Drying modulates volatile composition and enhances antimicrobial activity of essential oils from Campomanesia adamantium fruit-processing residues: a chemometric study

1 Introduction

Campomanesia adamantium (Cambess.) O. Berg, popularly known as guavira, gabiroba, or guabiroba, is a fruit-bearing shrub of the Myrtaceae family widely distributed throughout the Brazilian Cerrado and neighboring regions of Paraguay and northeastern Argentina (Oliveira et al., 2025). As one of the most emblematic native fruits of the Cerrado, guavira possesses remarkable ecological, cultural, and socioeconomic importance and contributes significantly to local food systems, traditional knowledge, and regional bioeconomy initiatives (Zorgetto-Pinheiro et al., 2023). Owing to its pleasant flavor and nutritional value, the fruit has gained increasing commercial interest and is widely consumed both fresh and as a raw material for processed products.

In addition to fresh consumption, guavira pulp is extensively used in the production of beverages, jams, sweets, ice creams, and other food products, contributing to value chains associated with sociobiodiversity and regional tourism. However, industrial processing of the fruits generates substantial amounts of residues composed mainly of peels and seeds, which remain largely underutilized and are often discarded. These by-products represent a potentially valuable source of bioactive compounds, including volatile metabolites and essential oils, but their high moisture content requires refrigerated storage, increasing operational costs and limiting large-scale utilization. In this context, the recovery of essential oils from guavira residues emerges as a promising strategy for adding value to agro-industrial by-products while promoting the sustainable use of Cerrado biodiversity (Bin et al., 2025; Yoshida et al., 2023).

Essential oils are complex mixtures of volatile secondary metabolites, composed mainly of monoterpenes, sesquiterpenes, and their oxygenated derivatives (Luque de Castro et al., 1999). Owing to their antimicrobial, antioxidant, anti-inflammatory, and aromatic properties, these metabolites have attracted considerable interest for pharmaceutical, food, cosmetic, and biotechnological applications (Burt, 2004; Nazzaro et al., 2013). Terpenes, the predominant constituents of essential oils, also play important ecological roles in plant defense and largely determine the biological activity and aroma of these natural products (Jiang et al., 2025; Rosenkranz et al., 2021).

In recent years, the global rise in antimicrobial resistance has intensified the search for novel bioactive compounds capable of combating multidrug-resistant pathogens, as antimicrobial resistance is now recognized as one of the greatest threats to global public health (GBD 2021 Antimicrobial Resistance Collaborators, 2024). Among clinically relevant pathogens, S. aureus is particularly important because it is frequently associated with skin and soft-tissue infections and has a remarkable ability to acquire antimicrobial resistance (Howden et al., 2023; Tong et al., 2015; Lee et al., 2018). Although methicillin-resistant Staphylococcus aureus (MRSA) remains the most concerning phenotype, β-lactamase-producing strains also represent a significant therapeutic challenge because β-lactam antibiotics account for approximately 60%–65% of antibiotics used in clinical practice, and enzymatic hydrolysis markedly reduces their efficacy (Moyo et al., 2026; Douglas et al., 2023; Lade and Kim, 2023). Consequently, essential oils and other plant-derived metabolites have attracted increasing attention as promising sources of novel antimicrobial agents and potential alternatives or adjuncts to conventional antibiotic therapy (Kumar and Tudu, 2023).

Within this context, essential oils have attracted increasing interest for dermatological and cosmetic applications due to their antimicrobial activity and multifunctional properties. Their terpenic constituents contribute to skin microbiological control and may improve the microbiological stability of cosmetic formulations, thereby reducing the dependence of synthetic preservatives (Orchard and van Vuuren, 2017; Herman, 2019). These effects are mainly attributed to disruption of bacterial membranes, increased membrane permeability, interference with enzymatic systems, and modulation of biofilm formation (Hyldgaard et al., 2012; Bassolé and Juliani, 2012).

Volatile metabolites present in essential oils are particularly susceptible to environmental and processing conditions and may undergo compositional alterations caused by oxidation, thermal decomposition, and selective loss of low-molecular-weight constituents during drying and storage. Different techniques have been employed for essential oil extraction, including hydrodistillation, steam distillation, microwave-assisted extraction, and supercritical fluid extraction (Kou et al., 2026; Villa et al., 2022). Among these approaches, hydrodistillation remains one of the most widely applied methods due to its operational simplicity, scalability, and suitability for processing large amounts of plant biomass. Nevertheless, extraction efficiency and the resulting chemical profile are strongly influenced not only by the extraction technique itself, but also by the pre-processing conditions applied to the plant material.

Drying is a key post-harvest strategy for preserving plant materials by reducing moisture content and improving storage stability. However, in aromatic and medicinal plants, it can significantly influence essential oil yield, chemical composition, and biological properties (Figiel et al., 2010; Sellami et al., 2011; Caputo et al., 2022). During drying, thermosensitive metabolites may degrade, volatile compounds may be selectively lost, and oxidative reactions may generate new constituents, resulting in qualitative and quantitative changes in essential oil composition (Sellami et al., 2011; Orphanides et al., 2013). Therefore, optimizing drying conditions is essential to preserve the chemical composition and functional properties of essential, particularly when intended for cosmetic and biotechnological applications.

