Biomacromolecule-based encapsulation of Hibiscus sabdariffa polyphenols for functional foods and nutraceuticals

1 Introduction

The genus Hibiscus comprises several plants that are morphologically and phytochemically diverse. One of the most well-documented species is H. sabdariffa (Hibiscus sabdariffa) for its nutritional and therapeutic value. H. sabdariffa, commonly known as red sorrel, roselle, or karkade, belongs to the family Malvaceae. It is widely distributed on a large scale in North African and Southeast Asian nations and in tropical and subtropical regions of the world.

Bioactive compounds present in H. sabdariffa occur in varying concentrations among its different plant parts, thereby making the choice of plant material critical for the extraction of bioactive components (Riaz et al., 2021; Ayo-Omogie et al., 2023). While the calyx constitutes the major commercially utilized part of the plant, the processes involved in the processing and cultivation of H. sabdariffa produce other biomass that can be used to extract various value-added components. Such biomass includes spent calyx following the preparation of beverages or decoctions, seed cake following the extraction of oil from the seeds, and other biomass generated through agricultural activities.

Due to the presence of anthocyanins, flavonoids, phenolic acids, and organic acids in H. sabdariffa, its biomass can be considered a raw material for obtaining value-added components. Nevertheless, the isolation of bioactives is dependent on the plant part, previous processing, extraction conditions, and the chemical stability of the isolated compounds. Anthocyanins are affected by several environmental factors that influence their chemical and physical characteristics, including pH, temperature, oxygen, and light. For this reason, both the effective isolation and protection of the obtained bioactive components are equally important.

Carbohydrates contribute 12%–54% of the total biomass in plants. These include polysaccharides such as cellulose and hemicellulose, together with storage carbohydrates in the form of starch and soluble sugars. Other major constituents include crude fiber (2.3%–27%), proteins (3%–27%), and fats (0.1%–13%) (Bevan et al., 2023). In H. sabdariffa, anthocyanin concentration is estimated at 1.5%, which is higher than in other major edible plant species (Hoang et al., 2023). The higher concentration of anthocyanins makes the plant an excellent candidate for use as a natural food colorant (Meftahizadeh et al., 2022). Anthocyanins and flavonoids are the phytochemicals of interest because of their structural features, including hydroxylation, glycosylation, and conjugation.

In this context, this review critically analyzes the valorization of H. sabdariffa biomass, considering the extraction of bioactive compounds from residues and underutilized parts of the H. sabdariffa plant and the stabilization of these compounds using biomacromolecular carriers. The use of conventional calyx and leaf studies, however, is included in this review as a reference for the compositional and technological aspects of residue valorization. Extraction approaches are discussed in terms of bioactive recovery and preservation, followed by assessment of food-grade biomacromolecular encapsulation systems based on encapsulation efficiency (EE), physicochemical stability, gastrointestinal release, and potential applications in functional foods and nutraceuticals. Where residue evidence is limited, these gaps are highlighted to distinguish established applications from future waste-to-value opportunities.

2 Phytochemical variability and functional relevance of Hibiscus sabdariffa

The cultivation of H. sabdariffa is linked to its high nutritional value and varied phytochemical profile. Different varieties of the plant can be found in different geographical locations, including red and green types, which are two well-known varieties/accessions (Delfin and Marutani, 2025). The red variety usually produces red calyces with a high anthocyanin content, while the green variety is characterized by light-green calyces with a lower anthocyanin content (Navidad-Murrieta et al., 2023).

There have been many studies on different accessions of H. sabdariffa showing significant variations in phytochemical composition, such as variations in phenolics, anthocyanins, flavonoids, and antioxidants (Delfin and Marutani, 2025). The red and green types also show variations in their nutritional and mineral compositions, thereby suggesting that the genotype and the environment of the plants can affect the production of secondary metabolites (Navidad-Murrieta et al., 2023).

Quantitative evidence shows that roselle agro-waste can retain valuable bioactives. Using optimized ultrasound-assisted extraction (UAE), calyx residue, stems, and leaves yielded 3.011, 0.077, and 0.073 mg cyanidin-3-glucoside (Cya3G)/g dry weight of total anthocyanins, respectively. Although calyx residue had lower anthocyanin content than fresh calyx, its total phenolic and flavonoid contents did not differ significantly (Abu Bakar et al., 2023). Similarly, roselle decoction residues retained substantial amounts of polyphenols, anthocyanins, flavonoids, and antioxidant activity after processing (Hernández-Bautista et al., 2025). Comparative characterization also showed differences in extractable and non-extractable phenolic and organic acid fractions between fresh calyces and decoction by-products. Used roselle calyces retained 23%–140% of the extractable polyphenols and organic acids present in the original calyces, while non-extractable constituents associated with dietary fiber increased to 126%–272% (Serna Tenorio et al., 2023). Thus, compositional data from fresh or untreated calyces should not be assumed to represent processing residues. Decoction residues from cordial and juice production also retained anthocyanins, phenolics, flavonoids, and antioxidant activity; cordial residues showed values closer to fresh calyces and higher antioxidant potential than juice residues, supporting their use as natural antioxidant sources in value-added foods (Yusoff et al., 2024). Further, decoction calyces have been incorporated into extruded corn-based snacks at 5% and 10% substitution levels, retaining anthocyanin-associated color and acceptable sensory characteristics and demonstrating direct food-product valorization (Hernández-Bautista et al., 2026a).

These differences have practical implications for downstream utilization. Residue-derived extracts should therefore be characterized based on their actual phytochemical profiles rather than relying only on data from untreated plant material, particularly when interpreting extraction and encapsulation studies.

