singularis	Curcuma petiolata
Proximate composition (g/100 g DW)
Moisture content	14.62 ± 0.69 b	17.81 ± 0.88 a	12.83 ± 0.66 c
Ash	17.04 ± 0.12 b	14.68 ± 0.16 c	18.27 ± 0.19 a
Fat	5.60 ± 0.07 b	5.36 ± 0.39 c	6.72 ± 0.01 a
Carbohydrate	81.68 ± 0.61 b	77.23 ± 0.06 c	83.47 ± 0.33 a
Fiber	19.64 ± 0.26	19.19 ± 1.14	19.49 ± 0.23
Protein	10.71 ± 0.30 c	12.74 ± 0.19 b	18.04 ± 1.18 a
Total energy	333.26 ± 0.04 b	318.40 ± 1.93 c	342.83 ± 3.66 a
Macro-elements (g/100 g DW)
Phosphorus	0.40 ± 0.00 a	0.28 ± 0.04 c	0.36 ± 0.01 b
Potassium	3.06 ± 0.01 a	2.60 ± 0.03 b	1.82 ± 0.01 c
Sodium	0.46 ± 0.01 b	0.48 ± 0.01 a	0.33 ± 0.00 c
Calcium	2.49 ± 0.00 a	1.01 ± 0.01 c	1.30 ± 0.01 b
Micro-elements (g/100 g DW)
Iron	0.47 ± 0.02 a	0.29 ± 0.00 b	0.22 ± 0.00 c
Magnesium	0.59 ± 0.01 a	0.36 ± 0.00 c	0.41 ± 0.00 b

Values are the mean of the triplicates + SD. Values of each parameter with different superscript letters within the same row are significantly different at p < 0.05.

. C. petiolata was the species with the highest carbohydrate, protein, and energy content at 83.47 g/100 g DW, 18.04 g/100 g DW, and 342.83 kcal/100 g DW, respectively. C. candida had the highest fat and fiber content at 6.80 g/100 g and 19.64 g/100 g, respectively. Generally, carbohydrates proved to be the most abundant macronutrients in floral parts, followed by proteins, with lipids exhibiting the lowest content. Furthermore, the fat content of the edible flowers fell within the typical range, aligning well with the existing literature (0.1 g/100 g to 8 g/100 g) [41,42]. In our previous work, the flower of C. plicata was considerably high in carbohydrate (ca. 30 g/100 g DW) and low in fat (ca. 5 g/100 g DW) as compared to other species of edible flowers within the Zingiberaceae family [7].

C. longa contains 11.80% moisture content, 8.30% ash, 9.40% crude protein, 2.50% crude fibre, 11.00% fat, and 68.80% Nitrogen free extract [43].

The mineral composition of the edible flowers revealed a high amount of macro-elements, including phosphorus, potassium, sodium, and calcium (Table 2). C. candida exhibited the highest content of phosphorus (0.40 g/100 g DW), potassium (3.06 g/100 g DW), and calcium (2.09 g/100 g DW). C. singularis had the highest sodium (0.48 g/100 g DW). The levels of these elements were slightly different to those detected from ornamental edible flowers, including Begonia × tuberhybrida, Tropaeolum majus, Calendula officinalis, Rosa sp., Hemerocallis sp., and Tagetes patula, as reported previously [44]. Their phosphorus and potassium content were in the ranges of 0.2 g/100 g DW and 3.0 g/100 g DW, with a substantial lower content of calcium at 0.3 g/100 g DW. Potassium and sodium help control cell volume, nerve and muscle function, and pH balance [35]. These elements are abundant in edible plants, including their edible floral parts [45]. Calcium, primarily obtained from food sources, including plant-based options, is the fundamental component of bones and teeth. It also plays a vital role in regulating muscle contractions and nerve impulses. Phosphorus, working in tandem with calcium, contributes to a strong bone structure and is essential for the production of ATP, the body’s primary energy source [46,47].

In terms of micro-elements, iron and magnesium were also the highest in C. candida at 0.47 g/100 g DW and 0.59 g/100 g DW, respectively. The levels seem to be a lot higher than those found in Mediterranean edible flowers, including Dianthus chinensis, Fuchsia regia, and Viola cornuta, which reported around 0.0005 g/100 g DW and 0.0006 g/100 g DW of these two elements, respectively. Iron plays an important role in oxygen transport and supporting the immune system, while magnesium supports the muscle and nerves system, bone health, and blood sugar levels [48]. The mineral content of floral herbs is influenced by several factors, including their origin, cultivation conditions, exposure to environmental pollution, and the specific plant parts used. These factors also impact the levels of other plant compounds such as tannins, phytates, oxalates, and dietary fiber. These compounds can form stable, insoluble bonds with minerals, potentially reducing their bioavailability [49].