Considering that guavira processing generates substantial amounts of peel and seed residues, sustainable strategies for their conservation and valorization are needed. Room temperature and oven drying represent simple and scalable post-harvest approaches compatible with local production chains; however, their effects on the chemical profile and biological activity of essential oils from C. adamantium fruit-processing residues remain poorly understood. Therefore, the present study aimed to compare these drying methods by evaluating their effects on essential oil yield, volatile composition using GC–MS coupled with chemometric analyses, and antibacterial activity against β-lactamase-producing S. aureus, providing new insights into the valorization of this agro-industrial residue for cosmetic, biotechnological, and industrial applications.

2 Materials and methods

2.1 General experimental procedures

The drying oven used for plant material dehydration was a Fanem model 002 C B (Fanem, Guarulhos, São Paulo, Brazil), with dimensions of 420 mm height × 300 mm width × 300 mm depth. Hydrodistillation procedures were performed using a heating mantle (Faithful, Huanghua, Hebei Province, China) suitable for round-bottom flasks up to 2 L capacity.

Gas chromatography–mass spectrometry (GC–MS) analyses were carried out using a Shimadzu GC/MS QP-2010 Plus system coupled to a mass spectrometer operating at 70 eV and equipped with an Rtx-MS capillary column (Restek®, Bellefonte, PA, United States) (30 m × 0.25 mm × 0.25 µm), consisting of 5%-diphenyl-95%-dimethylpolysiloxane stationary phase.

Ethyl ether (C₄H₁₀O) and dichloromethane (CH₂Cl₂) were obtained from Labsynth (Diadema, São Paulo, Brazil), whereas chloroform (CHCl₃) was purchased from Sigma-Aldrich (Milwaukee, WI, United States). Anhydrous sodium sulfate (Na₂SO₄) was obtained from Dinâmica (Indaiatuba, São Paulo, Brazil). All reagents and culture media used for antimicrobial assays were purchased from Sigma-Aldrich®.

2.2 Plant material and drying treatments

The plant material used in this study consisted of peels and seeds of C. adamantium obtained as residues from fruit pulp processing. The fruits were acquired from family farming and sociobiodiversity production chains in the state of Mato Grosso do Sul, Brazil, where guavira fruits are traditionally hand-harvested from native Cerrado areas and commercially distributed in local markets and small-scale agro-industrial initiatives. The plant material was donated by the company Cerrado em Pé, located in Campo Grande, Mato Grosso do Sul, Brazil (20° 23′16.19″S, 54° 36′24.41″W). Residues were collected during the harvest season between October 2024 and January 2025. The fruits were manually selected and processed to separate the edible pulp for food purposes, resulting in peels and seeds that were subsequently collected as fruit-processing residues. After pulp removal, the plant residues were stored in appropriate containers and maintained at −20 °C until the experiments were performed. Subsequently, the material was subjected to different drying treatments for essential oil extraction.

Two drying methods were evaluated. In the first treatment, samples were dried in an oven at a controlled and constant temperature of 40 °C. In the second treatment, samples were maintained at room temperature (∼22 °C) in a shaded environment protected from direct sunlight, simulating traditional air-drying conditions. Essential oil extractions were carried out after 1, 2, 4, 6, and 8 days of drying. Additionally, fresh plant material was extracted and used as experimental control to evaluate the effects of drying on essential oil yield and chemical composition.

The species was identified by Prof. Dr. Geraldo Alves Damasceno-Junior (Federal University of Mato Grosso do Sul, Brazil). A voucher specimen (CGMS 80831) was deposited in the CGMS Herbarium, Federal University of Mato Grosso do Sul, Campo Grande, MS, Brazil. Access to the genetic heritage associated with C. adamantium was registered in the Brazilian National System for the Management of Genetic Heritage and Associated Traditional Knowledge (SISGEN) under registration number A263620.

2.3 Moisture determination and simplified drying kinetics

Moisture determination was performed in triplicate using 50 g aliquots of plant material. Samples were distributed in Petri dishes and subjected to the same drying treatments employed for essential oil extraction. Daily weight measurements were performed using an analytical balance to monitor mass loss and moisture variation throughout the experimental period. At the end of the eighth drying day, residual mass and moisture content were determined for each treatment. Fresh material was analyzed only as a control for essential oil yield and was not included in the drying experiment.

To provide a comparative evaluation of moisture reduction during storage, a Normalized Moisture Ratio (NMR) was calculated throughout the experimental period. Because the study was not designed for mathematical modeling of drying kinetics and the equilibrium moisture content was not determined, the conventional moisture ratio equation was not applicable. Therefore, moisture values were normalized to the first drying day of each treatment according to the following equation:where NMR is the normalized moisture ratio, U _**t** is the moisture content at drying time t, and U _**1** is the moisture content measured on the first day of each drying treatment, used as the reference value. Normalized moisture ratio values were calculated separately for the room-temperature and oven-drying treatments and were used exclusively for comparative visualization of moisture changes during the drying period.

