Impact of Solar Drying Techniques on Bioactive Composition and Antibacterial Activity of Chamomile (Chamaemelum nobile L.)

ABSTRACT

Chamomile flowers (Chamaemelum nobile L.), widely known for their medicinal properties, were dried under different methods and conditions to preserve the plant and its health benefits. Sun drying with forced and natural convection was applied, and the effect of adding a mesh shading was evaluated to compare against controlled conditions (drying in an electric oven and a forced convective dryer). Bioactive compounds such as carotenoid content (3.15–7.95 mg/g), antioxidant activity (70.20–89.23%), and ascorbic acid (32.59–52.31 mg/100 g) were evaluated as response variables. Physical properties such as moisture content, water activity, and color parameters were also evaluated to ensure microbiological stability and visual acceptance. Chamomile flowers showed an excellent antibacterial capacity, finding the best results with solar drying with mesh shading and natural convection with minimum inhibitory concentrations of 0.375 mg/mL against E. coli and 0.300 mg/mL against S. aureus, while the minimum bactericidal concentrations were 0.750 mg/mL for E. coli and 0.600 mg/mL for S. aureus. The findings underscore solar drying's capacity to maintain both nutritional and medicinal integrity, positioning it as a promising approach for the food and herbal medicine industries seeking eco‐friendly processing solutions.

Practical Applications

The findings of this research support the use of solar drying as a sustainable and cost‐effective technique for preserving medicinal and nutritional value in chamomile. Potential applications include the production of high‐quality chamomile tea, herbal infusions, and natural medicinal products, as well as the development of sustainable drying methods for other medicinal herbs. The optimized solar drying conditions can also contribute to the development of eco‐friendly and energy‐efficient drying technologies for the food and herbal medicine industries.

1. Introduction

Medicinal plants continue to serve as a cornerstone of global healthcare, with the World Health Organization estimating that nearly 80% of the world's population relies on them as a primary source of treatment (Sellami et al. 2011). Among these, chamomile (Chamaemelum nobile L.) is one of the most popular herbs in the world that has been extensively used for medicinal purposes for centuries due to its wide pharmacological properties. Different classes of bioactive constituents are present in chamomile. Its effectiveness in relieving diarrhea, alleviating cold‐related symptoms, soothing throat inflammation, and addressing insomnia and anxiety includes anti‐inflammatory, antioxidant, antimicrobial, antinociceptive, analgesic, anxiolytic, sedative, and antispasmodic properties (Kolanos and Stice 2021). More than 120 secondary metabolites have been identified in chamomile flowers, including 36 flavonoids, 28 terpenoids, and coumarins, which are responsible for their medicinal properties (Sah et al. 2022). Chamomile‐based products, particularly teas, have been developed (Srivastava et al. 2010) in many parts of Europe, South America, and Mexico to treat children with colic and other digestive disorders (Zadeh et al. 2014).

Despite these benefits, the preservation of bioactive compounds responsible for therapeutic effects is crucial to ensuring the widespread use of medicinal plants. Traditionally, chamomile is consumed as a dried flower, but drying conditions significantly affect aroma, color, biomass yield, and chemical composition (Benković‐Lačić et al. 2023). Drying reduces moisture content to extend shelf life by ensuring microbiological stability, yet different drying methods—such as sun drying, shade drying, hot‐air drying, spray drying, or freeze drying—can significantly influence the preservation of sensitive compounds like carotenoids and vitamin C (Lee et al. 2022).

Numerous studies on diverse plant matrices demonstrate that various drying techniques effectively reduce moisture content and water activity. However, each method presents distinct advantages and limitations, and the selection of an appropriate drying approach should be guided by the specific physicochemical and bioactive properties intended for preservation. For example, Demircan et al. (2024) examined the effectiveness of seven drying methods (hot air, microwave, infrared‐assisted microwave, freezing, infrared, sun, and oven) for bergamot peels and found that hot air drying preserved the ascorbic acid content, whereas sun drying led to the greatest degradation. On the other hand, infrared drying preserved total phenolic compounds and flavonoids. Finally, they established that freeze‐drying was the most effective method for retaining bioactive compounds. Sousa et al. (2024) investigated the effects of different temperatures in convective drying of beetroot; among the four methods, freeze‐drying achieved the greatest reduction in moisture content while effectively preserving color and preventing browning reactions. It also retained higher levels of ascorbic acid, phenols, flavonoids, carotenoids, and bioactive compounds for antioxidant capacity. Infrared drying also preserved high levels of phenols and flavonoids but had a higher formation of browning products. Whereas solar drying showed a color more similar to fresh produce but did show a loss of bioactive compounds such as ascorbic acid and antioxidants. Finally, Pichaiyongvongdee et al. (2025) investigated the effects of different preprocessing and drying methods on the physicochemical properties of purple sweet potatoes and Chinese cabbage and found that Chinese cabbage in 1% NaCl solution and freeze‐drying preserved significant levels of chlorophyll, calcium, fiber, and antioxidants, while freeze‐dried sweet potatoes had higher content. Collectively, the evidence underscores that while drying achieves its primary goal of moisture reduction, the method employed critically influences the retention of key nutritional and functional properties. Therefore, in the case of chamomile, a medicinal herb, this issue acquires high relevance. Solar drying is a low‐cost, eco‐friendly option widely used in the food and pharmaceutical industry, yet its efficiency in preserving bioactive compounds, active ingredients, and therapeutic properties remains unexplored (Ghisleni et al. 2016). Considering the UN Sustainable Development Goals (SDGs), especially SDG 3 (Health and Wellness), SDG 7 (Affordable and Clean Energy), SDG 12 (Responsible Production and Consumption), and SDG 13 (Climate Action), there is a need to optimize solar drying processes that preserve both therapeutic quality and environmental sustainability. Key bioactive compounds in chamomile—such as flavonoids, terpenoids, and phenolic acids—are highly sensitive to heat and susceptible to thermal degradation during drying processes; therefore, optimizing solar drying conditions to minimize the degradation of heat‐sensitive compounds is essential for the production of high‐quality, sustainable herbal products (Mihyaoui et al. 2022). Therefore, the objective of this study is to compare solar and conventional drying techniques and evaluate their impact on the nutritional and therapeutic properties of chamomile flowers and on preserving antioxidant and antimicrobial activity linked to bioactive compounds such as carotenoids and vitamin C.