3.3.2. Free Fatty Acids

The comprehensive fatty acid profile of the edible flowers from the three Curcuma species are presented in

Table 3. Free fatty acid composition of edible flowers from the Curcuma spp.

Free fatty Acid Composition (mg/100 g DW)	Curcuma candida	Curcuma petiolata	Curcuma singularis
Behenic acid	1647.00 ± 106.07	Nd.	Nd.
Linoleic acid	30,323.50 ± 433.46 b	45,356.00 ± 181.02 a	34,953.50 ± 142.13 b
Oleic acid	10,266.50 ± 258.09 a	6851.50 ± 33.23 b	13,217.50 ± 190.21 a
Palmitic acid	42,943.00 ± 219.20 a	31,097.50 ± 96.87 b	32,978.50 ± 54.45 b
Stearic acid	6151.00 ± 8.49 a	3924.00 ± 2.83 c	4446.50 ± 116.67 b
α-Linolenic acid	8669.00 ± 55.15 c	12,770.50 ± 248.19 b	14,404.00 ± 15.56 a

Values are the mean of the triplicates ± SD. Values of each parameter with different superscript letters within the same row are significantly different at p < 0.05. Nd.: Not detected.

. The three species included a total of three unsaturated fatty acids (UFAs) and three saturated fatty acids (SFAs). Linoleic acid was the predominant UFA present in these species, exhibiting the highest content in C. petiolata (45,356.00 mg/100 g DW), followed by C. singularis (34,953.50 mg/100 g DW) and C. candida (30,323.50 mg/100 g DW). Moreover, α-linolenic acid was present in its highest concentration in Krachiao khao (C. singularis) (14,404.00 mg/100 g), following by C. petiolata (12,770.50 mg/100 g DW), and Dok din (C. candida) (8669.00 mg/100 g DW). Oleic acid was predominantly found in C. singularis (13,217.50 mg/100 g), followed by C. candida (10,266.50 mg/100 g DW), and C. petiolata (6851.50 mg/100 g DW). The predominant SFA observed was palmitic acid, which was found in the highest concentration in C. candida (42,943.00 mg/100 g DW), followed by C. singularis (32,978.50 mg/100 g) and C. petiolata (31,097.50 mg/100 g DW). Stearic acid was particularly abundant in C. candida (6151.00 mg/100 g DW), followed by C. singularis (4446.50 mg/100 g DW) and C. petiolata (12,770.50 mg/100 g DW). Nevertheless, C. candida alone exhibited behenic acid at a concentration of 1647.00 mg/100 g DW. Edible flowers generally contain varying amounts of lipids, ranging from low to high, with some reaching up to 30 g/100 g of dried weight. These lipids are notably rich in linoleic (C18:2) and α-linolenic (C18:3) acids, which are essential fatty acids [43]. In line with this, a study has shown that the floral structures of Zingiber mioga Roscoe have been found to be rich in these fatty acids, and the levels also increase through the developmental stages [50]. Linoleic and alpha-linolenic acids are crucial for human health. They play vital roles in growth, development, and the prevention of various diseases, including heart disease, high blood pressure, diabetes, arthritis, and certain cancers [51,52]. Palmitic acid can be obtained from our diet and produced within our bodies. While often linked to chronic diseases in adults, it is essential for forming cell membranes and other vital structures. It also plays a crucial role in protein modification and cell signaling [53].

3.4. Phytochemical Analyses

As reported in

Table 4. Phytochemicals of edible flowers from Curcuma spp.

Phytochemicals	Curcuma candida	Curcuma singularis	Curcuma petiolata
Total phenolics (mg GAE/g DW)	0.06 ± 0.00 c	0.26 ± 0.01 a	0.23 ± 0.02 b
Total flavonoids (mg QE/g DW)	0.09 ± 0.01 c	0.11 ± 0.01 b	0.20 ± 0.03 a
DPPH (mg TEAC/g DW)	3.06 ± 0.01 c	3.34 ± 0.08 b	4.98 ± 0.02 a
DPPH (IC50 mg/g DW)	10.01 ± 0.01 b	10.32 ± 0.09 c	8.80 ± 0.07 a
ABTS+ (mg TEAC/g DW)	0.70 ± 0.02 c	1.47 ± 0.03 b	2.57 ± 0.01 a

Values are the mean of the triplicates ± SD. Values of each parameter with different superscript letters within the same row are significantly different at p < 0.05.