NMR = U t U 1

2.4 Essential oil extraction

Essential oils from C. adamantium residues were obtained by hydrodistillation using a Clevenger-type apparatus coupled to a round-bottom flask heated with an electric mantle. For each extraction, 100 g of plant material and 500 mL of distilled water were used.

Hydrodistillation was performed for 4 h, counted from the beginning of hydrolate dripping. After extraction, the essential oil phase was separated from the aqueous phase using a Pasteur pipette, dried over anhydrous sodium sulfate (Na₂SO₄) to remove residual moisture, and stored in amber glass vials sealed with parafilm and protected from light with aluminum foil. All extractions were performed in triplicate for each drying treatment and drying time evaluated. After extraction, essential oil samples were stored at −20 °C until chemical analyses were performed.

2.5 Chemical composition analysis

2.5.1 GC–MS analysis

Chemical composition analyses were performed by gas chromatography coupled to mass spectrometry (GC–MS). Injector temperature was maintained at 250 °C and helium was used as carrier gas at a flow rate of 1 mL min^-1 under 86.7 kPa pressure. The oven temperature program ranged from 60 °C to 250 °C at 3 °C min^-1.

A homologous series of linear hydrocarbons (C₈–C₄₀ alkanes) was injected under the same chromatographic conditions for determination of experimental linear retention indices (LRIs). The LRIs were calculated from the retention times of the alkane series and used as complementary parameters for compound identification. Volatile constituents were identified by comparison of their mass spectra with the NIST 08 and Wiley 7 spectral libraries and by comparison of retention indices and fragmentation patterns with published literature data (Adams, 2007).

2.5.2 Chemometric analysis

GC–MS data were organized into a data matrix containing the relative peak areas (%) of the identified volatile constituents for each essential oil sample and exported as a comma-separated values (.csv) file. Chemometric analyses were performed using MetaboAnalyst 6.0 (Pang et al., 2024). Variables containing more than 50% missing values were excluded, and low-variance variables were filtered using the interquartile range (IQR) method (5% cutoff). Missing values were imputed using the left-censored data estimation (LoD) approach by replacing them with one-fifth of the minimum positive value of the corresponding variable. The dataset was normalized by sum, log10-transformed, and Pareto-scaled (mean-centered and divided by the square root of the standard deviation). These preprocessing parameters were selected based on the best model performance and sample discrimination.

Principal component analysis (PCA) was performed as an unsupervised exploratory method, followed by partial least squares-discriminant analysis (PLS-DA) to identify volatile compounds contributing to the discrimination among drying treatments. The PLS-DA model was validated using 5-fold cross-validation, evaluating models with up to three latent variables. The final model, comprising three latent variables, was selected according to the highest cross-validated Q² value and achieved an Accuracy of 0.85238, R ² of 0.92033, and Q² of 0.77092. Model robustness was further assessed by 100-permutation testing using the between/within separation distance (B/W) as the test statistic, yielding an empirical p-value = 0.01. Variables with VIP >1.0 were considered relevant discriminant markers.

Hierarchical clustering analysis (HCA) and heatmap visualization were also performed using the processed dataset. Heatmaps were generated from the normalized data using autoscaled features, Euclidean distance, and Ward’s clustering method.

2.6 Antimicrobial susceptibility assay

A clinical isolate of methicillin-susceptible S. aureus (MSSA), exhibiting resistance to erythromycin and penicillin G due to β-lactamase production and an inducible macrolide-lincosamide-streptogramin B (iMLSB) resistance phenotype, was provided by the Center of Clinical Analysis of the University Hospital of the Universidade Federal de Mato Grosso do Sul (Campo Grande, MS, Brazil).

The antimicrobial susceptibility assay was performed using the broth microdilution method according to Manda et al. (2018). Initially, essential oil samples were solubilized in dimethyl sulfoxide (DMSO) with 2% tween-80. Two-fold serial dilutions were prepared in 96-well microplates containing Mueller–Hinton broth, resulting in final concentrations ranging from 4000 to 3.75 μg mL^-1, with a final volume of 100 µL per well. Ampicillin and Gentamicin were included as control antiobiotics at concentrations ranging from 50 to 0.39 μg mL^-1 and from 60 to 0.5 μg mL^-1, respectively. Ampicillin was used to assess the β-lactamase-producing phenotype of the clinical isolate, whereas gentamicin served as the positive reference antimicrobial control.

Bacterial inoculum was prepared from an overnight culture grown on Mueller–Hinton agar and suspended in sterile saline solution (0.9%) to obtain turbidity equivalent to approximately 1 × 10⁸ CFU mL^-1 (0.5 McFarland standard), measured using an MS Tecnopon MCF-500 turbidimeter. The suspension was subsequently diluted 1:10 in sterile saline solution and 5 µL were added to each well containing the test samples.

