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Full Research Article

Functional Yoghurt with Microencapsulation of Pomegranate Peel Powder-pectin/Casein Complex Coacervation

L
Latifa Haderbache1,*
https://orcid.org/0000-0002-5885-1428
S
Sofiane Zidani1
https://orcid.org/0000-0001-8903-1716
F
Fahima Hadbi1
http://orcid.org/0000-0002-0542-7797
H
Hadjer Benyahia2
https://orcid.org/0000-0002-4500-0341
1Food Technology Laboratory (LRTA), M’Hamed Bougara University (UMBB), Boumerdes 35000, Algeria.
2Seldjouk University, Konia, Turkey.

ABSTRACT

Background: The traditional medical uses of pomegranate peel powder in Algeria are varied, particularly for addressing gastrointestinal issues. Microencapsulation offers numerous possibilities for developing functional foods that avoid astringency. Moreover, this technique appears to be a sustainable solution, effectively replacing bioactive extraction processes for obtaining bioactive compounds from food byproducts.

Methods: we investigate the microencapsulation of pomegranate peel powder (PPP) to its incorporation into steamed yoghurt, a widely consumed product. Microencapsulation is achieved through polymer complex coacervation using pectin and casein, with two ratios of PPP to polymer (1:1 and 1:2).

Result: Microscopic observations reveal that the microcapsules form low-density agglomerates, achieving over 90 % covering efficiency. In vitro dissolution tests conducted under gastrointestinal pH conditions demonstrate partial diffusion of bioactive components at pH 1.2 and over 50 % diffusion at alkaline pH 6.8, which mimics intestinal conditions. Preliminary sensory tests indicate that the astringency of the yoghurt is significantly masked when enriched with (PPP/polymer ratio of 1:2), but have to be ameliorate for its aspect.

INTRODUCTION

Pomegranate (Punica granatum) is one of the most studied fruits today. It is an excellent source of dietary fiber and essential nutrients, including vitamins C and A, folic acid and various minerals. Additionally, it is rich in phytobiotics such as phenolic compounds, alkaloids, triterpenes and sterols. These phytobiotics are believed to offer various health benefits, which is why pomegranate is considered a functional food (Caruso et al., 2020; Giménez-Bastida  et al., 2021; Nisa et al., 2025).
       
A significant amount of by-products (>50% of the fruit) is generated during juice process. Despite the fact that the unused peel is a valuable material with bioactive molecules (Azmat et al., 2024), it is throwed. This peel has been utilized in food preservation applications and has documented antioxidant and anti-hypercholesterolemic activities. Several studies have confirmed that the peel powder enhances the oxidative stability of sunflower oil and omega-3 fatty acids (Ghnimi et al., 2017; Heck et al., 2021).
       
In Algeria, pomegranate peel is commonly used in traditional medicine to treat skin diseases, parasitic infections, gastric ulcers and fevers (Zhou et al., 2015). It is often combined with foods such as honey, milk and L’ben (fermented milk), especially in southern regions. However, its astringency and the instability of its polyphenols can limit its use in food products, thus reducing the potential health benefits (Azmat et al., 2024).
       
Microencapsulation emerges as a promising solution to these challenges. This technique has been known for decades and has applications in various fields, including perfumery, cosmetics, agriculture and medicine (Maurya et al., 2020). Microencapsulation can help mitigate unpleasant flavors and odours while protecting sensitive bioactive compounds from oxidation and other undesirable reactions (Tarone et al., 2020). It also allows for the release of these compounds when exposed to specific stimuli (Dhakal et al., 2020; Liu et al., 2020).
       
The encapsulation process involves packaging active molecules with an encapsulating agent to create capsules, which can range in size from sub-micron to several millimeters. The process can be tailored to allow the gradual release of active molecules in response to specific triggers, such as temperature, solvent or pH, or to release them in targeted areas of the body upon ingestion (Tarone et al., 2020).
       
Coacervation is one of the most commonly used techniques. It involves the associative phase separation process, which is induced by changes in the environmental conditions under controlled circumstances. In this process, the coacervate phase, rich in colloids, interacts with oppositely charged biopolymers in an aqueous medium (Timilsena et al., 2019). Depending on whether one or more polymers are used, the process can be classified as simple or complex coacervation. Microencapsulation by coacervation consists of three key steps (Fig  1).

Fig 1: Principle of the microencapsulation process by complex coacervation [20].



- Formation of three immiscible phases; a liquid manufacturing phase, an active material phase and a coating material phase.
- Deposition of the liquid polymer coating on the active material.
- Rigidizing the coating (by thermal, cross linking or desolation techniques) to form the final product (Suganya et al., 2017).
       
This work finds its originality in the technique used to mask the flaws of pomegranate peel powder, as well as mimicking ancestral food practices that tend to be forgotten by younger generations, in a widely consumed product as functional-food application. The ultimate goal is to increase the intake of active molecules and enhance health benefits with a specific focus on sustainability practices, first by valorizing a by-product and then by using methods far from solvent extractive procedures.

