Trends
Sci.
2025; 22(9):
10316
Optimization of Eco-Friendly Mordant-Assisted Extraction and Stability of Natural Pigments from Six Plant Species for Pressed Paint Development
Nongnuch Klinpikul1, Somchye Dittapohn1,
Wongnapa Nakyai3 and Wannisa Keawbankrud2,*
1Division of Industrial Product Design, Department of Science, Faculty of Science and Technology,
Rajamangala University of Technology Krungthep, Bangkok 10120, Thailand
2Health Science and Aesthetic Program, Department of Science, Faculty of Science and Technology,
Rajamangala University of Technology Krungthep, Bangkok 10120, Thailand
3Faculty of Integrative Medicine, Rajamangala University of Technology Thanyaburi,
Pathum Thani 12130, Thailand
(*Corresponding author’s e-mail: [email protected])
Received: 6 April 2025, Revised: 20 April 2025, Accepted: 1 May 2025, Published: 5 July 2025
Abstract
This study aimed to optimize the decoction extraction efficiency of natural pigments from 6 plant species-Clitoria ternatea L., Scleropyrum pentandrum, Vitex pinnata L., Oroxylum indicum L., Xylia xylocarpa, and Careya sphaerica-by systematically varying extraction temperature (60 and 80 °C), time (30 - 90 min), and extraction conditions (normal and mordant-assisted). The main objective was to improve pigment yield and stability for potential use in sustainable natural dye and colorant applications. Results indicated that higher extraction temperatures (80 °C) and extended extraction times (90 min) significantly increased pigment yields, with Clitoria ternatea L. achieving the highest yield (12.92 % ± 0.03) under standard conditions. In contrast, the condition at 60 °C has a % yield of 11.47 ± 0.02. Mordant-assisted extractions increased overall yields (3.16 - 4.57 %) but required careful parameter optimization to avoid degradation of thermolabile compounds. UV-vis spectroscopy revealed that both extraction conditions and sodium chloride addition as a mordant significantly enhanced pigment absorption, particularly in Oroxylum indicum L., which showed optimal light absorption at 60 °C for 60 min (4.16 ± 0.09). Cytotoxicity assays demonstrated that most extracts exhibited minimal toxicity at low concentrations (< 0.1 mg/mL), with Oroxylum indicum L. showing the highest cell viability (95.65 ± 1.32 %). Pressed paint products formulated with sodium chloride-mordanted pigments displayed good stability under various conditions. The optimal extraction conditions identified in this experiment are as follows: the best temperature is 80 °C, the optimal extraction time is 90 min, and the use of a mordant is necessary for all plant species tested. Among the plants studied, Clitoria ternatea L. yielded the most intense color with a dark blue shade and the lowest L* value (38.14), indicating the highest color intensity under these conditions.
Keywords: Decoction extraction, Natural pigments, Mordant, Sodium chloride, Cytotoxicity, Pressed paint products
Introduction
Humanity has long utilized natural materials to dye fibers and fabrics for clothing and daily use. Natural pigments, valued for their color and potential health benefits, are increasingly applied across industries such as food, pharmacology, toxicology, textiles, printing, dairy, and fisheries due to their cost-effectiveness and environmental advantages [1]. To promote sustainability and affordability, research should focus on developing pigments that are easy to use, non-toxic, eco-friendly, inexpensive, and biodegradable [2]. Natural dyes are classified by source into mineral dyes-derived from metal compounds like copper, iron, and chromium, historically significant but now less used; animal dyes-obtained from insect secretions or marine animals [3], such as lac in Thailand for bright red hues; and plant dyes, the primary category, which produce a wide spectrum of colors. Plant-based reds come from sources like madder root and sappanwood; yellows from turmeric and ginger rhizomes [4]; browns from various lamduan barks [5]; blues from indigo leaves; and blacks from fruits like Malabar nut, reflecting a rich diversity of natural colorants traditionally employed in Thai culture and beyond.
Additionally, there are 6 types of plants that provide interesting colors, including Clitoria ternatea L., Scleropyrum pentandrum, Vitex pinnata L., Oroxylum indicum L., Xylia xylocarpa, and Careya sphaerica were selected for dye extraction because they are locally available, possess high pigment content and bioactive compounds, and have demonstrated potential for producing natural dyes with good color properties and additional benefits such as antimicrobial or anti-inflammatory activity, making them suitable and sustainable sources for natural dyeing [6-8]. In terms of natural pigment extraction from plants is crucial for various industries, including textiles, food, cosmetics, and pharmaceuticals. Traditional methods include decoction, maceration, infusion, and Soxhlet extraction, while modern techniques like microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE) are used. Decoction involves boiling plant materials, particularly roots, barks, and seeds, to extract water-soluble and heat-stable compounds. It is effective for extracting fibrous plant materials and produces concentrated extracts with higher potency [9]. Dyeing methods are typically classified into cold dyeing, which uses natural plant materials, and hot dyeing, which involves heating plant matter [10]. To improve dye adherence and color brightness, chemical mordants-mainly metal salts such as alum [11,12], copper, and iron-are commonly added [13,14]. Alum enhances reds and yellows, copper deepens greens and browns, and iron darkens shades or alters colors. These mordants form coordination complexes with both dye and fiber, stabilizing the color and improving fastness. For example, aluminum ions bond with hydroxyl or carboxyl groups on fibers and dyes, while copper ions coordinate with amino or hydroxyl groups, especially in protein-based or cellulose fibers. Although commercial mordants are effective, overuse can leave residues and damage fibers, particularly with iron. Natural mordants-including lime water, lye, plant acids, and rust water-can also fix and sometimes darken colors, offering a more environmentally friendly alternative. Salt has been shown to act as a natural mordant, enhancing color intensity, especially in eco-printing [15]. Because most natural dyes do not naturally adhere well to fibers, especially cellulose [16], mordants are essential for bridging dye molecules to fibers [17], creating a range of colors and improving colorfastness [18]. Recent research focuses on natural mordants to address environmental concerns associated with heavy metal mordants [19-22].
The research team selected 6 local Thai plants-Clitoria ternatea L., Scleropyrum pentandrum, Vitex pinnata L., Oroxylum indicum L., Xylia xylocarpa, and Careya sphaerica-for their natural pigments and traditional use in earth-tone dyeing. Each plant contributes distinct hues: Clitoria ternatea L. yields deep blues and purples, Scleropyrum pentandrum provides greenish-olive tones, Vitex pinnata L. offers yellow to brown shades, Oroxylum indicum L. and Xylia xylocarpa supply rich browns, and Careya sphaerica produces yellow to brown pigments. These plants were chosen for their sustainability, non-toxicity, local availability, and cultural relevance in Thai textile crafts. Dye extraction uses the decoction method, varying temperature, time, and mordant type, followed by testing for color properties and toxicity. Optimal conditions are then used to develop pressed paint products for art and potential industrial applications.