3 Advances in extraction strategies and polyphenolic composition of Hibiscus sabdariffa

3.1 Extraction approaches

The effectiveness of the extraction method and the stability of polyphenols from H. sabdariffa are largely dependent on the type of solvent used, temperature, extraction time, and other process parameters (Wen et al., 2020). Conventional techniques such as aqueous extraction and Soxhlet extraction have been widely used, while microwave-assisted extraction (MAE), UAE, enzyme-assisted extraction, pulsed electric field, and pressurized liquid extraction (PLE) have been studied to enhance mass transfer and reduce extraction time (Table 1) (Dehn et al., 2026; Mudau and Adebo, 2026; Wianowska and Gil, 2019). However, higher extraction efficiency does not necessarily mean better preservation of thermolabile compounds, especially anthocyanins. In PLE of H. sabdariffa calyces at temperatures ranging from 40 ^°C to 200 °C, the highest total phenolic extraction was obtained at 200 ^°C using 100% ethanol, whereas cyanidin-3-sambubioside was quantified only at 40 ^°C. This finding highlights that extraction conditions should balance bioactive recovery with preservation, rather than maximize yield alone (Pimentel-Moral et al., 2020).

TABLE 1. Extraction techniques for Hibiscus sabdariffa bioactive constituents: solvents, conditions, and outcomes.

In addition, supercritical CO₂ extraction and natural deep eutectic solvents have been studied as potential methods to extract compounds from plants using minimal amounts of organic solvents (Giribabu et al., 2026; Feng et al., 2026). For anthocyanin-rich H. sabdariffa plant materials, solvent sustainability should also be considered alongside the polarity and extraction intensity required for the target compounds. In the case of anthocyanins, mild extraction methods such as UAE with aqueous and natural deep eutectic solvents can be effective (Chua et al., 2024).

Residues obtained during aqueous beverage or decoction preparation can already have undergone extensive mass transfer. Other underutilized fractions can contain varying amounts of extractable and non-extractable constituents. Hence, parameters optimized for fresh calyces cannot necessarily be applied to residues. The UAE process using hydrophobic deep eutectic solvents on waste hibiscus flowers resulted in 147.73 ± 2.76 mg β-carotene equivalents (BCE)/100 g of carotenoids, 178.90 ± 2.64 mg quercetin equivalents (QE)/100 g of flavonoids, and 61.15 ± 1.15 mg gallic acid equivalents (GAE)/100 g of phenolic compounds. The residual biomass was found to contain 49.58% ± 0.53% total dietary fiber with a water-holding capacity of 7.8 g/g residual biomass (Verma et al., 2026).

Studying fresh or dried calyx samples can be considered valuable from the technical perspective as a source of information about solvent composition and extraction process severity, but it is important not to use this information as proof of residue valorization because processing can alter extractable and non-extractable phytochemical fractions.

Researchers have also studied seed-derived material as another potential source of recoverable phenolic compounds. MAE of defatted H. sabdariffa seeds with 70% ethanol-water resulted in the highest phenolic content, amounting to 18.2244 mg GAE/g under optimized conditions. However, the relatively high temperature attained in this process negatively affected the extraction of flavonoids, thus showing the importance of balancing bioactive recovery with thermal stability during the valorization of seed-derived material (Yusoff and Leo, 2017).

3.2 Phytochemical constituents

Major phenolic constituents include chlorogenic acid, gallic acid, protocatechuic acid (PCA), and flavonoids such as rutin, quercetin, and kaempferol (Wianowska and Gil, 2019). Phytochemical composition also varies among plant fractions, with tannins reported as important constituents of H. sabdariffa leaves (Clímaco et al., 2023). Table 2 summarizes the major phytochemical constituents of H. sabdariffa.

TABLE 2. Major bioactives identified in Hibiscus sabdariffa and their distribution in plant parts.

DW: dry weight; EC: catechin equivalent.

3.2.1 Polyphenols

Polyphenols are a significant group of compounds found in H. sabdariffa, with phenolic acids playing an important role in its antioxidant activity (Torres-Fuentes et al., 2025; Akhila et al., 2024).

According to a study of 31 accessions of H. sabdariffa, three main phenolic acids were found: neochlorogenic acid, chlorogenic acid, and cryptochlorogenic acid (Wang et al., 2016). Differences in the content of individual phenolic acids can affect the composition and functional characteristics of extracts obtained from H. sabdariffa accessions.

3.2.2 Anthocyanins

Anthocyanins are the primary class of pigments that confer the reddish color to the H. sabdariffa calyces and are among the most significant bioactive components. Some of the major anthocyanins reported in hibiscus are delphinidin-3-sambubioside and cyanidin-3-sambubioside (Nguyen et al., 2022b).

Being sensitive to light, temperature, pH, and oxygen can affect the stability of anthocyanins, thus limiting their use in foods; hence, stabilization is an important aspect to consider for anthocyanin-rich extracts. Studies have demonstrated that anthocyanin-rich Hibiscus extract can induce apoptosis in HL-60 human leukemia cells via the p38-FasL and Bid signaling pathway (Chang et al., 2005). Another study showed that delphinidin-3-sambubioside, when used alone, could induce apoptosis in HL-60 human leukemia cells through a reactive oxygen species-mediated mitochondrial pathway, involving Bid truncation and cytochrome c release (Hou et al., 2005).