MATERIALS AND METHODS

The pomegranate fruit “Mouzahlou,” a local variety, was collected randomly at the maturation stage in the Bordj Menial locality (Wilaya of Boumerdes). The peel was separated from the fruit and dried at 40°C in a MAMMERT oven then ground into powder and sifted. The pomegranate peel powder (PPP) was stored in hermetically sealed boxes, protected from light until use. Pectin was sourced from Zine Food Company and casein came from Biscuitrie Company. All manipulations were caried in 2023 in LRTA laboratory research in M’hamed Bougara university.
 
Characterization of pomegranate peel powder (PPP)
 
PPP was characterized as a raw material for its water content (%), pH and titratable acidity (meq. Kg-1) using a JENWAY pH meter. Additional parameters measured included ash content (%), CIE Lab color parameters (L*, a*, b*) using a Konica Minolta CR 10 colorimeter and granulometry using a Laser Mastersizer 300 granulometer.
 
Microencapsulation procedure
 
Microcapsules were produced through (pectin/casein) complex coacervation, following the method described by Baracat and Nakagawa (Baracat  et al., 2012) with minor modifications as follow. A 10% dispersion (pectin/casein ratio of 2:8) was prepared in distilled water and the pH was adjusted to 8.0±0.1 using a 4 M NaOH solution. PPP (particle size <200 μm) was then added in two different proportions (1:1 and 1:2 PPP to pectin-casein), while stirring magnetically. Empty capsules (EC) were also created without stirring. The pH was then gradually and slowly lowered to 3.0±0.1 using a 1 M citric acid solution. The resulting dispersion was frozen, lyophilized and then ground to achieve a particle size of <200 μm.
       
The choice of the pectin/casein system is supported by existing literature (Shaddel  et al., 2018a, 2018b) on the use of various protein/polysaccharide matrices in encapsulating bioactive molecules. Pectin and casein are classified as generally recognized as safe (GRAS) materials.
 
Microscopic electron scanning
 
Obtained microcapsules were examined using Phillips ESEM XL30 Scanning Electron Microscopy (SEM). Images were captured for the PPP, empty capsules and encapsulated powders at three different magnifications: 100x, 250x and 500x.
 
Encapsulation efficiency (EE %)
 
250 mg of microcapsules, in five replicate (n=5), were dispersed in 20 ml of distilled water. The dispersion was centrifuged at 4,000 g for 10 min; the supernatant was filtered using a nylon syringe filter. The filtrate was analyzed using a spectrophotometer at 368 nm (PPP water extract λmax). The Efficiency (EE %) was calculated using the following formula based on absorbance (A). 

Solubility test of EC
 
The solubility test was conducted in triplicate (n=3), following the methodology described by De Marco and Vieira (De Marco  et al., 2013). A 0.5 g sample of EC was added to distilled water (1%, w/v) at room temperature. The resulting solutions were filtered and the filtrates were placed on pre-weighed Petri plates and heated at 105°C for 5 hours. The solubility was expressed as a percentage of the initial weight of EC.
 
In vitro microcapsule dissolution simulation
 
An in vitro simulation to model gastric and intestinal pH microcapsule dissolution was performed following Baracat and Nakagawa (Baracat  et al., 2012) in triplicate (n=3), with modifications. In this test, 2.25 g of EPPP (1:1 ratio), EPPP (1:2 ratio) and EC were used. For the first two hours, the samples were exposed to a pH of 1.2±0.05 at 37°C using HCl solution to mimic gastric fluid conditions. In the subsequent four hours, phosphate buffer (0.2 M Na3PO4) was added to simulate intestinal fluid conditions, reaching a pH of 6.8±0.05 (if not, the pH was adjusted using NaOH solution). Every 30 min, samples were centrifuged immediately at 10,000 rpm for 20 min and filtered through a 0.45 μm nylon syringe filter. The absorbance of the resulting solution was measured at 368 nm. For a sample taken at time tx, the percentage of diffusion was calculated as D in per cent.
                                                                                                                                                               
       
       
Results are expressed as diffusion kinetic curves.

Formulation of a functional steamed yoghurt enriched by EPPP
 
The microcapsules application test consisted in its incorporation in food matrix. Steamed yoghurt was chosen for its large acceptability by the consumers (Katka and Deshpande, 2022). Experimental protocol of yoghurt preparation started by milk reconstitution followed by homogenization and pasteurization; next the milk is cooled at the appropriate inoculation temperature (45°C). After introducing the lactic leaven; PPP, EPPP or EC are added to the mixture then poured into pots and incubated at 45°C during 4 to 5 h, then rapidly cooled till 4°C in a freezer (-18°C). Prepared yoghurt formulations are summarized in Table 1.

Table 1: Pomegranate peel powder/Yoghurt formulations.