, the inflorescences of C. singularis showed the highest total phenolic value (0.26 mg GAE/g DW), followed by C. petiolate, while the total flavonoid content in the inflorescences of C. petiolata also exhibited the highest value (0.20 mg QE/g sample), followed by C. singularis (0.11 mg QE/g sample). In our previous work, C. plicata illustrated the content of total phenolics at 0.16 mg GAE/g extract and total flavonoids at 15.50 mg Rutin Equivalent (RE)/g extract, which were lower than those found in other species of the Zingiberaceae such as those from Zingiber spp. (ca. 0.2 mg GAE/g extract and ca. 20 mg RE/g extract [8]. Meanwhile, the rhizomes of C. aeruginosa, C. amada, C. aromatica, C. candida, C. latifolia, C. longa, and C. mangga exhibited total phenol levels ranging from 0.94 to 587.15 mg GAE/g extract. Notably, the ethanol extract of C. longa demonstrated the highest levels of total phenols [54]. Phenolic compounds, including flavonoids, are naturally occurring plant constituents. Flavonoids are a subclass of polyphenols known for their health-promoting properties, particularly their ability to counteract free radicals and reactive oxygen species (ROS). This antioxidant activity contributes to various biological effects, such as anti-inflammatory, anti-aging, anti-atherosclerotic, and anticancer properties [55,56]. Moreover, flavonoids help reduce the risk of neurodegenerative disorder and heart diseases and possess antioxidant and anti-cancer properties [57,58].

It is important to acknowledge that the phytochemical profiles observed in this study may exhibit variability due to factors such as a limited population size and inherent intraspecific diversity. The phytochemical properties of Curcuma species are intricately influenced by a complex interplay of genetic and environmental factors [59,60,61]. Genetic variations within and between species govern the enzymes involved in secondary metabolite biosynthesis, ultimately determining the types and quantities of phytochemicals produced [62,63]. Environmental factors, such as light intensity, temperature, and soil composition, can significantly influence gene expression and metabolic pathways, thereby impacting the accumulation of phytochemicals [64,65]. This is supported by the findings from a previous study on turmeric cultivars, where significant genotypic variations were observed for various morpho-physiological traits, highlighting the role of genetic inheritance [64]. Furthermore, studies have demonstrated that genotypes collected from the same source can exhibit significant variability, suggesting that geographical distribution alone may not accurately predict homogeneity within a species [66,67]. Considering these factors, our findings provide a valuable baseline for future investigations. Future research incorporating a broader sampling of diverse populations within each Curcuma species is crucial to comprehensively investigate the extent of intraspecific variation in aromatic profiles, nutritional composition, and phytochemical properties. Moreover, due to the phenolics, flavonoids, antioxidants, and other beneficial properties of edible flowers, there have been numerous efforts to utilize them for purposes beyond their traditional use as vegetables or side dishes, such as in cakes, teas, jams, salads, and beverages [17,41].

4. Conclusions

This study comprehensively characterized the aroma profiles, nutritional composition, and bioactive potential of three underutilized edible Curcuma species, namely C. candida, C. singularis, and C. petiolata. Our findings reveal distinct chemical profiles for each species, with C. petiolata notable for its high sabinene content and C. singularis characterized by a prominent camphor aroma. Furthermore, the nutritional analysis demonstrated that C. petiolata is a rich source of carbohydrates, protein, and energy, while all three species exhibited significant levels of essential minerals. The presence of diverse bioactive compounds, particularly high levels of phenolics in C. singularis and flavonoids in C. petiolata, coupled with strong antioxidant activity, suggests that these Curcuma species possess considerable health-promoting potential. These findings contribute valuable knowledge to the scientific understanding of edible Curcuma species and highlight their potential as promising sources of natural bioactive compounds for the development of novel functional foods and nutraceuticals. Future research should investigate the underlying mechanisms of action of these bioactive compounds and explore their potential applications in various health contexts.