Pomegranate Peels: A Promising Source of Biologically Active Compounds with Potential Application in Cosmetic Products

Abstract

As a rich source of biologically active compounds, pomegranate peel is a valuable by-product with applications in the food, pharmaceutical and cosmetic sectors. The present study aimed to investigate the phytochemical composition, antioxidant and antimicrobial activity, photoprotective activity and application in a cosmetic emulsion of extracts obtained from pomegranate peel by different solvents. The analysis of phenolic compounds was determined by high-performance liquid chromatography (HPLC); the total phenolic content (TPC) and the total flavonoid content (TFC) were evaluated using standard spectrophotometric methods; the antioxidant activity was assessed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging, ferric-reducing antioxidant power (FRAP) and 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays; antimicrobial screening was performed against twenty test microorganisms; the ultraviolet (UV) protection effect of extracts and cosmetic emulsion was assessed spectrophotometrically in the wavelength range of 290–320 nm. HPLC analysis revealed fourteen phenolic compounds, including four phenolic acids (ellagic, gallic, p-coumaric, and ferulic), two tannins (pedunculagin and punicalagin), six flavonoids (myricetin, hesperidin, quercetin, luteolin, kaempferol, and apigenin), and two quercetin glycosides (rutin and hyperoside). The four pomegranate peel extracts demonstrated high TPC, TFC and antioxidant potential (DMSO > 70% ethanolic > methanolic > aqueous), and significant antimicrobial activity. The four extracts showed a remarkable UV protection effect. When applied in a cosmetic emulsion, the ethanolic extract showed sun protection factor (SPF) values from 13.59 (0.5 mg/g) to 50.65 (5 mg/g). Based on the results obtained, we can conclude that pomegranate peel is a promising source of bioactive compounds, which can be successfully utilized by integration into various pharmaceutical and value-added skin health products.

1. Introduction

Pomegranate (Punica granatum L.) is a little tree from the family Lythraceae (formerly Punicaceae), which is indigenous to the Middle East, but currently distributed across the Mediterranean region, China, India, South Africa, and North and South America. Pomegranates are widely used in human nutrition and traditional medicine due to their rich chemical composition, high nutritional value and a wide range of health benefits. Pomegranate fruits, which are usually consumed in fresh form or processed into juice, can be divided into three main parts—peels, juice, and seeds. During the production of pomegranate juice, a significant quantity of waste is generated, with peels constituting around 26–30% of its overall weight [1,2].

It has been established that pomegranate peels are a rich source of biologically active compounds including phenolic acids (gallic, caffeic, ferulic, cinnamic, p-coumaric, ellagic, vanillic), flavonoids (catechin, epicatechin, quercetin, rutin, kaempferol, hesperidine), and tannins (ellagitannins, gallotannins, punicalin, pedunculagin, granatins A and B, corilagin, tellimagrandin, gallagyl, hexoside). They are contained in the peels in greater amounts compared to the other parts of the fruit, thus contributing to their high antioxidant activity and remarkable pharmacological properties [3,4]. Pomegranate fruit is abundant in anthocyanins (cyanidin 3-glucoside, cyanidin 3,5-diglucoside, delphinidin 3-glucoside, delphinidin 3,5-diglucoside, pelargonidin 3-glucoside, and pelargonidin 3,5-diglucoside), which are mainly contained in the peel, conferring its color, but are also known to possess significant antioxidant capacity [5]. Chemical compounds including carbohydrates, alkaloids, saponins, quinones, terpenoids, cardiac glycosides, coumarins, steroids and others have also been identified, with the highest levels detected in ethanolic extracts [6]. Pomegranate peel is a rich source of dietary fibers and pectin (6.8–10.1%), which is used as a natural gelling, coloring, stabilizing, emulsifying and thickening agent in the food industry [7]. Considering the low industrial price of pomegranate peels as well, they represent an attractive by-product that has received significant attention in recent decades for utilization in the food and pharmaceutical sectors [3].

