Abstract The practical use of Moringa oleifera Lam. polyphenols as natural antioxidants in food is limited by their poor stability. This study developed a simple and low-cost ß-cyclodextrin/maltodextrin/gum arabic microencapsulation system using coprecipitation to improve polyphenol stability while retaining antioxidant functionality. Sequential screening of ethanol concentration, gum arabic concentration, and extract loadings led to a formulation with an encapsulation yield of 81.01 ± 0.99 % and an encapsulation efficiency of 54.54 ± 0.36 %. Microencapsulation increased the estimated polyphenol half-life from 12.7 to 37.3 days, corresponding to an approximately threefold improvement in stability. The protective effect was also retained in a lipid-rich seafood matrix: after 12 days of refrigerated storage, the microcapsules reduced peroxide values in cobia (Rachycentron canadum) fillets by 68.9 % and 81.6% at microcapsule concentrations of 9 and 18 mg/mL, respectively.

Keywords: Moringa extract, Encapsulation, ß-cyclodextrin, Stability, Lipid oxidation

Citation:  Anh, T.T.P., Ngoc, T.T.M., and Vinh, P.T.K. 2027. Enhanced stability of Moringa oleifera Lam. polyphenols through microencapsulation: Potential application in food preservation. Natural and Life Sciences Communications. 26(1): e2027012.

Graphical Abstract:

INTRODUCTION

Polyphenols are naturally occurring bioactive compounds with diverse health-promoting properties and applications in food, pharmaceutical, and nutraceutical products (Cheynier et al., 2013; Abbas et al., 2017; Rasouli et al., 2017). Moringa (Moringa oleifera Lam.) leaves are rich in polyphenols, particularly flavonoids and phenolic acids, which exhibit strong antioxidant activity, especially in inhibiting lipid oxidation, supporting their potential as natural antioxidants for food preservation (Moyo et al., 2011; Coppin et al., 2013; Muthukumar et al., 2014; Shah et al., 2015; Papuc et al., 2017). Growing consumer demand for clean-label foods has further increased interest in natural antioxidants as alternatives to synthetic preservatives such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) (Chauhan and Raoe, 2024). However, the practical application of moringa polyphenols remains limited by their instability under environmental conditions such as light, oxygen, temperature, and humidity, as well as their low water solubility and undesirable taste (Abbas et al., 2017). Encapsulation has therefore emerged as an efficient strategy to protect polyphenols, improve stability, and facilitate their application in food processing, storage, and preservation (Belščak-Cvitanović et al., 2011; Nedovic et al., 2011).

Various encapsulation techniques, including spray drying, ionic gelation, liposomes, and electrospinning, have been investigated for Moringa extracts, with improvements in encapsulation efficiency (EE), antioxidant activity, and storage stability reported (Castro-López et al., 2021; Kurtulbaş et al., 2022; Vonghirundecha et al., 2022; Gimenis et al., 2023). However, some of these approaches require specialized equipment or complex processing.

Cyclodextrin-based systems offer a simpler alternative for polyphenol encapsulation. ß-cyclodextrin (ß-CD) can form inclusion complexes with polyphenols through its hydrophobic cavity, while maltodextrin (MD) and gum Arabic can contribute matrix-forming, emulsifying and film-forming properties that support extract retention and protection (Del Valle, 2004; Watson et al., 2017; Yinbin et al., 2018). The combination of these food-grade materials may therefore provide complementary molecular inclusion, matrix formation, and interfacial protection at relatively low material cost (Zhao et al., 2022).

However, the use of ß-CD/MD/gum arabic systems prepared by coprecipitation to stabilize Moringa polyphenols for application in seafood remains underexplored. We hypothesized that encapsulation could enhance polyphenol stability while maintaining antioxidant activity in a lipid-rich seafood matrix. Accordingly, this study developed ß-CD/MD/gum Arabic microcapsules containing a polyphenol-enriched Moringa oleifera leaf extract using coprecipitation. Ethanol concentration, gum Arabic concentration, and extract loading were sequentially screened, followed by evaluation of microcapsule properties, polyphenol stability under different environmental conditions, and inhibition of lipid oxidation in cobia (Rachycentron canadum) fillets during refrigerated storage. Given the susceptibility of cobia lipid to oxidation, peroxide value was used to assess the protective effect of the microcapsules during storage (Abuja and Albertini, 2001; Cui et al., 2022). 