3.2.3 Flavonoids

Analysis of chemical compounds in 31 H. sabdariffa genotypes through quadrupole time-of-flight mass spectrometry and high-performance liquid chromatography (HPLC) found that the major flavonoids present include rutin, quercetin, and kaempferol derivatives. Other flavonoids such as myricetin and kaempferol have also been reported to be present in roselle calyces along with anthocyanins and phenolic acids (Wang et al., 2016; Hamrita et al., 2022). The presence of various types of structurally different flavonoids is significant for understanding the functional properties of H. sabdariffa extracts because different substitution patterns and glycosylation may affect their physicochemical properties and antioxidant activity.

3.2.4 Organic acids

H. sabdariffa is also rich in organic acids, such as hibiscus, malic, tartaric, hydroxycitric, citric, and ascorbic acids. Other organic acids reported include hibiscus acid dimethyl ester and hibiscus acid hydroxyethyl ester (Hapsari et al., 2021). MAE has also been reported to improve the recovery of hibiscus acids and their derivatives, with concentrations of individual compounds reaching up to 70 mg/g extract under the conditions investigated (Pimentel-Moral et al., 2018a). Gas Chromatography–Mass Spectrometry (GC-MS) analysis of H. sabdariffa leaves also identified several organic compounds, including cyclopropane carboxylic acid methyl ester, n-hexadecanoic acid, oleic acid, hexadeca-2,11-dienoic acid, octadecanoic acid, E−11-hexadecenal, and E−13-docosenoic acid (Okore et al., 2021).

4 Structure-activity relationships and biological roles of polyphenols

The biological and functional properties of H. sabdariffa polyphenols depend on their molecular structure. Hydroxylation, glycosylation, and conjugation influence electron-donating capacity, metal chelation, stability, and interactions with biological or formulation matrices, affecting their performance during extraction, processing, and delivery.

4.1 Molecular determinants, pigment chemistry and degradation kinetics

The molecular structure of the anthocyanins of H. sabdariffa greatly affects their antioxidant behavior and physicochemical stability. Hydroxylation, glycosylation, and conjugation influence electron-donating capacity, radical stabilization, hydration, oxidation, and pigment stability. Increased hydroxylation of the B-ring enhances the electron-donating ability while at the same time increasing the susceptibility to oxidation. This is because of the presence of the catechol structure in cyanidin derivatives and the additional hydroxyl group in delphinidin derivatives, which contribute to differences in redox properties and stability (Ahmed et al., 2026). These features also affect hydrogen-atom and electron-transfer reactions, radical stabilization, and metal chelation, helping to explain differences in antioxidant activity.

Glycosylation also affects anthocyanin stability. 3-O-glycosylation generally converts unstable anthocyanidins into water-soluble and more stable pigments and also affects hydration, molecular interactions, and color stability. The major roselle anthocyanins, delphinidin-3-O-sambubioside and cyanidin-3-O-sambubioside, are 3-O-glycosides bearing sambubiose at C3; therefore, this substitution can influence their stability and antioxidant behavior (Fu et al., 2026).

pH is important in the stabilization of anthocyanins since the flavylium chromophore displays reversible structural changes in aqueous environments. In acidic conditions, the red flavylium cation is dominant, while an increase in pH favors the formation of the colorless carbinol pseudobase, followed by the quinoidal and chalcone forms. The above-mentioned changes affect the chromophore, color, spectral properties, and chemical stability of the compound. Anthocyanins in H. sabdariffa extracts also show faster degradation with increasing temperature and increasing pH (less acidic conditions), supporting the need for protective encapsulation during processing and storage (Saidji et al., 2024).

However, in roselle, delphinidin-3-O-sambubioside, which has a more highly hydroxylated B-ring than cyanidin-3-O-sambubioside, shows differences in redox reactivity and degradation behavior. A kinetic study at 4–37 °C for 60 days showed first- order degradation, with a higher rate constant for delphinidin-3-O-sambubioside (9.2 × 10⁻⁷ s^-1) than cyanidin-3-O-sambubioside (8.4 × 10⁻⁷ s^-1) at 37 ^°C. Activation energies were 90 and 80 kJ mol^-1, respectively, indicating greater temperature sensitivity of delphinidin-3-O-sambubioside. Degradation produced gallic acid and PCA and increased polymeric color formation (Sinela et al., 2017).

4.2 Antioxidant activity and redox potential

Roselle by-products contain higher levels of non-extractable polyphenols and dietary fiber than calyces. Ultra-Performance Liquid Chromatography–Quadrupole Time-of-Flight Mass Spectrometry (UPLC-QTOF-MS) analysis tentatively identified 34 extractable polyphenols, three hydrolyzable polyphenols, and two organic acids in the calyx and by-product, highlighting the retention of diverse bioactive constituents in processing-derived material (Amaya-Cruz et al., 2019).

Variations in phytochemical content and antioxidant activity of methanolic extracts of calyces, leaves, and stems of H. sabdariffa have been observed. The total phenolic content of the extracts was 4.22 ± 0.04 mg/g (calyx), 3.41 ± 0.03 mg/g (leaves), and 2.34 ± 0.01 mg/g (stems) (Adusei, 2020). These variations indicate that antioxidant activity depends on the amount and type of phenolics present within the plant matrix.

From a molecular point of view, the mechanism of action of antioxidants is generally associated with the scavenging of reactive oxygen and nitrogen species, stabilization of phenoxyl radicals, metal chelation, and modulation of endogenous antioxidant defenses, with their relative contributions depending on the structure of individual polyphenols and their surrounding chemical environment.

4.3 Antimicrobial activity and food preservation potential

Another functional property associated with phenolic compounds is antimicrobial activity, which may depend on their chemical composition and interactions with microbial cells. Since phenolic compounds can interact with microbial membranes and cellular components, affecting membrane integrity and cellular functions, different phenolic compositions may result in variations in the antimicrobial activities of H. sabdariffa extracts.