Materials and methods
Materials and equipment
The plant-using test includes Clitoria ternatea L., Scleropyrum pentandrum, Vitex pinnata L., Oroxylum indicum L., Xylia xylocarpa, and Careya sphaerica purchased from Thai herb commercials in Thailand. The materials purchased from sChemipan, Thailand, include sodium chloride, magnesium stearate, silicon dioxide, phenoxyethanol (and) chlorphenesin (and) glycerin, and cornstarch. The toxicity test used sodium lauryl sulfate (SLS) was a standard substance, which involved human skin fibroblast cells from passage 66, and the cell culture medium was Dulbecco’s modified Eagle medium (DMEM) with 10 % fetal bovine serum (FBS) and 1 % penicillin/streptomycin. The equipment used in the experiment included the extraction using a magnetic hotplate stirrer (IKA, C-MAG HS7, Germany), evaporation using a rotary evaporator (BUCHI, R-300, Switzerland), the toxicity test using equipment including a microplate reader (BMG Labtech, SPECTROstar Nano, Germany) and Laminar Flow Cabinet (Thermo Scientific, HERA Guard Eco 1.2, Germany).
Extraction of color from plants
The extraction of natural colorants from 6 plant sources-Clitoria ternatea L. (flower), Scleropyrum pentandrum (heartwood), Vitex pinnata L. (heartwood), Oroxylum indicum L. (bark), Xylia xylocarpa (bark), and Careya sphaerica (bark)-involves a systematic process of washing, oven-drying at 50 °C for 48 h [23], size reduction, and decoction extraction under varied temperature-time parameters (60 - 80 °C for 30 - 90 min) as shown in Table 1. The extraction process concludes with filtration through Whatman No. 1 paper and concentration via rotary evaporation, with experiments conducted in triplicate for statistical validity. Research indicates decoction is superior for antioxidant extraction compared to methods such as maceration and sonication, with extraction efficiency significantly influenced by temperature and duration parameters [24]. Studies demonstrate that optimal extraction conditions vary by plant material, with 44 °C for 93 min maximizing anthocyanin yield, while heat-sensitive plants benefit from temperatures of 60 - 80 °C for 90 - 120 min [25]. Additionally, mordants-particularly NaCl at concentrations of 10 % w/v-play a crucial role in enhancing color fastness, depth, and brightness when applied to cotton fabrics, either independently or in combination with metal mordants such as CuSO4 and FeSO4 Various extraction parameters directly affect pigment yield and color characteristics, as evidenced in studies of black tea waste extraction at 80 °C across different time intervals [26,27].
Table 1 Extraction conditions for 6 plant types using decoction: Temperature, time, and parameter variations.
Condition |
Temperature (°C) |
Time (min) |
Parameter |
1 |
60 |
30 |
Normal |
2 |
60 |
60 |
Normal |
3 |
60 |
90 |
Normal |
4 |
80 |
30 |
Normal |
5 |
80 |
60 |
Normal |
6 |
80 |
90 |
Normal |
7 |
60 |
30 |
Mordant (10 % w/w NaCl) |
8 |
60 |
60 |
Mordant (10 % w/w NaCl) |
9 |
60 |
90 |
Mordant (10 % w/w NaCl) |
10 |
80 |
30 |
Mordant (10 % w/w NaCl) |
11 |
80 |
60 |
Mordant (10 % w/w NaCl) |
12 |
80 |
90 |
Mordant (10 % w/w NaCl) |
Light absorption measurement using UV-Visible spectroscopy method
The experiment involved scanning the solutions of six types of plants, including Clitoria ternatea L., Scleropyrum pentandrum, Vitex pinnata L., Oroxylum indicum L., Xylia xylocarpa, and Careya sphaerica, to find the wavelength that absorbs the maximum light (λmax) using a UV spectrophotometer (JASCO, V-730, Japan) in the wavelength range of 200 - 1,000 nm. Once the maximum light wavelength (λmax) for each type of plant was obtained, the amount of light absorbed was measured, compared, and recorded. Previous research determined λmax by scanning the wavelength range, starting from preparing the sample solution and then scanning the absorbance in the predicted wavelength range (200 - 1,000 nm) to find the λmax that gives the highest absorbance [28].
Color measurement method
The color measurement protocol employs a Hunter LAB Miniscan XE plus colorimeter (USA) to analyze plant extract color values under various conditions. Prior to each measurement, the device is calibrated using a standard white plate (L* = 92.65, a* = −0.82, b* = 1.31) to ensure accuracy. Color assessment utilizes the CIE Lab* system, which measures color through 3 dimensions: L* (lightness), a* (red-green spectrum), and b* (yellow-blue spectrum), under standardized D65 Observer 10 ° lighting conditions (6,500 K daylight, 10 ° viewing angle). Each measurement is conducted in triplicate to minimize variability and enhance result reliability, with values recorded after completion.
Pressed paint product method
The pressed paint product development process involves selecting optimal plant-specific conditions using ingredients shown in Table 2. The production begins by thoroughly mixing Phase A ingredients before incorporating Phase B until well combined. The combined mixture is then prepared for molding by weighing 10 g of pigment powder into a 54 mm pan. Finally, the product is formed using a mold machine operating at 150 bars of pressure to create the finished pressed paint product.
Table 2 The formulation of pressed paint product.
Phase |
Ingredient |
% w/w |
Function |
A |
Extract of plant |
23 |
Coloring agent |
A |
Silicon dioxide |
3 |
Absorbent agent |
B |
Magnesium stearate |
8 |
Binder |
B |
Corn starch |
65 |
Texture |
B |
Phenoxyethanol (and) chlorphenesin (and) glycerin |
1 |
Preservative |
Drop test
The drop test was conducted to evaluate the durability of the pressed paint product. In this test, a 10 g pan was dropped from 3 different heights: 5, 10 and 15 cm [29]. Each test was repeated ten times, and the results were recorded.
Stability test
The stability of the pressed paint product was evaluated under various conditions, including storage without sunlight exposure and exposure to sunlight combined with heating-cooling cycles (45 - 4 °C) for 6 cycles [30]. The samples were assessed visually at both 0 and 28 days, and color differences (∆E) were quantified using a colorimeter based on CIE L*, a*, and b* values immediately after preparation and after 28 days.
Toxicity test
The pressed paint product and sodium lauryl sulfate were dissolved and prepared for testing in cell culture medium. The sample was sterilized by filtering through a membrane with a pore size of 0.2 microns. The test sample solution was then diluted to the desired concentration using sterilized cell culture medium. Subsequently, the cytotoxicity of the sample was evaluated using the sulforhodamine B (SRB) staining method. The results are expressed as the percentage of cell survival relative to the control group, with values presented as mean ± standard deviation (S.D.) based on 4 independent experiments [31,32].
Statistical analysis
The statistical analysis for this experiment included calculating the percentage yield of extract and the maximum average absorbance values (λMax) under both normal and mordant conditions. To compare means among sample groups, one-way ANOVA was performed, followed by Scheffé’s post hoc test for multiple comparisons. Additionally, comparisons of λMax between normal and mordant conditions were conducted using the Independent-Samples T-Test, and correlations were assessed using Pearson’s correlation coefficient. All analyses were carried out using SPSS version 13, with statistical significance set at 0.05.