MATERIALS AND METHODS

Materials

Moringa leaves were harvested in March 2024 from a residential area in Dien Khanh District, Khanh Hoa Province, Vietnam. Damaged leaves were carefully removed, and the remaining ones were washed with water. They were then air-dried in the shade to preserve their quality. To ensure even drying, the leaves were mixed thoroughly every 15 min. Once dried, the Moringa leaves were finely ground into a powder using a Philips blender (model HR2222/00, China) and then sieved through a 50-mesh nylon cloth. The resulting powder exhibited a dark green color, a pleasant aroma, and a slightly bitter taste. It was stored in a dark bottle at 4°C for further analysis.

Folin Ciocalteu solution, and gallic acid were purchased from Sigma Aldrich Pte. Ltd, Vietnam. Solvents and other analysis reagents were of analytical grade, and Maltodextrin (DE10, food grade) was purchased from Xilong Scientific Co., China.

Preparation of Moringa polyphenol-enriched extract

Moringa extract from leaf powder was prepared following the procedure by Tran et al. (2024). Briefly, 10 grams of leaf powder were mixed with 96 % ethanol maintaining a material to solvent ratio of 1:20 (w/v). The mixture was then subjected to sonication at room temperature for 60 min using an ultrasonic tank (Branson CPX 1800-E-USA), with 10-min intervals of pausing for every 20 min of sonication. The resulting mixture was centrifuged at 1956 RCF (using a Hettich EBA 21 centrifuge, Germany) for 10 min at room temperature, and additional rounds of extraction were performed by adding the same volume of solvent. To detect remaining traces of polyphenol in the residue, the ferric chloride test was utilized. The collected supernatants were adjusted to 500 mL with ethanol and stored at 4°C until further use.

Determination of total polyphenol content

Total polyphenol content (TPC) in the Moringa extract was determined according to the method of Tran et al. (2024) with minor modifications. 0.8 mL of the Moringa extract was mixed with 1 mL of Folin-Ciocalteu reagent solution (diluted 1:10 v/v in distilled water), and the mixture was allowed to stand for 10 min at room temperature. 0.32 mL of a 7.5 % (w/w) Na₂CO₃ solution was then added to adjust the mixture to pH 10. The mixture was incubated in the dark at room temperature for 30 min. The final solution was made up to 10 mL with distilled water and the absorbance at 750 nm was recorded by UV-VIS Spectrophotometer (Libra S50, USA). TPC was calculated using a calibration curve performed with standard gallic acid in the concentration range from 12 to 44 µg/mL. TPC was expressed as a mg of gallic acid equivalent (GAE) per g of dried leaves.

Encapsulation of the Moringa extract

The preparation of the microcapsule containing Moringa extract was referenced from the study of Cai et al. (2019) with certain modifications. A mixture of 10 g coating materials, ß-CD/MD (9:1 w/w), and gum arabic (at ratios ranging from 6% to 10% w/w with the coating) was blended with ethanol (0-45 % v/v) using a magnetic stirrer (ARE Heating Magnetic Stirrer, Velp Scientifica, Usmate, Italy) at 45°C until completely dissolved. Then, the Moringa extract (12-23 % v/v in ethanol) was gradually added to the solution while being homogenized for 10 min in a high-speed homogenizer (IKA Ultra-Turrax T25 DIGITAL, Staufen, Germany) at 15,000 rpm. The resulting mixture was incubated at 45°C for 6 h to facilitate complex formation, followed by overnight cooling at 10°C. The mixture was then subjected to vacuum filtration to separate the solid product, which was subsequently dried under vacuum drying at 40°C overnight to achieve a final water content of about 6-8 %. Finally, the dried product was finely ground and stored in a polyethylene bag at 4°C for further analysis.

