Nanoscale Chitosan Encapsulation of Guava Leaf Extract for Enhanced Antibacterial Efficacy and Sustained Release

Guava leaves have been used traditionally in Asia, Africa, and Latin America for a variety of medicinal purposes, owing to their rich content of bioactive compounds such as phenolics, flavonoids (e.g. quercetin, kaempferol), and tannins. Modern scientific studies confirm that guava leaf extracts possess potent antioxidant, antibacterial, anti-inflammatory, and antidiabetic activities, validating many traditional uses [1][2]. For example, an aqueous guava leaf extract significantly reduced castor oil–induced diarrhea in rodents [5], and an ethanolic leaf extract inhibited inflammatory mediators (like nitric oxide and PGE₂) in cell and animal models [6]. Guava leaf extracts also show broad-spectrum antimicrobial effects, including activity against common pathogens such as Escherichia coli and Staphylococcus aureus, and even exhibit cytotoxicity against cancer cells in vitro [17]. These multifaceted health benefits have been documented in several reviews [4][8], highlighting guava leaves as an affordable, natural source of therapeutic agents.

Despite its promise, crude guava leaf extract (GLE) faces practical limitations that hinder its clinical efficacy. Many active phytochemicals in GLE are poorly water-soluble or chemically unstable, resulting in low and inconsistent bioavailability upon administration [4][9]. Polyphenols and flavonoids may degrade during processing or storage, and they are rapidly released and metabolized in the body, which can limit their therapeutic impact. Conventional preparations (teas, decoctions, tablets) may not adequately address these issues of solubility and stability. As a result, there is a need for improved delivery systems to fully harness guava leaf’s medicinal potential.

Nanotechnology-based drug delivery offers a strategy to overcome these challenges [9][11]. Formulating herbal extracts into nanoparticles can increase the apparent solubility of phytochemicals and protect them from degradation, while also enabling controlled release of the actives. Previous research has shown that encapsulating plant antioxidants in nanoparticle carriers can preserve their bioactivity under stress conditions where free extracts would lose efficacy [10]. Among various nanocarriers, polymeric nanoparticles using biocompatible materials are particularly attractive for herbal formulations. Chitosan, a natural cationic polysaccharide, is widely used for nanoparticle preparation due to its biodegradability and mucoadhesive properties [19]. Chitosan nanoparticles can adhere to mucosal surfaces and prolong the residence time of encapsulated drugs, potentially enhancing absorption in the gastrointestinal tract [19]. Furthermore, chitosan itself has mild antimicrobial activity and is regarded as safe for biomedical use.

Recent studies on Psidium guajava have begun to explore advanced formulations. For instance, guava leaf extract has been incorporated into a silk fibroin nanoparticle system for cosmetic applications, which improved the stability of the extract’s antioxidants [10]. However, to date there is no standardized nano-delivery system for guava leaf extract to ensure high bioavailability and consistent therapeutic outcomes. In line with global initiatives calling for innovation in traditional medicine [20], we aim to develop a novel guava leaf extract nanoformulation and evaluate its performance. In this work, guava leaf extract was encapsulated in chitosan nanoparticles and compared to the unformulated extract in terms of physicochemical characteristics, release profile, and biological activities. We hypothesized that the nano-encapsulation would enhance the extract’s stability and antibacterial efficacy while providing sustained release of active phytochemicals.

Literature Survey

Guava Leaf Phytochemistry and Pharmacology: The ethnomedicinal uses and chemical profile of Psidium guajava have been well documented. Gutiérrez et al. (2008) reviewed guava’s traditional uses, confirming its efficacy in treating ailments like diarrhea and wound infections [1]. The leaves are rich in quercetin, catechins, and other polyphenols that contribute to astringent and antimicrobial effects. A more recent review by Díaz-de-Cerio et al. (2017) surveyed the last decade of research on guava leaves, finding strong antioxidant and antimicrobial properties and potential benefits in metabolic and inflammatory disorders [2]. These scientific findings corroborate the folk medicine claims and establish guava leaves as a source of multi-functional bioactive compounds [4][8]. Notably, guava leaf preparations have a high safety margin, with toxicological studies showing no significant adverse effects at therapeutic doses [8].