Results and discussion
The study evaluated crude extract yields from 6 plant species (Clitoria ternatea L., Scleroptyrum pentandrum, Vitex pinnata L., Oroxylum indicum L., Xylia xylocarpa, and Careya sphaerica) under different extraction conditions, including temperatures of 60 and 80 °C, extraction times of 30 - 90 min, and both standard and mordant-assisted methods. Extraction yields generally ranged from 9 to 13 % under standard conditions as shown in Figure 1. Notably, increasing the temperature to 80 °C and extending the extraction time to 90 min significantly improved yields for most species [33]. Clitoria ternatea L. achieved the highest yield (12.92 % ± 0.03), likely due to its distinctive cellular structure and high concentrations of water-soluble phytochemicals such as anthocyanins and phenolics. Higher temperatures increase cell wall permeability in this species, enhancing solvent penetration and extraction efficiency. These findings are consistent with previous studies, which report that Clitoria ternatea L. reliably outperforms other plants in extraction yield due to its unique cellular composition and favorable response to thermal processing [34,35], as summarized in Tables 3 and 4. Mordant-assisted extractions produced notably inferior results (3.16 - 4.57 %) regardless of species or parameters, while temperature significantly enhanced extraction efficiency. This improvement stems from increased cell wall permeability and reduces solvent viscosity at higher temperatures [36], confirming temperature’s critical role in affecting compound solubility and enhancing mass transfer rates during extraction. However, excessive heat may degrade thermolabile compounds, necessitating careful temperature regulation to balance efficiency and stability [37,38]. Plant species demonstrated significant increases in response variables (p < 0.05) at 60 °C, while all experimental conditions showed statistically significant increases (p < 0.05) at 80 °C. Extended extraction periods facilitate improved solute diffusion and optimize mass transfer between plant material and solvent, with research consistently showing positive correlations between extraction duration and yield, particularly when using polar solvents like ethanol or water. Nevertheless, while longer durations typically increase yields, they risk degrading bioactive compounds due to heat or enzymatic activity, highlighting the necessity of balancing extraction parameters to maximize efficiency while preserving compound integrity [39-41]. The extraction method critically influences both yield and quality, impacting industrial and research applications [42,43]. For Clitoria ternatea L., optimal extraction was achieved at 80 °C for 90 min under atmospheric pressure, yielding 12.92 %, consistent with previous studies. Comparatively, polyphenol extraction from rambutan peel at 60 °C for 34 min yielded 28.68 % [44]. The higher yield from Clitoria ternatea L. at 80 °C is attributed to improved solute solubility, enhanced mass transfer [45], and reduced solvent viscosity, which together promote cell wall disruption and greater release of intracellular compounds [46]. Increasing the extraction temperature from 60 to 80 °C for 90 min led to a 12.64 % increase in yield. The optimized conditions balance extraction efficiency and anthocyanin stability, reflecting patterns seen in other anthocyanin-rich species such as Oryza sativa L. Thus, extraction at 80 °C for 90 min maximizes yield while preserving compound integrity [47-49].
Table 3 The comparison of the percentage yield of extract under normal conditions.
Plant Species |
Normal Parameter % Yield (Mean) ± (S.D.) |
|||||
Temp. 60 °C |
Temp. 80 °C |
|||||
30 min |
60 min |
90 min |
30 min |
60 min |
90 min |
|
Clitoria ternatea L. |
11.38 ± 0.01b |
11.29 ± 0.01c |
11.47 ± 0.02a |
11.79 ± 0.02b |
11.37 ± 0.01c |
12.92 ± 0.03a |
Scleropyrum pentandrum |
9.37 ± 0.04c |
9.42 ± 0.03b |
9.58 ± 0.05a |
9.26 ± 0.05c |
9.46 ± 0.09b |
9.76 ± 0.05a |
Vitex pinnata L. |
9.37 ± 0.03c |
10.15 ± 0.04a |
9.79 ± 0.03b |
9.88 ± 0.06b |
9.16 ± 0.01c |
10.80 ± 0.04a |
Oroxylum indicum L. |
10.81 ± 0.09a |
9.37 ± 0.03c |
10.54 ± 0.06b |
10.12 ± 0.07c |
10.25 ± 0.03b |
11.12 ± 0.06a |
Xylia xylocarpa |
10.81 ± 0.01b |
10.80 ± 0.02b |
11.13 ± 0.02a |
10.81 ± 0.02b |
10.48 ± 0.01c |
11.48 ± 0.02a |
Careya sphaerica |
10.12 ± 0.01a |
9.72 ± 0.03b |
10.02 ± 0.01a |
9.40 ± 0.01b |
9.35 ± 0.01c |
10.14 ± 0.01a |
Note: Values in the same row with the same uppercase letter are not significantly different (p > 0.05).
Table 4 The comparison of the percentage yield of extract under conditions mordant (NaCl, 10 % w/w).
Plant Species |
Mordant Parameter % Yield (Mean) ± S.D. |
|||||
Temp. 60 °C |
Temp. 80 °C |
|||||
30 min |
60 min |
90 min |
30 min |
60 min |
90 min |
|
Clitoria ternatea L. |
3.90 ± 0.01b |
3.95 ± 0.01a |
3.85 ± 0.01c |
4.18 ± 0.02c |
4.57 ± 0.01a |
4.36 ± 0.01b |
Scleropyrum pentandrum |
3.29 ± 0.03a |
3.22 ± 0.04b |
3.16 ± 0.04c |
3.18 ± 0.03a |
3.19 ± 0.01a |
3.48 ± 0.03a |
Vitex pinnata L. |
3.61 ± 0.01a |
3.47 ± 0.01b |
3.41 ± 0.01c |
3.72 ± 0.03a |
3.49 ± 0.01b |
3.73 ± 0.01a |
Oroxylum indicum L. |
3.61 ± 0.01b |
4.14 ± 0.01a |
3.61 ± 0.02b |
3.98 ± 0.01c |
4.07 ± 0.02b |
4.30 ± 0.02a |
Xylia xylocarpa |
3.91 ± 0.01b |
4.04 ± 0.01a |
3.79 ± 0.01c |
3.24 ± 0.01c |
3.85 ± 0.01b |
4.25 ± 0.01a |
Careya sphaerica |
3.84 ± 0.02a |
3.48 ± 0.01b |
3.36 ± 0.01c |
3.59 ± 0.01c |
3.84 ± 0.01b |
4.04 ± 0.01a |
Note: Different letters (a, b and c) in the sam raw indicated significant differences (p < 0.05)
Figure 1 The comparison of the percentage yield of extract under mordant conditions at during times. Different letters (a, b and c) above the bars within the same plant species indicate significant differences (p < 0.05). Values with the same letter are not significantly different.