Determination of encapsulation yield and encapsulation efficiency of microencapsulated Moringa extract

Encapsulation yield (EY, %) is defined as the ratio of the total amount of polyphenol encapsulated - comprising both the polyphenols on the microcapsule surface and those encapsulated within the microcapsule- to the total amount of the initial polyphenol used for encapsulation. Encapsulation efficiency (EE, %), on the other hand, specifically refers to the polyphenols encapsulated inside the microcapsule, compared to the total polyphenol encapsulated. These measurements were conducted following the method outlined by Osamede Airouyuwa and Kaewmanee (2019).

To determine the EY, 1 g of the microcapsule powder was immersed in 5 mL of acetone. The mixture was manually shaken for 1 min and sonicated for 25 min using a Branson CPX 1800-E-USA sonicator. Afterward, centrifugation was performed at 1,585 RCF at room temperature for 20 min using a Hettich EBA 21 centrifuge to separate the phases. The supernatants were combined and adjusted to a final volume of 25 mL with acetone. The polyphenols were determined using a similar procedure as TPC determination method in the extract mentioned previously and were expressed as mg GAE per gram of dried powder microcapsules (mg GAE/ g dried weight, DW). EY (%) was calculated based on equation (1):

EY (%) = Q/Q₀ * 100 %          (1)

where:  Q₀ represents the initial amount of polyphenols used for encapsulation (in milligrams DW).

 Q represents the total amount of polyphenols in the dried microcapsule powder (in milligrams DW).

For the EE determination, the same steps were carried out as in the EY determination, except that ethanol was used as the extracting solvent instead of acetone, which could determine the surface polyphenol content of the microcapsules. After centrifugation at 704 RCF for 5 min and subsequent filtration, supernatants were adjusted to 25 mL in ethanol. The surface polyphenol content was calculated using a previously described procedure and expressed as mg GAE per gram of dried powder microcapsules (mg GAE/ g dried weight, DW). The EE was measured using equation (2):

EE (%) = (Q-q)/Q * 100 %        (2)

q represents the surface polyphenol content of the dried microcapsule powder (in milligrams DW).

Surface morphology of the Moringa extract microcapsule particles

The surface morphology of the microcapsules was analyzed using a scanning electron microscope (HITACHI S-4800, Japan). The imaging conditions included an accelerating voltage of 2.0 kV, and images were captured at 500 x SE(M) magnification. The focal length ranged from 100 to 300 μm.

Particle size distribution

The particle size distribution of the microcapsules was determined by dynamic light scattering (DLS) using a Zetasizer Nano ZS (Malvern Instruments, UK). The microcapsule powder was dispersed in deionized water prior to measurement and analyzed at 25°C. The instrument operates with a laser source at 633 nm and has a particle-size measurement range of 0.6 nm - 6µm. The Z-average hydrodynamic diameter and polydispersity index (PDI) were recorded as measures of particle size and distribution width, respectively.

Storage stability of the Moringa extract microcapsule

The storage stability of the TPC in the microcapsules was assessed under varying environmental conditions. One-gram microcapsules were subjected to temperature changes from 5 to 100°C for 2 h to evaluate the impact of temperature. They were also stored at room temperature and exposed to natural light (28 ± 2 °C) for 6 weeks, with weekly evaluations. Additionally, the microcapsules were exposed to different lighting conditions - darkness, sunlight, and ultraviolet (UV) light (254 nm) - for 24 to 120 h at ambient temperature. The changes in the remaining TPC of the microcapsule were carefully examined to determine the effects of each environmental condition on the microcapsule’s storage durability. A 3 mL sample of the Moringa extract was evaluated under the same conditions as a control (Wang et al., 2016).

Kinetic analysis of total polyphenol content degradation

The data were best described by a first-order kinetics model, represented by the equation:

ln (TPC_t) = ln (TPC₀) – kt        (3)

Where TPC₀ represents the initial TPC (at t = 0) and TPC_t denotes the TPC after t (time) during stability treatment at a specified temperature. The degradation rate constant k was derived from the slope of a plot of the natural logarithm of the percentage retention of TPC. For a first-order reaction, half-life values at a given temperature were calculated using the equation:

t_1/2 = ln (2)/k                     (4)

Sample preparation for evaluating lipid oxidation prevention using the Moringa extract and the microcapsules