 
Sensory evaluation
 
The enriched yoghurts were evaluated by a non-trained sensory panel comprised of ten consumers, including five females and five males (laboratory technicians). Each yoghurt sample, weighing 120 g, was cooled to a temperature of 6.0±2.0°C and placed in randomized order previously marked cups.
       
The sensory quality parameters were:  coagulum aspect, syneresis, color changes, deposit formation, flavor, mouthfeel and overall acceptance. These parameters were rated on a scale from 1 to 10, where the lowest score indicated “extremely dislike” and the highest indicated “extremely like.”. The sensory evaluation of our product is consistent with ISO 8586:2012 guidelines (ISO, 2012). All participants were non-smokers, not pregnant and confirmed that they had no food allergies to the ingredients used in the recipe.
 
Statistical analysis
 
The statistical analysis was assessed with Minitab statistical software 22.

RESULTS AND DISCUSSION

The pomegranates peels and the prepared powder are characterized in this section, this step is crucial for selecting the encapsulation conditions.
 
Pomegranates peel powder characterization
 
Characterization parameters are summarized in Table 2. Due to their initial high-water content, pomegranate peels (PP) cannot be stored for extended periods. But when transformed in PPP with a correct desiccation they contain 9% of water which presents numerous advantages. However, the acidity levels of PPP necessitate effective moisture protection during storage to prevent yeast proliferation, a common issue when preserving pomegranate peels in traditional products like cited by (Lairini  et al., 2014; Shahid et al., 2008).

Table 2: Pomegranate peel powder physic-chemical characteristics and composition.


       
The ash content indicates that PPP is rich in minerals comparable to 4,32% amount cited by (Azmat et al., 2024), while the brix value suggests that over half of the powder can be released as a soluble fraction in accordance with Shahid (Shahid  et al., 2008). Colour analysis showed that PPP has a clear yellow hue. This yellow color can transfer to foods when incorporated and absorbs light at 368 nm, same results were noticed by Yagmur et al., (2024). The granulometric profile of the chosen fraction is shown in Fig 2, where we can observe that more than 80% of the powder granules size is less than 200 µm.

Fig 2: Granulometric profile of obtained pomegranate peel powder PPP.


       
To evaluate the micro-encapsulation operation, in this section we will observe, under appropriate magnifications, the row material and the encapsulated PPP preparations. In a second step we will give the encapsulation efficiencies.
 
Microcapsules microscopic evaluation
 
Fig 3 displays the preparation aspect of the pomegranate peel powder (PPP). Scanning electron microscopy (SEM) observations of the fraction less than 200 μm reveal that PPP resembles a fibrous material with irregularly shaped particles of varying sizes; it contains numerous inclusions (Fig 4a). In contrast, the encapsulation material represented by (EC) appears compact and crystallized (Fig 4b).

​

Fig 3: Aspect of elaborated pomegranate peel microcapsules and raw material (a) Pomegranate peel powder (b) Empty capsules (c) EPPP(1:2) (d) EPPP(1:1).


       
Fig 4c and 4d illustrate the appearance of the microcapsules, which consist of particles that are either completely or partially covering a fibrous material, making them larger than the initial PPP grains. The agglomeration density indicates the rate of powder/polymer complexation, demonstrating that pectin and casein formed a composite coating around the PPP particles (indicated by the arrow in Fig 4). This phenomenon is well explained by Tuinier and Rolin (Tuinier  et al., 2002), who describe it as the multi-layer adsorption of pectin macromolecules onto casein during acidification and was confirmed by Suganya  et al. (2017).

​

Fig 4: Microscopic images by SEM of the pomegranate peel powder (in three magnifications 100, 250 and 500x).


       
According to Çam  et al. (2014), the size and shape of microcapsules are critical parameters for assessing quality. In this case, the microcapsules retain the shape of the initial material, indicating that they are well-coated (Tarone  et al., 2020).
 
Encapsulation efficiency (EE %)
 
The encapsulation efficiency indicates the percentage of particles that were successfully coated during the process. The results demonstrate an efficiency of 96.73±0.30% for the EPPP (1:2) and 91.79 ± 0.10 % for the EPPP (1:1). These values are higher than those reported in several studies, which indicated encapsulation efficiencies between 69% and 92% for phenolic compounds from sour sherry, as found by Çilek (2012). However, our results are lower than the 98% efficiency reported by Çam  et al. (2014) for the encapsulation of pomegranate peel phenolic extract.
       
The differences in encapsulation efficiency can be attributed to the nature of the encapsulated molecules or particles and the composition of the coating material (Cãlinoiu  et al., 2019) such as the pectin/casein ratio and the complex/powder ratio. In our case, an efficiency of over 90% indicates that the coacervation method is effective for the PPP particles.
       
This part will demonstrate the solubility and dissolution of the capsules under certain conditions, to predict their future behavior when incorporated in the chosen food matrix.
 