Absorption of plants using UV-Visible spectroscopy method
The study demonstrated that temperature, duration, and sodium chloride addition significantly influenced light absorption in plant pigment extracts using UV-Vis spectroscopy. Increasing temperature from 60 to 80 °C enhanced absorption due to improved pigment solubility and cell wall disruption. Extended extraction duration (9 min) increased absorption values, likely from prolonged solvent-pigment interaction. Sodium chloride improved absorption by facilitating pigment release through ionic disruption of plant matrices, consistent across all species. Maximum absorption bands ranged between 444.80 - 490.20 nm, aligning with chlorophyll and carotenoid absorbance profiles [50-52]. However, when examining specific extraction conditions, Oroxyium indicum L exhibited the highest absorption yield of 4.16 ± 0.09 at 60 °C for 60 min., suggesting this combination provides optimal extraction efficiency for this species. The optimum condition yielding the highest absorption was observed for Oroxyium indicum L at 60 °C for 60 min (4.16 ± 0.09). This can be attributed to the specific thermostability profile of the bioactive compounds in this species. At 60 °C, cell wall disruption occurs efficiently, facilitating the release of intracellular compounds, while avoiding thermal degradation that becomes evident at higher temperatures (80 °C) or with prolonged extraction times (90 min). The plant contains significant amounts of polyphenols and flavonoids that exhibit peak extraction efficiency within this thermal range. Additionally, recent research suggests that medium-polarity compounds found in Oroxylum indicum L. require moderate heat treatment for optimal solubilization, as they balance between requiring sufficient thermal energy for extraction while maintaining structural integrity of heat-sensitive bioactive molecules [53]. This research examined the maximum average absorbance values of crude extracts from 6 plant species under normal conditions and with mordant addition (sodium chloride 10 % w/w). The results demonstrated that Careya sphaerica exhibited the highest absorbance values in all conditions, followed by Clitoria ternatea L. The optimal extraction condition for most plants was 60 °C for 60 -90 min. under normal conditions, while all plants showed optimal results at 60 °C for 60 min. when mordant was added. The addition of mordant significantly enhanced absorbance values across all plant extracts, with increases of 25 - 40 % compared to normal conditions. These findings align with recent research suggesting that mordant application improves dye fixation and color intensity while maintaining eco-friendly dyeing processes, making these plant extracts promising candidates for sustainable natural dyeing applications in the textile industry [54-60]. The absorption spectrum of plants, as shown in the provided figure, highlights the efficiency of chlorophyll pigments in capturing light for photosynthesis. Chlorophyll-a and chlorophyll-b exhibit peak absorption in the blue (400 - 500) and red (600 -700 nm) regions, while green light (500 -600 nm) is less absorbed, leading to the characteristic green appearance of leaves [61,62]. Analysis of data comparing the absorbance of the mordant parameter and the absorbance of the normal parameter between temperatures of 60 and 80 °C at different times (30, 60 and 90 min) found that the group with significant differences (p < 0.05) is Xylia xylocarpa at 60 min (F-test = 95.61, p-value = 0.0103).
Table 5 The comparison of the maximum average absorbance values (λMax) of extract under normal conditions.
Plant Species |
λMax |
Absorbance of normal parameter (Mean ± S.D.) |
|||||
Temp. 60 °C |
Temp. 80 °C |
||||||
30 min |
60 min |
90 min |
30 min |
60 min |
90 min |
||
Clitoria ternatea L. |
657.30 |
2.82 ± 0.01 c |
3.18 ± 0.01b |
3.22 ± 0.01 a |
2.90 ± 0.01 c |
3.20 ± 0.01 b |
3.22 ± 0.02 a |
Scleropyrum pentandrum |
403.50 |
0.57 ± 0.01 c |
1.07 ± 0.01 b |
1.28 ± 0.01 a |
0.83 ± 0.01 c |
1.18 ± 0.01 b |
2.23 ± 0.01 a |
Vitex pinnata L. |
468.80 |
0.55 ± 0.01 c |
0.90 ± 0.01 b |
1.39 ± 0.01 a |
0.60 ± 0.01 c |
1.48 ± 0.01 b |
3.09 ± 0.01 a |
Oroxylum indicum L. |
400.10 |
3.38 ± 0.03 c |
4.16 ± 0.49 b |
4.32 ± 0.58 a |
2.38 ± 0.01 c |
3.50 ± 0.06 b |
3.75 ± 0.16 a |
Xylia xylocarpa |
357.10 |
0.97 ± 0.01 c |
1.77 ± 0.01 b |
2.54 ± 0.01 a |
1.79 ± 0.01 c |
2.26 ± 0.01 b |
2.79 ± 0.01 a |
Careya sphaerica |
455.10 |
1.03 ± 0.01 c |
1.07 ± 0.01 b |
1.69 ± 0.01 a |
1.99 ± 0.01 c |
2.12 ± 0.01 b |
2.71 ± 0.01 a |
Note: The values are significantly different (p < 0.05).
Table 6 The comparison of the maximum average absorbance values (λMax) of extract under mordant conditions (NaCl, 10 % w/w).
Plant Species |
λMax |
Absorbance of mordant parameter Mean ± S.D. |
|||||
Temp. 60 °C |
Temp. 80 °C |
||||||
30 min |
60 min |
90 min |
30 min |
60 min |
90 min |
||
Clitoria ternatea L. |
658.80 |
3.80 ± 0.01 c |
4.22 ± 0.06 b |
4.52 ± 0.63 a |
3.98 ± 0.01 c |
4.48 ± 0.01 b |
4.91 ± 0.04 a |
Scleropyrum pentandrum |
448.20 |
1.13 ± 0.11 c |
1.56 ± 0.01 b |
2.59 ± 0.21 a |
2.40 ± 0.01 c |
2.55 ± 0.06 b |
3.25 ± 0.01 a |
Vitex pinnata L. |
471.60 |
1.37 ± 0.01 c |
2.09 ± 0.01 b |
2.71 ± 0.01 a |
1.92 ± 0.06 c |
2.32 ± 0.23 b |
2.88 ± 0.06 a |
Oroxylum indicum L. |
450.20 |
3.87 ± 0.03 c |
4.64 ± 0.04 b |
4.70 ± 0.19 a |
3.69 ± 0.07 c |
3.93 ± 0.57 b |
4.20 ± 0.01 a |
Xylia xylocarpa |
470.30 |
1.34 ± 0.06 c |
1.78 ± 0.01 b |
3.57 ± 0.03 a |
2.15 ± 0.01 c |
2.37 ± 0.12 b |
3.46 ± 0.01 a |
Careya sphaerica |
490.10 |
1.97 ± 0.01 c |
2.51 ± 0.01 b |
3.41 ± 0.01 a |
2.45 ± 0.01 c |
3.27 ± 0.01 b |
3.36 ± 0.01 a |
Note: The values are significantly different (p < 0.05).