All experiments were performed in triplicate. Microplates were incubated at 36 °C for 18 h. Subsequently, 20 µL of triphenyltetrazolium chloride solution (TTC, 0.5%) were added to each well followed by incubation at 36 °C for an additional 2 h. Wells showing bacterial growth exhibited reduction of TTC with color change from colorless to red.

The minimum inhibitory concentration (MIC) was defined as the lowest concentration at which no visible color change was observed, and the results were expressed as μg mL^-1. Mueller–Hinton broth was used as the negative control, whereas DMSO containing 2% Tween-80 served as the solvent control. The solvent inhibited bacterial growth only at concentrations up to 25%; therefore, these concentrations were excluded from MIC determination. At lower concentrations, the solvent showed no inhibitory effect on bacterial growth.

3 Results and discussion

3.1 Drying behavior and essential oil yield

The drying process directly influenced moisture reduction, drying behavior, and essential oil yield from C. adamantium residues. The results presented in Table 1 demonstrated progressive decreases in moisture content and normalized moisture ratio (NMR), accompanied by increased essential oil recovery throughout the drying period.

TABLE 1. Moisture content (%), normalized moisture ratio (NMR), and essential oil yield (%) of Campomanesia adamantium residues subjected to room temperature and oven drying during different storage periods.

NMR was calculated as M R = U t / U 1, using Day 1 as the reference for each drying treatment.

Fresh residues (control, 0 h) presented an essential oil yield of 0.105%, which was higher than values previously reported by Vallilo (2006) for C. adamantium residues (0.06%) and within the range described by Bin et al. (2005) (0.37% ± 0.08%). Nevertheless, all drying treatments resulted in higher yields than fresh material, reinforcing the positive effect of drying on essential oil recovery. The highest yields were observed after 8 days of drying, reaching 0.276% (2.63-fold increase) for oven-dried samples and 0.2297% (increase 2.18-fold) for room temperature drying. Overall, oven drying promoted superior yields throughout the experimental period, with increases ranging from 16.78% to 41.54% compared with Room temperature drying at equivalent time points.

Drying exerted a pronounced influence on both moisture removal and the yield and chemical composition of C. adamantium essential oils. Moisture content decreased progressively throughout the drying period under both treatments, accompanied by reductions in sample mass and a corresponding increase in essential oil recovery (Table 1). The yields obtained after drying are likely associated with reduced water activity and structural modifications of the plant matrix, which facilitate the release of volatile constituents and improve mass transfer during hydrodistillation. Similar effects have been reported for Laurus nobilis and other aromatic plants, where controlled dehydration enhanced essential oil extraction efficiency while simultaneously modifying the volatile profile (Sellami et al., 2011; Figiel et al., 2010).

To facilitate comparison of moisture reduction between drying treatments, moisture values were normalized relative to the first drying day (Normalized Moisture Ratio, NMR). Although this normalization does not represent the conventional moisture ratio used in drying kinetics, it provides a comparative indication of moisture loss over time. Room-temperature drying promoted a gradual decrease in normalized moisture values, whereas oven drying resulted in faster initial dehydration followed by stabilization after prolonged drying. The slight increase observed on the eighth day of oven drying likely reflects moisture re-adsorption from the surrounding atmosphere as the dried material approached hygroscopic equilibrium (Tsami et al., 1999; Dalgıç et al., 2012; Chua et al., 2019).

The progressive reduction in moisture content was accompanied by increased essential oil recovery, indicating that dehydration enhanced extraction efficiency (Table 1). However, drying also induced significant modifications in the volatile profile, demonstrating that optimization of oil yield does not necessarily correspond to preservation of the original chemical composition (Omolola et a., 2017). In particular, prolonged thermal exposure may promote oxidation, volatilization, and degradation of thermolabile constituents, whereas milder drying conditions tend to better preserve volatile metabolites (Turek and Stintzing, 2013). Similar drying-induced compositional changes have been widely reported for aromatic and medicinal plants rich in terpenoids. A recent meta-analysis of Lamiaceae species demonstrated that dehydration frequently alters the balance among volatile constituents through selective volatilization, oxidation reactions, and structural rearrangements occurring during moisture removal (Boukraâ et al., 2026). Comparable trends have also been observed in thyme, oregano, rosemary, mint, and bay leaves subjected to controlled drying processes (Sellami et al., 2011; Boukraâ et al., 2026).

3.2 Effects of drying on the chemical composition of essential oils

The chemical composition of C. adamantium essential oils obtained from fresh and dried residues was characterized by gas chromatography coupled to mass spectrometry (GC–MS), and the identified compounds are presented in Table 2. A total of 68 volatile compounds were identified, corresponding to 88.03%–99.59% of the total composition of the essential oils. Monoterpene hydrocarbons represented the predominant chemical class in all samples, followed by oxygenated monoterpenes and sesquiterpenes.