Calyx extracts from H. sabdariffa have also been shown to possess antimicrobial activity against food-borne pathogens. These extracts were obtained by autoclaving (30 min at 121 ^°C) and membrane filtration (0.22 μm) and displayed antimicrobial activity. Autoclaving increased the bacteriostatic effect of H. sabdariffa extracts against Escherichia coli and Staphylococcus aureus in milk. Although autoclaving decreased the anthocyanin concentration, it did not significantly affect the phenolic content, indicating that the antimicrobial activity of H. sabdariffa extracts was not solely dependent on anthocyanins (Higginbotham et al., 2014).

The aqueous and ethanolic extracts from dried H. sabdariffa calyces demonstrated antioxidant and antimicrobial activities. The phenolic compounds present in the extracts were determined using LC-MS and included 3-caffeoylquinic acid, 5-feruloylquinic acid, and myricetin; in addition, the extracts inhibited swarming of Pseudomonas aeruginosa and displayed high 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity (Hamrita et al., 2022). Based on the results obtained, the antimicrobial properties of H. sabdariffa extracts may reflect the combined contribution of structurally diverse phenolic constituents.

The antimicrobial and antioxidant activities of H. sabdariffa extracts suggest that they could be useful for food preservation. However, their effectiveness can be influenced by several factors, including the extract composition, concentration, processing conditions, and interactions within the food matrix. Therefore, further validation under practical storage conditions is needed.

4.4 Anti-inflammatory effects

The anti-inflammatory potential of H. sabdariffa has been investigated in different experimental models and may vary according to extract composition, bioactive constituents, and the biological model used (Zhang et al., 2024).

Polyphenolic extracts of H. sabdariffa have been investigated in HaCaT skin cells stimulated with tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ). The treatment reduced inflammatory markers, including interleukin (IL)-6, IL-8, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1), while increasing IL-10 and reducing the aging-associated matrix metalloproteinase-1 (MMP-1). In addition, increased expression of elastin and collagen IV was observed. At the molecular level, the polyphenolic treatment suppressed activation of the mitogen-activated protein kinase (MAPK) pathway, indicating a potential role of roselle polyphenols in regulating inflammation-associated cellular signaling (Zhang et al., 2024).

The potential of H. sabdariffa extracts in inflammation-related applications has also been investigated in wound-healing models. Researchers formulated 70% ethanolic flower extract as a 10% w/w ointment using a paraffin-based base and evaluated its formulation stability, skin safety, and wound-healing activity. Treatment with the extract formulation was associated with improved wound-healing responses and reduced oxidative damage following burn injury, while antibacterial activity against P. aeruginosa was also reported (Khalil et al., 2022).

Taken together, these findings support the anti-inflammatory potential of H. sabdariffa polyphenols, but further studies are needed to clarify the roles of individual compounds, dose–response relationships, and the effectiveness of encapsulated polyphenols in cosmetic and other applications.

4.5 Anticancer potential and cellular signaling pathways

The anticancer potential of anthocyanins and other phenolic compounds of H. sabdariffa has been explored in relation to oxidative stress, apoptosis, and tumor cell proliferation (Nguyen et al., 2022b).

Ethanol extracts of H. sabdariffa exhibited moderate cytotoxicity against human hepatocellular carcinoma HepG2 cells, with an IC₅₀ value of 629.919 μg/mL using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay (Anggi et al., 2023). On the other hand, a methanolic extract of H. sabdariffa leaves exhibited greater cytotoxicity against Ehrlich Ascites Carcinoma cells, with an IC₅₀ of 26.15 μg/mL (Islam et al., 2021). Nevertheless, the cytotoxic potency of the two extracts cannot be compared directly because the two experiments used different cancer cell models, extraction solvents, and experimental conditions.

Other mechanistic investigations have shown that extracts of H. sabdariffa rich in anthocyanins may affect the processes involved in apoptosis in cancer cell models. In colorectal cancer cells, apoptosis induction by anthocyanin-rich extracts is dose- and time-dependent through the AMP-activated protein kinase (AMPK) signaling pathway and Fas-mediated apoptotic mechanisms, including caspase-8/tBid, cytochrome c release, and cleavage of caspase-3 (Tsai et al., 2023). The current scientific literature has mainly focused on preclinical investigations, and the role of individual anthocyanins and their molecular targets needs to be further studied.

4.6 Antihypertensive effects

Another potential benefit associated with H. sabdariffa is its possible use as an antihypertensive agent. Clinical evidence has demonstrated that the consumption of H. sabdariffa preparations can lead to a decrease in blood pressure (BP). During the study carried out in Iraq, 121 patients with hypertension and BP ≥ 140/90 mmHg consumed H. sabdariffa decoction at a dose of 10 g/day for 6 weeks. After the 6-week intervention, 61.8% of the participants in the treatment group had BP below 140/90 mmHg, whereas only 6.7% in the control group achieved this result. Systolic and diastolic BP decreased by 23.1 and 12.0 mmHg, respectively. The decoction used in this research included about 36 mg of anthocyanins and 2.13 g of hibiscus acid (Al-Anbaki et al., 2021).

Several mechanisms have been suggested to explain the antihypertensive effects of H. sabdariffa, such as the modulation of angiotensin-converting enzyme (ACE) activity, nitric oxide-mediated vascular responses, and the enhancement of endothelial function. The action of anthocyanins and organic acids could be due to their interactions with vascular and metabolic pathways, but the relative contribution of each component cannot be clearly defined due to the presence of many bioactive components in H. sabdariffa preparations.