Phenolic acids, flavonoids and tannins (especially ellagitannins) are known to determine the antioxidant potential and antimicrobial activity of the pomegranate peels and their extracts. In addition to these, other therapeutic effects such as anticarcinogenic, antiulcerogenic, anti-inflammatory, anti-allergic, antiatherogenic, anti-hyperglycemic, anti-angiogenic and wound healing have been reported [8,9,10]. It is noteworthy that ellagic acid has been identified as a possible chemotherapeutic agent for cancer treatment due to its cytoprotective and antioxidant effects but is also known to reduce body fat deposits and triglyceride levels in the blood. Punicalagin (an ellagitannin) is another main bioactive compound that has also been found to exhibit antiproliferative activity in addition to its antioxidant and antimicrobial properties [9].

Recent studies have demonstrated that bioactive pomegranate components are effective in the treatment and prevention of skin diseases. Pomegranate polyphenols have been found to be able to prevent ultraviolet (UV)-induced oxidative stress by absorbing UVA (320–400 nm) and UVB (290–320 nm) photons before radiation reaches the epidermal and dermal layers, thereby delaying skin alterations such as erythema, skin burn, DNA fragmentation and depigmentation [11]. Pomegranate phenolic compounds have demonstrated efficacy in vitro and in vivo for the treatment of skin aging and hyperpigmentation [12] but also inhibit human epidermal keratinocyte damage and tumorigenesis of the skin in CD1 mice [13]. The reduction in oxidative damage, antimicrobial and anti-inflammatory activity of the different parts of pomegranate fruit can be successfully used for skincare (skin whitening, hair color protection, prevention of premature aging and wrinkling, etc.) as well as for the treatment of dermatological diseases such as sunburns, chronic dandruff, acne vulgaris, psoriasis, striae distensae, and various bacterial and fungal skin infections [6,7].

This article focuses on the phytochemical composition, antioxidant properties, antimicrobial and ultraviolet (UV) protection activity of different types of extracts of pomegranate (Punica granatum L.) peels in view of their utilization as a valuable by-product of fruit processing, with special emphasis on their potential in skin protection and application in cosmetic products.

2. Materials and Methods

2.1. Plant Material

Pomegranate (Punica granatum L.) fruits were obtained from a private yard in the town of Krichim, Plovdiv district, Bulgaria (42°04′ N 24°46′ E). The trees/fruits were not treated with chemicals (pesticides). The fruits were harvested at commercial maturity, washed with tap water and dried. The peels were manually removed, cut into pieces and left to air dry completely at room temperature. Next, the pomegranate peels were finely ground, placed in a tightly closed plastic box and stored in darkness prior to analysis.

2.2. Test Microorganisms

Five Gram-positive bacteria (Bacillus subtilis ATCC 6633, Bacillus cereus NCTC 11145, Staphylococcus aureus ATCC 6538P, Listeria monocytogenes NBIMCC 8632, Enterococcus faecalis RC-21), five Gram-negative bacteria (Salmonella typhimurium NBIMCC 1672, Klebsiella pneumoniae RC-20, Escherichia coli ATCC 25922, Proteus vulgaris ATCC 6380, Pseudomonas aeruginosa ATCC 9027), two yeasts (Candida albicans NBIMCC 74, Saccharomyces cerevisiae ATCC 9763) and eight fungi (Aspergillus niger ATCC 1015, Aspergillus ochraceus, Aspergillus flavus, Penicillium chrysogenum, Fusarium moniliforme ATCC 38932, Fusarium oxysporum, Rhizopus sp. and Mucor sp.) were used as test microorganisms in the antimicrobial activity test.

2.3. Culture Media

Luria–Bertani agar medium with glucose (LBG agar)

LBG agar was used for the cultivation of test bacteria. A quantity of 50 g of LBG–solid substance mixture (containing 10 g tryptone, 5 g yeast extract, 10 g NaCl, 10 g glucose and 15 g agar) was dissolved in 1 L of deionized water, pH 7.5 ± 0.2.

Malt extract agar (MEA)

MEA was used for cultivation of test yeasts and fungi. A quantity of 50 g of the MEA–solid substance mixture (containing 30 g malt extract, 5 g mycological peptone and 15 g agar) was dissolved in 1 L of deionized water, pH 5.4 ± 0.2.

The culture media were prepared according to the manufacturer’s instructions (Scharlab SL, Barcelona, Spain) and autoclaved at 121 °C for 20 min (liquid phase) before use.