Freshly (recently dead) cobia (Rachycentron canadum) was purchased from a local Dam market, Nha Trang, and immediately transported to the laboratory on the same date on ice. One fish was used for the experiment. The fish was filleted to remove bones, skin, and dark meat, and then cut into 1 × 1 cm pieces. The samples were blended using a blender (Philips, model HR2222/00, China) to obtain a homogeneous puree. Five 1-g portions were prepared from the homogenized puree for each sampling. The control sample consisted of puree immersed in distilled water, while the other samples consisted of puree immersed in Moringa extract or microcapsule solution at concentrations of 9 and 18 mg/mL in distilled water, respectively. In each group, 20 mL of treatment solution was added per gram of fish puree (20:1 mL/g). The mixtures were homogenized using an Ultra-Turrax T25 DIGITAL homogenizer and refrigerated in a plastic container at 4°C. Peroxide values were determined by a volumetric method after 0, 3, 6, 9, and 12 days. At each sampling time, peroxide values were determined in triplicate as analytical replicates.

Evaluation of potential prevention of lipid peroxidation by the Moringa extract microcapsule

Lipid fraction in sample was extracted following the method described by Xie et al. (2017).  Initially, the sample was homogenized with 96% ethanol (the fish-to-solvent was 1:12 w/v) for 4 min, incubated for 2 h at room temperature. Subsequently, the mixture was subjected to centrifugation at 1,585 RCF for 10 min. The resulting solution, containing the fat, was collected. The solution was then concentrated under reduced pressure at a temperature of 50°C using IKA Rotary Evaporator RV 10 Basic V, Germany.

The method for determining the peroxide value was carried out as described by Low (1992) with some minor changes). Approximately 0.5 g of lipid sample was taken into a 100 mL flask with a stopper. Then, 10 mL of an acetic acid/isooctane (3:2 v/v) mixture was added to dissolve the lipid by shaking. Next, 1 mL of freshly prepared saturated KI solution was added, and the flask was immediately stoppered and placed in the dark for 5 min. Afterward, 20 mL of distilled water was added and shaken. The released iodine was titrated using a standardized solution 0.01 N Na₂S₂O₃ until a pale-yellow color appeared. 1 mL of starch was added, and titration continued until the color disappeared. The volume of Na₂S₂O₃ solution used was recorded as V_s (mL). Three test samples were titrated in parallel. 

The calibration of the 0.01 N Na₂S₂O₃ was performed using an indirect titration method. A 0.02 N K₂Cr₂O₇ solution was reacted with 5 mL of 10% (w/v) KI solution in an acid medium of 1 M H₂SO₄. The mixture was incubated in the dark for 15 min. The amount of iodine produced was titrated in a similar manner as described above.

The peroxide value of lipid is calculated as the number of milliequivalents (meq) active oxygen per kilogram of lipid which is determined using the following formula (5):

Where: V_s: titration volume of sample (mL)

            V_b: titration volume of blank (mL)

            W: weight of lipid used (g)

            N: calibrated Na₂S₂O₃ (eq. L^-1)

Data analysis

Data are reported as mean ± standard deviation (mean ± SD). Microsoft Excel 2019 software was utilized for data calculations and graph plotting. The statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) version 26.0. Mean values were subjected to analysis of variance (ANOVA) followed by Tukey’s test. A p-value of less than 0.05 was considered statistically significant indicating the presence of a meaningful difference.

RESULTS

Encapsulation of the Moringa extract

Effect of ethanol concentration

The microcapsule powder was initially prepared using coprecipitation method, with various chemical factors influencing the encapsulation process. During each evaluation, the main factor was examined while the remaining factors were kept constant: 30% (v/v) ethanol, ethanol to coating 9:1 (v/w), 9% w/w gum Arabic in coating blend, and the Moringa concentration at 18 % v/v.

Table 1 shows that EY and EE significantly increased as the ethanol concentration rose from 0 to 30% (v/v), peaking at 30% of ethanol. Beyond this point, these parameters gradually declined, with the statistical analysis indicating no significant difference in EY and EE between 30% and 35% ethanol.

Table 1. Effect of ethanol concentration (% v/v) in the coating solution, ranging from 0 to 40%, on the encapsulation yield (EY, %) and encapsulation efficiency (EE, %) of microcapsules. Values are expressed as mean ± SD (n = 3). Within each row, means sharing different superscript letters are significantly different (P < 0.05, one-way ANOVA followed by Tukey’s post hoc test).