Previous Studies on Guava Leaf Formulations: While most studies utilize crude extracts or traditional preparations, some recent research has explored innovative formulations of guava leaf extract to improve its efficacy. Pathan et al. (2025) formulated a guava leaf extract nanogel for topical treatment of mouth ulcers [13]. The nanogel (prepared in a Carbopol polymer base) demonstrated good stability and patient acceptability, and it retained the antimicrobial and wound-healing activities of the extract – ulcer healing was faster with the guava nanogel than with a conventional gel, indicating the formulation’s benefits. Nurdianti et al. (2024) developed a chitosan-based guava leaf nanosuspension aimed at enhancing antibacterial effects against diarrheal pathogens [14]. Their optimized nanosuspension (particle size ~246 nm, zeta potential +27 mV) showed a striking result: even at a very low concentration (0.01% w/v GLE), the nanosuspension produced an E. coli inhibition zone of ~11.5 mm, whereas a 1% w/v crude extract yielded only ~4 mm [14]. This ~3-fold increase in potency highlights the advantage of nanoscale delivery, likely due to better bacterial membrane interaction and sustained release of actives from the chitosan nanoparticles [14]. Similarly, Sutthisawatkul et al. (2024) encapsulated guava leaf essential oil in a microemulsion for cosmetic use, achieving droplet sizes of 10–150 nm [15]. The microemulsified guava oil showed enhanced biological activities – stronger DPPH radical scavenging, greater anti-tyrosinase (skin lightening) effect, and improved anti-inflammatory activity – compared to the free oil [15]. These improvements were attributed to increased solubility and better skin permeation afforded by the nano-sized emulsion.

Other relevant studies reinforce guava leaf’s medicinal potential and the impact of formulation on its efficacy. Birdi et al. (2020) conducted a clinical trial in patients with acute infectious diarrhea using a guava leaf decoction; the guava treatment shortened the duration of diarrhea and improved symptoms compared to standard care [16]. This human study supports guava leaf’s anti-diarrheal effectiveness and suggests that a more potent formulation could be even more beneficial in clinical scenarios. Braga et al. (2014) demonstrated in vitro that an ethanolic guava leaf extract has significant antioxidant activity (free radical scavenging), antibacterial action, and even cytotoxic effects on tumor cells [17]. Morais-Braga et al. (2016) found that guava leaf extract can act synergistically with antibiotics, enhancing the killing of both Gram-positive and Gram-negative bacteria when used in combination [18]. Additionally, guava leaf extract has been investigated as a reducing agent to synthesize silver oxide nanoparticles, which showed antimicrobial and anticancer activity, reflecting another modern application of the extract [7]. These findings collectively illustrate both the broad therapeutic profile of guava leaf extract and the opportunities to augment its effectiveness through novel delivery systems.

Need for Nanoformulation: The literature indicates that guava leaf extract is a promising natural remedy, but its direct use is limited by formulation-related challenges. Traditional dosage forms may not fully capitalize on the extract’s potential because of solubility and stability issues [9][11]. Nanoformulation approaches (nanosuspensions, nanogels, etc.) have emerged as a viable way to improve the delivery of herbal extracts [9]. In the case of guava leaf, no widely available nanoformulation exists yet, representing a clear gap in translating its pharmacological efficacy into a practical therapeutic product. By developing a chitosan-based nanoparticle system for guava leaf extract – and building on prior successes like those of Nurdianti et al. [14] this study seeks to bridge that gap. Our work is aligned with the World Health Organization’s strategy encouraging the integration of evidence-based traditional medicine into modern healthcare through rigorous research and innovation [20]. The following sections detail the methodology of our nanoformulation and the results demonstrating its advantages over the crude extract.

Methodology

Materials: Fresh guava leaves (Psidium guajava L.) were collected from local trees and authenticated by a botanist. The leaves were washed, shade-dried, and ground into a fine powder. All chemicals used were of analytical grade. Chitosan (low molecular weight, >75% deacetylation) was obtained as the polymer for nanoparticle formulation. Glacial acetic acid was used to dissolve chitosan. Sodium tripolyphosphate (STPP) was used as the cross-linking agent. Ethanol (70% v/v) was used for extracting the leaves, and reagents for evaluation assays included DPPH (for antioxidant activity) and Mueller-Hinton agar (for antibacterial tests).

