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Properties and Stability of Encapsulated Pomegranate Peel Extract Prepared by Co-Crystallization

Evangelos Chezanoglou
Athanasia M. Goula
Department of Food Science and Technology, School of Agriculture, Forestry and Natural Environment, Aristotle University, 541 24 Thessaloniki, Greece
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(15), 8680;
Submission received: 7 July 2023 / Revised: 24 July 2023 / Accepted: 25 July 2023 / Published: 27 July 2023


Recently, there has been much interest in the phenolics of pomegranate peels because of their health-promoting effects. The incorporation of encapsulated phenolic extracts in functional foods, beverages, and dietary supplements can enhance their nutritional and health benefits. This paper aims to provide an overview of the encapsulation of pomegranate peel phenolic extract by co-crystallization, focusing on the properties of the encapsulated extract. Pomegranate peel extract encapsulated in sucrose by co-crystallization under conditions determined in our previous work is characterized by evaluating its properties—moisture content, solubility, bulk density, hygroscopicity, color, degree of encapsulation (using thermograms), crystallinity (using X-ray scattering), microstructure (with scanning electron microscopy), and storage stability in terms of total phenolic content and antioxidant activity. The co-crystallized powder had a low moisture content (0.59%) and hygroscopicity (0.011%) and a high bulk density (0.803 g/cm3) and solubility (61 s). Its total phenolic content decreased by only 0.56% after storage at 60 °C for 45 days, whereas its antioxidant activity was maintained at levels higher than 84%. The differential scanning calorimetry and X-ray scattering techniques proved the successful encapsulation in the sucrose matrix and the fact that the extract remained liquid inside the porosity of the sucrose crystals.

1. Introduction

Due to its numerous bioactive components, particularly phenolic compounds present in various regions of the fruit, the pomegranate (Punica granatum L.) has attracted much interest recently. Pomegranate peel, a byproduct of the pomegranate fruit and juice industries, contains a sizable amount of phenolic compounds, such as ellagitannins, anthocyanins, and flavonoids, that have been shown to have a number of health benefits, including antioxidant, anti-inflammatory, and anticancer properties [1].
Pomegranate peel extracts have been shown to possess antioxidant, anti-inflammatory, anticancer, and antiproliferative properties in numerous investigations. Pomegranate peel extract (PPE) was shown to be extremely effective at scavenging hydroxyl radicals by Kanatt et al. [2] when they investigated the antioxidant and antibacterial capabilities of PPE. PPE also demonstrates anti-bacterial activity against Staphylococcus aureus and Bacillus cereus, with a lowest inhibitory content of 0.01%, and has the potential to reduce and chelate iron. Pseudomonas is inhibited by a higher concentration of 0.1%, whereas Salmonella typhimurium and Escherichia coli are unaffected. PPE can therefore be employed in a variety of industries due to its adaptability (e.g., as an addition in functional meals).
The isolation of phenols from pomegranate peels has been the subject of numerous investigations utilizing a variety of extraction methods, including pressured-water extraction, enzyme-assisted extraction, ultrasonic extraction, and microwave extraction [3,4,5].
However, the intrinsic constraints of phenolic compounds, such as their low stability, poor solubility, and sensitivity to degradation, frequently obstruct their practical utilization. Encapsulation techniques have become a successful method for boosting the stability and bioavailability of phenolic compounds, helping to overcome these obstacles and realize their full potential. Co-crystallization is one of the many encapsulation techniques that has lately come to be recognized as a potential method for the encapsulation of phenolic extracts. Co-crystals are crystalline substances made up of two or more molecules held together by non-covalent interactions, giving them special physicochemical features [6]. In order to address their drawbacks and increase their scope of use, phenolic compounds can have their properties, such as solubility, dissolving rate, and stability, modified by forming co-crystals with other chemicals [7].
Several benefits over conventional encapsulation methods are provided by the co-crystallization of phenolic extracts [8,9]. First, co-crystals offer phenolic compounds a solid-state structure that improves their chemical stability and shields them from oxidation and degradation. Second, a better solubility and dissolution rate, as well as improved bioavailability, are made possible by the controlled creation of co-crystals. Additionally, the co-crystallization method allows for the addition of a variety of excipients, such as natural polymers or surfactants, which can improve the stability and functional qualities of phenolic encapsulates.
Co-crystals are, however, more frequently utilized in the pharmaceutical sector [10]. Based on the encapsulating active ingredient, these uses can be divided into three major categories. Co-crystals of phenolic or carotenoid extracts fall under the first category. Examples include extracts of banana pulp and peel [11], green tea [12], butterfly pea flower [13], brasella rubra [8], propolis [14], carrot [15], aronia [16], mint polyphenols [17], and pomegranate peel [18]. Pure substances such as glucose [6,19], fructose [19], combinations of glucose and fructose [19], magnesium sulfate and calcium lactate [20,21], zinc sulfate [22], curcumin [23], vitamin B12 [24], soluble fiber [25], and catechin hydrate and curcumin [26] are included in the second group. Oils and oleoresins, such as orange peel oil [27], cardamom oleoresin [9,28], capsicum oleoresin [29], and ginger oleoresin [30], are included in the third group. It is important to note that the co-crystallization approach has not been used to encapsulate pomegranate peel extracts, according to the literature.
In one of our earlier studies [18], three different experimental approaches were used to successfully co-crystallize pomegranate peel phenolic extract and encapsulate it in sucrose. The optimum conditions were established after considering the effects of numerous parameters, including the temperature of the extract during its addition to the sucrose matrix, the extract’s solids content, and the ratio of dry extract to sucrose. The goal of the current work is to characterize the co-crystallized pomegranate peel extract by assessing its properties, such as moisture content, bulk density, solubility, hygroscopicity, color, degree of encapsulation in the sucrose matrix with thermograms, crystallinity with X-ray scattering, and microstructure with SEM. This work is a continuation of our investigation into the use of pomegranate peels.
The extract’s storage stability must be taken into account when creating a technique for extracting value from food waste. As a result, we investigated how stable the crude and encapsulated phenolics were in terms of their overall phenolic concentration and antioxidant activity. The present work is intended to shed light on the co-crystallization of pomegranate peel extract as a promising strategy to overcome the drawbacks of phenolic chemicals. This work aims to develop encapsulation technologies and their applications in the field of phenolic chemical delivery systems by providing a thorough understanding of the co-crystallization process and its consequences.