2.4. Preparation of Pomegranate Peel Extracts

In the present study, four types of pomegranate peel extracts in solvents of various polarity (water, 70% ethanol, methanol and dimethylsulphoxide—DMSO) were investigated. For this purpose, 4 g of ground pomegranate peel material was macerated with 40 mL of deionized water/70% ethanol/methanol/DMSO (1:10 ratio); afterwards, the samples were vortexed and left for 72 h in darkness at room temperature for extraction. Next, the extracts were filtered through a filter paper and stored at identical conditions until analysis.

2.5. Preparation of Cosmetic Emulsion (Body Lotion) with the Addition of Pomegranate Peel Extract

Cosmetic emulsion base (body lotion) was prepared according to the following prescription (

Table 1. Formulation of an oil-in-water (O/W) cosmetic emulsion.

Phase	Ingredient INCI *	Properties	Content, %
A	Aqua	solvent	ad 100
	Glycerin	moisturizer	2.00–4.00
B	Glyceryl stearate (and) ceteareth-20 (and) ceteareth-12 (and) cetearyl alcohol (and) cetyl palmitate	emulsifier	3.00–5.00
	Isopropyl palmitate	emollient	2.00–4.00
	Isopropyl myristate	emollient	2.00–4.00
	Paraffinum liquidum	emollient	5.00–7.00
	Cera alba	co-emulsifier consistency regulator	0.50–2.00
	Methylparaben	preservative	0.05–0.10
	Propylparaben	preservative	0.05–0.10
C	2-bromo-2-nitropropane-1,3-diol	preservative	0.02–0.05

* The names are given according to the International Nomenclature Cosmetic Ingredient (INCI).

):

The cosmetic emulsion of the oil-in-water (O/W) type was prepared in laboratory conditions by applying the following technology. Initially, the components of phases A and B were weighed and heated to a temperature of 80–85 °C. This was followed by emulsification of the two phases with continuous vigorous stirring. The resulting emulsified mass was gradually cooled while being continuously stirred. Phase C was added to the emulsion that was already cooled to 40 °C.

The cosmetic emulsion base was divided into equal portions in sterile containers. The first was kept as an untreated control, while to the other four portions, 70% ethanolic pomegranate peel extract (ethanol was pre-evaporated under vacuum) at concentrations of 0.5, 1, 2 and 5 mg/g was added and mixed (Figure 1).

2.6. Total Phenolic Content

The total phenolic content (TPC) of pomegranate peel extracts was assessed according to the method of Ivanov et al. [14] using Folin–Ciocalteu reagent (Sigma-Aldrich, St. Louis, MO, USA). The absorbance was measured at 765 nm and the results were expressed as mg equivalents of gallic acid (GAE)/g dw.

2.7. Total Flavonoid Content

The total flavonoid content (TFC) of pomegranate peel extracts was evaluated following the method described by Ivanov et al. [14]. The absorbance was measured at 415 nm and the results were expressed as mg of quercetin equivalents (QE)/g dw.

2.8. Total Proanthocyanidin Content

The total proanthocyanidin content (TPAC) of pomegranate peel extracts was determined according to Ivanov et al. [15]. The absorbance was measured at 550 nm and the results were expressed as mg of leucocyanidin equivalents (LE)/g dw.

2.9. Antioxidant Activity

2.9.1. DPPH Radical-Scavenging Assay

The DPPH assay was performed by the method of Ivanov et al. [14] using DPPH (2,2-diphenyl-1-picrylhydrazyl) reagent (Sigma-Aldrich, St. Louis, MO, USA). The absorbance was measured at 517 nm and the results were expressed as mM Trolox equivalents (TE)/g dw. The half-maximal inhibitory concentration values (IC₅₀) were expressed as mg/mL of extract.

2.9.2. Ferric-Reducing Antioxidant Power (FRAP) Assay

The FRAP assay was performed according to the method of Ivanov et al. [14] using 2,4,6-Tris (2-pyridyl)-s-triazine (TPTZ) (Sigma-Aldrich, St. Louis, MO, USA). The absorbance was measured at 593 nm and the results were expressed as mM Trolox equivalents (TE)/g dw.

2.9.3. 2,2′-Azinobis (3-Ethylbenzothiazoline-6-Sulfonic Acid) (ABTS) Assay

The ABTS radical-scavenging ability was determined using the method of Ivanov et al. [14].