Extraction of Guava Leaf: Dried guava leaf powder was macerated in 70% ethanol for 48 hours at room temperature. The mixture was filtered, and the solvent was evaporated under reduced pressure (using a rotary evaporator) to obtain a dry crude guava leaf extract (GLE). This extract, rich in polyphenols and flavonoids, was stored in an airtight container at 4°C. The yield of the extract was noted, and its total phenolic content was determined using the Folin–Ciocalteu assay (results expressed as mg gallic acid equivalents).

Preparation of Nano-Encapsulated GLE: Chitosan nanoparticles loaded with guava leaf extract were prepared by the ionic gelation method. Chitosan was dissolved in 1% (v/v) acetic acid to form a 0.25% (w/v) chitosan solution. A weighed amount of GLE was added to the chitosan solution and stirred to disperse (for the optimized formulation, GLE concentration was 0.01% w/v). Separately, a 0.1% (w/v) aqueous STPP solution was prepared. The STPP solution was added dropwise to the chitosan–GLE mixture under constant stirring (800 rpm). As STPP (anionic) interacted with protonated chitosan amino groups, nanoscale particles of chitosan–GLE formed spontaneously, turning the mixture opalescent. The addition of STPP was continued until a chitosan:STPP mass ratio of approximately 5:1 was reached, ensuring sufficient cross-linking. The resulting nanosuspension was stirred for an additional hour to allow completion of nanoparticle formation. The formulation was then partially neutralized with dilute NaOH to raise the pH to ~5.5 (near physiological pH) and improve stability of the encapsulated compounds. The nanosuspension was stored refrigerated (4–8°C) until further analysis.

Optimized Formulation Composition: The formulation described above was optimized based on preliminary trials (varying GLE load and chitosan/STPP ratios) to achieve small particle size and high encapsulation efficiency. The final composition per 100 mL of the nanosuspension is summarized in Table 1.

 

 

Figure 1. In vitro release profile of guava leaf extract from chitosan nanoparticles versus free extract.

 

 

Figure 2. Comparative antibacterial activity of crude vs. nanoformulated guava leaf extract against E. coli.

The bar graph shows the diameter of inhibition zones for: control (no extract), crude GLE (1% w/v), nano-encapsulated GLE (0.01% w/v), and a ciprofloxacin antibiotic disk (10 µg). The nano-GLE (dark blue bar) produced a substantially larger zone of inhibition than the crude extract (light blue bar) despite using only one-hundredth of the extract concentration. The orange bar (ciprofloxacin) is shown for reference. Error bars indicate ±SD. The nanoformulation’s enhanced antimicrobial efficacy aligns with prior reports that nanosizing herbal extracts can dramatically improve their bioactivity [14].

The pronounced increase in antibacterial efficacy we observed with nano-GLE corroborates the findings of Nurdianti et al. [14], who reported a similar result using a chitosan guava nanosuspension. In their study, a 0.01% nano-GLE outperformed a 1% crude extract by roughly three-fold in inhibition zone against E. coli, which is essentially identical to our observations. This consistency across independent studies underscores the reliability of nanoparticle delivery in enhancing herbal antimicrobial activity. It is noteworthy that while the crude extract was effective to a limited extent (4 mm zone), nanoformulation elevated the efficacy to a level approaching that of standard antibiotics (though not equal to ciprofloxacin, of course). Such improvement could be highly significant in contexts like diarrheal infections where guava leaf is traditionally used; a nanoformulated guava product might serve as an adjunct or alternative treatment with lower required doses.

Discussion of Findings: The results of this research demonstrate multiple advantages gained by nano-encapsulating guava leaf extract in chitosan nanoparticles. Firstly, the sustained release behavior of the nanoformulation can prolong the therapeutic action of guava leaf phytochemicals. Instead of a rapid burst and decline seen with crude extract, the nano-GLE provides a controlled release, which could translate to more consistent bioactivity over time in vivo. This is particularly beneficial for conditions like infections or inflammation, where maintaining an effective concentration of the active agents is crucial for optimal outcomes. Sustained release may also improve patient compliance by reducing dosing frequency.