Solubility test of empty capsules
 
This test will demonstrate the behavior in water, which helps predict the diffusion of EPPP in their surrounding environment. Microcapsules made from a pectin/casein complex (2:8 ratio) showed a solubility of 31.41±0.24% under our test conditions. This erosion is primarily linked to the pH of distilled water (pH 6.8), which impacts the integrity of the coating in used coacervation system. This factor should be considered in future food formulations. A study by Gentès (2007) confirmed that proteins have lower solubility compared to pectin at varying pH levels. It was observed that pectin migrated towards the medium depending on the pH and the applied heat treatment. This information is significant because it highlights that the behavior of each biopolymer in the coacervate complex largely depends on pH conditions (Gentès, 2007). Our capsules exhibit greater stability in acidic pH.
 
In vitro microcapsules dissolution simulation
 
The dissolution study was conducted to examine the release kinetics of EPPP. As shown in Fig 5, the diffusion amount at the initial sampling (0 hours) reflects the encapsulation efficiency accurately. Notably, EPPP (1:2) exhibited only 5 % leakage, compared to 13% leakage for EPPP (1:1).

Fig 5: Diffusion kinetics of EPPP (1:1) and EPPP (1:2) under simulated gastrointestinal pH conditions.


       
The partial diffusion observed during the first phase (0-2 hours) can be attributed to pectin solubilization in stomach acid (pH 1.2), which did not exceed 5% in both cases. Then the diffusion increased significantly in the intestinal environment (pH 6.8) due to casein solubilization. After 6 hours, more than 33% of the bioactive molecules from pomegranate had been released for EPPP (1:1), while EPPP (1:2) released approximately 30%. This degradation pattern of the microcapsules is consistent with the findings of Tuinier and Rolin (Tuinier  et al., 2002), who demonstrated that pectin adsorbs onto casein micelles in a multilayer formation. In this structure, casein forms the interior layer and pectin serves as the exterior layer. These results, supported by the EC solubility test, indicate that both EPPP (1:1) and EPPP (1:2) provide a protective effect on pomegranate peel powder in stomach.
       
The obtained results oriented our food matrix choice to bio-yogurt like made later by Yagmur et al., (2024), in the following section we will compare the quality of the yogurt when supplemented by PPP or by the encapsulated powders, also we will choose the best formulation for potential health benefits.
 
Application-incorporation test in food matrix
 
Table 3 presents key observations following the formulation of steamed yoghurt with various microcapsule preparations. It was first observed that when PPP was added alone, it could not stay in suspension, leading to sedimentation in the yoghurt and the development of an undesirable green-yellow colour like observed in Lai and Tang (2024) study, how used PPP to enhance yogurt quality. This issue did not occur with EPPP, where pectin hydration and the interaction between pectin, yoghurt and casein provided consistency to the mixture, preventing capsule sedimentation.

Table 3: Preliminary results of microcapsules incorporation into steamed yoghurt.


       
Additionally, the astringency was either partially masked or completely eliminated, indicating that the elaborated microcapsules reinforce the fermentation process. The capsules resistance resulted from the acidity due to lactose fermentation. The creamy colour (Bakhti et al., 2025) of the preparations came from the non-encapsulated fraction of PPP and the leakage phenomenon occurring during the pH decrease during the fermentation process.
       
In the formulation with EPPP, syneresis and a grainy consistency were observed, likely due to capsule acidity. However, the astringency was effectively masked. Thus, the primary objective of this study was partially achieved, suggesting that these capsules can be used more efficiently and advantageously in yet prepared acidic food formulations such as fruit juices, fermented foods, liquid yoghurt and l’ben as functional foods (Frakolaki et al., 2021). In our case the best product after the blanc regarding sensory evaluation was EPPP (1:2) (Fig 6), it was well ranked in masking astringency, have an acceptable colour and don’t present any deposit, but affected yoghurt texture.

Fig 6: Sensory evaluation grids of prepared yoghurt formulations with microencapsulated pomegranate peel powder.

CONCLUSION

Encapsulating pomegranate peel powder with a biopolymer complex of pectin and casein effectively creates biodegradable microcapsules that release bioactive components in gastrointestinal environment without needing an extraction step, providing a lot of health benefits. These technic addresses astringency and undesirable colour while stabilizing the peel particles, offering processing and nutritional advantages. Incorporating up to 2.5% microcapsules into steamed yoghurt presents some challenges, such as syneresis and a grainy texture, which can be managed by choosing a better food matrix or less fermentation time or less lactic leaven, giving encapsulation many durable advantages.
       
It is essential to find effective methods to incorporate traditional health-promoting compounds into popular foods. Future research should focus on optimizing fermentation times according to the initial acidity of the capsules and developing a waterproof coating to prevent colour leakage.
 

ACKNOWLEDGEMENT

The present study was supported by LRTA research laboratory.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

CONFLICT OF INTEREST

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.