2. Materials and Methods

2.1. Raw Material

The chamomile flower (Chamaemelum nobile L.) was obtained from a local producer in Hueyapan, Morelos, Mexico, situated on the slopes of the Popocatepetl volcano (geographic coordinates: O 98° 39′ 14″—O 98° 43′ 51″ / N 18° 48′ 32″—N 18° 55′ 15″). The altitude of this area ranges from approximately 2200 to 2500 meters above sea level. The region exhibits a subhumid temperate climate and is characterized by Phaeozem, Andosol, and Regosol soils; the latter two are of volcanic origin and noted for their suitability for cultivation. According to the producers, chamomile was planted between November and December 2023, and the study was developed in January and February 2024. About 1 kg of flowers was collected to introduce 100 g per mesh in the solar dryer for each drying condition. The flowers were gathered one day prior to solar drying and hydrated constantly to maintain sample freshness. Before the drying process, chamomile flowers were separated from the stems, thoroughly washed, and disinfected using a diluted disinfectant detergent solution (Swipe Veggiefruit Wash at a 1:100 ratio) for 15 min, followed by rinsing and draining.

2.2. Drying Process

In this study, the solar drying process was carried out in a mixed‐type solar dryer with integrated fans and a flat‐plate solar air heater. The dryer was manufactured with a 6 mm polycarbonate cover with ultraviolet protection, and the dryer was operated in direct mode (Figure 1a) and with mesh shading (70% shading) to reduce solar irradiance and lower internal temperatures (Figure 1b). Forced and natural convection were also applied using the integrated fans to promote heat transfer. Solar drying experiments were conducted on January 22 and February 2, 8, and 13, 2023. A data acquisition system (Agilent‐34972A) automatically recorded drying parameters at one‐minute intervals. On the other hand, an electric forced convection dryer (air velocity of 1 m/s) and an oven at 50 and 65°C, respectively, were used to compare the solar dryer and electric systems and their effect on the physicochemical characteristics of chamomile flowers. The electric forced convection dryer (Figure 2a) had a variable frequency drive to adjust the air velocity, and a Dwyer anemometer (473B‐1) was used. The maximum volumetric flow capacity of the fan was 570 m³/h, and the heating system contained three 1500 W electric heaters. The air was driven by an electric motor (1/20 hp) coupled to a centrifugal fan. The electric oven (Model RIOSA HCFD‐48 × 48, adjustable temperature 5–220°C, 14 Amperes) operated at natural convection (Figure 2b). After drying, the samples were packed under high vacuum in polyethylene bags and stored in a dark place for preservation. Nevertheless, all analyses were carried out as soon as possible in the days following the drying procedures.

FIGURE 1.

Mixed‐type solar dryer (a) Direct and (b) with mesh shading.

FIGURE 2.

(a) Forced convective dehydrator and (b) electric oven.

2.3. Experimental Design

A one‐factor experimental design comprising eight drying conditions was established (see Table 1). The drying condition was designated as an independent variable. Both experimentation and analytical methods were conducted in triplicate.

TABLE 1.

Drying conditions of chamomile flower.

Experiment	Drying condition
1	Sun drying/Forced convection/Mesh shading
2	Sun drying/Natural convection/Direct
3	Sun drying/Forced convection/Direct
4	Sun drying/Natural convection/Mesh shading
5	Electric forced convection dryer/ 50°C/1 ms−1 air velocity.
6	Electric forced convection dryer/ 65°C/1 ms−1 air velocity.
7	Oven 50°C
8	Oven 65°C

2.4. Statistical Analysis

Statistical analyses were conducted using one‐way analysis of variance (ANOVA) with Minitab 2019 software. Statistical significance was established at α = 0.05, and post hoc comparisons were made using the Tukey test. The study assessed response variables including moisture content, water activity, color, antioxidant activity, carotenoids, vitamin C, lipid content, and antibacterial capacity. Each drying condition outlined in Table 1 was selected to represent a range of traditional and modern drying methods, varying in temperature, airflow, and solar irradiance exposure.