TABLE 2. Chemical composition (%) of essential oils obtained from Campomanesia adamantium residues subjected to Room temperature and oven drying, determined by GC–MS analysis.

RI_lit: retention index reported in the literature (Adams, 2007); RI_calc.: retention index calculated in the present study.

Overall, room temperature drying promoted better preservation of volatile monoterpenes, whereas oven drying induced more pronounced compositional changes, particularly involving oxygenated compounds. These findings indicate that drying conditions strongly influence volatile metabolite stability and may directly affect the biological properties of the essential oils. Similar behavior was reported by Sellami et al., 2011 during the drying of L. nobilis leaves, in which thermal dehydration promoted significant reductions in hydrocarbon monoterpenes and increased relative abundance of oxygenated constituents due to oxidation and volatilization processes. Comparable effects were also observed for Lippia thymoides essential oil, where drying conditions significantly altered the abundance of thymol, p-cymene, and γ-terpinene, directly influencing the biological activity of the oil (Nascimento et al., 2021). These compositional changes have been associated with thermal degradation, oxidative conversion pathways, and selective loss of highly volatile constituents, as previously discussed by Turek and Stintzing (2013).

Limonene was the major constituent identified in all samples, ranging from 18.10% to 35.92%, followed by β-pinene, 1,8-cineole, linalool, and α-terpineol. Fresh residues presented high proportions of monoterpene hydrocarbons, particularly limonene and β-pinene, which are commonly associated with the characteristic aroma and biological activities of Myrtaceae essential oils (Bakkali et al., 2008; Nazzaro et al., 2013).

Room-temperature drying better preserved limonene levels compared with oven drying, suggesting lower volatilization and thermal degradation under milder drying conditions. In contrast, oven drying promoted a relative reduction in monoterpene hydrocarbons and a concomitant increase in oxygenated monoterpenes. The observed compositional shifts are consistent with previous reports demonstrating that thermal drying promotes volatilization, oxidation, and secondary transformation pathways of terpene hydrocarbons, ultimately modifying the balance between hydrocarbon and oxygenated fractions in essential oils (Turek and Stintzing, 2013; Sellami et al., 2011).

One of the most notable changes was the appearance of 1,8-cineole in dried samples, whereas this compound was absent in fresh residues. 1,8-cineole reached concentrations of approximately 20.32% under room-temperature drying and 20.12% under oven drying, indicating that drying may have favored oxidative conversion pathways or release of previously bound volatile constituents. Likewise, linalool and α-terpineol showed increased relative abundance after drying, especially under oven conditions. These oxygenated monoterpenes are frequently associated with antimicrobial, antioxidant, and cosmetic properties (Burt, 2004; Hyldgaard et al., 2012), suggesting that drying may positively modulate the functional properties of the essential oils.

The marked increase in 1,8-cineole observed after drying was accompanied by a pronounced decrease in limonene and a progressive increase in α-terpineol, indicating substantial alterations in the monoterpene profile of C. adamantium essential oil. Previous studies have proposed limonene and α-terpineol as potential precursors of 1,8-cineole based on compositional changes observed in grapes and wines (Fariña et al., 2005; Capone et al., 2011). Although the compositional trends observed in the present study are consistent with the hypothesis that chemical transformations among monoterpenes could occur during drying, there is currently no experimental evidence demonstrating the thermal conversion of limonene or α-terpineol into 1,8-cineole during the drying of natural plant materials. Therefore, further mechanistic studies are required to elucidate the pathways responsible for these compositional changes.

The compositional alterations observed after drying indicate that thermal and oxidative processes significantly influenced the volatile profile of C. adamantium essential oils. Monoterpene hydrocarbons are generally more susceptible to volatilization and oxidative degradation due to their lower molecular weight and higher vapor pressure (Turek and Stintzing, 2013). Consequently, compounds such as limonene and β-pinene may undergo partial degradation or conversion during prolonged drying.

In contrast, oxygenated monoterpenes exhibited increased relative abundance after drying, particularly under oven conditions. This behavior may be associated with oxidative reactions, dehydrogenation processes, and structural rearrangements promoted by heat exposure and reduced moisture content (Sellami et al., 2011; Turek and Stintzing, 2013; Orphanides et al., 2013). Similar increases in oxygenated compounds following drying have been reported for several aromatic and medicinal plants, including oregano, mint, basil, and thyme (Figiel et al., 2010).

Additionally, drying may promote selective volatilization of highly volatile constituents, resulting in enrichment of more chemically stable metabolites in the remaining oil fraction. The observed increase in oxygenated compounds is particularly relevant because these metabolites are frequently associated with enhanced antimicrobial and antioxidant activities (Burt, 2004; Bassolé and Juliani, 2012). Therefore, although drying may reduce the abundance of certain thermolabile monoterpenes, it may simultaneously improve the biological functionality of the resulting essential oils, particularly for cosmetic and dermatological applications.