2. Materials and Methods

2.1. Raw Materials

Food-grade crystal sucrose was bought for the co-crystallization procedure. Wonderful variety pomegranate peels from the Parthenon in Chalkidonos, Thessaloniki, Greece, were bought and stored at −30 °C until use. The peels were divided into smaller pieces and dried at 40 °C for two days (Gallenkamp PCL, Leister, UK) until the moisture content dropped to roughly 10% w/w wet basis. The peels were pulverized in a mill (IKA Labortechnik, Staufen, Germany) after drying. The average powder particle size was 0.4 mm.

2.2. Extraction

Using a 13 mm Ti-Al-V probe in pulsed mode, the extraction was carried out with a Sonics and Materials (Danbury, Newtown, CT, USA) 130 W, 20 kHz, VCX-130 ultrasound-assisted extraction system. The best conditions for extracting phenolics from pomegranate peels, according to Kaderides et al. [4], are: solvent, water; solvent/peels, 33/1 mL/g; amplitude, 40% (50 W); pulse duration/interval ratio, 7/6 s/s; time, 10 min; temperature, 35 °C. The container was in a thermostatically regulated water bath during the extraction process. The resultant extract was then filtered on Whatman filter paper No. 2 and evaporated using a rotary evaporator (R114, water bath B480, Büchi, Flawil, Switzerland) at 40 2 °C with a vacuum of 150 mbar to a solids concentration of 60° Brix. The extract was stored in a dark bottle at −18 °C.