2.5. Analytical Methods

Moisture content was measured by a thermobalance (OHAUS, MB4) at 105°C and reported as percentage values (% X). Water activity (a_w) was determined by a Rotronic water activity meter (Higrolab C1) at 25°C. Color parameters were determined by a high‐quality colorimeter (NR60CP+). The results were expressed as L* (lightness), a* (red‐green), b* (yellow‐blue), H (hue angle), and C (chroma‐saturation). From these color parameters, it was possible to calculate the color difference (∆E) between the fresh and dried samples of chamomile flowers, chroma (C), and hue (H) using the following equations:

$$\mathrm{\Delta }E={\left(\mathrm{\Delta }{L}^{\ast 2}+\mathrm{\Delta }{a}^{\ast 2}+\mathrm{\Delta }{b}^{\ast 2}\right)}^{\frac{1}{2}}$$ (1)

$$C=\sqrt{{\left(a\right)}^2+{\left(b\right)}^2}$$ (2)

$$H=\arctan \left(\frac{b}{a}\right)$$ (3)

The fat content of chamomile flowers was determined by Soxhlet extraction. Carotenoid content was determined by weighing 0.1 g of the sample and dissolving it in 10 mL of acetone in a volumetric flask. The mixture was stirred for 10 min and then vortexed at 5000 rpm for 10 min. The supernatant was collected, and absorbance was measured at 472 and 508 nm using a UV‐Vis spectrophotometer. Carotenoid assays were performed in triplicate, and calculations were carried out using the equations shown below:

$$C^R=\frac{A_{508}\ast 2144.0-A_{472}\ast 403.3}{270.9}$$ (4)

$$C^Y=\frac{A_{472}\ast 1724.3-A_{508}\ast 2450.1}{270.9}$$ (5)

$$C^T=C^R+C^Y$$ (6)

Where C ^R represents the red isochromatic fraction content (mg/g), C ^Y represents the yellow isochromatic fraction content (mg/g), and C ^T is the total carotenoid content (mg/g).

Ascorbic acid was quantified following the methodology described by García‐Valladares et al. (2022) by iodometric titration. Antioxidant activity was made following the methodology reported by Luna‐Solano et al. (2019) with slight modifications, and the percent inhibition of (2,2‐Diphenyl‐1‐Picrylhydrazyl) percent inhibition of DPPH radical was calculated according to Equation (7):

$$\begin{array}{ccc}& & \%\mathrm{DPPH}\hfill \\ & & =\left(1-\mathrm{absorbance}\mathrm{of}\mathrm{sample}/\mathrm{absorbance}\mathrm{of}\mathrm{control}\right)\hfill \\ & & x100\hfill \end{array}$$ (7)

2.6. Antibacterial Activity

For the antibacterial activity study, the bacteria used were Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213. These bacteria were incubated at 37°C for 24 h to calculate the Minimum Inhibitory Concentrations (MIC) and the Minimum Bactericidal Concentrations (MBC) at a concentration of 1 × 10⁶ colony‐forming units. The microdilution method was used to calculate MIC, using Müller‐Hinton broth as the growth medium. For the calculation of MBC, the samples in which no growth was observed in the MIC tests were used and were incubated at 37°C for 24 h using the same Müller‐Hinton culture medium. The positive control was the Müller‐Hinton culture medium with the bacteria suspension, and the negative control was the Müller‐Hinton culture mixture with the dilution of the leaves to the highest concentration, and a tube with the culture medium alone was also placed to confirm that there was no bacterial growth in either.

3. Results and Discussion

3.1. Characterization of Fresh Chamomile

The initial moisture content and water activity of the chamomile flower were 81.16% and 0.970, respectively (see Table 2). According to López‐Agama et al. (2019), the moisture content of flowers typically reaches values up to 80%. Some studies (Amer et al. 2018) have reported a moisture content of chamomile ranging from 72% to 78%. In contrast, El Sayed et al. (2019) reported different moisture content in chamomile flowers, from 82.70% to 86.53%. For the pumpkin flower (García‐Valladares et al. 2023), a moisture content from 85.03% to 96% was reported, and 89.03% for the Zompantle flower (García‐Valladares et al. 2024). Regarding color analyses, parameters a and b resulted in positive values, 11.63 and 61.19, respectively. These values indicate that the color of fresh chamomile flowers spans the red‐to‐yellow spectrum. On the other hand, the hue angle measures the color transition from red to yellow in the product, within a range from 0° to 90° (Wrolstad and Smith 2017). In this case, the chamomile flower presented a hue angle of 79.23. The chroma value in the chamomile flower was 62.29. Finally, for the remaining physicochemical properties, ascorbic acid, fat content, and antioxidant activity, values of 33.48, 0.57, and 93.35%, respectively, were found. It is important to mention that the evaluation of these properties in fresh chamomile flowers provides information about the bioactive compounds of chamomile herbs before the drying process and the variation of the same after the different experimental drying. The above is fundamental to considering chamomile flowers in food and medicine. The high chroma and hue angle suggest vibrant yellow tones, which are typically associated with higher consumer appeal in herbal infusions.

