The leaves of Brazilian plume (Justicia carnea) are utilized in traditional medicine to treat various ailments in developing countries. The leaves are commonly employed for managing nutritional anemia, a condition affecting over 2 million people globally [1], particularly in Nigeria. The leaves of J. carnea contain an array of natural antioxidants and bioactive constituents, which contribute to the diverse pharmacological activities attributed to the plant [2]. These compounds include phenolics, flavonoids, pigments (such as carotenoids, anthocyanins, and chlorophyll), saponins, tannins, and phytates, alongside essential minerals such as calcium, iron, zinc, magnesium, and vitamins A, B-complex, C, and E [3, 4]. Specifically, the leaf extract is reported to demonstrate high levels of vitamin C (232.32 mg/100 g) and iron (8.61 mg/kg) [1, 3]. Processing techniques, both thermal and non-thermal, can significantly impact the stability and bioavailability of these bioactive compounds, necessitating the need for encapsulation.

Encapsulation involves the formation of a thin layer protection around bioactive components of the food matrix to prevent environmental and enzymatic degradation, preserve bioactivity, and control the release of the substance at the active site [5]. Encapsulation can be achieved on a nano scale (1–100 nm) or micro scale (1–1,000 μm). The thin layer formed is referred to as the cell wall/wall matrix or nano/micro carrier, while the bioactive substance entrapped is the core matrix. Encapsulation, either micro or nano encapsulation, significantly enhances the nutritional value and functionality of food products. It protects bioactive compounds from degradation due to environmental factors such as heat, light, and oxidation, thereby improving their stability and shelf life [6, 7].

Encapsulation allows the controlled release of the bioactive ingredients in food matrices, thereby extending bioavailability and effectiveness upon consumption. It also helps to mitigate challenges associated with the direct incorporation of bioactive compounds, such as undesirable effects on sensory characteristics [6–8]. Encapsulation has been used to fortify bread with bioactive substances without adversely affecting its physicochemical and textural properties [8]. Plant bioactive compounds are substances found in plants that have beneficial effects on human health. The bioactive compounds often possess therapeutic properties and act as antioxidant and anti-inflammatory agents. Pigments such as carotenoids, anthocyanins, betalains, and chlorophylls are examples of such bioactive compounds [9, 10]. Some micronutrients (e.g., Fe, Se, Zn, vitamins B₆, B₁₂, C, D, and E) also exhibit biological activities, including antioxidant functions and contributions to the proper functioning of the immune system [11, 12]. Since these substances are sensitive to environmental degradation, incorporating them into food products through encapsulation helps minimize their degradation and loss during food processing.

Various wall materials have been explored for food encapsulation purposes, including chitosan, starches, alginates, proteins, lipids, maltodextrin, gum arabic, gelatin, and combinations thereof. For example, a combination of maltodextrin and whey protein isolate has been reported to produce microcapsules with a high blueness index, whereas a blend of gum arabic and whey protein isolate yielded the highest microencapsulation efficiency (91.19%) for phycocyanin encapsulation [13]. Similarly, maltodextrin/alginate mixtures have been shown to yield more homogeneous microcapsules with higher oil-encapsulation efficiency (EE; 90%) and enhanced stability at elevated temperatures compared to β-glucan/alginate mixtures [14]. The choice of wall material is, therefore, critical to determine the properties of the microcapsules.

Currently, there are limited or no studies on the encapsulation of J. carnea leaf bioactive compounds. Therefore, this study aims to evaluate the influence of different blends of cell wall materials on the bioactive substances in encapsulated J. carnea leaf extract for potential use in food fortification. The wall materials were selected on the basis of their common usage in food encapsulation, availability, and cost effectiveness.

The moisture content of the microcapsule samples was below the 10% threshold recommended for keeping quality of powdery products, indicating that J. carnea leaf microcapsules may exhibit good storage stability. The presence of maltodextrin in the wall materials facilitated a greater reduction in moisture content compared to wall combinations without maltodextrin, which is consistent with the findings of Tatasciore et al. [16] for microcapsules with maltodextrin walls. Moisture content observed for samples AGM and BGEM is comparable to the values reported for probiotic cell microcapsules (4.5%) encapsulated with gum arabic/gelatin [23] and hop extract encapsulated with gum arabic and maltodextrin (5.27%) [16], whereas samples CGS and DGES (containing starch wall) exhibited higher moisture levels. This suggests that the inclusion of starch in the wall materials increases the final moisture content. According to Paula et al. [23], low moisture content prevents the agglomeration of microcapsules and limits molecular mobility, thereby reducing the diffusion rate of external factors that could adversely affect the core.

The lower solubility observed in sample DGES suggests that this sample may be more stable than others in aqueous medium, exhibiting slower, controlled release properties [24]. Conversely, the higher solubility observed in the microcapsules containing maltodextrin-based wall materials could be attributed to the high water solubility of maltodextrin [25]. The solubility values obtained in this study were comparable to those reported for microcapsules of date pit phenolic compounds encapsulated with maltodextrin (60.39%) [26] and papaya seed extract encapsulated with chitosan (61.5–62.7%) [27], except for sample AGM (70.86%). However, the solubility of black cumin seed oil encapsulated with gum arabic and maltodextrin was up to 88.71% [28], higher than the values obtained in the current study (60.85–70.86%). Such variations could be attributed to differences in core-to-wall ratio, wall material composition, core material characteristics, and drying conditions.