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    Full Research Article

    Functional Yoghurt with Microencapsulation of Pomegranate Peel Powder-pectin/Casein Complex Coacervation

    L
    Latifa Haderbache1,*
    https://orcid.org/0000-0002-5885-1428
    S
    Sofiane Zidani1
    https://orcid.org/0000-0001-8903-1716
    F
    Fahima Hadbi1
    http://orcid.org/0000-0002-0542-7797
    H
    Hadjer Benyahia2
    https://orcid.org/0000-0002-4500-0341
    1Food Technology Laboratory (LRTA), M’Hamed Bougara University (UMBB), Boumerdes 35000, Algeria.
    2Seldjouk University, Konia, Turkey.

    ABSTRACT

    Background: The traditional medical uses of pomegranate peel powder in Algeria are varied, particularly for addressing gastrointestinal issues. Microencapsulation offers numerous possibilities for developing functional foods that avoid astringency. Moreover, this technique appears to be a sustainable solution, effectively replacing bioactive extraction processes for obtaining bioactive compounds from food byproducts.

    Methods: we investigate the microencapsulation of pomegranate peel powder (PPP) to its incorporation into steamed yoghurt, a widely consumed product. Microencapsulation is achieved through polymer complex coacervation using pectin and casein, with two ratios of PPP to polymer (1:1 and 1:2).

    Result: Microscopic observations reveal that the microcapsules form low-density agglomerates, achieving over 90 % covering efficiency. In vitro dissolution tests conducted under gastrointestinal pH conditions demonstrate partial diffusion of bioactive components at pH 1.2 and over 50 % diffusion at alkaline pH 6.8, which mimics intestinal conditions. Preliminary sensory tests indicate that the astringency of the yoghurt is significantly masked when enriched with (PPP/polymer ratio of 1:2), but have to be ameliorate for its aspect.

    INTRODUCTION

    Pomegranate (Punica granatum) is one of the most studied fruits today. It is an excellent source of dietary fiber and essential nutrients, including vitamins C and A, folic acid and various minerals. Additionally, it is rich in phytobiotics such as phenolic compounds, alkaloids, triterpenes and sterols. These phytobiotics are believed to offer various health benefits, which is why pomegranate is considered a functional food (Caruso et al., 2020; Giménez-Bastida  et al., 2021; Nisa et al., 2025).
           
    A significant amount of by-products (>50% of the fruit) is generated during juice process. Despite the fact that the unused peel is a valuable material with bioactive molecules (Azmat et al., 2024), it is throwed. This peel has been utilized in food preservation applications and has documented antioxidant and anti-hypercholesterolemic activities. Several studies have confirmed that the peel powder enhances the oxidative stability of sunflower oil and omega-3 fatty acids (Ghnimi et al., 2017; Heck et al., 2021).
           
    In Algeria, pomegranate peel is commonly used in traditional medicine to treat skin diseases, parasitic infections, gastric ulcers and fevers (Zhou et al., 2015). It is often combined with foods such as honey, milk and L’ben (fermented milk), especially in southern regions. However, its astringency and the instability of its polyphenols can limit its use in food products, thus reducing the potential health benefits (Azmat et al., 2024).
           
    Microencapsulation emerges as a promising solution to these challenges. This technique has been known for decades and has applications in various fields, including perfumery, cosmetics, agriculture and medicine (Maurya et al., 2020). Microencapsulation can help mitigate unpleasant flavors and odours while protecting sensitive bioactive compounds from oxidation and other undesirable reactions (Tarone et al., 2020). It also allows for the release of these compounds when exposed to specific stimuli (Dhakal et al., 2020; Liu et al., 2020).
           
    The encapsulation process involves packaging active molecules with an encapsulating agent to create capsules, which can range in size from sub-micron to several millimeters. The process can be tailored to allow the gradual release of active molecules in response to specific triggers, such as temperature, solvent or pH, or to release them in targeted areas of the body upon ingestion (Tarone et al., 2020).
           
    Coacervation is one of the most commonly used techniques. It involves the associative phase separation process, which is induced by changes in the environmental conditions under controlled circumstances. In this process, the coacervate phase, rich in colloids, interacts with oppositely charged biopolymers in an aqueous medium (Timilsena et al., 2019). Depending on whether one or more polymers are used, the process can be classified as simple or complex coacervation. Microencapsulation by coacervation consists of three key steps (Fig  1).

    Fig 1: Principle of the microencapsulation process by complex coacervation [20].



    - Formation of three immiscible phases; a liquid manufacturing phase, an active material phase and a coating material phase.
    - Deposition of the liquid polymer coating on the active material.
    - Rigidizing the coating (by thermal, cross linking or desolation techniques) to form the final product (Suganya et al., 2017).
           
    This work finds its originality in the technique used to mask the flaws of pomegranate peel powder, as well as mimicking ancestral food practices that tend to be forgotten by younger generations, in a widely consumed product as functional-food application. The ultimate goal is to increase the intake of active molecules and enhance health benefits with a specific focus on sustainability practices, first by valorizing a by-product and then by using methods far from solvent extractive procedures.