The 30% aqueous ethanol solution was employed to determine the amount needed to dissolve the coating material. Table 2 illustrates that as the volume of ethanol increased, both EY and EE improved, peaking at the 9:1 (v/w) ethanol-to-coating blend ratio.

Table 2. Effect of ethanol-to-coating blend ratio (v/w), ranging from 7.5/1 to 9.5/1, on the encapsulation yield (EY, %) and encapsulation efficiency (EE, %) of microcapsules, using 30% ethanol concentration. Values are expressed as mean ± SD (n = 3); within each row, means sharing different superscript letter are significantly different (P < 0.05, one-way ANOVA followed by Tukey’s post hoc test).

In this context, the 30% ethanol concentration at the 9:1 (v/w) solvent to coating blend is preferred for the inclusion complexation.

Effect of gum arabic

Table 3 presents the parameters of encapsulation process, which vary with different ratios of gum arabic to the coating materials.

Table 3. Effect of gum arabic content in the coating blend, ranging from 6 to 10% (w/w relative to ß-CD/MD), on the encapsulation yield (EY, %) and encapsulation efficiency (EE, %) of microcapsules. Within each row, means sharing different superscript letters are significantly different (P < 0.05, one-way ANOVA followed by Tukey’s post hoc test).

Results indicate that EY and EE peak at 9% (w/w) of gum arabic in the coating blend. However, at 10%, EY and EE begin to decline.

Effect of the Moringa extract concentration

To form a complex, only a portion of the guest molecule needs to fit into the cavity of the ß-CD (Watson et al., 2017). Therefore, it is essential to investigate the appropriate concentration of the Moringa extract that can be effectively entrapped to maximize yield and minimize waste.

Table 4. Effect of the Moringa extract concentrations, ranging from 12 to 23%, on the encapsulation yield (EY, %) and encapsulation efficiency (EE, %) of microcapsules, using 30% ethanol concentration. Values are expressed as mean ± SD (n = 3). Within each row, means sharing different superscript letters are significantly different (P < 0.05, one-way ANOVA followed by Tukey’s post hoc test).

Table 4 presents the results, showing that the EY and EE reached their peak values at 18% (v/v) of the Moringa extract. Beyond 18%, these parameters begin to decline.

Based on the sequential screening, the conditions showing the best overall performance among those tested were selected for the preparation of the final microcapsule formulation. Under these selected conditions, the final preparation showed an EY of 81.01 ± 0.99 % and an EE of 54.54 ± 0.36 % (Table S1).

Morphological properties of the particles powder

The obtained powders were analyzed using SEM to assess their crystalline characteristics and morphology at a scale of 100 µm with 500× magnification.

Figure 1.  SEM micrographs of native ß-cyclodextrin (A) and the microcapsules (B), acquired at 2.0 kV accelerating voltage and 500× magnification (scale bar = 100 µm).

Figure 1A shows that the ß-CD polymer particles displayed a range of sizes and irregular orientations. Similarly, the encapsulated Moringa extract displayed a flake-like morphology with rough, and dented surfaces, with particle sizes in the range of tens of micrometers (Figure 1B). The observed dents may be attributed to particle shrinkage during the drying process. Some particles appeared agglomerated, forming clusters that may contribute to the heterogeneous particle morphology. Dynamic light scattering (DLS) analysis showed a Z-average hydrodynamic diameter of 431.5 nm with a PDI of 0.468, indicating a relatively broad particle-size distribution in aqueous dispersion (Figure S1).

Storage stability of the particles powder

The stability of the microcapsules during storage under varying conditions - temperature, storage time, and light exposure- was investigated.

Figure 2 shows both the extract and the microcapsules experienced a decrease in % TPC as the temperature increased.

Figure 2. Thermal degradation profile of total phenolic content (TPC) in the free Moringa extract and the microcapsules, expressed as percentage of TPC remaining relative to the initial value (at 5°C), following exposure to temperatures ranging from 5 to 100 ºC for 2 h. Data points represent mean ± SD (n = 3). Different letters at each temperature indicate significant differences between treatments (Tukey’s HSD, P < 0.05)

While %TPC decreased slightly between 5-30 °C for both, it dropped more rapidly in the extract beyond 30°C, indicating that temperature impacts the extract more than the microcapsules. The Moringa exhibited nearly 50% loss of TPC at 60°C, whereas the microcapsules reached a similar loss at 100°C where the Moringa extract was completely charred.