Overall, clinical evidence suggests that H. sabdariffa has the potential to be used as a dietary source for supporting cardiovascular health. When correlating the reported antihypertensive effect with specific polyphenols or organic acids, it is important to account for variation in extract composition, dose, preparation method, and compound bioavailability. Further studies linking compound structure with biological activity would strengthen the mechanistic basis for their potential use in nutraceutical applications.

5 Encapsulation technologies for stabilization of Hibiscus sabdariffa polyphenols

The process of encapsulation allows H. sabdariffa polyphenols to be introduced into protective matrices. It helps facilitate their handling, storage, and incorporation into food and nutraceutical formulations. This section focuses on physical encapsulation technologies that allow the production of powders, particles, and hydrogels, with emphasis on processing conditions, carrier composition, and physicochemical characteristics.

5.1 Spray drying

The spray-drying method is one of the most commonly used methods for the encapsulation of thermolabile polyphenols due to its scalability, cost-effectiveness, and suitability to produce stable powder formulations (Rahul et al., 2024). This is an industrial-scale technique where the bioactive-loaded emulsion is atomized into a hot chamber, leading to rapid evaporation of the solvent and the formation of microencapsulated particles (Suhag et al., 2025; Gençdağ et al., 2022).

The spray-drying process greatly affects the physicochemical stability of H. sabdariffa polyphenols. A formulation that consists of 8% isomalt and 12% whey protein concentrate processed at an inlet temperature of 140 °C, an outlet temperature of 85 °C, and a feed rate of 12 mL/min showed improved retention of anthocyanins, flavonoids, and total phenolic compounds, as well as favorable powder characteristics (Minh, 2020).

The EE of spray-dried H. sabdariffa anthocyanins using a maltodextrin-gum arabic (MD-GA) carrier system was 93.87%, while the anthocyanin content was 100.22 mg/g at 144 ^°C and a 7 mL/min feed rate (Hoang et al., 2024). The resulting particles had a moisture content of 5.14% and a particle size between 2 and 10 µm. According to the scanning electron microscopy (SEM) analysis, the particles were mostly spherical and had only minor surface irregularities, whereas the Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirmed the successful encapsulation of anthocyanins and the powder system’s low crystallinity.

Therefore, spray drying (Figure 1) can be considered a scalable approach for food applications, whose performance is mainly evaluated based on EE, bioactive retention, moisture content, particle size, and powder morphology.

5.2 Nano spray drying

Nano spray drying can be considered a more sophisticated approach to particle engineering and provides better control over particle size, morphology, and surface properties compared to traditional spray drying, and is expected to offer some advantages in terms of the solubility, dispersibility, and delivery of encapsulated bioactive compounds (Singh et al., 2023). Nano spray drying involves the use of specialized components such as a vertical drying chamber, a piezoelectric/vibrating-mesh atomizer, an electrostatic particle collector, and porous metal foam for flow control of drying gas (Piñón-Balderrama et al., 2020). These modifications enable the production and collection of smaller particles with controlled characteristics.

Nevertheless, information regarding the use of nano spray drying for H. sabdariffa is insufficient. While considerable research on conventional spray drying provides data on EE, anthocyanin retention, particle size, and powder characteristics, the same cannot be said for nano spray-dried H. sabdariffa extracts. Thus, its relative performance cannot currently be established. Further research should look into EE, anthocyanin retention, particle characteristics, storage stability, and gastrointestinal release of nano spray-dried H. sabdariffa extracts to determine whether the greater particle control offered by nano spray drying provides a meaningful advantage for H. sabdariffa polyphenols.

5.3 Freeze drying

Freeze-drying is widely used for preserving thermolabile phytochemicals because it minimizes thermal degradation by freezing the material followed by sublimation of ice under vacuum, thereby helping to preserve sensitive phytochemicals such as anthocyanins and phenolic acids (Nyamgero et al., 2025).

A comparative analysis of fresh, air-dried, oven-dried, and freeze-dried H. sabdariffa materials showed that freeze-drying provided the highest retention of phenolics and antioxidant potential (Hashim et al., 2024). Anthocyanins and phenolics isolated from H. sabdariffa calyces by UAE (45 min, 60 °C, 25% ethanol) were subsequently freeze-dried to enhance shelf-life (Paraíso et al., 2020). Freeze-drying provided the highest stability when samples were stored at 4 ^°C under dark conditions, with bioactive losses ranging from 3% to 26%; under illumination, decomposition reached 43%. The addition of 4% gelatin also improved the sensory properties and color stability of the final product.

Freeze-drying (Figure 2) is especially well-suited for valuable nutraceuticals and natural colorants, but its high cost and hygroscopicity remain important disadvantages.

5.4 Ionic gelation using calcium alginate

Calcium alginate encapsulation can stabilize oxidation-sensitive polyphenols from H. sabdariffa through ionic gelation, in which antioxidant-containing extracts are incorporated into hydrogel matrices. H. sabdariffa extracts incorporated into calcium alginate beads reduced lipid oxidation in oil–water emulsions, with approximately 80% reduction in hydroperoxides and nearly 20% reduction in thiobarbituric acid reactive substances. The polyphenol release rate ranged from 0.068 to 0.079 mg GAE/mL, while antioxidant activity remained stable under acidic and ethanolic conditions (Bevan et al., 2023).

Calcium alginate beads provide a non-thermal encapsulation approach and can be incorporated into beverages and emulsions. However, bead size, swelling behavior, matrix stability, and retention of the encapsulated compounds need to be matched to the intended food matrix and processing requirements.