The results in Tables 5 - 6 indicate that the absorbance values (λMax) of plant extracts vary significantly under normal and mordant conditions, influenced by temperature, time, and the presence of NaCl (10 % w/w). Under normal conditions, Oroxylum indicum L. exhibited the highest absorbance at 80 °C after 90 min (3.75 ± 0.16), while Clitoria ternatea L. also showed high stability across conditions. In mordant conditions, absorbance values increased overall, with Oroxylum indicum L. and Clitoria ternatea L. achieving the highest values at 80 °C after 90 min (4.20 ± 0.01 and 4.91 ± 0.04, respectively). The primary mechanism for enhancing dye adsorption and color fastness involves the formation of complex compounds between mordants and dye molecules. Metal ions in mordants interact with the dye’s electron system, reducing overall energy and altering light absorption properties [63]. Elevated temperatures improve dye adsorption by increasing dye exhaustion, with color strength peaking at 70 °C [64]. Extended durations (30, 60 and 90 min) further enhance adsorption, as shown in absorption spectra, due to improved penetration and more complete complex formation. This synergy of temperature and time ensures greater dye stability and durability, as prolonged exposure allows deeper molecular interactions and robust complexation between dyes and mordants. The comparison of maximum absorption wavelengths (λMax) between normal and mordant conditions shows that the mordant condition has a higher absorbance value because it is darker in color in all samples, as shown in Figure 2.
Figure 2 Comparison of λMax absorption spectra under normal and mordant conditions. The absorbance spectra for each extract are as follows: (a) Clitoria ternatea L., (b) Scleropyrum pentandrum, (c) Vitex pinnata L., (d) Oroxylum indicum L., (e) Xylia xylocarpa, and (f) Careya sphaerica.
The statistical analysis comparing λMax values between normal and mordant conditions for 6 plant species revealed no significant differences, as indicated by p-values greater than 0.05 for all species. Pearson correlation coefficients varied widely, ranging from strong negative to strong positive values, but none reached statistical significance. This suggests that the use of mordant does not significantly alter the λMax of the plant extracts studied, and the relationship between normal and mordant conditions is inconsistent across different species. Overall, the findings indicate that mordant treatment does not have a significant impact on the λMax parameter in these plant species, as shown in Table 7.
This study used UV-Vis spectroscopy to analyze light absorption in plant-derived dyes under different temperatures, extraction times, and sodium chloride (NaCl) concentrations. The results showed that increasing the temperature to 80 °C and extending the extraction time to 90 min boosted light absorption by 50 - 1.5 times. Adding 10 % w/v NaCl increased absorbance values by 25 - 40 %, along with improved color intensity and dye stability. Oryza sativa L. showed a peak absorbance of 4.91 ± 0.04 under optimal conditions, while Careya sphaerica reached 3.36 ± 0.01, indicating efficient extraction of chlorophyll and carotenoid pigments. The maximum absorbance between 400 - 490 nm corresponded to anthocyanin and carotenoid spectra, responsible for red-orange-yellow hues. NaCl functioned as an effective mordant by promoting ionic interactions [65], which strengthened dye-fiber binding and colorfastness.
These findings highlight the importance of optimizing extraction parameters to achieve high dye performance and pigment stability. Sodium chloride facilitated extraction through 2 main mechanisms. First, chloride ions (Cl⁻) disrupted cell wall structures, releasing pigments trapped in vacuoles and chloroplasts [65,66]. Second, sodium ions (Na⁺) formed bonds with negatively charged pigments, improving stability and preventing aggregation during extraction. This approach ensured efficient pigment recovery while maintaining the structural integrity of the dye.
Comparison with previous studies confirmed that NaCl can help maintain color stability under acidic conditions. It was also found that increasing the temperature above 80 °C or extending the extraction time beyond 90 min could lead to pigment degradation, as indicated by the high standard deviation (S.D.) found in Oroxylum indicum L. (4.32 ± 0.58). This instability may be due to the presence of heat-sensitive compounds in these plant species
Table 7 The analysis of statistical comparison between λMax normal and mordant parameter.
Plant Species |
λMax |
Statistical comparison between λMax mordant and normal parameter |
||
Normal |
Mordant |
Pearson Correlation |
p-value |
|
Clitoria ternatea L. |
657.30 |
658.80 |
−0.327 |
0.788 |
Scleropyrum pentandrum |
403.50 |
448.20 |
−0.961 |
0.179 |
Vitex pinnata L. |
468.80 |
471.60 |
0.866 |
0.333 |
Oroxylum indicum L. |
400.10 |
450.20 |
−0.500 |
0.667 |
Xylia xylocarpa |
357.10 |
470.30 |
0.327 |
0.788 |
Careya sphaerica |
455.10 |
490.10 |
s0.052 |
0.967 |
Note: The values are not significantly different (p > 0.05).
Color measurement
The comparative L*a*b* values of 6 plant species at 60 and 80 °C under normal conditions. In both tables, the lightness (L*) value generally decreases with longer heating durations, indicating darkening over time. The values (red-green axis) show minor fluctuations, while the b values (yellow-blue axis) tend to increase for most species, suggesting a shift toward warmer tones. Comparing the 2 tables, higher temperatures (80 °C) accelerate these changes, as evidenced by lower L* values and more pronounced shifts in a and b values at equivalent time intervals. The results suggested temperature stress rapidly initiates a cascade of molecular and metabolic responses in plants. These responses include the breakdown of pigments and the activation of various stress-related pathways [67]. However, with extended or severe heat exposure, overall pigmentation typically declines, resulting in lighter or modified coloration. The complex interplay between pigment synthesis, degradation processes, and cellular damage fundamentally explains the observed changes in color metrics (L*a*b*) that correlate with increasing temperature intensity and exposure duration. Heating duration and temperature demonstrate significant influence on the visual properties of plant materials. Tables 8 and 9 present Lab* values of various plant species under normal conditions at 60 and 80 °C, while Tables 10 and 11 display the corresponding values under mordant conditions at the same temperatures. At both temperature levels, substantial variations in lightness (L*), redness/greenness (a*), and yellowness/blueness (b*) parameters are evident across different plant species and treatment durations (30, 60 and 90 min). Clitoria ternatea L., for instance, exhibits progressive decrease in lightness (L*) values concurrent with increased blueness (negative b*) as mordanting time extends at both temperature settings. Conversely, Oroxylum indicum and Xylia xylocarpa display elevated L*, a*, and b* values, indicating brighter and warmer color tones. Comparative analysis between the 2 conditions reveals that higher temperatures (80 °C) generally reduce L* values while intensifying a* and b* parameters for most plant species, suggesting enhanced dye fixation or deeper color absorption. The correlation between temperature, duration, and color intensity indicates that elevated temperatures combined with extended mordanting periods tend to produce more vivid and saturated colorations. These findings underscore the critical importance of optimizing temperature and duration parameters to achieve desired dyeing outcomes for specific plant species. Statistical comparison of L*, a*, and b* values further elucidate the differential effects between normal and mordant conditions. Statistical analysis revealed significant color parameter differences (p < 0.05) among several plant species, particularly Clitoria ternatea L., Scleropyrum pentandrum, and Vitex pinnata L., when subjected to mordanting at 80 °C. This testing identified optimal dyeing conditions for maximum color darkness across six plant species, with mordant application at 80 °C for 90 min proving most effective for five species: Clitoria ternatea L. (L* 38.14), Vitex pinnata L. (L* 57.02), Oroxylum indicum L. (L* 70.02), Xylia xylocarpa (L* 56.58), and Careya sphaerica (L* 52.75), yielding minimal L* values and elevated a* and b* values for enhanced color intensity. Notably, Sclerocarya pentandra exhibited unique temperature sensitivity, achieving optimal darkness at 60 °C with mordant (L* 62.59). These findings demonstrate species-specific optimization requirements while confirming the general effectiveness of higher temperatures (80 °C) and mordant application for enhancing color depth in plant-based dyes, as evidenced in the experimental data presented in Tables 12 and 13.