2.3. Co-Crystallization Procedure

75 g of sucrose was mixed with distilled water (12.5 mL). The mixture was continuously swirled (at a speed of 500 rpm) in a metal jar heated to 140 °C, which was found to be the ideal temperature [18]. When the mixture reached the desired temperature, the heating process was stopped, stirring continued at a constant speed of 700 rpm, and pomegranate peel extract was added to the sucrose syrup at a concentration of 0.591 g/g of dry extract [18]. The mixture was then placed in a water bath (about 25 °C) and agitated until it reached a temperature of less than 60 °C (about 45 °C). After that, the powder was put in a glass container and kept in a desiccator for 24 h.

2.4. Characterization of the Product

Moisture content
The moisture content of the product was calculated by drying at 105 °C [31].
The solubility was determined by adding 1 g of powder to 25 mL of distilled water at room temperature with agitation at 890 rpm [32].
Bulk density
The bulk density was estimating by dividing the mass of a powder sample (about 2 g) by its volume in a 50 mL graduated cylinder [33].
About 1 g of powder was put in a desiccator with HNO3 solution (23 °C and 76% relative humidity) on dishes to generate a high surface area. The increase or decrease in the powder weight per gram of its solids was measured [16].
A Minolta colorimeter (CR-400, Japan) was used for the evaluation of color using the CIE-L* a* b* uniform color space. The powder was placed in dishes in a layer with a thickness of approximately 0.5 cm.
Differential scanning calorimetry
According to Kaderides and Goula [34], samples (2–10 mg) of pure crystalline sucrose, co-crystallized sucrose without the active ingredient, and co-crystallized sucrose with the encapsulated ingredient were used for differential scanning calorimetry (DSC) analysis. In an inert environment, the samples were heated at a rate of 10 °C/min from 25 to 250 °C.
Degree of crystallinity
The X-Ray diffraction pattern was determined using a continuous scan mode (3003 TT, Rich. Seifert) at 40 kV with radiation of 40 mÅ and 2θ data 5–60°. All samples were dried at 60 °C before the assay.
Particle morphology was examined with a Quanta-200 scanning electron microscope system (FEI, Raleigh, NC, USA) under vacuum conditions with a 10 kV accelerating voltage.
Storage stability
During storage at 60 °C, the phenolic content and antioxidant activity of the unencapsulated and encapsulated extracts were investigated. For roughly 45 days, extract samples were kept at the observed temperature in a dark oven (Memmert, Schwabach, Germany). Every two to three days, duplicate samples were collected for analysis. The Folin–Ciocalteu method was used to quantify the phenolic content (TPC), whereas the DPPH method was used to determine the antioxidant activity [32].

2.5. Statistical Analysis

All characterizations were made using triplicate samples and the results are expressed as mean ± standard deviation. ANOVA analysis was performed and a p value lower than 0.05 was characterized as statistically significant.