Although samples containing starch in the wall materials exhibited lower solubility, maltodextrin-containing walls, with their higher solubility, may facilitate rapid dissolution, which could be leveraged for targeted release under specific conditions (e.g., in the gut, presence of enzyme). However, it should be noted that highly soluble wall material may lead to a burst release of the core, potentially compromising the overall stability of the microcapsules.

The higher brightness observed in microcapsules with maltodextrin walls can be attributed to the white color of maltodextrin. The color, due to positive a* and b* values, indicates that the microcapsules are composed of red and yellow hues, respectively, while the proximity of these values to zero suggests a greyish appearance, with maltodextrin-containing samples appearing brighter. The L*-values of samples containing gum arabic in the wall materials were not significantly different (P ≤ 0.05). In the present study, the coloring power, L* is lower, the b* values were in agreement, and a* values were higher (though less than 1) compared to values reported for hop extract and black cumin seed oil encapsulated with gum arabic and maltodextrin [27, 28]. These differences may be due to variations in the nature of the core and ratio of the wall materials.

The combination of gelatin and maltodextrin resulted in the lowest EE (32.24%), while a blend of gelatin and starch achieves the highest, implying that gelatin and maltodextrin may not be an optimal combination for encapsulating J. carnea leaves extract. The higher EE observed with a blend of gelatin and starch wall may be attributed to a higher molecular weight of starch compared to maltodextrin. Prior studies have shown that EE improves when higher molecular weight carbohydrates are utilized [19, 29]. The EE reported for the sample containing gum arabic and maltodextrin wall (59.87%) was comparable to that reported for hop extract encapsulated with the same wall combination [16], whereas the EE for the gelatin-starch blend, though the highest in this study, was lower than values reported for black cumin seed oil and probiotics cells [23, 28]. Differences in EE could be due to variations in the encapsulation process, including the drying method employed. High EE indicates effective enclosure of the core material within the cell wall.

The sample containing a gelatin-starch blend exhibited the highest concentration of the pigments, except betalain, which was more in the sample containing gelatin-maltodextrin blend. This may be due to the presence of gelatin, a protein-based wall material. Díaz-Montes [30] reported that polysaccharide-based walls may not be optimal for encapsulating chlorophyll and carotenoids, while protein-based walls, either alone or combined with polysaccharides, enhance microcapsule characteristics. Protein-based walls, having amphipathic properties, interact with both hydrophilic (e.g., betalain) and hydrophobic (e.g., chlorophyll and carotenoids) pigments [30]. Wall materials serve as barriers protecting pigments from degradation by external factors such as light, oxygen, and heat.

The highest mineral and vitamin retention was observed in sample DGES, except for vitamin B₂, indicating that the combination of gelatin and starch as wall materials is more effective at preserving these nutrients than other combinations. This finding aligns with the report by Bajaj et al. [31] for the microencapsulation of vitamin B₁₂ and D₃ using modified starch and maltodextrin. Carbohydrate- and protein-based polymer blends are considered optimal for encapsulating bioactive compounds [32], and encapsulation within such matrices effectively extends the shelf-life of substances susceptible to oxidation and thermal deterioration [33].

SEM characterization revealed smooth surfaces and polyhedral shapes with varying sizes. Samples containing gelatin exhibited smoother surfaces compared to those without gelatin, suggesting that blending gelatin with either maltodextrin or starch improves microcapsule stability and enhances bioavailability of bioactive compounds in J. carnea leaf. Alves et al. [22] also reported smooth surfaces for encapsulated essential oil containing maltodextrin as wall material. According to Bajaj et al. [31], smooth surfaces promote higher retention of encapsulated materials. Moreover, smooth, regular shapes are associated with low gas permeability, thus leading to retention of the core within the microcapsules [28]. The variation in particle size observed is consistent with the report of other researchers [21, 28, 34]. However, the particle sizes obtained in this study were larger than those reported for papaya seed extract and vitamin B and D microcapsules produced via spray drying [27, 31]. Santiworakun et al. [28] reported collapsed, irregular shapes for black cumin oil microcapsules encapsulated with a blend of gum arabic and maltodextrin, contrasting with the regular shapes observed in this study, likely due to differences in the method of encapsulation and drying process.

The endothermic site observed in the DSC curves indicates that the samples absorb heat and undergo melting at the active sites. The poorly defined peaks are an indication that a complex phase transition may be occurring in the sample at the active site. It may also be an indication of an irreversible transition process. According to Michael et al. [35], broad or poorly defined DSC peaks often indicate complex thermal behavior or overlapping transformations, making it challenging to determine characteristic properties of the products. The amorphous nature exhibited by the samples indicates that the wall materials effectively encapsulate the bioactive substances in J. carnea leaves extract. Amorphous nature is reported to be a confirmation that the core is properly encapsulated by the cell wall material [22]. The transition temperatures revealed that the samples are thermally stable and resist structural changes up to approximately 76°C, with the sample containing a blend of gum arabic and maltodextrin exhibiting thermal and structural stability up to 87°C. These findings show that the wall materials can protect the bioactive compounds in J. carnea leaves during food processing temperatures up to 76°C. Low transition temperatures are considered crucial for biological systems [36, 37] such as food systems meant for human consumption.