Table 8 The comparison of L*a*b* color values of plant species under normal conditions at 60 °C.
Plant Species |
Normal Parameter (Mean ± S.D.) |
||||||||
Temp. 60 °C |
|||||||||
30 min |
60 min |
90 min |
|||||||
L* |
a* |
b* |
L* |
a* |
b* |
L* |
a* |
b* |
|
Clitoria ternatea L.
|
59.34 ± 0.13 |
−1.75 ± 0.04 |
−5.07 ± 0.13 |
57.13 ± 0.19 |
−1.64 ± 0.05 |
−5.41 ± 0.17 |
56.31 ± 0.66 |
−1.55 ± 0.08 |
−5.85 ± 0.18 |
|
|||||||||
Scleropyrum pentandrum |
80.44 ± 0.04 |
2.79 ± 0.05 |
10.64 ± 0.10 |
79.81 ± 0.02 |
2.70 ± 0.05 |
11.13 ± 0.12 |
78.82 ± 0.06 |
2.62 ± 0.05 |
12.17 ± 0.16 |
|
|||||||||
Vitex pinnata L.
|
77.21 ± 0.01 |
1.26 ± 0.04 |
25.49 ± 0.14 |
76.12 ± 0.04 |
1.73 ± 0.05 |
27.40 ± 0.25 |
74.21 ± 0.10 |
2.49 ± 0.51 |
28.10 ± 0.48 |
|
|||||||||
Oroxylum indicum L.
|
82.58 ± 0.02 |
1.27 ± 0.04 |
18.52 ± 0.12 |
81.99 ± 0.14 |
1.29 ± 0.03 |
18.66 ± 0.04 |
79.33 ± 0.06 |
1.59 ± 0.09 |
18.74 ± 0.23 |
|
|||||||||
Xylia xylocarpa
|
84.85 ± 0.12 |
5.79 ± 0.08 |
20.11 ± 0.23 |
78.29 ± 0.27 |
10.24 ± 0.19 |
22.86 ± 0.19 |
63.30 ± 0.02 |
19.22 ± 0.04 |
24.97 ± 0.09 |
|
|||||||||
Careya sphaerica
|
64.71 ± 0.23 |
12.78 ± 0.54 |
19.63 ± 0.68 |
63.21 ± 0.19 |
19.46 ± 0.18 |
23.55 ± 0.41 |
62.09 ± 0.29 |
22.62 ± 0.25 |
25.81 ± 0.66 |
|
|||||||||
Table 9 The comparison of L*a*b* color values of plant species under normal conditions at 80 °C.
Plant Species |
Normal Parameter (Mean ± S.D.) |
||||||||
Temp. 80 °C |
|||||||||
30 min |
60 min |
90 min |
|||||||
L* |
a* |
b* |
L* |
a* |
b* |
L* |
a* |
b* |
|
Clitoria ternatea L. |
55.74 ± 0.08 |
−1.54 ± 0.13 |
−6.10 ± 0.09 |
52.20 ± 0.15 |
−1.43 ± 0.11 |
−6.69 ± 0.23 |
48.01 ± 0.08 |
−1.40 ± 0.05 |
−6.79 ± 0.05 |
|
|||||||||
Scleropyrum pentandrum |
74.46 ± 0.09 |
2.40 ± 0.03 |
12.98 ± 0.11 |
74.22 ± 0.04 |
1.99 ± 0.04 |
13.05 ± 0.06 |
73.69 ± 0.01 |
1.95 ± 0.02 |
14.79 ± 0.13 |
|
|
||||||||
Vitex pinnata L.
|
74.35 ± 0.01 |
2.80 ± 0.03 |
29.48 ± 0.05 |
73.77 ± 0.04 |
2.90 ± 0.02 |
31.03 ± 0.11 |
72.52 ± 0.03 |
2.99 ± 0.01 |
35.54 ± 0.20 |
|
|
||||||||
Oroxylum indicum L.
|
80.24 ± 0.02 |
1.68 ± 0.05 |
18.82 ± 0.07 |
77.95 ± 0.02 |
1.99 ± 0.02 |
18.92 ± 0.15 |
75.61 ± 0.95 |
2.01 ± 0.02 |
19.02 ± 0.12 |
|
|||||||||
Xylia xylocarpa
|
82.55 ± 0.01 |
9.84 ± 0.04 |
20.34 ± 0.06 |
75.72 ± 0.06 |
12.46 ± 0.02 |
22.44 ± 0.08 |
60.25 ± 0.07 |
18.25 ± 0.04 |
24.27 ± 0.27 |
|
|||||||||
Careya sphaerica
|
60.13 ± 0.23 |
14.75 ± 0.48 |
20.28 ± 0.03 |
59.84 ± 0.99 |
22.03 ± 0.47 |
30.69 ± 0.97 |
55.94 ± 0.17 |
24.75 ± 0.12 |
37.65 ± 0.11 |
|
|
||||||||
The development of pressed paint products
The experiment successfully demonstrated the potential of natural pigments extracted from 6 plant species - Clitoria ternatea L., Carexa sphaerica, Xylia xylocarpa, Sclerocarya pentandra, Vitex pinnata L., and Oroxylum indicum L.- for use in pressed paint products. The optimal conditions for extraction involved temperatures of 60 - 80 °C and durations of 90 min, with the application of mordants enhancing color intensity and stability. The resulting colors ranged from deep blue (Clitoria ternatea L.) to earth tones such as medium brown (Sclerocarya pentandra and Xylia xylocarpa), yellow (Vitex pinnata L.), light brown (Oroxylum indicum L.), and dark brown (Carexa sphaerica). The pressed paint products exhibited fine texture, smooth application, ease of blending, and clear pigmentation, as shown in Figure 3.
Result of stability test
Compression test of the formulation
The compression test results demonstrated that all formulations of the colored powders exhibited excellent adhesion to the pan surface. After subjecting the powders to approximately 30 repetitions of the drop test on a table surface, no cracking or dispersion of the powders was observed. This indicates that the formulations possess robust mechanical integrity and are suitable for applications requiring high durability.