3. Results and Discussion

3.1. Powder Properties

Powders produced at the optimum conditions were studied for moisture content, solubility, bulk density, hygroscopicity, and color.
The co-crystallized product had a moisture content of roughly 0.59%, which was less than what was found when spray drying was utilized [35]. Similar outcomes were attained by Bhandari and Hartel [19], who found that when sucrose was used to encapsulate glucose, fructose, and their mixes, the moisture content of co-crystallized powders ranged from 0.67% to 3.22%. In addition, Irigoiti et al. [14] noted that co-crystallized powders of propolis extracts had a moisture content of 0.03–2.09%. In general, the ratio of the powder’s crystalline to amorphous structure and the active ingredient are two parameters that influence the moisture content [9,36]. In their studies on the encapsulation of simple sugars, mineral or propolis extracts, and yerba mate extracts, Bhandari and Hartel [19], Irigoiti et al. [14], and Deladino et al. [20] came to the conclusion that as the amount of the active ingredient in sucrose grew, so did the product’s moisture content. This observation might be the result of the fact that, as the ratio of extract solids to sucrose rises, more extract is also added to the sugar, which, on the one hand, reduces the amount of water that can be removed from the powder that is formed and, on the other, affects the hydrophilic regions of the polysaccharide chain where water can be retained [37].
A powder’s moisture content is typically an important factor in determining its density. In particular, the likelihood of particles to agglomerate increases and the bulk density decreases with increasing water content [16]. The co-crystallized product’s bulk density was about 0.803 g/cm3. When encasing marjoram and aronia extract, Sarabandi et al. [36] and Tzatsi and Goula [16] discovered that the bulk density of the powder was between 0.7 and 0.73 g/cm3 and 0.63 and 0.97 g/cm3, respectively. The bulk density of co-crystallized propolis was also discovered by Irigoiti et al. [14] to vary between 0.63 and 0.87 g/cm3. The literature claims that bulk density provides important information about economic fundamentals since it reduces the quantity of material required to fill an anticipated volume of packing [36]. A high bulk density also typically indicates that there is less space between particles for air to occupy, which aids in preventing oxidation and enhances powder stability, according to Kurozawa et al. [38].
The powder solubility was about 61 s. Similar results were obtained by Irigoiti et al. [14] and Kaur et al. [15], who mentioned that the solubility of co-crystallized powders was 41–47 s and 45–50 s, respectively. In addition, Rai et al. [30] noted that the final powder’s solubility ranged from 32 to 57 s during the co-crystallization of ginger oleoresin. To manage the release of the active component in the sucrose and to determine whether the product is suitable for oral delivery of the active ingredient, solubility is essential [36]. The additives and insoluble elements present, the kind of matrix, and the size, microstructure, shape, and surface finish of the particles all affect how well powders dissolve [9,20,36].
Another characteristic that was measured is the color of the powder, more precisely, the brightness parameter L*. The most important aspect of a product’s aesthetic appeal, according to Kaur et al. [15], is its color, and the amount of the active ingredient that is encapsulated in the sucrose directly impacts the powder’s color [36,39]. The powder was found to be 83.24 percent light. The literature indicates that there have been very few studies on a co-crystallized product’s color. According to Karangutkar and Ananthanarayan [8], the L* value ranged from 49.35 to 62.10 during the co-crystallization of Basella rubra extract into sucrose. Additionally, Irigoiti et al. [14] noted that the co-crystallized propolis extract had a lightness range of 62–82.26. The higher temperature and extract solids concentration levels applied in the particular studies may be responsible for these lower findings. Greater co-crystallization temperatures increase the chance of caramelization, increasing the likelihood of a darker-colored powder with lower L*. Additionally, the reduction in L* that happens when the concentration of extract solids increases could be due to the extract evaporating. The extract’s color becomes deeper and more deteriorated as it evaporates more.
The co-crystallized product’s moisture absorption rate is less than 2% and is around 0.011%; therefore, the powder cannot be said to be hygroscopic. Deladino et al. [20] and Sarabandi et al. [36] both reported humidity readings of less than 2% at relative humidity levels of around 85%. These low values might be explained by the fact that the crystalline structure absorbs less water than the amorphous form [19]. The proportion of amorphous crystals in the glucose–fructose combination, according to Sardar et al. [28], controls the hygroscopicity of the co-crystals. Spray-dried phenolic extracts are often less fluid than co-crystallized products because they are more viscous. By using the co-crystallization process, the stickiness and hygroscopicity issues with spray-dried extracts are resolved.

3.2. Differential Scanning Calorimetry

Three separate samples, including pure crystalline sucrose, co-crystallized sucrose without the active ingredient, and co-crystallized sucrose with the encapsulating substance, were each subjected to the DSC technique (Figure 1). The thermogram of pure sucrose shows three endothermic peaks, the smallest of which is extremely minor and occurs about 155 °C, the second closest to 192 °C, and the third occurring at a temperature greater than 200 °C and close to 220 °C. The initial very small peak, according to the literature, might be caused by moisture that is still present in the amorphous areas of sucrose crystals and other components, primarily metal salts [9,10,36,39]. The majority of researchers who also came to the same conclusion [9,19,21,36,39] concur that the second peak represents the melting of sucrose crystals. According to [9,36], the third peak describes the heat breakdown of sucrose. Finally, the minor exothermic peak at a temperature of about 215 °C can be attributed to either the byproducts of sucrose caramelization or to potential interactions between contaminants and sucrose [21].
Exactly the same pattern is shown in the second thermogram, which represents co-crystallized sucrose without the encapsulated component. Deladino et al. [21], who likewise discovered no variations in the thermograms of pure and co-crystallized sucrose, are in agreement with this observation. However, other study teams stress that the co-crystallized sucrose thermogram shows a minor shift of the peaks to the left, which is caused by the defective and amorphous crystals that are present in part of the co-crystallized sucrose’s crystals [9].
The third thermogram, which is the last, describes co-crystallized sucrose that has been combined with the active component. There are no variations between the first and third thermograms, as can be seen. The endothermic peak of the active ingredient, which would be present at temperatures lower than the melting temperature of sucrose crystals, is absent, and this must be noted. This fact suggests that co-crystallization improved the extract’s thermal stability and that its successful encapsulation in the sucrose matrix was achieved [8].