3.3 Chemometric analysis of drying-induced chemical changes

To obtain a comprehensive overview of the changes in the chemical profile induced by drying, chemometric analyses were performed using GC–MS data from essential oils obtained from fresh and dried C. adamantium residues. Partial least squares discriminant analysis (PLS-DA) and hierarchical clustering heatmap analysis were applied to evaluate global metabolic modulation, investigate sample discrimination, and identify the metabolites most strongly associated with each drying treatment.

The PLS-DA score plot revealed a clear discrimination among fresh and dried samples, confirming that drying substantially altered the volatile profile of C. adamantium essential oils (Figure 1A). Fresh residues formed a compact and well-defined cluster, clearly separated from all dried samples, indicating high chemical similarity among untreated materials and highlighting the marked effect of dehydration on essential oil composition. Component 1 (33.9%) was primarily associated with the separation between fresh and dried samples, whereas Component 2 (26.9%) contributed to the discrimination between the two drying conditions.

Oven-dried samples exhibited greater within-group variation and broader clustering patterns, indicating more pronounced chemical transformations induced by thermal exposure. The higher variability observed among oven-dried samples may reflect intensified oxidation, volatilization, and thermal rearrangement of terpene constituents during prolonged drying.

The PLS-DA biplot (Figure 1B) provided additional insight into the metabolites responsible for sample discrimination. Fresh samples were more strongly associated with monoterpene hydrocarbons such as (E)-β-ocimene, p-mentha-2,4 (8)-diene, and α-cadinol, compounds characterized by high volatility and greater susceptibility to thermal degradation. These metabolites were positioned opposite to the oven-dried samples along Component 1, reinforcing the strong influence of drying on monoterpene stability.

In contrast, room temperature and oven dried samples were positively associated with p-cymene, 1,8-cineole, and γ-muurolene, indicating that drying promoted substantial modulation of the volatile profile. Notably, 1,8-cineole exhibited stronger association with room temperature dried samples, suggesting that thermal drying favored oxidative conversion pathways and formation of oxygenated monoterpenes. Similar behavior has been reported for aromatic and medicinal plants subjected to thermal dehydration, in which oxygenated compounds increase as a consequence of oxidation and structural rearrangement of terpene hydrocarbons (Sellami et al., 2011; Turek and Stintzing, 2013).

All selected compounds exhibited VIP values >1.0, confirming their relevance to the PLS-DA model. The highest VIP scores were observed for (E)-β-ocimene and p-mentha-2,4(8)-diene, followed by α-cadinol, γ-eudesmol, and viridiflorene, indicating that these compounds were the main drivers of sample discrimination. Importantly, the highest VIP scores were associated with compounds showing the greatest treatment-dependent variation rather than the highest relative abundance, such as D-limonene, β-pinene, and linalool. Consequently, the discrimination among fresh, room-temperature dried, and oven-dried samples resulted from coordinated changes in multiple monoterpenes and sesquiterpenes, reflecting a substantial reorganization of the volatile profile induced by the drying process.

The hierarchical heatmap corroborated the PLS-DA results by revealing distinct abundance patterns among fresh, room-temperature dried, and oven-dried essential oils (Figure 3). Fresh samples exhibited a characteristic chemical profile that clearly differed from dried materials, characterized by high relative abundance of hydrocarbon monoterpenes and sesquiterpenes, including α-himachalene, α-longipinene, guaiol, and bulnesol. On the other hand, room-temperature and oven-dried samples shared several compositional changes while retaining treatment-specific differences. The clustering pattern also demonstrated high similarity among biological replicates within each treatment, whereas oven-dried samples exhibited greater within-group variability, consistent with the broader dispersion observed in the PLS-DA score plot. Furthermore, the heatmap highlighted coordinated changes in the discriminant metabolites identified by the VIP analysis, reinforcing that drying reshaped the overall volatile profile rather than altering only individual constituents.

The heatmap further highlighted treatment-dependent changes in the volatile profile. Drying promoted a marked reduction in several highly volatile monoterpene hydrocarbons, including (E)-β-ocimene, phellandrene, and γ-terpinene, whereas oxygenated monoterpenes metabolites after drying. These changes are consistent with the preferential volatilization of thermolabile monoterpenes together with oxidation and rearrangement reactions commonly reported during essential oil drying and storage (Sellami et al., 2011; Turek and Stintzing, 2013).

Among the oxygenated monoterpenes, 1,8-cineole was consistently associated with dried samples in both the PLS-DA and heatmap analyses. This observation is particularly relevant because previous studies identified 1,8-cineole as an important contributor to the antimicrobial activity of essential oils (Pries et al., 2023). However, considering that several other discriminant compounds also exhibited high VIP scores, the enhanced antibacterial activity observed after room-temperature drying is more likely associated with coordinated modifications in the overall volatile profile and potential synergistic interactions among multiple constituents than with changes in any individual compound.