T
able
11 The
comparison of L*a*b*
color
values of plant species under mordant conditions at 80 °C.
Plant Species |
Mordant Parameter (Mean ± S.D.) |
||||||||
Temp. 80 °C |
|||||||||
30 min |
60 min |
90 min |
|||||||
L* |
a* |
b* |
L* |
a* |
b* |
L* |
a* |
b* |
|
Clitoria ternatea L.
|
40.36 ± 0.13 |
−1.03 ± 0.02 |
−7.99 ± 0.05 |
40.25 ± 0.06 |
−1.02 ± 0.12 |
−8.82 ± 0.14 |
38.14 ± 0.12 |
−1.00 ± 0.15 |
−8.90 ± 0.23 |
|
|||||||||
Scleropyrum pentandrum
|
61.43 ± 0.01 |
1.03 ± 0.05 |
16.60 ± 0.08 |
60.21 ± 0.02 |
1.01 ± 0.06 |
16.94 ± 0.06 |
55.30 ± 0.06 |
1.00 ± 0.05 |
17.06 ± 0.13 |
|
|||||||||
Vitex pinnata L.
|
67.24 ± 0.03 |
3.80 ± 0.03 |
44.23 ± 0.05 |
60.14 ± 0.04 |
3.95 ± 0.03 |
49.07 ± 0.09 |
57.02 ± 0.07 |
3.99 ± 0.07 |
50.19 ± 0.32 |
|
|||||||||
Oroxylum indicum L.
|
72.15 ± 0.01 |
2.39 ± 0.90 |
20.36 ± 0.70 |
70.92 ± 0.02 |
2.41 ± 0.02 |
21.37 ± 0.02 |
70.02 ± 0.02 |
2.52 ± 0.03 |
22.45 ± 0.29 |
|
|||||||||
Xylia xylocarpa
|
73.64 ± 0.05 |
12.05 ± 0.04 |
24.71 ± 0.17 |
59.02 ± 0.09 |
22.49 ± 0.05 |
32.81 ± 0.39 |
56.58 ± 0.08 |
22.53 ± 0.03 |
45.47 ± 0.05 |
|
|||||||||
Careya sphaerica
|
58.24 ± 0.24 |
24.15 ± 0.11 |
5.02 ± 0.12 |
56.78 ± 0.96 |
26.01 ± 0.11 |
13.51 ± 0.37 |
52.75 ± 0.73 |
29.16 ± 0.35 |
22.10 ± 0.49 |
|
|||||||||
Table 12 The comparison of statistical analysis between L*a*b* each condition.
Parameter |
Plant Species |
Normal (60 and 80 °C) |
Mordant (60 and 80 °C) |
Normal and Mordant (60 and 60 °C) |
Normal and Mordant (80 and 80 °C) |
||||||||
L* |
a* |
b* |
L* |
a* |
b* |
L* |
a* |
b* |
L* |
a* |
b* |
||
F-test |
Clitoria ternatea L. |
0.071 |
0.237 |
0.006 |
3.831 |
7.663 |
9.924 |
0.028 |
0.042 |
0.051 |
27.89 |
102.49 |
31.88 |
Scleropyrum pentandrum |
0.106 |
0.049 |
0.002 |
6.001 |
9.163 |
6.267 |
0.006 |
0.016 |
0.021 |
64.39 |
58.30 |
28.77 |
|
Vitex pinnata L. |
0.245 |
0.000 |
0.013 |
10.185 |
5.533 |
16.782 |
0.008 |
0.012 |
0.014 |
15.47 |
162.63 |
37.61 |
|
Oroxylum indicum L. |
0.274 |
0.014 |
0.093 |
3.917 |
13.517 |
5.590 |
0.006 |
0.007 |
0.002 |
21.99 |
22.91 |
16.65 |
|
Xylia xylocarpa |
0.286 |
0.009 |
0.242 |
0.053 |
0.312 |
0.678 |
0.0005 |
0.001 |
0.010 |
1.33 |
1.65 |
3.80 |
|
Careya sphaerica |
0.351 |
0.004 |
0.372 |
0.890 |
1.766 |
3.642 |
0.00009 |
0.013 |
0.044 |
1.63 |
3.18 |
5.14 |
|
p-value |
Clitoria ternatea L. |
0.803 |
0.652 |
0.944 |
0.122 |
0.050 |
0.035* |
0.875 |
0.847 |
0.832 |
0.0062* |
0.0005* |
0.0048* |
Scleropyrum pentandrum |
0.761 |
0.836 |
0.969 |
0.070 |
0.039* |
0.067 |
0.944 |
0.906 |
0.891 |
0.0013* |
0.0016* |
0.0058* |
|
Vitex pinnata L. |
0.647 |
0.991 |
0.913 |
0.033* |
0.078 |
0.015* |
0.934 |
0.917 |
0.916 |
0.0171* |
0.0002* |
0.0036* |
|
Oroxylum indicum L. |
0.628 |
0.911 |
0.776 |
0.119 |
0.021* |
0.077 |
0.944 |
0.936 |
0.963 |
0.0094* |
0.0087* |
0.0151* |
|
Xylia xylocarpa |
0.621 |
0.928 |
0.649 |
0.829 |
0.606 |
0.456 |
0.983 |
0.974 |
0.927 |
0.3138 |
0.2678 |
0.1231 |
|
Careya sphaerica |
0.586 |
0.954 |
0.575 |
0.399 |
0.255 |
0.129 |
0.993 |
0.913 |
0.844 |
0.2709 |
0.1490 |
0.0860 |
|
Note: *Significant differences (p < 0.05).
Table 13 The optimal condition in this experiment.
Plant Species |
Optimal Condition |
Temp(°C) & Time (min) |
L* Value |
Color Intensity |
Clitoria ternatea L. |
Mordant |
80, 90 |
38.14 |
Dark blue |
Sclerocarya pentandra |
Mordant |
60, 90 |
62.59 |
Medium brown |
Vitex pinnata L. |
Mordant |
80, 90 |
57.02 |
Yellow |
Oroxylum indicum L. |
Mordant |
80, 90 |
70.02 |
Light brown |
Xylia xylocarpa |
Mordant |
80, 90 |
56.58 |
Medium brown |
Careya sphaerica |
Mordant |
80, 90 |
52.75 |
Dark brown |
Figure 3 Pressed paint products: (a) Clitoria ternatea L., (b) Careya sphaerica, (c) Xylia xylocarpa, (d) Scleropyrum pentandrum, (e) Vitex pinnata L., and (f) Oroxylum indicum L.
Stability test of various conditions
The stability test results demonstrated consistent physical stability across all tested conditions during the 28-day observation period. Visual inspections under 4 conditions (no sunlight, sunlight exposure, 45 °C oven, and 4 °C) showed no observable changes in color or appearance at 14-day and 28-day intervals. The quantitative analysis revealed that ∆E values were < 1 in all conditions except the 45 °C oven; 45 °C oven samples showed ∆E = 2 - 3.5 (indicating measurable color shift); increased L* values suggested brightness changes as the primary factor. Notably, the color difference in oven-treated samples (∆E 2 - 3.5) remained below the visual detection threshold for human observers. This discrepancy between instrumental measurements and visual assessment highlights the importance of combining both quantitative and qualitative methods in stability testing. The results suggest the formulation maintains adequate stability under typical storage conditions, though thermal stress at 45 °C may induce subtle physicochemical changes detectable only through instrumentation.