3.3. Degree of Crystallinity with X-ray Scattering

The preservation of X-ray scattering (XRD) crystallinity in both pure crystalline and co-crystallized sucrose without or with the encapsulated component is another significant aspect that was studied, as shown in Figure 2. The graphs show that co-crystallized sucrose both without the active ingredient and in the presence of it were maintained at levels higher than 55% in terms of crystallinity. Karangutkar and Ananthanarayan [8] state that items with a degree of crystallinity greater than 50% are classified as extremely crystalline, between 20 and 50% as moderately crystalline, and below 20% as weakly crystalline.
Other research teams who looked into the encapsulation of phenolic extracts in a sucrose matrix managed to preserve crystallinity as well. For instance, it was discovered by Deladino et al. [21] and Kaur et al. [15] that crystallinity was preserved during the co-crystallization of yerba mate phenolic extract and carotenoid extract. Additionally, they state that no new peak can be seen in the XRD graphs of the co-crystallized products, proving that the encapsulated extract maintained its amorphous structure and did not crystallize. Similar to the previous study, the active ingredient was added to this one without increasing the level of crystallinity, demonstrating that the phenolic extract from pomegranate peels did not crystallize but rather remained liquid inside the porosity of the sucrose crystals. As a result, when the co-crystallized powder is added to a product, it exhibits a more controlled release.
According to the literature, the ability of the extract’s polar nature to integrate unhindered into the sucrose matrix and the preservation of sucrose’s covalent bonds, which prevented changes in the substance’s structure and, ultimately, prevented reactions between the encapsulated components, may be the reasons for the preservation of crystallinity [8,36,40]. Researchers who noticed a shift in the co-crystallized products’ degree of crystallinity—more particularly, a decline in crystallinity when compared to pure sucrose—encapsulated substances of a hydrophobic character. For instance, Rai et al. [30] found that the crystallinity degree of ginger oleoresins dropped by roughly 20% during co-crystallization.