The duration for which the powder maintains its bioactivity is crucial for assessing the quality of polyphenol microcapsules. This was evaluated through a degradation kinetic study conducted during the storage period at room temperature (28 ± 2 °C). Figure 3 illustrates a strong linear relationship (R² > 0.95) between ln (TPC_t/TPC₀) and storage time (in days) for both the Moringa extract and the microcapsules, confirming that TPC degradation follows first- order reaction kinetics.

Figure 3. First-order degradation regression lines of total polyphenolic content (TPC) in the free Moringa extract (circles) and the microcapsules (triangles) stored at ambient temperature (28 ± 2 ºC) over 6 weeks. Data are plotted as ln (TPC/TPC₀), where TPC₀ is the initial TPC value (day 0).  Different letters at each week indicate significant differences between treatments (Tukey’s HSD, P < 0.05)

Table 5 presents the first-order degradation rate constant (k) determined from the slopes of logarithmic plots of TPC versus time, with corresponding half-life values (t_1/2) calculated from these rates.

Table 5.  First-order degradation kinetic parameters (k), half-life (t_1/2), and coefficients of determination (R²) of polyphenols in the Moringa extract and microcapsule during 6-week ambient storage.

The results show that the TPC in the Moringa extract degraded approximately three times faster than in the microcapsules, as reflected by the higher rate constant and shorter half-life at ambient temperature.

Similar results were also observed in the evaluation of samples under different light storage conditions.  Data derived from the first-order degradation regression lines of each sample, presented in Table 6, show that the polyphenols in the microcapsules degrade with slower rates than their free extract form, as evidenced by consistently lower rate constants (k).

Table 6. First-order degradation kinetic parameters (k), half-life (t_1/2), and determination coefficients (R²) of polyphenol in Moringa extract and microcapsules under light exposure conditions at ambient temperature for 120 h.

Potential of the microcapsules to prevent lipid oxidation in cobia fish

Figure 4 illustrates the changes of peroxide value during 12 days of storage at 4°C. The initial peroxide value ranged from 1.286 to 2.251 meq/kg and increased progressively during storage, with the blank showing the greatest increase, from 2.251 to 34.989 meq/kg. In contrast, all samples treated with Moringa extract or microcapsules showed substantially lower increases in peroxide value. At day 12, the peroxide values were 12.198 and 7.689 meq/kg for the treatments at 9 and 18 mg/mL, respectively, compared with 10.894 and 6.430 meq/kg for the corresponding microcapsules treatments. Thus, increasing the treatment concentration from 9 to 18 mg/mL consistently resulted in lower peroxide values for both formulations.

The corresponding TPC for the microcapsules was 8.73 µg GAE and 17.46 µg GAE; while the TPC for the extracts was significantly higher, at 211.01 µg GAE and 422.03 µg GAE (Table S2). Thus, the measured TPC of the free extract was approximately 24-fold higher than that of the corresponding microcapsule treatments.

Figure 4. Effect of the free Moringa extract and the microcapsule on the peroxide value of the oil matrix during storage at 4°C for 12 days. Data points represent mean ± SD (n = 3); Different letters (a-c) at each day indicate significant differences between treatments (Tukey’s HSD, P < 0.05).

DISCUSSION

Encapsulation of the Moringa extract

The influence of ethanol concentration may be related to the formation of inclusion complexes between Moringa phenolics and the ß-CD cavity. Water and ethanol can facilitate guest replacement within the ß-CD cavity, promoting the formation of thermodynamically stable inclusion complexes, whereas excessive solvent may weaken guest-host interactions (Yoshii et al., 1994, 1998; Del Valle, 2004). Gum arabic can improve extract dispersion and interaction with the coating materials, while excessive gum arabic may increase viscosity and consequently reduce EE, as reported during the encapsulation of thyme extract (Cai et al., 2019). The decrease in EE at higher extract loading may indicate saturation of the available ß-CD cavities, resulting in greater amounts of uncomplexed polyphenol remaining outside the ß-CD cavity (Waleczek et al., 2003). In addition, incomplete inclusion complex formation and loss of unencapsulated compounds into the mother liquor during coprecipitation may contribute to the overall EE (Del Valle, 2004).