2.10. High-Performance Liquid Chromatography (HPLC) Analysis of Phenolic Compounds

The phenolic acids and tannins of pomegranate peel extracts were determined using an HPLC unit Elite LaChrome (VWR™ Hitachi, Tokyo, Japan) equipped with a diode array detector (DAD) as previously described [16]. The results were expressed as mg/g dw.

The flavonoids were detected using a Waters 1525 Binary Pump HPLC system (Waters, Milford, MA, USA) equipped with a Waters 2484 dual Absorbance Detector (Waters, Milford, MA, USA) and a Supelco Discovery HS C18 column (5 µm, 25 cm × 4.6 mm) operating under the control of Breeze 3.30 software [14]. The results were expressed as mg/g dw.

The quercetin glycosides (rutin and hyperoside) were analyzed using the same HPLC system by gradients of 2% (v/v) acetic acid (Sigma) (solvent A) and acetonitrile (Sigma) (solvent B). Detection was carried out at 370 nm as previously described [14]. The results were expressed as mg/g dw.

2.11. HPLC Analysis of Organic Acids

The organic acid analysis was performed on the Elite LaChrome (Hitachi, Tokyo, Japan) HPLC system equipped with DAD as previously described by Mihaylova et al. [17]. The separation was conducted on a Discovery^® SH C18 column (25 cm × 4.6 mm, 5 μm) (Supelco) at 30 °C, and isocratic elution with a mobile phase consisting of 25 mM KH₂PO₄ (pH 2.4 with H₃PO₄). L-(+)-ascorbic acid was detected at 244 nm, while citric, fumaric and L-malic acids were detected at 210 nm. The flow rate was 0.5 mL/min. The results were expressed as mg/g dw.

2.12. HPLC Analysis of Carbohydrates

The carbohydrate analysis was performed on the Elite LaChrome (Hitachi, Tokyo, Japan) HPLC system equipped with a refractive index detector (RID), Chromaster 5450 (WVR, Hitachi, Tokyo, Japan), as previously described by Hadjikinova et al. [18]. The HPLC separation was carried out on a Shodex^® Sugar SP0810 column with Pb²⁺ (300 mm × 8.0 mm) and a guard column Shodex SP-G (6 mm × 50 mm, 5 μm) at a temperature of 80 °C, a temperature of RID 35 °C and mobile-phase distilled water with a flow rate of 0.5 mL/min. The results were expressed as mg/g dw.

2.13. Antimicrobial Activity

The antimicrobial activity of pomegranate peel extracts was assessed by the agar well diffusion method as previously described by Tumbarski et al. [19]. For the purposes of the antimicrobial activity test, the ethanol from the ethanolic extract was evaporated under vacuum, and then the extract was re-diluted in sterile deionized water to the initial concentration (100 mg/mL). The antibiotics kanamycin (against bacteria) and nystatin (against yeasts and fungi) at a concentration of 10 mg/mL were used as controls.

2.14. UV Absorption and Calculation of Sun Protection Factor (SPF)

2.14.1. SPF Calculation

The absorbance of the pomegranate peel extracts was measured spectrophotometrically in the wavelength range of 290–320 nm at 5 nm intervals. The SPF was calculated using the following equation [20,21]:

$$SPF=CF \times \sum _{290\mathrm{nm}}^{320\mathrm{nm}}EE\left(\lambda \right) \times I\left(\lambda \right) \times ABS \left(\lambda \right)$$

where CF is the correction factor.

EE(λ) is the erythemal effect spectrum at each wavelength λ.

I(λ) is the solar intensity spectrum at each wavelength λ.

Abs(λ) is the absorbance of the sample at each wavelength λ.

The product EE(λ) × I(λ) is considered a constant set of values across the 290–320 nm range and has been normalized based on originally reported data [20,21].

2.14.2. Critical Wavelength and UVA/UVB Ratio Determination

The critical wavelength λ_c, an indicator of UVA protection, was calculated using the following equation [22]:

$${\lambda }_C=0.9{\int }_{290\mathrm{nm}}^{400\mathrm{nm}}{A}_{\lambda } d\lambda$$

where A_λ is the absorbance at wavelength λ. For each absorption spectrum, the area under the absorbance curve was estimated using trapezoidal integration, with absorbance values recorded at 5 nm intervals.