TABLE 2.

Physicochemical analysis of fresh chamomile flowers.

Analysis	Mean values
Water activity	0.97 ± 0.01
Moisture content (%)	81.16 ± 3.89
Ascorbic acid (mg/100 g)	33.48 ± 1.82
Fat content (%)	0.57 ± 0.03
Carotenoids (mg/g)	5.63 ± 0.009
Antioxidant activity (%)	93.36 ± 0.229
L*	59.64
a*	11.63
b*	61.19
Chroma	62.29
Hue	79.23

Abbreviations: L*, whiteness‐darkness; a*, greenness‐redness; b*, yellowness‐blueness.

3.2. Drying Kinetics

3.2.1. Mixed‐Type Solar Dryer

The mixed‐type solar dryer with natural convection (Experiment 2) was the most efficient, reducing moisture content below 10% in just 360 min. When the solar dryer was operated with a fan (Experiment 3), the drying time increased to 660 min. This behavior is explained by the drying chamber temperatures reached in each condition. As shown in Table 3, Experiment 2 recorded a higher average drying temperature of 52.78°C and solar irradiance of 746.99 W/m², whereas Experiment 3 exhibited a lower average drying temperature of 41.94°C and solar irradiance of 635.29 W/m².

TABLE 3.

Environmental parameters recorded during solar drying of Chamomile flowers.

Experiment	Average drying temperature (°C)	Average ambient temperature (°C)	Average solar irradiance (W/m2)	External relative humidity (%)	Average air velocity (m/s)
1	41.90	32.30	301.32	45	2.66
2	52.78	30.82	746.99	46	—
3	41.94	29.11	635.29	49	2.57
4	43.77	30.89	394.138	47	—

3.2.2. Mixed‐Type Solar Dryer With Shading Mesh

Mixed‐type solar dryer with shading mesh/natural convection (Experiment 4) and forced convection (Experiment 1) tests lasted 540 and 720 min, respectively (Figure 3). Mesh shading and fan usage significantly affected drying chamber temperatures and drying time; this outcome is attributed to the attenuated solar irradiance levels observed in Experiment 1 (301.32 W/m²) and Experiment 4 (394.14 W/m²), which corresponded with lower average drying temperatures of 41.90°C and 43.77°C, respectively (Table 3). The observed drying time under natural convection (360 min) was shorter than previously reported for herbs like stevia (Téllez et al. 2018), suggesting that chamomile has a favorable dehydration profile.

FIGURE 3.

Moisture content versus drying time at different sun‐drying conditions and electric systems of chamomile flowers.

3.2.3. Electric Systems Drying Kinetics

Experiments 6 and 8 developed a rapid loss of moisture (300 min); these experiments correspond to drying at 65°C temperature in an electric forced convection dryer and electric oven. This faster drying behavior is explained by the constant temperature and the absence of fluctuations compared to sun drying. According to the drying of rosella (Hibiscus sabdariffa) reported by Tajudin et al. (2019), sun drying described the longest drying time because the temperatures involved varied according to ambient temperatures, which were lower than the drying air temperature in a laboratory‐scale heat pump dryer that needed 360 min (60°C, 100 g). For all other conditions, the forced convection electric dryer and oven at 50°C took 780 min and 600 min, respectively.

3.3. Physicochemical Analysis of Dried Chamomile Flowers

3.3.1. Water Activity and Moisture Content

The initial water activity of chamomile flowers was 0.97, and the final values after each drying condition ranged from 0.18 to 0.259 (see Table 4). However, all experiments showed below the limit of inhibition of microorganism growth (which is <0.6). The statistical analysis (Tukey's test, p = 0.032) revealed a significant difference between experiments 1 and 8, which corresponded to solar drying (mesh shade‐forced convection) and electric oven drying at 65°C, respectively, with a notable reduction observed when the electrical oven was employed. The remaining experiments (2–7) exhibited water activity values ranging from 0.200 to 0.247, with no statistically significant differences among them. On the other hand, the moisture content decreased from 81.16% (fresh chamomile) to values between 2.825% and 5.985%.

TABLE 4.

Water activity, moisture content and color properties of dried chamomile flowers.