The obtained EE was lower than those reported for several other polyphenol-rich extracts, including green tea extract (trapping efficiency of 63%; Cruz-Molina et al., 2021), grape cane phenolic extract (80.5%; Escobar-Avello et al., 2021), sugar maple leaf phenolic extract (> 95%; Yeasmen and Orsat, 2024). Such differences may be related to variations in extract composition, wall materials, extract-to-wall ratio, and encapsulation process. Therefore, these differences should be interpreted in relation to both the chemical composition of the extracts and the encapsulation system employed.

Morphological properties of the particle powder

Morphological analysis revealed flake-like structures composed of micro-sized particles, which may be associated with the coprecipitation of the encapsulation matrix. Similar flake-like morphologies have been reported for freeze-dried ß-CD-polyphenol complexes, whereas spray-drying typically produces spherical particles (Pasrija et al., 2015). Studies on encapsulated Moringa extract have also demonstrated that wall materials and drying methods strongly influence particle morphology (Osamede Airouyuwa and Kaewmanee, 2019; Vonghirundecha et al., 2022). DLS analysis showed a Z-average hydrodynamic diameter of 431.5 nm and a PDI of 0.468, indicating a relatively broad particle-size distribution in aqueous dispersion. The difference between the microscale structures observed by SEM and the smaller hydrodynamic diameter measured by DLS may be related to differences in measurement conditions, as SEM examines dried particles whereas DLS measures dispersed particles in suspension. The relatively high PDI is also consistent with the heterogeneous morphology and aggregation observed by SEM. These findings indicate that the developed microcapsules exhibit irregular microscale morphology and a broad size distribution, which should be considered in further development of the encapsulation system.

Storage stability of the particle powder

Storage studies demonstrated that encapsulation significantly improved the stability of Moringa polyphenols under thermal and light exposure. Similar improvements in thermal stability have been reported for encapsulated tea polyphenols and Hypericum perforatum extracts. (Kalogeropoulos et al., 2010; Wang et al., 2016). High temperatures accelerate oxidative degradation and structural changes in polyphenols, whereas the ß-CD cavity and surrounding coating matrix can provide a protective microenvironment that reduces their exposure to degradation factors. In the present study, polyphenols in the free extract degraded approximately three times faster than those in the microcapsules, as reflected by the increase in half-life from 12.7 days for the free extract to 37.3 days for the microcapsules. This enhanced stability may be attributed to the physical protection provided by the ß-CD/MD/gum arabic matrix, which can limit direct exposure of the encapsulated polyphenols to oxygen and other environmental stressors. Similar improvements in stability of encapsulated polyphenol-rich extracts have been reported for cornelian cherry and roselle extracts (Idham et al., 2012; Moldovan et al., 2016), as well as for Moringa extracts, with half-lives up to 44 days at 25°C (Castro-López et al., 2020).

Light exposure also strongly affected polyphenol stability. Samples stored in darkness exhibited the slowest degradation, whereas UV and sunlight accelerated polyphenol loss and shortened the half-lives (t_1/2). The degradation profiles generally followed first-order kinetics, with R² > 0.95 for most conditions; a slightly lower R² of 0.8989 was obtained for the microcapsules under continuous UV exposure, although the degradation trend remained reasonably described by the model. Similar first-order kinetics have been reported for polyphenol-rich extracts to UV treatment (Hunuka Katz et al., 2020). The lower degradation rates observed for the microcapsules may be attributed to the barrier effect of the coating matrix, which can reduce UV penetration and oxygen accessibility, while confinement within the matrix may restrict molecular mobility and further limit degradation. These protective effects are consistent with previous reports of improved photostability of encapsulated resveratrol derivatives and grape polyphenols (Aizpurua-Olaizola et al., 2016; Courtois et al., 2019).