To evaluate UVA effectiveness, the UVA/UVB ratio was calculated as the ratio of total absorption in the UVA range (320–400 nm) to that in the UVB range (290–320 nm), according to the following equation:

$${\displaystyle \frac{\alpha UVA}{\alpha UVB}}={\displaystyle \frac{{\int }_{320\mathrm{nm}}^{400\mathrm{nm}}{A}_{\lambda }d\lambda }{{\int }_{290\mathrm{nm}}^{320\mathrm{nm}}{A}_{\lambda }d\lambda }}$$

Absorbance values were measured at 5 nm intervals, and the integrals were computed using Simpson’s rule for numerical approximation [23].

Based on the calculated UVA/UVB ratio, the pomegranate peel extracts were categorized using the Boots Star Rating System (

Table 2. UVA/UVB ratio classification according to the Boots Star Rating System.

UVA Ratio	Star Category	Category Descriptor
0.0 to <0.2	-	Too low for UVA claim
0.2 to <0.4	*	Moderate
0.4 to <0.6	**	Good
0.6 to <0.8	***	Superior
≥0.8	****	Maximum

).

2.15. Assessment of the Photoprotective Capacity of the Cosmetic Emulsions

The sample preparation was carried out according to the method described by Gutierrez Mesias et al. [24] with modifications. One gram of each cosmetic emulsion was weighed in a centrifuge tube and mixed with 5 mL of 70% ethanol. Next, the samples were stirred on a rotary shaker (220 rpm, 37 °C, 45 min). Afterwards, 4 mL of 70% ethanol was added to each tube (to complete the volume of 10 mL) and mixed well. The samples were centrifuged at 6000 rpm for 10 min. The supernatants obtained were used for spectrophotometric analyses.

The determination of sun protection factor (SPF), critical wavelength (λ_c) and UVA/UVB ratio of cosmetic emulsions was performed according to the methods and equations described above.

2.16. Assessment of Stability of the Cosmetic Emulsions

The stability of cosmetic emulsions was evaluated using the centrifugation test according to the Bulgarian State Standard [25]. For this purpose, centrifuge tubes were filled to a volume of 10 mL with each of the emulsions to be tested. The tubes were centrifuged at 6000 rpm for 5 min at room temperature, and then the samples were observed for phase separation. Absence of phase separation means 100% emulsion stability.

2.17. Statistical Analysis

Data from triplicate experiments were processed with MS Office Excel 2010 software using statistical functions to determine the standard deviation (±SD) and maximum estimation error at significance levels p < 0.05. Statistical comparisons between the sample groups were performed using Duncan’s multiple range test, with significance set at p < 0.05. Data analyses were conducted using SPSS statistical software v. 30 (IBM Corp., Armonk, NY, USA).

The integrals in the UVB (290–320 nm) and UVA (320–400 nm) spectral regions were calculated by numerical integration using the trapezoidal rule in MATLAB R2023 (MathWorks, Natick, MA, USA). The critical wavelength was determined using the same software via cumulative numerical integration of absorbance values in the range of 290–400 nm.

3. Results and Discussion

3.1. Total Phenolic Content (TPC), Total Flavonoid Content (TFC), Total Proanthocyanidin Content (TPAC) and Antioxidant Activity of the Pomegranate Peel Extracts

As seen from the results in

Table 3. Total phenolic content (TPC), total flavonoid content (TFC) and total proanthocyanidin content (TPAC) of the pomegranate peel extracts.

Pomegranate Peel Extracts	TPC, mg GAE/g dw	TFC, mg QE/g dw	TPAC, mg LE/g dw
Aqueous	91.15 ± 0.28 d	30.47 ± 0.60 c	1.40 ± 0.18 c
Ethanolic (70%)	172.86 ± 1.63 b	45.06 ± 1.03 b	2.29 ± 0.18 b
Methanolic	152.04 ± 1.15 c	43.90 ± 1.07 b	2.11 ± 0.20 b
DMSO	220.60 ± 1.82 a	56.15 ± 1.24 a	3.10 ± 0.10 a

Means in a column with a common superscript letter (a–d) differ (p < 0.05) as determined by Duncan’s test. Values with the same letter are not significantly different according to Duncan’s test (p < 0.05).