Experiment	Water activity	Moisture content (%)	Color properties
			ΔL*	Δa*	Δb*	Δc	Δh	ΔE
1	0.259 ± 0.02a	5.985 ± 0.742a	−3.02 ± 0.48a	3.43 ± 0.141ab	−0.83 ± 0.365	−0.08 ± 0.287a	−3.53 ± 0.431ab	4.64 ± 0.226d
2	0.206 ± 0.02ab	2.825 ± 0.445b	−7.48 ± 0.191ab	−1.2 ± 0.141c	−16 ± 0.608b	−15.88 ± 0.629b	−2.32 ± 0.007a	17.7 ± 0.643a
3	0.242 ± 0.044ab	5.665 ± 1.648ab	−5.93 ± 0.453ab	0.4 ± 0.056bc	−13.89 ± 0.382b	−13.43 ± 0.375b	−3.61 ± 0.035abc	15.11 ± 0.523ab
4	0.235 ± 0.003ab	4.000 ± 0.396ab	−8.79 ± 0.98ab	5.04 ± 0.382ab	−17.31 ± 0.26b	−15.81 ± 0.28b	−8.67 ± 0.141f	11.76 ± 0.950c
5	0.247 ± 0.005ab	5.590 ± 0.042ab	−8.6 ± 0.552ab	6.62 ± 0.375a	−8.99 ± 0.056ab	−7.38 ± 0.163ab	−8.38 ± 0.375ef	14.09 ± 0.453ab
6	0.200 ± 0.0ab	4.800 ± 0.226ab	−7.95 ± 0.46ab	4.06 ± 0.99ab	−8.04 ± 0.29ab	−7.12 ± 0.76ab	−5.51 ± 0.42bcd	12.01 ± 0.276a
7	0.221 ± 0.001ab	4.590 ± 0.608ab	−7.16 ± 0.431ab	4.03 ± 0.028ab	−10.48 ± 0.219ab	−9.48 ± 0.219ab	−6.02 ± 0.021cde	13.32 ± 0.396bc
8	0.18 ± 0.006b	4.180 ± 0.764ab	−12.14 ± 0.834b	5.12 ± 0.315ab	−13.26 ± 0.43b	−11.91 ± 0.69ab	−7.75 ± 0.870def	18.69 ± 0.99a

Note: The mean values that do not share letters are significantly different.

Experiment 1 showed the highest moisture content (statistically different from the rest of the drying conditions; p = 0.041); this experiment was carried out with solar energy, forced convection, and mesh shade, resulting in lower drying temperatures inside the drying chamber and, consequently, higher moisture values. A similar behavior was observed with the onion drying study (Abbasi et al. 2009), where the moisture content of the samples decreased with temperature so that the moisture content on a dry basis was 2.721 (highest value) and 1.148 (lowest value), which belonged to the samples dried at 60°C and 90°C, respectively. These values, well below the microbial growth threshold of 0.6, indicate excellent microbiological stability across all treatments.

3.3.2. Color Properties

Color can be considered one of the most important quality parameters of dried products and often affects consumer acceptance (Wrolstad and Smith 2017). The mean color values of the different drying methods are presented in Table 4. It is shown that all the experiments presented negative ΔL* values that indicate that samples get darker compared to the standard (fresh chamomile flowers). Usually, convective drying generates darker products; however, according to the one‐way ANOVA, Experiment 1 presented the smallest difference. This result is attributed to the protection of the shading mesh and the low temperatures reached in the solar drying chamber. On one hand, Δa* represents a red (+) or green (−) color change. In all experiments except Experiment 2, the change was positive, which indicates a change in the herb toward greenness. The ∆a* values for the remaining experiments were positive, indicating a hue shift from yellow toward red due to pigment degradation during drying, in comparison with fresh herb, potentially influenced by the drying conditions. Concerning ∆b*, which is the color blue (−) or yellow (+), it could be observed that all the results of the experiments were negative. Therefore, dried chamomile flowers showed a tendency to be less yellow after the drying process. However, experiment 1 was significantly different from the rest, showing a lower susceptibility to changing the original yellow color of the chamomile flowers. On the other hand, negative values of ∆c for dried flowers describe that all samples are less saturated or have a lower intensity compared to the original standard, and negative values of ∆h indicate a shift towards the opposite side of the color, in this case to redness. Finally, the parameter ∆E, which represents the total color difference, was significantly lower in Experiment 1; however, it only indicates the magnitude of the color difference, not the direction, so samples with the same ∆E numbers will not necessarily have the same visual appearance. According to the results, it is possible to establish that chamomile flowers could have some alterations in pigment composition or degradation processes during drying. Nevertheless, the values are not very large and can be acceptable, as is observed in Figure 4, Chamomile flowers dried under different conditions. Despite measurable differences in ΔE, the overall visual quality of dried flowers remained acceptable, as observed in Figure 4. Therefore, to evaluate whether the biocomponents are not affected by the drying process, an exhaustive analysis of their main components was carried out.

FIGURE 4.

Chamomile flowers dried at different conditions.

3.4. Nutritional Profile

Chamomile flower is widely used thanks to its nutritional profile; therefore, it is important to evaluate its nutritional values before and after drying. For example, vitamin C and carotenoids are considered antioxidants of this herb, and their preservation after exposure can be considered as part of the product acceptance by customers since their presence can confirm the quality and good organoleptic properties of this flower.