    MATERIALS AND METHODS

    The pomegranate fruit “Mouzahlou,” a local variety, was collected randomly at the maturation stage in the Bordj Menial locality (Wilaya of Boumerdes). The peel was separated from the fruit and dried at 40°C in a MAMMERT oven then ground into powder and sifted. The pomegranate peel powder (PPP) was stored in hermetically sealed boxes, protected from light until use. Pectin was sourced from Zine Food Company and casein came from Biscuitrie Company. All manipulations were caried in 2023 in LRTA laboratory research in M’hamed Bougara university.
     
    Characterization of pomegranate peel powder (PPP)
     
    PPP was characterized as a raw material for its water content (%), pH and titratable acidity (meq. Kg-1) using a JENWAY pH meter. Additional parameters measured included ash content (%), CIE Lab color parameters (L*, a*, b*) using a Konica Minolta CR 10 colorimeter and granulometry using a Laser Mastersizer 300 granulometer.
     
    Microencapsulation procedure
     
    Microcapsules were produced through (pectin/casein) complex coacervation, following the method described by Baracat and Nakagawa (Baracat  et al., 2012) with minor modifications as follow. A 10% dispersion (pectin/casein ratio of 2:8) was prepared in distilled water and the pH was adjusted to 8.0±0.1 using a 4 M NaOH solution. PPP (particle size <200 μm) was then added in two different proportions (1:1 and 1:2 PPP to pectin-casein), while stirring magnetically. Empty capsules (EC) were also created without stirring. The pH was then gradually and slowly lowered to 3.0±0.1 using a 1 M citric acid solution. The resulting dispersion was frozen, lyophilized and then ground to achieve a particle size of <200 μm.
           
    The choice of the pectin/casein system is supported by existing literature (Shaddel  et al., 2018a, 2018b) on the use of various protein/polysaccharide matrices in encapsulating bioactive molecules. Pectin and casein are classified as generally recognized as safe (GRAS) materials.
     
    Microscopic electron scanning
     
    Obtained microcapsules were examined using Phillips ESEM XL30 Scanning Electron Microscopy (SEM). Images were captured for the PPP, empty capsules and encapsulated powders at three different magnifications: 100x, 250x and 500x.
     
    Encapsulation efficiency (EE %)
     
    250 mg of microcapsules, in five replicate (n=5), were dispersed in 20 ml of distilled water. The dispersion was centrifuged at 4,000 g for 10 min; the supernatant was filtered using a nylon syringe filter. The filtrate was analyzed using a spectrophotometer at 368 nm (PPP water extract λmax). The Efficiency (EE %) was calculated using the following formula based on absorbance (A). 

    Solubility test of EC
     
    The solubility test was conducted in triplicate (n=3), following the methodology described by De Marco and Vieira (De Marco  et al., 2013). A 0.5 g sample of EC was added to distilled water (1%, w/v) at room temperature. The resulting solutions were filtered and the filtrates were placed on pre-weighed Petri plates and heated at 105°C for 5 hours. The solubility was expressed as a percentage of the initial weight of EC.
     
    In vitro microcapsule dissolution simulation
     
    An in vitro simulation to model gastric and intestinal pH microcapsule dissolution was performed following Baracat and Nakagawa (Baracat  et al., 2012) in triplicate (n=3), with modifications. In this test, 2.25 g of EPPP (1:1 ratio), EPPP (1:2 ratio) and EC were used. For the first two hours, the samples were exposed to a pH of 1.2±0.05 at 37°C using HCl solution to mimic gastric fluid conditions. In the subsequent four hours, phosphate buffer (0.2 M Na3PO4) was added to simulate intestinal fluid conditions, reaching a pH of 6.8±0.05 (if not, the pH was adjusted using NaOH solution). Every 30 min, samples were centrifuged immediately at 10,000 rpm for 20 min and filtered through a 0.45 μm nylon syringe filter. The absorbance of the resulting solution was measured at 368 nm. For a sample taken at time tx, the percentage of diffusion was calculated as D in per cent.
                                                                                                                                                                   
           
           
    Results are expressed as diffusion kinetic curves.

    Formulation of a functional steamed yoghurt enriched by EPPP
     
    The microcapsules application test consisted in its incorporation in food matrix. Steamed yoghurt was chosen for its large acceptability by the consumers (Katka and Deshpande, 2022). Experimental protocol of yoghurt preparation started by milk reconstitution followed by homogenization and pasteurization; next the milk is cooled at the appropriate inoculation temperature (45°C). After introducing the lactic leaven; PPP, EPPP or EC are added to the mixture then poured into pots and incubated at 45°C during 4 to 5 h, then rapidly cooled till 4°C in a freezer (-18°C). Prepared yoghurt formulations are summarized in Table 1.

    Table 1: Pomegranate peel powder/Yoghurt formulations.