5.5 Complex coacervation

Decoction of H. sabdariffa calyces leaves a substantial proportion of functional constituents in the resulting residue. The decoction residues contained 407.4–457.0 g kg^-1 dry matter of dietary fiber and 50.7–121.8 µmol Trolox equivalent g^-1 dry matter of natural antioxidants, indicating their potential as antioxidant dietary fiber sources (Sáyago-Ayerdi et al., 2014). Further valorization of these residues through complex coacervation using gelatin and GA, followed by lyophilization, preserved 82.7% of total polyphenol content and maintained antioxidant capacity at 71.9%, 67.9%, and 58.2% for DPPH, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and ferric reducing antioxidant power (FRAP) assays, respectively (Hernández-Bautista et al., 2026b). The resulting microcapsules also retained antioxidant capacity during simulated gastrointestinal digestion in a food matrix (porridge), with the highest retention observed in the small intestine. These findings demonstrate that H. sabdariffa decoction residues can be valorized through biomacromolecule-based encapsulation.

6 Carrier molecular architecture for Hibiscus sabdariffa polyphenol delivery

Improved delivery strategies may be used to enhance the bioavailability and control the release of phytochemicals through modulation of interactions between the phytochemicals and carrier matrices under gastrointestinal conditions (Jalali-Jivan et al., 2025). Figure 3 shows some examples of biomacromolecular delivery architectures studied in this section. The remaining subsections will concentrate on carrier structure, protection of polyphenolic compounds, release behavior under simulated gastrointestinal conditions, and feasibility for incorporation into food matrices, with emphasis on H. sabdariffa-specific evidence where available.

6.1 Carbohydrate-based systems

Carbohydrate-based carriers include MD, GA, starch, pectin, and chitosan. These materials have been extensively researched for carrier applications because of their film-forming properties and stabilization capabilities, in addition to being food-compatible (Villanueva-Carvajal et al., 2013). Their selection depends on the properties of the core material, the encapsulation process, and the intended application.

MD and GA have been widely used as wall materials for polyphenol encapsulation due to their favorable solubility, low viscosity, and film-forming properties (Younesi et al., 2023; Nguyen et al., 2022a). MD with a dextrose equivalent (DE) of 10–20 is considered most appropriate for encapsulation processes, as it provides good solubility and low viscosity at high concentrations, although its emulsifying capacity is low. In contrast, GA contains approximately 2% protein, which provides excellent emulsifying properties; however, its viscosity increases at high concentrations. MD and GA are thus capable of delivering complementary carrier functions, where MD enhances processability, while GA provides interfacial and film-forming properties. Thus, an appropriate MD ratio could provide a balance between processability and protection of encapsulated bioactives. In another study on the effects of freeze-drying on the components, a combination of 3% MD-GA at a ratio of 60:40 exhibited the highest amount of total phenolics, while formulations having 3% GA or 3% MD alone had the highest amounts of anthocyanins (Cid-Ortega and Guerrero-Beltran, 2022). The results suggest that the composition of the carrier can differentially affect the retention of phenolics and anthocyanins during drying, highlighting the importance of optimizing carrier combinations according to the target bioactive and processing technology (Table 3).

TABLE 3. Encapsulation materials and techniques used to preserve bioactive compounds from Hibiscus sabdariffa.

NR: not reported; TMA: total monomeric anthocyanins; C3G: cyanidin-3-glucoside; TPC: total phenolic content; CaCl₂: calcium chloride; PGPR: polyglycerol polyricinoleate; HSE: Hibiscus sabdariffa extract.

6.2 Protein-based complexes

Interactions between proteins and polyphenols offer a way to stabilize and deliver H. sabdariffa bioactive compounds. The interactions of whey proteins, caseins, and ovalbumins with roselle anthocyanins have been studied for their ability to improve anthocyanin stability during simulated digestion (Wang et al., 2024). Nanocomplexes of whey protein isolate with apple pectin were prepared and showed improved anthocyanin retention during gastrointestinal digestion (Jing et al., 2025).

Some of the protein-based systems include complexes of whey protein concentrate and GA for the stabilization of roselle extract emulsions, and films and hydrogels containing whey protein for polyphenol release and microencapsulation (Pimentel-Moral et al., 2018b; Serrano-Cruz et al., 2013; Castro et al., 2025). However, protein-based systems for H. sabdariffa waste-derived extracts have not been explored to any significant extent, highlighting an opportunity for waste-to-value delivery systems.

6.3 Lipid vesicles

6.3.1 Phytosomal

Phytosomes are delivery systems that rely on phospholipids to enhance the membrane permeability of polyphenols derived from plants (Ghanbarzadeh et al., 2016). In these delivery systems, the interaction between the phytochemicals and the phospholipid polar head groups occurs via hydrogen bonding. This creates a molecular complex that can aid in the stabilization and membrane permeation of these phytochemicals. The phospholipid-to-extract ratios used for the formation of these complexes range from 1:1 to 2:1, depending on the formulation requirements of the delivery system. Nevertheless, specific phytosomes containing polyphenols from H. sabdariffa have not been sufficiently reported. Therefore, their potential to stabilize anthocyanins and phenolic acids or enhance their absorption in H. sabdariffa-based products remains to be established.

6.3.2 Liposomal

Liposomal carrier systems (Figure 4) are mainly composed of phospholipid bilayers, which can incorporate bioactive compounds and provide their protection and delivery (Kyriakoudi et al., 2021). The vesicle nature of liposomal carriers allows them to be used for controlled release and improved dispersion of less-soluble constituents.