Overall, the chemometric analyses demonstrate that drying substantially reshaped the volatile composition of C. adamantium essential oils. These compositional changes are particularly relevant because several metabolites associated with dried samples, including 1,8-cineole, linalool, α-terpineol, α-cadinol, and γ-eudesmol, have previously been associated with antimicrobial and antioxidant activities (Burt, 2004; Hyldgaard et al., 2012), suggesting that drying may positively modulate the biological properties of the resulting essential oils. Nevertheless, only room-temperature drying produced a marked enhancement of antibacterial activity against S. aureus, indicating that biological activity was influenced not only by the presence of individual compounds but also by the overall balance among volatile constituents generated under each drying condition.

3.4 Antimicrobial activity against Staphylococcus aureus

The antimicrobial activity of essential oils obtained from fresh and dried C. adamantium residues against β-lactamase producer S.aureus is presented in Table 3. The β-lactamase producer, methicillin sensitive S. aureus strain was selected due to its increasing clinical and dermatological relevance, particularly its association with multidrug resistance, biofilm formation, skin and soft tissue infections, and reduced susceptibility to antibiotics commonly employed in topical and systemic therapies (Tong et al., 2015). In addition to its importance in healthcare-associated infections, S. aureus is frequently associated with inflammatory skin disorders, microbiological imbalance of the skin, and contamination of cosmetic products, making it an important target for evaluation of natural compounds intended for dermocosmetic applications (Orchard and van Vuuren, 2017).

TABLE 3. Minimum inhibitory concentration (MIC) of essential oils obtained from fresh and dried Campomanesia adamantium residues against Staphylococcus aureus.

Fresh residues (control, 0 h) exhibited low antimicrobial activity, with MIC values ≥2000 μg mL^-1, indicating limited inhibitory potential prior to drying. In contrast, drying significantly influenced the antimicrobial activity of the essential oils, particularly under room temperature conditions. Interestingly, room-temperature dried samples at 6 and 8 days exhibited a pronounced increase in antimicrobial activity, with MIC values decreasing to 7.5 μg mL^-1, representing a substantial improvement compared with fresh residues and all other treatments. Conversely, oven-dried samples maintained moderate activity throughout the drying period, with MIC values remaining at 125 μg mL^-1. These findings demonstrate that drying conditions strongly influenced not only the chemical composition but also the biological functionality of the essential oils.

The enhanced antimicrobial activity observed for room-temperature dried samples appears to be directly associated with drying-induced compositional modulation revealed by the chemometric analyses. Although oven-drying promoted greater overall chemical transformation and enrichment of oxygenated compounds, room-temperature drying likely provided a more favorable balance between preservation of monoterpene hydrocarbons and formation of bioactive oxygenated metabolites. This combination may have contributed synergistically to the stronger antibacterial activity observed after prolonged room-temperature drying.

Among the metabolites associated with increased antimicrobial activity, 1,8-cineole, linalool, and α-terpineol deserve particular attention. These oxygenated monoterpenes exhibited increased relative abundance after drying and have been widely reported for their antibacterial activity against Gram-positive bacteria, including S. aureus (Burt, 2004; Nazzaro et al., 2013). Gram-positive bacteria are generally more susceptible to essential oils due to differences in cell wall structure and membrane permeability, which facilitate penetration of hydrophobic volatile compounds into the bacterial membrane (Nazzaro et al., 2013). 1,8-cineole is known to promote disruption of bacterial membrane integrity and permeability, whereas linalool and α-terpineol have been associated with membrane destabilization, leakage of intracellular constituents, inhibition of bacterial growth, and impairment of biofilm formation (Hyldgaard et al., 2012; Bassolé and Juliani, 2012).

The MIC values observed for room-temperature dried samples (7.5 μg mL^-1) are remarkably low when compared with most reports available for essential oils active against S. aureus. In general, essential oils exhibiting MIC values below 100 μg mL^-1 are already considered highly active against Gram-positive bacteria (Burt, 2004). Studies involving terpene-rich essential oils commonly report MIC values ranging from 125 to 1000 μg mL^-1 against S. aureus strains (Nazzaro et al., 2013; Bassolé and Juliani, 2012). Even essential oils recognized for strong antimicrobial activity, such as tea tree (Melaleuca alternifolia) and oregano (Origanum vulgare) essential oils commonly exhibit MIC values ranging from 62.5 to 250 μg mL⁻¹ against S. aureus, depending on strain and experimental conditions (Nostro el al., 2004; Carson et al., 2006; Orchard and van Vuuren, 2017). Therefore, the strong activity observed after room temperature drying suggests that drying-induced metabolic modulation substantially enhanced the antibacterial potential of C. adamantium essential oils.