Drop test
The drop test results indicate that the packaging effectively protects the product under rigorous conditions. After being dropped 10 times in specified directions from a height corresponding to the weight of the packaged product, all packages remained intact without any visible damage, such as dents, scratches, cracks, breaks, or loose parts. This demonstrates the durability and reliability of the packaging design in maintaining product safety during handling and transportation, as illustrated in Figure 4.
The application of press colors in creative painting
The creative painting as shown in Figure 5 demonstrates the successful application of natural dyes extracted from 6 types of plants, combined with mordant sodium chloride, to create vivid and imaginative artwork. This approach highlights the potential of using eco-friendly, plant-based colors in artistic practices, achieving aesthetically pleasing results while promoting sustainable and natural alternatives to synthetic pigments.
Figure 4 The pressed paint products in packaging.
Figure 5 Creative painting using natural colors extracted from 6 plant species.
Table 14 The percent of cell viability of human skin fibroblast cells.
Sample |
%Cell Viability Conc. (mg/mL) |
||||
0.001 |
0.01 |
0.1 |
1 |
10 |
|
Clitoria ternatea L. |
97.85 ± 1.54 |
93.81 ± 3.75 |
93.49 ± 3.24 |
87.31 ± 3.16 |
81.93 ± 1.68 |
Scleropyrum pentandrum |
94.91 ± 3.24 |
94.02 ± 2.47 |
92.38 ± 1.29 |
91.30 ± 3.97 |
78.43 ± 2.56 |
Vitex pinnata L. |
96.49 ± 2.39 |
94.75 ± 0.52 |
91.87 ± 1.16 |
90.89 ± 1.27 |
80.69 ± 1.30 |
Oroxylum indicum L. |
95.05 ± 1.32 |
93.93 ± 1.46 |
92.37 ± 1.57 |
82.74 ± 1.28 |
77.34 ± 1.27 |
Xylia xylocarpa |
94.94 ± 1.47 |
93.46 ± 1.95 |
91.93 ± 1.35 |
85.94 ± 1.43 |
79.32 ± 1.60 |
Careya sphaerica |
96.62 ± 1.89 |
94.36 ± 1.92 |
93.35 ± 1.27 |
89.75 ± 1.75 |
82.53 ± 1.44 |
Clitoria ternatea L. |
97.85 ± 1.54 |
95.64 ± 1.24 |
92.35 ± 1.49 |
85.48 ± 1.95 |
84.83 ± 1.38 |
Sodium lauryl sulfate |
93.07 ± 1.33 |
90.47 ± 2.84 |
4.22 ± 0.49 |
2.62 ± 0.19 |
1.86 ± 0.06 |
Note: The values are shown as mean ± S.D., based on 4 repeated experiments.
Toxicity test
The cell viability data demonstrates varying cytotoxic effects of plant extracts and compounds on human skin fibroblast cells across different concentrations. At lower concentrations (0.001 - 0.1 mg/mL), most samples exhibited minimal toxicity with cell viability above 90 %, indicating good biocompatibility. Notably, Oroxylum indicum L. showed the highest cell viability (95.65 ± 1.32 %) at 0.001 mg/mL, suggesting its potential safety for topical applications. However, as concentrations increased to 1-10 mg/mL, all samples demonstrated dose-dependent cytotoxicity, with sodium lauryl sulfate showing the most severe effect (only 1.86 ± 0.06 % viability at 10 mg/mL), serving as a positive control for cytotoxicity as shown in Figure 6. Among the plant extracts, Vitex pinnata maintained relatively higher cell viability (80.69 ± 1.30 %) even at 10 mg/mL, as shown in Table 14. Recent research relates to sodium chloride as an eco-friendly mordant alternative in natural dyeing processes, addressing growing concerns about the toxicity of conventional mordants identified sodium chloride as a non-toxic fixator that provides good colorfastness while minimizing environmental impact compared to metal-based mordants [68,69]. Furthermore, demonstrated that natural mordants like sodium chloride can effectively replace toxic metal salts in textile dyeing applications, showing promising results particularly with cotton and jute yarns, though with some trade-offs in wash fastness properties More recently, A research confirmed that sodium chloride serves as an effective mordant for natural dye extraction, promoting sustainable textile production without the need for hazardous chemicals typically used in conventional dyeing processes. These findings collectively support the shift toward chemical-free dyeing methodologies that maintain color efficacy while reducing toxicity concerns [70].
Clitoria
ternatea
L.
Xylia
xylocarpa
sodium
lauryl sulfate
Scleropyrum
pentandrous
Figure 6 The example of toxicity test of extracts and sodium lauryl sulfate on human dermal fibroblast cells using the sulforhodamine B staining method.
Conclusions
The optimal extraction conditions in this study were determined to be 60 °C for 60 min. when using sodium chloride as a mordant, with this combination providing enhanced pigment extraction efficiency across all 6 plant species tested. The addition of sodium chloride (10 % w/w) significantly improved absorbance values by 25 - 40 % compared to standard conditions, resulting in more vibrant colorations with clear pigmentation. Notably, while standard extraction conditions yielded higher crude extract percentages (9.16 - 12.92 %), the mordant-assisted approach proved superior for color intensity and stability. The natural pigment extracts demonstrated excellent physical properties when formulated into pressed paint products, exhibiting fine texture, smooth application, and outstanding adhesion properties. Stability testing confirmed product durability under various environmental conditions, with minimal color changes (ΔE values < 1) in most scenarios over a 28-day period. This research validates sodium chloride as an effective, eco-friendly mordant alternative for natural dye extraction that result in this approach yields bright, durable pigments with reduced toxicity, suitable for cosmetics and art products. Future work should focus on broader commercial applications and long-term safety to promote sustainable industry practices.
Acknowledgements
This research was funded by Rajamangala University of Technology Krungthep, Thailand (fiscal year 2023). The author thanks the Faculty of Integrative Medicine, Rajamangala University of Technology Thanyaburi, Pathum Thani, Thailand.
Declaration of generative AI and AI-assisted technologies in the writing process
The authors declare that Quillbot, an AI-based language editing tool, was used to improve the English language and enhance the readability of this manuscript.
CRediT Author Statement
Nongnuch Klinpikul: Responsible for the conceptualization of the study and the development of the methodology. Wongnapa Nakyai: Managed data curation and took the lead in preparing the original draft of the manuscript. Somchye Dittapohn: Contributed to the visualization of data and conducted the investigation. Wannisa Keawbankrud: Provided supervision and was actively involved in writing, reviewing, and editing the manuscript.
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