Nano-liposomal systems containing H. sabdariffa extracts were tested for dermal delivery in skin-aging models. Liposomal systems with a particle size of about 400 nm exhibited enhanced skin penetration and increased levels of glutathione, with reduced levels of malondialdehyde, collagenase, and elastase activity in UV-induced skin aging models (Nassar et al., 2025). These findings indicate the potential of liposomal carriers for improving H. sabdariffa extract delivery.

Nevertheless, the existing literature supporting the use of liposomes for delivering H. sabdariffa polyphenols is still scarce, especially when considering food-based applications. Studies should thus be performed regarding EE, gastrointestinal release profiles, and bioaccessibility in order to allow direct comparisons with other delivery systems.

6.4 Nanostructured delivery systems

6.4.1 Polymeric encapsulation

Polymeric delivery systems can aid in improving the stability, bioavailability, and controlled release of biologically active compounds in food and pharmaceutical formulations (Chia et al., 2023; Jang et al., 2026). Natural polymers, such as chitosan, pectin, starch, and gum matrices, are desirable due to their characteristics of being biodegradable, biocompatible, and food-grade (Hua et al., 2023). Synthetic polymers, such as poly(lactic-co-glycolic acid) (PLGA) and N-(2-hydroxypropyl)methacrylamide (HPMA), can serve as structural protection and provide controlled release, despite being costly, with regulatory considerations that may limit their use in foods (Barbosa-Nuñez et al., 2025).

As far as the use of H. sabdariffa is concerned, there has been less information about encapsulation in polymeric materials, and the available literature is not enough to establish the performance of individual polymeric systems for roselle polyphenols. The choice of an appropriate polymeric carrier would require considerations such as biocompatibility, biodegradability, physicochemical stability, release behavior, and compatibility with the matrix of foods or nutraceuticals (Rojas et al., 2024). More studies on H. sabdariffa reporting EE, particle characteristics, polyphenol retention, and target release will be needed to make a meaningful comparison with other delivery systems.

6.4.2 Nanostructured lipid carriers (NLCs)-based encapsulation

NLCs represent advanced lipid-based delivery vehicles that have the potential to improve the physicochemical stability, controlled release, and gastrointestinal delivery of labile polyphenolics (Blanco-Llamero et al., 2022; Caballero et al., 2022). The partially crystalline lipid matrix of NLCs may enhance EE while reducing compound leakage and oxidative degradation during storage.

NLCs have successfully been loaded with samples of H. sabdariffa extracts prepared using PLE and MAE techniques. In the preparation of the lipid matrix, the ratio of solid lipids and liquid lipids was 70% and 30%, respectively, and the matrix was stabilized using Tween 80 and Span 80 at a ratio of 90:10. Then, 10 mg of H. sabdariffa extract was added, followed by high-speed stirring and sonication at 60 °C, and then rapid cooling to solidify the system. The NLCs were incorporated into functional dairy drinks using skimmed milk and water at a ratio of 70:20:10. When tested for 48 h at 40 °C, 22 °C, and 4 °C, it was found that extract-loaded NLCs were more stable than the blank NLCs, had a more uniform particle-size distribution, and showed reduced creaming and sedimentation, particularly at lower temperatures. The bioactive compounds were gradually released in vitro over 24 h under simulated intestinal conditions (Pimentel-Moral et al., 2024).

These findings provide H. sabdariffa-specific evidence for NLC delivery and highlight its potential for incorporation into functional food systems. Comparison of the findings with those of other delivery systems is constrained by differences in formulation and reported performance parameters.

Across all the delivery systems listed above, the performance of H. sabdariffa encapsulation can be assessed based on certain performance metrics, such as EE, particle size, bioactive retention, and release behavior. However, quantitative comparison of these parameters may not be possible because of differences in extract composition, carrier formulation, encapsulation conditions, and analytical approaches, and there are some cases in which at least one of these performance parameters is missing. Thus, according to the available literature, quantitative comparison is feasible only for those performance parameters that have been reported, while cases in which no numerical values are available for a given performance parameter cannot be considered directly quantitatively comparable. This distinction is particularly important for phytosomal and polymeric systems, for which H. sabdariffa-specific performance data remain insufficient.

7 Advantages and limitations of encapsulation in preserving polyphenols

The use of encapsulation technology can improve the stability, solubility, bioaccessibility, controlled release, and bioavailability of polyphenols depending on the type of carrier and method used. However, there are some challenges related to production cost, carrier compatibility, scalability, and the maintenance of physicochemical stability.

7.1 Advantages

7.1.1 Improved solubility

The dispersibility and aqueous solubility of poorly water-soluble phytochemicals could be increased using encapsulation technology, such as liposomes and nanoemulsions (Kyriakoudi et al., 2021). This can facilitate the incorporation of phytochemicals into aqueous food products, such as fruit juices and milk-based beverages, allowing them to be evenly distributed.

7.1.2 Protection from degradation

Polyphenols could be safeguarded against degradation caused by various factors, including oxygen, light, pH changes, temperature, and enzymatic conditions (Ahamed et al., 2025). This is of particular importance for anthocyanins, which are sensitive to environmental and processing stresses.

7.1.3 Improved bioaccessibility

When developing health-improving products, the bioaccessibility and subsequent absorption of bioactive substances should be considered. Polyphenols can occur either in free form or associated with dietary fibers in the food matrix, and this association may influence their bioaccessibility (Blanco-Llamero et al., 2022). If polyphenols are associated with dietary fibers, they may require degradation by enzymes or microorganisms during gastrointestinal transit before becoming available for absorption, which can potentially affect their metabolic fate and biological activity. Different encapsulation approaches, such as liposomes, microencapsulation, and nanoemulsions, have therefore been explored to improve the delivery and bioavailability of various compounds. Moreover, the chemical structure of polyphenol molecules, including the type and position of sugar groups in flavonoids, may influence their absorption. Oil-based systems have been shown to provide greater bioaccessibility than dry powder systems, but the effectiveness of delivery depends on factors such as the emulsifier, lipid phase, and particle size (Nicolescu et al., 2023). Such parameters should therefore be optimized based on the particular bioactive and its intended food application.