3.4.1. Vitamin C

It is known that ascorbic acid is easily degraded by several factors such as pH, temperature, light, and the presence of enzymes. Ascorbic acid is highly sensitive to thermal oxidation and photodegradation, both of which are exacerbated under prolonged sunlight exposure. Given that vitamin C is a key indicator of nutritional quality in herbal products, its retention under mesh‐shaded solar drying underscores, for example, the potential of this method for functional tea production. In Table 5, the content of the main bioactive components in chamomile flowers after the drying process is reported. ANOVA (p = 0.004) indicated that ascorbic acid content was higher (52.31 mg/100 g) in the shading mesh solar drying with forced convection (Experiment 1); these results can be attributed to the reduction of solar irradiation on the flowers and the low drying temperatures, which normally affect and oxidize vitamin C. Higher compound concentrations were observed with the electric forced convection dryer at 65°C and the electric oven at 50°C, yielding contents of 41.768 mg/100 g and 41.725 mg/100 g, respectively, with no significant differences between them, describing a minor thermal degradation in comparison to the rest of the drying conditions. On the other hand, Experiments 2, 3, 4, 5, and 8 reduced ascorbic acid to 32.596–34.704 mg/100 g. According to Oboh and Akindahunsi (2004), sunlight likely inactivated vitamin C, especially due to prolonged exposure and high‐temperature conditions, which increased the volatile nature of this compound. According to Mashitoa et al. (2021), the consistent reduction in vitamin C levels across all drying techniques suggests that ascorbic acid is highly sensitive to thermal and oxidative stress regardless of the drying methods used. Santos and Silva (2008) reported that retention of ascorbic acid not only depends on the drying procedure but also on the kind of product, growing conditions, climate, and season; therefore, some products can present higher ascorbic acid retention in sun drying, solar drying, or shade drying. In the present study, the highest ascorbic acid content (52.3 mg/100 g and 38.36 mg/100 g) was observed when the solar irradiance was attenuated by the mesh shade (301.32 W/m² and 394.138 W/m²), whereas vitamin C decreased when solar irradiance was higher (746 and 635 W/m²).

TABLE 5.

Nutritional values of chamomile flower after different drying processes.

Experiment	Vitamin C (mg/100 g)	Carotenoid content (mg/g)	Lipid content (%)
1	52.313 ± 0.01a	5.551 ± 0.091abc	3.447 ± 0.222a
2	34.704 ± 0.242b	3.012 ± 0.368bcd	2.64 ± 0.012bc
3	33.675 ± 0.182b	4.735 ± 0.101bcd	1.811 ± 0.203d
4	38.369 ± 6.547b	7.951 ± 0.616a	1.98 ± 0.028cd
5	32.596 ± 2.932b	3.158 ± 0.01cd	2.641 ± 0.421bc
6	41.768 ± 2.461ab	5.898 ± 1.484ab	2.016 ± 0.11cd
7	41.725 ± 2.4ab	3.979 ± 0.449bcd	3.381 ± 0.144ab
8	37.555 ± 3.596b	4.608 ± 0.148bcd	2.756 ± 0.125abc

Note: The mean values that do not share letters are significantly different.

Preserving the ascorbic acid present in chamomile flowers after the drying process is a fundamental objective, given its great biological importance for human health. Ascorbic acid plays a fundamental role in collagen synthesis. Deficient or impaired collagen formation is an early indicator of scurvy, a disease resulting from ascorbic acid deficiency (Ali et al. 2024).

Ascorbic acid has also been described as acting as an antioxidant and free radical scavenger in the non‐enzymatic reduction of superoxide, hydroxyl, alkoxyl, peroxyl, tocopheroxyl, and other radicals. Because of these properties, vitamin C is widely used in the prevention and treatment of chronic and acute pathological conditions such as diabetes, cataracts, glaucoma, macular degeneration, atherosclerosis, stroke, cardiovascular disease, and cancer (Susa and Pisano 2023).

3.4.2. Carotenoids

The carotenoid content shown in Table 5 presented a significant increase in solar drying when natural convection and shading mesh were applied. This parameter increased from 5.63 mg/g to 7.95 mg/g for Experiment 4, indicating that after dehydration, carotenoids (under these drying conditions) are more available in the chamomile flower. Generally, dehydration and pulverization of vegetables increase the surface area and lead to poor stability of carotenoids unless the products are protected from air and light. A comparable enhancement in carotenoid availability post‐drying was also reported in leafy greens subjected to gentle dehydration (Mulokozi and Svanberg 2003), supporting the relevance of temperature modulation. Statistical analysis (ANOVA, p = 0.001) indicated that mixed‐type solar drying without the use of shading mesh and natural convection (Experiment 2) resulted in the greatest reduction of carotenoid content. This outcome is primarily attributed to the combination of superior temperatures as compared to the rest of the solar drying conditions (52.78°C) and higher solar irradiance (746.99 W/m²). Recent studies (Guillén‐Velázquez et al. 2025) have highlighted the significance of carotenoids in plants, noting their strong antioxidant, reparative, anti‐proliferative, anti‐inflammatory, and anti‐aging properties. As a result, these compounds may contribute to the prevention of diseases linked to oxidative stress and chronic inflammation.