Importantly, the superior activity observed for room-temperature dried samples suggests that excessive thermal exposure may partially reduce synergistic interactions among volatile metabolites. Although oven drying favored accumulation of oxygenated compounds, it may also have promoted degradation or volatilization of thermolabile constituents capable of contributing to the overall antimicrobial effect. In terpene-rich essential oils, antimicrobial activity is frequently associated not only with the major constituents but also with synergistic interactions among multiple metabolites (Bakkali et al., 2008). These interactions may enhance antimicrobial efficacy through complementary mechanisms of action and have been experimentally demonstrated by checkerboard assays, in which complex botanical extracts exhibited greater antimicrobial activity than their isolated major constituents (Simões et al., 2009; Efferth and Koch, 2011; de Jesus et al., 2023).

Skin and Soft Tissue Infections (SSTI) caused by S. aureus represent a major global public health burden. This pathogen readily acquires antimicrobial resistance through spontaneous mutations and horizontal gene transfer from other bacteria, contributing to its widespread clinical impact. Globally, SSTIs associated with S. aureus accounted for an estimated 37,500 all-cause deaths in 2019. In the United States, S. aureus is the pathogen most frequently isolated from cultures of SSTIs (Linz et al., 2023), while a study conducted in the Netherlands identified S. aureus as the most commonly isolated pathogen among patients with cellulitis and necrotizing fasciitis admitted to intensive care units (Cranendonk et al., 2017). The strong activity observed against S. aureus is particularly relevant considering the increasing prevalence of drug-resistant strains associated with skin and soft tissue infections. Moreover, S. aureus strains associated with biofilm formation are particularly problematic in chronic skin infections and contaminated cosmetic products due to their increased tolerance to conventional antimicrobials (Tong et al., 2015).

From a cosmetic perspective, the observed antimicrobial activity highlights the potential application of C. adamantium essential oils as multifunctional ingredients in dermocosmetic formulations. In addition to fragrance and antioxidant properties, these oils may contribute to microbiological stabilization of formulations while simultaneously providing biological activity against skin-associated pathogens. Such multifunctionality is particularly attractive for development of natural cosmetic products with reduced dependence on synthetic preservatives and enhanced bioactive functionality (Orchard and van Vuuren, 2017; Herman, 2019). Therefore, the strong activity observed against S. aureus highlights the potential of C. adamantium essential oils as promising multifunctional ingredients for dermocosmetic formulations aimed at microbiological control of the skin and reduction of multidrug-resistant bacterial proliferation.

Overall, the results demonstrated that controlled drying not only modulated the chemical profile of C. adamantium essential oils, but also significantly influenced their antimicrobial potential. Room-temperature drying for 6–8 days provided the most promising balance between preservation of volatile constituents and enhancement of antibacterial activity, reinforcing the importance of optimized post-harvest processing strategies for obtaining bioactive essential oils intended for cosmetic and biotechnological applications.

Some limitations of the present study include the need for toxicity studies, the identification of minor volatile constituents that may also contribute to the observed antimicrobial activity, and mechanistic investigations to elucidate the enhanced antimicrobial activity observed after drying. These aspects warrant further investigation to better explore the therapeutic potential of C. adamantium essential oils.

4 Conclusion

The present study demonstrated that drying significantly influenced the yield, chemical composition, and antimicrobial activity of essential oils obtained from Campomanesia adamantium residues. Both room temperature and oven drying proved effective for stabilization of guavira agro-industrial residues, as an alternative for refrigerated storage while enhancing essential oil recovery. Oven drying promoted the highest extraction yields, whereas room-temperature drying maintained a volatile profile more similar to that of the fresh essential oil and resulted in superior antimicrobial activity against the iMLSB S. aureus.

GC–MS coupled with chemometric analyses demonstrated that drying markedly reshaped the volatile profile of C. adamantium essential oils through coordinated changes in both monoterpenes and sesquiterpenes. PLS-DA and VIP analyses identified the key discriminant constituents associated with each drying treatment, indicating that sample discrimination resulted from changes across the overall volatile profile rather than from variations in individual major compounds.

Notably, essential oils obtained after 6 and 8 days of room-temperature drying exhibited remarkable antibacterial activity against clinical S. aureus, with MIC values of 7.5 μg mL^-1, substantially lower than those commonly reported for terpene-rich essential oils against Gram-positive bacteria. These findings suggest that controlled drying may enhance the antibacterial potential of C. adamantium essential oils through changes in the balance of volatile metabolites, potentially preserving or promoting synergistic interactions among volatile constituents.

Overall, this study demonstrates that controlled room-temperature drying is an effective post-harvest strategy for modulating the volatile composition and enhancing the antibacterial activity of C. adamantium essential oils. These findings support the sustainable valorization of Cerrado agro-industrial residues and reinforce their potential as promising sources of bioactive ingredients for cosmetic, dermatological, and other biotechnological applications. Further toxicological and skin compatibility studies are required to support future therapeutic and commercial applications.

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Footnotes

Edited by: Carmen Lucia Cardoso, University of São Paulo, Brazil

Reviewed by: Precious Uahomo, University of Abuja, Nigeria

Lam Bach Bao Phuong, Industrial University of Ho Chi Minh City, Vietnam