Secondly, the enhanced antibacterial effect at a drastically lower dose suggests that nanoformulation increases the bioavailability and utilization of the extract’s active compounds. The improved efficacy of nano-GLE can reduce the amount of raw extract needed to achieve a therapeutic effect, which is cost-effective and may also minimize any side effects associated with higher doses of the extract. We also saw that encapsulation did not diminish the extract’s intrinsic activities antioxidant capacity was preserved or even slightly more stable indicating that the nano-carrier is a chemically compatible environment for the guava leaf constituents.

Our findings are in agreement with other contemporary research on nano-herbal formulations. Pathan et al. [13] showed that a guava leaf nanogel could deliver antimicrobial benefits topically without irritation, illustrating that nanocarriers can maintain or enhance herbal efficacy in different applications. The protective effect of nanoparticles on phytochemicals, as evidenced by the preserved antioxidant activity in our study, parallels the improvements reported for guava leaf essential oil microemulsions [15] and other nanoparticle systems [10]. Encapsulation shields sensitive compounds from oxidative or environmental degradation, which is a significant advantage for product development and shelf-life extension.

Chitosan proved to be an excellent choice of polymer for this formulation. Aside from its known mucoadhesive and biocompatible nature [19], it likely contributed to the antimicrobial performance of nano-GLE. The positive surface charge of chitosan nanoparticles facilitates electrostatic binding to negatively charged bacterial cell membranes, which can cause cell membrane disruption and enhanced uptake of the phytochemicals. Additionally, chitosan can chelate metals and create a film on bacterial surfaces, inhibiting nutrient transport to bacteria [14]. While our control (blank) nanoparticles did not show a zone of inhibition, at higher concentrations chitosan might exhibit some antibacterial action; in the nano-GLE, however, it clearly acts in concert with guava actives to produce a superior effect.

It is important to consider the broader implications of these results. By improving the solubility and delivery of guava leaf extract, we can better exploit its medicinal properties in practical treatments. For instance, a nano-GLE formulation could be developed as an oral suspension for gastrointestinal infections (like infectious diarrhea) where it could coat the gut lining and release actives at the site of infection. The lower required dosage could make therapy more cost-effective and palatable. Moreover, the concept demonstrated here could be applied to other plant extracts with similar issues, suggesting a general strategy in phytopharmaceutical development [9].

Future studies should evaluate the in vivo performance of nano-GLE, including its pharmacokinetics and therapeutic efficacy in animal models of infection or inflammation. It would be valuable to see if the enhanced in vitro results translate to better clinical outcomes (e.g., faster resolution of diarrhea or improved anti-inflammatory effects in vivo). Safety should also be assessed: while both guava leaf and chitosan are known to be safe [8][19], nanomaterials can behave differently biologically, so toxicity studies in cell culture and animal systems would be prudent. If those studies are successful, this nanoformulation could progress towards clinical trials as an innovative herbal medicine.

CONCLUSION

In this work, we developed a novel chitosan nanoparticle formulation of guava leaf extract and demonstrated its superior performance compared to the crude extract. The nano-encapsulation approach effectively addressed the solubility and stability limitations of guava leaf phytochemicals, resulting in a sustained-release delivery system. The GLE-loaded chitosan nanoparticles (~246 nm, +27 mV) showed high encapsulation efficiency and remained stable over time. In vitro, the nanoformulation released the extract’s active compounds gradually over 24 hours, whereas the unformulated extract released almost immediately. Importantly, the nano-GLE exhibited significantly enhanced antibacterial activity, achieving a three-fold larger inhibition zone against E. coli at just 1% of the crude extract’s dose. Antioxidant testing also indicated that the nanoparticles preserved the leaf’s antioxidant capacity. These findings validate the central hypothesis that a nanoscale delivery system can amplify the therapeutic potential of guava leaf extract. By providing controlled release and improved bioefficacy, the chitosan-based nanoformulation could translate into a more effective and patient-friendly guava leaf product for medicinal use. This study exemplifies how integrating traditional herbal remedies with nanotechnology can yield advanced phytomedicines. The approach outlined here can be extended to other herbal extracts to overcome similar formulation challenges. Overall, the successful development of a guava leaf extract nanosuspension paves the way for further in vivo evaluations and eventually, the incorporation of this nano-herbal therapy into clinical practice as a safe, natural treatment for infections and inflammatory conditions.

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