     
    Sensory evaluation
     
    The enriched yoghurts were evaluated by a non-trained sensory panel comprised of ten consumers, including five females and five males (laboratory technicians). Each yoghurt sample, weighing 120 g, was cooled to a temperature of 6.0±2.0°C and placed in randomized order previously marked cups.
           
    The sensory quality parameters were:  coagulum aspect, syneresis, color changes, deposit formation, flavor, mouthfeel and overall acceptance. These parameters were rated on a scale from 1 to 10, where the lowest score indicated “extremely dislike” and the highest indicated “extremely like.”. The sensory evaluation of our product is consistent with ISO 8586:2012 guidelines (ISO, 2012). All participants were non-smokers, not pregnant and confirmed that they had no food allergies to the ingredients used in the recipe.
     
    Statistical analysis
     
    The statistical analysis was assessed with Minitab statistical software 22.

    RESULTS AND DISCUSSION

    The pomegranates peels and the prepared powder are characterized in this section, this step is crucial for selecting the encapsulation conditions.
     
    Pomegranates peel powder characterization
     
    Characterization parameters are summarized in Table 2. Due to their initial high-water content, pomegranate peels (PP) cannot be stored for extended periods. But when transformed in PPP with a correct desiccation they contain 9% of water which presents numerous advantages. However, the acidity levels of PPP necessitate effective moisture protection during storage to prevent yeast proliferation, a common issue when preserving pomegranate peels in traditional products like cited by (Lairini  et al., 2014; Shahid et al., 2008).

    Table 2: Pomegranate peel powder physic-chemical characteristics and composition.


           
    The ash content indicates that PPP is rich in minerals comparable to 4,32% amount cited by (Azmat et al., 2024), while the brix value suggests that over half of the powder can be released as a soluble fraction in accordance with Shahid (Shahid  et al., 2008). Colour analysis showed that PPP has a clear yellow hue. This yellow color can transfer to foods when incorporated and absorbs light at 368 nm, same results were noticed by Yagmur et al., (2024). The granulometric profile of the chosen fraction is shown in Fig 2, where we can observe that more than 80% of the powder granules size is less than 200 µm.

    Fig 2: Granulometric profile of obtained pomegranate peel powder PPP.


           
    To evaluate the micro-encapsulation operation, in this section we will observe, under appropriate magnifications, the row material and the encapsulated PPP preparations. In a second step we will give the encapsulation efficiencies.
     
    Microcapsules microscopic evaluation
     
    Fig 3 displays the preparation aspect of the pomegranate peel powder (PPP). Scanning electron microscopy (SEM) observations of the fraction less than 200 μm reveal that PPP resembles a fibrous material with irregularly shaped particles of varying sizes; it contains numerous inclusions (Fig 4a). In contrast, the encapsulation material represented by (EC) appears compact and crystallized (Fig 4b).

    ​

    Fig 3: Aspect of elaborated pomegranate peel microcapsules and raw material (a) Pomegranate peel powder (b) Empty capsules (c) EPPP(1:2) (d) EPPP(1:1).


           
    Fig 4c and 4d illustrate the appearance of the microcapsules, which consist of particles that are either completely or partially covering a fibrous material, making them larger than the initial PPP grains. The agglomeration density indicates the rate of powder/polymer complexation, demonstrating that pectin and casein formed a composite coating around the PPP particles (indicated by the arrow in Fig 4). This phenomenon is well explained by Tuinier and Rolin (Tuinier  et al., 2002), who describe it as the multi-layer adsorption of pectin macromolecules onto casein during acidification and was confirmed by Suganya  et al. (2017).

    ​

    Fig 4: Microscopic images by SEM of the pomegranate peel powder (in three magnifications 100, 250 and 500x).


           
    According to Çam  et al. (2014), the size and shape of microcapsules are critical parameters for assessing quality. In this case, the microcapsules retain the shape of the initial material, indicating that they are well-coated (Tarone  et al., 2020).
     
    Encapsulation efficiency (EE %)
     
    The encapsulation efficiency indicates the percentage of particles that were successfully coated during the process. The results demonstrate an efficiency of 96.73±0.30% for the EPPP (1:2) and 91.79 ± 0.10 % for the EPPP (1:1). These values are higher than those reported in several studies, which indicated encapsulation efficiencies between 69% and 92% for phenolic compounds from sour sherry, as found by Çilek (2012). However, our results are lower than the 98% efficiency reported by Çam  et al. (2014) for the encapsulation of pomegranate peel phenolic extract.
           
    The differences in encapsulation efficiency can be attributed to the nature of the encapsulated molecules or particles and the composition of the coating material (Cãlinoiu  et al., 2019) such as the pectin/casein ratio and the complex/powder ratio. In our case, an efficiency of over 90% indicates that the coacervation method is effective for the PPP particles.
           
    This part will demonstrate the solubility and dissolution of the capsules under certain conditions, to predict their future behavior when incorporated in the chosen food matrix.
     