3.4.3. Lipid Content

The results indicated a concentration of fat content in flower tissue compared to fresh flowers. While not indicative of lipid synthesis, the observed fat content increase reflects the relative enrichment of lipid fractions due to water removal. This can be attributed to the loss of water in the chamomile flower. Experiment 1, according to one‐way ANOVA (p = 0.0002), showed a significant increase in fat content (3.447%) compared to the rest of the experiments and fresh chamomile; this experiment corresponds to the shading mesh/forced convection, which also presented the lowest drying temperatures where the process was carried out. Although minor, this enrichment found in the results could contribute to the lipophilic profile relevant for essential oil formulations or encapsulation systems.

3.5. Therapeutic Properties

Antioxidant and antibacterial activities are considered the most important therapeutic properties of the chamomile flower. This term includes all the benefits this herb provides to its consumers regarding health and wellness, since they may attack oxidative stress and cellular damage and avoid bacterial infections. Therefore, it is important to evaluate which conditions help to preserve these properties.

3.5.1. Antioxidant Activity

Antioxidant activity of chamomile flowers was expressed as the percentage of DPPH radical reduction. Results from ANOVA indicated significant differences among experiments when the Tukey test was applied (p = 0.0003). The percentage of inhibition of DPPH reached its highest value under direct solar drying with natural convection (Experiment 1). No significant differences in antioxidant activity were observed when compared to results from the electric forced convection dryer at 50°C (see Table 6). The results are similar to those obtained by Benković‐Lačić et al. (2023), where the highest content of polyphenolic compounds and antioxidant activity were measured in sun‐dried chamomile flower samples. These findings are consistent with Oboh and Akindahunsi (2004), who also reported increased phenolic content in sun‐dried greens, likely due to the breakdown of tannins and release of bound antioxidants. As indicated by the results, the initial antioxidant activity of chamomile flower (93.35%), expressed as DPPH inhibition, decreased during the drying processes due to thermal and oxidative effects; the maximum reduction was recorded in the electric oven at 50°C (Experiment 7) and in the forced convection electric dryer (70.20%) at 65°C (Experiment 6), which may be attributed to the contact with the prolonged high temperatures from the beginning of the drying process. According to Speisky et al. (2022), antioxidants exert their protective effect by donating electrons to neutralize free radicals and reactive oxygen species. This electron transfer leads to the oxidation of the antioxidant molecule, resulting in structural modifications that diminish its antioxidant capacity. Environmental factors such as light exposure and elevated temperatures can accelerate this oxidative process, thereby reducing the overall efficacy of antioxidant compounds. The observed retention of antioxidant capacity under natural solar drying conditions highlights the potential of this method for preserving the functional properties of chamomile, making it a promising approach for its incorporation into nutraceutical formulations. Currently, a growing number of studies highlight the antioxidant potential of medicinal plants and food products. New consumer trends reflect greater health awareness, driving interest in incorporating natural antioxidants and functional peptides into food formulations to meet changing nutritional and therapeutic demands (Abeyrathne et al. 2022). Antioxidants, particularly those synthesized by plants, ensure the elimination of free radicals, reducing the risk of associated diseases such as stroke, diabetes mellitus, rheumatoid arthritis, Parkinson's disease, Alzheimer's disease, and cancer (Jideani et al. 2021).

TABLE 6.

Therapeutic evaluation of chamomile flower after different drying processes.

Experiment	Antioxidant activity (% inhibition DPPH)	Dried chamomile flower				Microextraction mL/g	Extract of chamomile flower
		E. coli		S. aureus			E. coli		S. aureus
		MIC mg/mL	MBC mg/mL	MIC mg/mL	MBC mg/mL		MIC mg/mL	MBC mg/mL	MIC mg/mL	MBC mg/mL
1	80.064 ± 6.876abc	7.50	15.00	6.75	13.50	0.7	0.450	0.900	0.420	0.840
2	89.236 ± 1.58a	5.25	10.50	6.75	13.50	0.8	0.420	0.840	0.420	0.840
3	76.882 ± 0.75bcd	6.75	13.50	5.25	10.50	0.8	0.420	0.840	0.375	0.750
4	82.980 ± 0.83ab	4.50	9.00	4.50	9.00	0.6	0.375	0.750	0.300	0.600
5	88.759 ± 1.50a	7.50	15.00	3.75	7.50	0.7	0.420	0.840	0.375	0.750
6	70.201 ± 2.077cd	5.25	10.50	3.00	6.00	0.8	0.450	0.900	0.420	0.840
7	65.695 ± 3.67d	4.50	9.00	3.00	6.00	0.7	0.450	0.900	0.420	0.840
8	86.161 ± 0.38ab	3.00	6.00	2.25	4.50	0.7	0.420	0.840	0.375	0.750

Note: The mean values that do not share letters are significantly different.

3.5.2. Antibacterial Capacity

To assess whether after drying the antibacterial activity of chamomile flowers is preserved or affected, it is important to perform inhibitory and bactericidal tests. In general, if their therapeutic effects can be guaranteed. E. coli and S. aureus are two of the most important bacteria concerning food safety, as they are pathogenic microorganisms that can transmit infectious diseases when food and herbs are consumed. In addition, chamomile flowers are widely consumed to treat gastrointestinal discomfort, so it is very important to evaluate which drying conditions will best preserve the bioactive compounds.