Encapsulation of polyphenols could also help in their gradual release during gastrointestinal transit, potentially influencing the exposure of polyphenols to different gastrointestinal regions and their interaction with colonic microbiota. Nevertheless, the extent to which encapsulation enhances the bioaccessibility and colonic delivery of H. sabdariffa polyphenols remains dependent on the carrier system used and requires further validation under simulated gastrointestinal and in vivo conditions.

7.1.4 Enhanced bioavailability

Bioavailability is an important factor affecting the functionality of bioactive phytochemicals in the human body. Bioavailability refers to the proportion of an ingested bioactive substance or nutrient that reaches systemic circulation in an active form and is subsequently available for utilization or storage. The bioavailability of a bioactive molecule depends on its structure and physicochemical properties, solubility, resistance to digestive conditions, and compatibility with surrounding food ingredients (Kyriakoudi et al., 2021).

These factors are important when developing nutraceuticals, as maintaining bioactive stability during digestion can help preserve the functional integrity of bioactive compounds from ingestion to the site of delivery (Villanueva-Carvajal et al., 2013). Encapsulation can enhance the bioavailability of phytochemicals by protecting them during digestion and facilitating their absorption into systemic circulation, which may improve their biological effectiveness.

7.1.5 Controlled release

Bioactive agents can be released from carriers through diffusion, carrier degradation, or matrix degradation, depending on the bioactive compound, the carrier used, the surrounding environment, and the site of administration. Controlled release can potentially increase the duration of action and decrease the frequency of dosing in therapeutic applications, consistent with the principles of pharmacokinetics and nutraceutical delivery (Zaitoon and Lim, 2022). For dietary polyphenols, controlled release can potentially limit their rapid loss during gastrointestinal transit and help maintain effective concentrations for longer periods. In functional foods, controlled release can preserve antioxidant activity during digestion while reducing premature release that may cause undesirable sensory changes.

7.2 Disadvantages of encapsulation

The methods of encapsulation have their own drawbacks, including high production costs, low EE, carrier incompatibility, particle aggregation, and instability in large-scale processing (Figure 5) (Mehta et al., 2022). Inappropriate selection of carriers can affect the sensory attributes of food products, including flavor, texture, color, and overall sensory quality (Quirós-Sauceda et al., 2014).

This issue is also associated with the extract of H. sabdariffa, which has high levels of polyphenols and may be difficult to formulate due to its intense color and acidity. If formulation conditions are not controlled properly, especially pH, these attributes could influence the stability of protein- or polysaccharide-based matrices. Modern nanoencapsulation technologies can provide enhanced protection and targeted delivery, but may involve more complex processing, lower EE, and higher production costs.

Scalability might also result in changes in particle size, aggregation, and release behavior, impacting the performance of the encapsulated compounds. It is possible that some types of encapsulation methods might result in the loss of volatile compounds, thus potentially reducing their functionality during storage. In light of this, scalability, particle-size uniformity, regulatory requirements for food applications, and environmental considerations associated with certain carrier materials should be considered before scaling up encapsulation processes from laboratory scale to commercial production.

8 Future research directions

Future research should focus on the potential of underutilized H. sabdariffa residues, particularly calyx residues from beverage or decoction processing, seed-processing residues, and agricultural pruning waste. These materials should first be characterized for their remaining bioactive constituents, followed by residue-specific extraction and recovery studies.

Further work should develop H. sabdariffa-specific biomacromolecular delivery systems and assess their EE, bioactive retention, stability, particle characteristics, and gastrointestinal release using standardized approaches. Quantitative release-kinetic studies under simulated gastrointestinal conditions are also needed to better establish controlled-release behavior and bioaccessibility.

Finally, scale-up, food-matrix compatibility, regulatory requirements, and environmental sustainability should be considered alongside formulation performance. Artificial intelligence and machine learning may also help predict polyphenol–carrier interactions and optimize extraction and encapsulation conditions. Together, these approaches could support the development of value-added H. sabdariffa-derived ingredients for functional foods and nutraceuticals.

9 Conclusion

H. sabdariffa should be viewed not simply as a source of individual bioactive compounds, but as a multifractional biomass resource whose value depends on how effectively its chemical diversity is preserved and translated into functional ingredients. The evidence reviewed indicates that no single extraction or encapsulation strategy can be considered universally optimal. Rather, the choice of processing conditions and carrier architecture should be guided by the characteristics of the recovered fraction, the stability requirements of the target compounds, and the intended food or nutraceutical application. This fit-for-purpose perspective is particularly relevant for anthocyanin-rich materials, where chemical instability can limit the practical value of otherwise promising extracts. Importantly, the potential of residual and underutilized biomass extends the relevance of H. sabdariffa beyond conventional calyx-based applications. Future translation will require stronger links between raw-material characterization, process design, carrier–bioactive interactions, and end-use functionality. Establishing these connections could support the development of more predictable and application-oriented H. sabdariffa-derived ingredients while strengthening its role in a circular, Waste-to-Value food system.

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Footnotes

Edited by: Soubhagya Tripathy, Indian Institute of Technology Kharagpur, India

Reviewed by: Apolonio Vargas-Torres, Autonomous University of the State of Hidalgo, Mexico

Bharat Singh Irom, Institute of Chemical Technology, India