, the DMSO pomegranate peel extract showed the highest TPC, TFC and TPAC, followed by the 70% ethanolic and methanolic extracts, whereas the aqueous extract exhibited the lowest TPC, TFC and TPAC values. As can be seen from the results presented, the type of solvent used for extraction is an important factor affecting the amount of biologically active compounds in the pomegranate peel extracts.

The results presented in

Table 4. Antioxidant activity of the pomegranate peel extracts.

Pomegranate Peel Extracts	DPPH		ABTS		FRAP, mM TE/g dw
	mM TE/g dw	IC50, mg/mL	mM TE/g dw	IC50, mg/mL
Aqueous	2152.42 ± 39.42 d	0.22 ± 0.02 a	2362.12 ± 42.08 d	0.14 ± 0.01 a	2138.21 ± 32.02 d
Ethanolic (70%)	3175.30 ± 54.38 b	0.15 ± 0.01 b	3129.61 ± 51.61 b	0.10 ± 0.01 b	2725.28 ± 24.03 b
Methanolic	3090.70 ± 21.76 c	0.16 ± 0.01 b	2933.41 ± 46.90 c	0.11 ± 0.01 b	2385.77 ± 20.01 c
DMSO	3767.50 ± 52.27 a	0.13 ± 0.01 b	3960.58 ± 60.09 a	0.08 ± 0.01 b	3475.03 ± 21.29 a

Means in a column with a common superscript letter (a–d) differ (p < 0.05) as determined by Duncan’s test. Values with the same letter are not significantly different according to Duncan’s test (p < 0.05).

demonstrate that the highest antioxidant activity values of the pomegranate peel extracts corresponded to the highest TPC, TFC and TPAC values (Table 3) as well as to the highest individual phenolic compounds in these extracts identified by HPLC analysis (Table 5 and Table 6). In this regard, DMSO extract exhibited the highest antioxidant potential determined by three methods distinguished by their mechanism of action (DPPH, ABTS and FRAP) and the lowest IC₅₀ values, followed by the 70% ethanolic and methanolic extracts, while the aqueous extract showed the lowest antioxidant activity (which coincided to the lowest TPC, TFC and TPAC values) and the highest IC₅₀ values. Consequently, the antioxidant activity assessed by the DPPH, ABTS and FRAP methods was also influenced by the nature of the solvent used for extraction.

The most crucial considerations in the selection of a solvent for the extraction of biologically active compounds are its polarity, toxicity, and environmental safety. As a polar solvent, ethanol provides a high yield of bioactive substances during the extraction process. On the other hand, due to its low toxicity, it represents a safe solvent suitable for food and cosmetic applications. The solvent concentration also influences the extraction yield. Experimental data showed that the use of 70% ethanol resulted in the highest amounts of bioactive compounds in plant extracts compared to the other ethanol concentrations [26].

The solvent type and extraction conditions are among the main factors affecting the yield of bioactive components and biological activities of the plant materials. Hadjadj et al. [27] obtained a similar TPC value to ours for 70% ethanolic pomegranate peel extract (170.5 mg GAE/g dw); however, the authors reported a higher TFC value (85.74 mg rutin equivalents (RE)/g dw) in comparison with our result for the same type of extract. The amount of condensed tannins in the extract was 8.98 mg catechin equivalents (CE)/g dw. Mohamed et al. [28] investigated three pomegranate peel extracts obtained using different solvents, and stated that the 80% ethanolic extract exhibited the highest TPC and TFC values (216.129 mg GAE/g dw and 12.764 mg CE/g dw, respectively), followed by the ethanolic extract (153.87 mg GAE/g dw and 8.869 mg CE/g, respectively), while the lowest values were observed for the water extract (75.164 mg GAE/g dw and 4.31 mg CE/g dw). The estimated TPC was similar, but the TFC values were lower compared to our results. Thitipramote et al. [29] investigated pomegranate peel samples extracted by three different solvents—water, 95% ethanol and 70% acetone. The results obtained showed that the acetone extraction of pomegranate peel resulted in the greatest amounts of TPC, TFC and TPAC (1.14 mg GAE/g extract, 0.249 mg QE/g extract and 0.097 mg CE/g extract, respectively) as well as the highest DPPH (2.957 mg TEAC/g extract) and FRAP values (7.078 mg TEAC/g extract) compared to the other extracts. A research conducted by Suleria et al. [30] on ethanolic peel extracts of twenty various Australian fruits demonstrated that the results for pomegranate peel extract were as follows: TPC—3.89 mg GAE/g; TFC—0.97 mg QE/g; total tannins (TTC)—0.99 mg CE/g; DPPH—4.60 mg ascorbic acid equivalents (AAE)/g; ABTS—3.34 mg AAE/g; and FRAP—1.25 mg AAE/g.