3.4. Morphology with Scanning Electron Microscopy

Figure 3 depicts the morphology of pure crystalline sucrose, co-crystallized sucrose without the active component, and co-crystallized sucrose with the encapsulated ingredient as determined with scanning electron microscopy. Starting with pure sucrose, a smooth, void-free surface with tiny, sharp corners is seen. Tzatsi and Goula [16] and Deladino et al. [21] also came to similar conclusions and stated that the particular arrangement is caused by the consecutive positions of the atoms in the sucrose molecules. It is evident from looking at the micrograph of the co-crystallized sucrose without the addition of the encapsulated component that the structure of the sucrose has changed, with gaps appearing between the crystals but the corners remaining sharp, proving the retention of crystallinity. When encapsulating carotenoid extract, Kaur et al. [15] reported reaching a similar finding.
Interstices with significant porosity are also visible in the micrograph of the co-crystallized sucrose with the active component. Additionally, the amorphous regions and sharp corners at the interstices occur simultaneously, indicating that the pomegranate peel extract is still in an amorphous form between the sucrose crystal gaps. As the low-molecular-weight sugars of the phenolic extract that remained on the surface tended to absorb moisture, it has been discovered that the extract is also on the surface of the sucrose crystals in some locations, which confirms the hygroscopicity value. Almost all research teams that used scanning electron microscopy came to the same conclusion: the active ingredient was found between the gaps and was kept in its original form in all of their crystalline products. After co-crystallization, sucrose’s solid, compressed, flawless crystal structure transforms into asymmetrical, agglomerated, and spongy crystals with larger voids and surface areas, according to Tzatsi and Goula [16], who encapsulated extract from discarded chokeberries. Similar findings were reported by researchers who explored the co-crystallization of yerba mate extract, cardamom oleoresin, and cranberry extract, such as Deladino et al. [20], Sardar and Singhal [9], and Karangutkar and Ananthana-rayan [8].
On the other hand, when PPE is encapsulated by spray drying, the particles’ shape is different. The encapsulated powders were reported to be spherical with uneven surfaces that displayed indentations by Kaderides and Goula [35], who utilized conventional wall materials and orange juice by-products as encapsulating agents. This indicates that the walls had solidified before swelling commenced. The microcapsules with orange waste had a corrugated, spherical surface and the particles had few splits or fissures in comparison to capsules manufactured from maltodextrin and skimmed milk. Tan et al. [41] claim that crashes created during encapsulation cause increased heat exposure during drying as well as increased exposure to bioactive chemicals within particles. Similar discrepancies were documented by Tzatsi and Goula [16], who encapsulated chokeberry extract using both spray drying and co-crystallization. The spray-dried product includes round particles, a matte surface, and wall spaces, some of which may be caused by air entrained during homogenization or atomization [32,42]. The co-crystallized encapsulated extracts, on the other hand, exhibited aggregates and porous co-crystals.

3.5. Change in Total Phenolic Content

Figure 4 illustrates how the phenolic extract that was enclosed in a matrix of sucrose was more effectively maintained than the liquid extract. The inclusion of unstable phenolic components into the porosity of the sucrose aggregates ensures that they reduce the interaction of the active ingredient with environmental factors, providing protection against oxidation and degradation reactions and improving the stability of the co-crystallized product [8].
Regarding the variation in the phenolic concentration of the capsuled extract, it can be noted that the total phenolic content fluctuated throughout the course of the 40 days. According to the findings, the phenolic content barely decreased by 0.56% from its starting point. As a result, the phenolic components in the sucrose matrix were successfully protected and preserved using the co-crystallization approach. According to Sarabandi et al. [36], co-crystallization guarantees a good stability of the active ingredient. This development can be linked to the sucrose crystal structure’s capacity to effectively shield the encapsulated chemicals. It is important to note that after around 12 days, the curve showing the change in the total phenolic content of the co-crystallized powder shows an upward trend, indicating an increase in the concentration of phenolic components. During the examination of the stability of encapsulated samples, there are numerous literature references that report an increase in the concentration of total phenolic content. For instance, Kaderides et al. [43] reported that the spray-drying method resulted in a rise in phenolics, primarily in the first ten days, in the encapsulated phenolic extract from pomegranate peels. The generation of chemicals that react with the Folin–Ciocalteu reagent as well as the hydrolysis of conjugated polyphenols and changes in the structure of phenolic compounds were both responsible for this rise. Similar results were obtained by Flores et al. [44], who combined raspberry peel extract with whey protein and discovered that the storage time increased the phenolic concentration. Other study teams have similarly noted the preservation of phenolic content at the conclusion of the 40-day period. Irigoiti et al. [14] observed a good retention of phenolic content in propolis extract when encapsulating it in a sucrose matrix, and they even stressed that the final product is more stable the higher the concentration of the extract in the sucrose is. They assumed that this trend is caused by the fact that larger amounts of the active ingredient can be retained in the porosity of the sucrose aggregates.
In comparison to the outcome of the current study, the spray-dried powder from pomegranate peel extract generated by Kaderides et al. [43] displayed superior stability since it had a flat surface with dents, indicating that the wall had formed before expansion and shrinkage started. The spray-dried powder demonstrated superior stability than the co-crystallized product, according to Tzatsi and Goula [16], who encapsulated chokeberry extract using both spray drying and co-crystallization. This is because the spray-dried powder had a flat surface, indicating that the wall had hardened before shrinking. The co-crystallized products, in contrast, showed better stability when compared to spray-dried powders, claim Sarabandi et al. [36]. This pattern was attributed to sucrose’s crystallized structure, which outperforms the amorphous powder produced by spray drying in protecting the encapsulated compounds. Additionally, the pores of some spray-dried capsules reduce entrapment.
A drop of 9.93% was seen over time in the stability of the liquid, non-encapsulated extract in comparison to the beginning value. It was discovered that the total phenolic content increased significantly in the second measurement. This may have been caused by the thermal degradation of phenolics, which produces derivative products that are recognized as phenolic components [18], or by the emergence of compounds that react with the Folin–Ciocalteu reagent and affect the absorbance measurement [13]. Then, though, a steady decline is noticed, which can be linked to the polyphenols’ oxidation and hydrolysis since direct contact with external elements caused some of their phenolic content to be destroyed. Similar conclusions were drawn by Kaderides et al. [43], who noted a decrease in the concentration of total phenolic components over the course of storage in the liquid extract of pomegranate peels. The hydrolysis and oxidation of the polyphenols were responsible for this result. Laine et al.’s [45] theories included the production of ellagic acid during hydrolysis [46], interactions with carbohydrates that result in complex formation [47], and polymerization events during oxidation as potential causes of ellagitannin loss during storage. In contrast to Cam et al. [1], who examined the phenolic components of pomegranate peels during storage and discovered a considerable drop in the amount of phenolic compounds, Xu et al. [48] reported that the phenolic content of mulberry powder decreased by 34.21% after 20 days when it was exposed to air and light.