According to the results in Table 6, after the drying process, MIC and MBC values ranged from 3.00 to 15.00 mg/mL, respectively, for E. coli and from 2.25 to 13.50, respectively, for S. aureus. It is well known that S. aureus is a Gram‐positive bacterium; therefore, it has only a cell membrane for protection, which makes it more susceptible to antibacterial action, which may explain the lower concentrations needed to inhibit compared to the Gram‐negative bacterium, E. coli. The superior inhibition against S. aureus may be attributed to its thinner peptidoglycan wall, which renders it more susceptible to the phytocomplex present in chamomile. According to the results, it is possible to establish an influence on the type of drying and the antibacterial activity.

For example, higher capacity was found in the dryers with the shortest exposure time; Experiments 8 and 7 correspond to the electrical oven, while regarding the sun dryer, the best result was Experiment 4, sun drying/natural convection/shading mesh. The above agrees with the results regarding bioactive ingredients (vitamin C and carotenoids). More content is available when direct solar irradiation is diminished by using the mesh as both a protective and heat‐regulating device and minimizing the exposure time for degradation. The MIC and MBC were measured first in dried chamomile because this information provides more precise information on the real conditions of use as a medicinal plant, since in this presentation there is greater representativeness of the sample and ease of availability. However, to eliminate undesirable compounds that could interfere with the antibacterial tests and improve the reproducibility of the results, the compounds of interest were extracted to concentrate and purify them. The results are also shown in Table 6, as well as the amount of extract obtained for each sample from the different experiments. When extracts were analyzed, again the best antibacterial activity corresponded to the sample from experiment 4 (sun drying/natural convection/shading mesh), indicating that this drying is the best for preserving nutritional and therapeutic properties. An MIC of 0.375 mg/mL was found against E. coli and 0.300 mg/mL against S. aureus, while the MBC was 0.750 mg/mL for E. coli and 0.600 mg/mL for S. aureus. These results are better than those reported in the literature; for example, Yousefbeyk et al. (2022) found a MIC in the range of 0.78 and 12.5 mg/mL against S. aureus when they extracted active compounds from golden chamomile. Mekinić et al. (2014) reported an MIC of 0.50 mg/mL against S. aureus, while for E. coli no MIC was detected for Matricaria aurea L. (Schultz Bip). Finally, the MIC values reported here (0.300–0.375 mg/mL) are notably lower than those reported by Alkuraishy et al. (2015), indicating enhanced activity likely due to preservation of thermolabile bioactives during drying. These results suggest that chamomile dried under optimized solar conditions could be a viable ingredient in herbal antimicrobial formulations, topical gels, or preservative systems for food and beverages.

4. Conclusions

The drying of chamomile flowers was performed in different conditions to preserve bioactive compounds and physical properties. A comparative study was conducted to evaluate the effects of different solar drying conditions, highlighting their advantages over conventional electric dryers to obtain a product with water activity and moisture content between 0.206‐0.259 and 2.825%‐5.985%, respectively. Solar experiments 1 and 4 with shading mesh demonstrated to protect vitamin C (52.31 mg/100 g), carotenoids (7.95 mg/g), and fat content (3.44%) obtaining a maximum concentration of these parameters, finding the more content was available when direct solar irradiation was diminished. Concerning antibacterial capacity, it was concluded that both the decrease in solar radiation and the time of exposure to high temperatures were determinants. Experiment 4 presented the best results for the MIC (0.375 mg/mL, E. Coli; 0.300 mg/mL, S. aureus) and MBC (0.750 mg/mL, E. Coli; 0.600 mg/mL, S. aureus). Solar drying presents a viable and sustainable alternative to conventional convective drying methods for preserving foodstuffs and medicinal plants and flowers such as Chamaemelum nobile L. (chamomile). This technique effectively retains key bioactive compounds, which contribute to chamomile's therapeutic potential against various ailments. The findings underscore solar drying's capacity to maintain both nutritional and medicinal integrity, positioning it as a promising approach for the food and herbal medicine industries seeking eco‐friendly processing solutions.

Author Contributions

Paulina Guillén‐Velázquez: writing–original draft, data curation, investigation. Octavio García‐Valladares: writing–review and editing, supervision. Iris Santos‐González: conceptualization, investigation, formal analysis. Mariana Gisela Peña‐Juárez: formal analysis, investigation, writing–review and editing. Alfredo Domínguez‐Niño: methodology, conceptualization.

Conflicts of Interest

The authors declare no conflicts of interest.

Guillén‐Velázquez, P. , García‐Valladares O., Santos‐González I., Peña‐Juárez M. G., and Domínguez‐Niño A.. 2025. “Impact of Solar Drying Techniques on Bioactive Composition and Antibacterial Activity of Chamomile (Chamaemelum nobile L.).” Journal of Food Science 90, no. 11: e70670. 10.1111/1750-3841.70670

Data Availability Statement

Data supporting the findings of this study are available from the corresponding author upon reasonable request.