Potential of the microcapsules to prevent lipid peroxidation in cobia fish

The progressive increase in peroxide value in the blank sample indicates continuous formation of primary lipid oxidation products during refrigerated storage. The peroxide value increased by approximately 1,454% from day 0 to day 12, whereas the antioxidant-treated samples showed substantially lower increases. At day 12, the extract treatments reduced peroxide value by 65.1% and 78.0% at 9 and 18 mg/mL, respectively, while the corresponding microcapsule treatments achieved reductions of 68.9% and 81.6%. The higher treatment concentration also provided greater protection against lipid oxidation for both formulations.

Importantly, the free extract contained approximately 24-fold higher TPC than the corresponding microcapsules (211.01 vs. 8.73 µg GAE/mL at 9 mg/mL and 422.03 vs. 17.46 µg GAE/mL at 18 mg/mL) (Table S2). Despite this substantial difference in measured TPC, the microcapsules showed slightly lower peroxide values than the corresponding free extracts under the tested conditions. This difference should not be interpreted as direct evidence of greater antioxidant activity resulting from encapsulation, because the treatments were not matched on a GAE basis. Moreover, the extract contains a complex mixture of phenolic and other compounds that may collectively contribute to its antioxidant activity.

Encapsulation may also provide controlled release of phenolic compounds, allowing their gradual availability over time rather than immediate release, which could contribute to the sustained antioxidant protection observed for the microcapsules (Del Valle, 2004). Similar antioxidant effects of plant polyphenols in seafood preservation have been widely reported, although studies specifically addressing encapsulated polyphenols remain limited (Yang et al., 2024). However, release kinetics were not directly evaluated in the present study; therefore, controlled release remains a possible explanation rather than a demonstrated mechanism. Overall, these findings indicate that both free Moringa extract and microcapsules can retard lipid oxidation, while the microcapsules showed promising protective effects under the tested conditions.

CONCLUSION

This study demonstrated that Moringa oleifera polyphenols could be successfully encapsulated using a ß-CD/MD coating system supplemented with gum arabic. The selected formulation achieved an EY of 81.01% and an EE of 54.54%, and the resulting microcapsules exhibited flake-like structures with heterogeneous microscale morphology. Encapsulation improved polyphenol stability, resulting in an approximately threefold increase in estimated half-life, indicating the potential to extend the storage stability of Moringa polyphenols under the tested environmental conditions. In the cobia fillet model, the microcapsules also effectively retarded lipid oxidation during refrigerated storage, with peroxide value reductions of 68.9% and 81.6% at 9 and 18 mg/mL, respectively.

Overall, the ß-CD/MD/gum arabic system shows potential as a practical approach for improving the stability and preserving the antioxidant performance of Moringa polyphenols in a seafood matrix. Further studies should investigate the molecular interactions and inclusion mechanisms, release kinetics, gastrointestinal bioaccessibility, antioxidant activity using complementary assays, and dose-matched food-model applications to further establish the functionality and practical potential of the developed microcapsules.

ACKNOWLEDGEMENTS

The authors acknowledge the support of time and facilities from Nha Trang University (NTU) for this study.

AUTHOR CONTRIBUTIONS

Tran Thi Phuong Anh: Conceptualization (Lead), Data Curation (Lead), Formal Analysis (Lead), Investigation (Lead), Methodology (Lead), Validation (Lead), Writing-Original Draft (Lead); Ta Thi Minh Ngoc: Conceptualization (Equal), Formal Analysis (Supporting), Validation (Supporting), Writing-Review & Editing (Supporting); Phan Thi Khanh Vinh: Data Curation (Supporting), Formal Analysis (Supporting), Writing-Review & Editing (Supporting).

CONFLICT OF INTEREST

The authors declare that they have no conflicts of interest.

DISCLOSURE REQUIREMENT

During the preparation of this manuscript, the authors used ChatGPT (OpenAI) to assist with English language editing and refinement of academic writing. The authors reviewed and edited the output as necessary and take full responsibility for the final content of the publications.

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Natural and Life Sciences Communications

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Supplementary materials

Table S1. Characterized parameters of microcapsules prepared under the selected formulation.

Table S2. Conversion of TPC values used in the cobia lipid oxidation experiments.

Figure S1.  Particle size distribution of the microcapsules determined by dynamic light scattering (DLS).