3.6. Change in Antioxidant Capacity

The co-crystallized powder’s ability to maintain antioxidant activity while being stored at 60 °C is another crucial quality. Figure 5 shows that the antioxidant activity of the capsuled extract was kept higher than that of the liquid extract, in fact exceeding 84%.
The encapsulated extract was discovered to follow a similar trend to the total phenolic content curve in terms of antioxidant activity. More particularly, there are some variations throughout the course of the 40 days that correspond to those in Figure 4. As a result, in this particular research investigation, there is a direct association between the samples’ antioxidant activity and total phenolic content. Many researchers find that a sample’s phenolic content and antioxidant action are correlated. The strong antioxidant activity of encapsulated mate tea, for instance, was linked by Negrao-Murakami et al. [49] to the high phenolic stability of the tea during storage. Additionally, Fang and Bhandari [50] and Flores et al. [44] demonstrated that, for laurel powder and encapsulated extract of bilberry peels, respectively, the variation of antioxidant activity throughout storage was similar to that of total phenolic content. The modest differences in antioxidant activity could be attributed to the modification of the phenolic profiles. The “team players” mentality of phenolic compounds, as described by Laine et al. [51], refers to their ability to support one another’s antioxidant effects. The loss of the original phenolics may be compensated for by the synthesis of phenolics with similar or greater antioxidant activity. As an illustration, according to Bors and Michel [52], the hydrolysis of elagitannins may increase the antioxidant activity by increasing the number of hydroxyl groups, whereas the oxidation of hydrolyzable tannins may lead to oligomerization, which then increases the number of reactive places and improves the antioxidant activity. The durability of pomegranate peel extract capsuled by spray drying was investigated by Kaderides et al. [5], who came to the conclusion that the antioxidant activity remained at high levels (>90%) for the full storage period (60 °C, 45 days). They also stated that the loss of original phenolics might be compensated for by newly generated phenolics with equivalent or better antioxidant capacities. For instance, punicalagin is hydrolyzed to generate chemicals like punicalin, gallagic acid, gallic acid, and ellagic acid, all of which have the potential to be antioxidants [53].
A sudden spike is first seen in the liquid extract, which is then followed by a fluctuation and then a further reduction. At the conclusion of the particular 40-day period, the overall decline in antioxidant activity was 7.86%. This is interesting because it confirms the relationship between the total phenolic content and antioxidant activity once more and shows that the causes of variation in antioxidant activity are often the same as those of variation in the total phenol concentration.