The total phenols, total flavonoids, proanthocyanidins and antioxidant activity of the peels can vary greatly depending on the pomegranate cultivar. Significant differences in TPC, TFC and total proanthocyanidins (TPAC) in the peels of six pomegranate cultivars from different regions of China were observed by Yan et al. [31]. The analyses revealed that TPC values varied between 57.66 and 155.88 mg GAE/g, TFC values varied from 45.45 to 84.02 mg RE/g, and TPAC values ranged from 5.98 to 11.27 mg CE/g, which were close to our results. Sweidan et al. [32] investigated six types of Jordanian pomegranate peel extracts, and stated that the ethanolic extract displayed the highest TPC (297.70 mg GAE/g dw), the highest TFC (116.08 mg RE/g dw), and the highest values of hydrolysable tannins (688.50 mg tannic acid equivalents—TAE/g dw) and condensed tannins (13.87 CE/g dw) compared to the other tested extracts. High antioxidant activity in methanolic peel extracts of four pomegranate cultivars from Sri Lanka was observed by Panapitiya et al. [33]. IC₅₀ values ranged between 0.0046 mg/mL and 0.0206 mg/mL, as determined by the DPPH assay (which were values close to our results), while FRAP values ranged from 4.270 Fe²⁺ mM/g to 6.690 Fe²⁺ mM/g. TFC values ranged from 52.64 RE mg/g to 75.99 RE mg/g, whereas the TPAC values varied between 21 mg CE/g and 69 mg CE/g.

3.2. HPLC Analysis of Phenolic Compounds of the Pomegranate Peel Extracts

In order to determine the polyphenolic profile of the investigated pomegranate peel extracts, an HPLC analysis was performed. Fourteen phenolic compounds (four phenolic acids, two tannins, six flavonoids and two quercetin glycosides) were identified (Table 5 and Table 6).

As seen in Table 5, ellagic acid was detected in high concentrations in all extracts tested (ethanolic—5.23 mg/g dw; methanolic—4.89 mg/g dw; and aqueous—2.64 mg/g dw). Gallic acid was the most abundant phenolic acid in the water extract (4.21 mg/g dw), followed by the ethanolic one (3.11 mg/g dw). Ferulic acid was present in lower concentrations, while p-coumaric acid had the lowest values in all tested extracts. Tannins pedunculagin and punicalagin dominated in the methanolic extract (5.87 mg/g dw and 5.10 mg/g dw), followed by the ethanolic one (2.39 mg/g dw and 4.66 mg/g dw). DMSO extract was not analyzed due to the incompatibility of the high DMSO concentration we used for extraction with the chromatographic column.

Table 5. Results from the HPLC analysis of phenolic compounds (phenolic acids and tannins) of the pomegranate peel extracts.

Pomegranate Peel Extracts	Phenolic Acids, mg/g dw				Tannins, mg/g dw
	Gallic	p-Coumaric	Ferulic	Ellagic	Pedunculagin	Punicalagin
Aqueous	4.21 ± 0.08 a	0.04 ± 0.00 c	0.93 ± 0.02 b	2.64 ± 0.05 c	1.51 ± 0.02 c	0.30 ± 0.00 c
Ethanolic (70%)	3.11 ± 0.06 b	0.19 ± 0.00 a	1.17 ± 0.02 a	5.23 ± 0.07 a	2.39 ± 0.05 b	4.66 ± 0.09 b
Methanolic	0.79 ± 0.01 c	0.15 ± 0.00 b	0.96 ± 0.02 b	4.89 ± 0.06 b	5.87 ± 0.05 a	5.10 ± 0.06 a

Means in a column with a common superscript letter (a–c) differ (p < 0.05) as determined by Duncan’s test. Values with the same letter are not significantly different according to Duncan’s test (p < 0.05).