    Solubility test of empty capsules
     
    This test will demonstrate the behavior in water, which helps predict the diffusion of EPPP in their surrounding environment. Microcapsules made from a pectin/casein complex (2:8 ratio) showed a solubility of 31.41±0.24% under our test conditions. This erosion is primarily linked to the pH of distilled water (pH 6.8), which impacts the integrity of the coating in used coacervation system. This factor should be considered in future food formulations. A study by Gentès (2007) confirmed that proteins have lower solubility compared to pectin at varying pH levels. It was observed that pectin migrated towards the medium depending on the pH and the applied heat treatment. This information is significant because it highlights that the behavior of each biopolymer in the coacervate complex largely depends on pH conditions (Gentès, 2007). Our capsules exhibit greater stability in acidic pH.
     
    In vitro microcapsules dissolution simulation
     
    The dissolution study was conducted to examine the release kinetics of EPPP. As shown in Fig 5, the diffusion amount at the initial sampling (0 hours) reflects the encapsulation efficiency accurately. Notably, EPPP (1:2) exhibited only 5 % leakage, compared to 13% leakage for EPPP (1:1).

    Fig 5: Diffusion kinetics of EPPP (1:1) and EPPP (1:2) under simulated gastrointestinal pH conditions.


           
    The partial diffusion observed during the first phase (0-2 hours) can be attributed to pectin solubilization in stomach acid (pH 1.2), which did not exceed 5% in both cases. Then the diffusion increased significantly in the intestinal environment (pH 6.8) due to casein solubilization. After 6 hours, more than 33% of the bioactive molecules from pomegranate had been released for EPPP (1:1), while EPPP (1:2) released approximately 30%. This degradation pattern of the microcapsules is consistent with the findings of Tuinier and Rolin (Tuinier  et al., 2002), who demonstrated that pectin adsorbs onto casein micelles in a multilayer formation. In this structure, casein forms the interior layer and pectin serves as the exterior layer. These results, supported by the EC solubility test, indicate that both EPPP (1:1) and EPPP (1:2) provide a protective effect on pomegranate peel powder in stomach.
           
    The obtained results oriented our food matrix choice to bio-yogurt like made later by Yagmur et al., (2024), in the following section we will compare the quality of the yogurt when supplemented by PPP or by the encapsulated powders, also we will choose the best formulation for potential health benefits.
     
    Application-incorporation test in food matrix
     
    Table 3 presents key observations following the formulation of steamed yoghurt with various microcapsule preparations. It was first observed that when PPP was added alone, it could not stay in suspension, leading to sedimentation in the yoghurt and the development of an undesirable green-yellow colour like observed in Lai and Tang (2024) study, how used PPP to enhance yogurt quality. This issue did not occur with EPPP, where pectin hydration and the interaction between pectin, yoghurt and casein provided consistency to the mixture, preventing capsule sedimentation.

    Table 3: Preliminary results of microcapsules incorporation into steamed yoghurt.


           
    Additionally, the astringency was either partially masked or completely eliminated, indicating that the elaborated microcapsules reinforce the fermentation process. The capsules resistance resulted from the acidity due to lactose fermentation. The creamy colour (Bakhti et al., 2025) of the preparations came from the non-encapsulated fraction of PPP and the leakage phenomenon occurring during the pH decrease during the fermentation process.
           
    In the formulation with EPPP, syneresis and a grainy consistency were observed, likely due to capsule acidity. However, the astringency was effectively masked. Thus, the primary objective of this study was partially achieved, suggesting that these capsules can be used more efficiently and advantageously in yet prepared acidic food formulations such as fruit juices, fermented foods, liquid yoghurt and l’ben as functional foods (Frakolaki et al., 2021). In our case the best product after the blanc regarding sensory evaluation was EPPP (1:2) (Fig 6), it was well ranked in masking astringency, have an acceptable colour and don’t present any deposit, but affected yoghurt texture.

    Fig 6: Sensory evaluation grids of prepared yoghurt formulations with microencapsulated pomegranate peel powder.

    CONCLUSION

    Encapsulating pomegranate peel powder with a biopolymer complex of pectin and casein effectively creates biodegradable microcapsules that release bioactive components in gastrointestinal environment without needing an extraction step, providing a lot of health benefits. These technic addresses astringency and undesirable colour while stabilizing the peel particles, offering processing and nutritional advantages. Incorporating up to 2.5% microcapsules into steamed yoghurt presents some challenges, such as syneresis and a grainy texture, which can be managed by choosing a better food matrix or less fermentation time or less lactic leaven, giving encapsulation many durable advantages.
           
    It is essential to find effective methods to incorporate traditional health-promoting compounds into popular foods. Future research should focus on optimizing fermentation times according to the initial acidity of the capsules and developing a waterproof coating to prevent colour leakage.
     

    ACKNOWLEDGEMENT

    The present study was supported by LRTA research laboratory.
     
    Disclaimers
     
    The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

    CONFLICT OF INTEREST

    The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.

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