4. Conclusions

The increased interest in the investigation of efficient and affordable natural antioxidants is a result of growing concerns regarding the safety of synthetic antioxidants. Pomegranate peels may be separated and stabilized using a variety of techniques, making them a potential commercial source of phenolic chemicals. The goal of the current study is to characterize pomegranate peel extract that has been co-crystallized under circumstances established by earlier research. It was established that:
  • The moisture content of the co-crystallized product is about 0.59%, a value lower than those reported when spray drying was used.
  • The moisture absorption rate for the co-crystallized product is about 0.011%, so the powder cannot be considered to be hygroscopic.
  • The co-crystallized powder has a high bulk density (0.803 g/cm3) and solubility (61 s).
  • The phenolic extract does not crystallize but is still in an amorphous state between gaps in the sucrose crystals.
  • The obtained thermographs indicate both the improvement of the thermal stability of the extract by the co-crystallization and its successful encapsulation in the sucrose matrix.
  • The co-crystallized powder has an excellent storage stability, as it preserves its phenolic content and antioxidant activity at high levels after storage at 60 °C for 45 days.
Overall, the co-crystallization of the phenolic extract from pomegranate peel opens up a viable path for harnessing and boosting the bioactivity of these priceless components. The goal of this study is to advance knowledge of the co-crystallization method for pomegranate peel phenolic extract and encourage further investigation of its applications. This will encourage the sustainable use of pomegranate byproducts and the creation of functional products that may have positive health effects.

Author Contributions

Conceptualization, A.M.G.; methodology, A.M.G.; software, E.C.; validation, E.C.; formal analysis, E.C.; investigation, E.C. and A.M.G.; resources, A.M.G.; data curation, E.C.; writing—original draft preparation, E.C. and A.M.G.; writing—review and editing, A.M.G.; visualization, E.C.; supervision, A.M.G.; project administration, A.M.G.; funding acquisition, A.M.G. All authors have read and agreed to the published version of the manuscript.


This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be available upon request.

Conflicts of Interest

The authors have no conflict of interest.


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Figure 1. DSC thermographs of (a) pure crystalline sucrose; (b) co−crystallized sucrose without the active ingredient; (c) co−crystallized sucrose with the encapsulated ingredient.
Figure 1. DSC thermographs of (a) pure crystalline sucrose; (b) co−crystallized sucrose without the active ingredient; (c) co−crystallized sucrose with the encapsulated ingredient.
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Figure 2. X-ray diffraction characterization of (a) pure crystalline sucrose; (b) co-crystallized sucrose without the active ingredient; (c) co-crystallized sucrose with the encapsulated ingredient.
Figure 2. X-ray diffraction characterization of (a) pure crystalline sucrose; (b) co-crystallized sucrose without the active ingredient; (c) co-crystallized sucrose with the encapsulated ingredient.
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Figure 3. SEM microphotographs of (a) pure crystalline sucrose; (b) co-crystallized sucrose without the active ingredient; (c) co-crystallized sucrose with the encapsulated ingredient.
Figure 3. SEM microphotographs of (a) pure crystalline sucrose; (b) co-crystallized sucrose without the active ingredient; (c) co-crystallized sucrose with the encapsulated ingredient.
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Figure 4. Total phenolic content of crude and encapsulated extract during storage at 60 °C.
Figure 4. Total phenolic content of crude and encapsulated extract during storage at 60 °C.
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Figure 5. Antioxidant activity of crude and encapsulated extract during storage at 60 °C.
Figure 5. Antioxidant activity of crude and encapsulated extract during storage at 60 °C.
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Chezanoglou, E.; Goula, A.M. Properties and Stability of Encapsulated Pomegranate Peel Extract Prepared by Co-Crystallization. Appl. Sci. 2023, 13, 8680.

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Chezanoglou E, Goula AM. Properties and Stability of Encapsulated Pomegranate Peel Extract Prepared by Co-Crystallization. Applied Sciences. 2023; 13(15):8680.

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Chezanoglou, Evangelos, and Athanasia M. Goula. 2023. "Properties and Stability of Encapsulated Pomegranate Peel Extract Prepared by Co-Crystallization" Applied Sciences 13, no. 15: 8680.

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