Table 5. Results from the HPLC analysis of phenolic compounds (phenolic acids and tannins) of the pomegranate peel extracts.

Pomegranate Peel Extracts	Phenolic Acids, mg/g dw				Tannins, mg/g dw
	Gallic	p-Coumaric	Ferulic	Ellagic	Pedunculagin	Punicalagin
Aqueous	4.21 ± 0.08 a	0.04 ± 0.00 c	0.93 ± 0.02 b	2.64 ± 0.05 c	1.51 ± 0.02 c	0.30 ± 0.00 c
Ethanolic (70%)	3.11 ± 0.06 b	0.19 ± 0.00 a	1.17 ± 0.02 a	5.23 ± 0.07 a	2.39 ± 0.05 b	4.66 ± 0.09 b
Methanolic	0.79 ± 0.01 c	0.15 ± 0.00 b	0.96 ± 0.02 b	4.89 ± 0.06 b	5.87 ± 0.05 a	5.10 ± 0.06 a

Means in a column with a common superscript letter (a–c) differ (p < 0.05) as determined by Duncan’s test. Values with the same letter are not significantly different according to Duncan’s test (p < 0.05).

As seen in Table 6, the established quantities of flavonoids quercetin and kaempferol were equal in all the analyzed pomegranate peel extracts (0.04 ± 0.00 and 0.02 ± 0.00 mg/g dw, respectively). Luteolin predominated in the ethanolic extract, but it was not identified in the methanolic one. Quercetin glycosides (rutin and hyperoside) were detected in the highest amounts in the ethanolic extract, followed by the methanolic and aqueous extracts.

Table 6. Results from the HPLC analysis of phenolic compounds (flavonoids and quercetin glycosides) of the pomegranate peel extracts.

Pomegranate Peel Extracts	Flavonoids, mg/g dw						Quercetin Glycosides, mg/g dw
	Myricetin	Hesperidin	Quercetin	Luteolin	Kaempfe-rol	Apigenin	Rutin	Hyperoside
Aqueous	0.16 ± 0.02 a,b	0.17 ± 0.04 a	0.04 ± 0.00 a	0.14 ± 0.00 b	0.02 ± 0.00 a	0.04 ± 0.01 c	1.23 ± 0.08 c	3.76 ± 0.05 c
Ethanolic (70%)	0.17 ± 0.00 a	0.19 ± 0.00 a	0.04 ± 0.00 a	0.27 ± 0.01 a	0.02 ± 0.00 a	0.08 ± 0.00 a	2.41 ± 0.09 a	5.58 ± 0.17 a
Methanolic	0.15 ± 0.00 b	0.18 ± 0.01 a	0.04 ± 0.00 a	nd *	0.02 ± 0.00 a	0.06 ± 0.00 b	2.05 ± 0.09 b	4.92 ± 0.37 b

Means in a column with a common superscript letter (a–c) differ (p < 0.05) as determined by Duncan’s test. Values with the same letter are not significantly different according to Duncan’s test (p < 0.05). * nd—not detected.

Table 6. Results from the HPLC analysis of phenolic compounds (flavonoids and quercetin glycosides) of the pomegranate peel extracts.

Pomegranate Peel Extracts	Flavonoids, mg/g dw						Quercetin Glycosides, mg/g dw
	Myricetin	Hesperidin	Quercetin	Luteolin	Kaempfe-rol	Apigenin	Rutin	Hyperoside
Aqueous	0.16 ± 0.02 a,b	0.17 ± 0.04 a	0.04 ± 0.00 a	0.14 ± 0.00 b	0.02 ± 0.00 a	0.04 ± 0.01 c	1.23 ± 0.08 c	3.76 ± 0.05 c
Ethanolic (70%)	0.17 ± 0.00 a	0.19 ± 0.00 a	0.04 ± 0.00 a	0.27 ± 0.01 a	0.02 ± 0.00 a	0.08 ± 0.00 a	2.41 ± 0.09 a	5.58 ± 0.17 a
Methanolic	0.15 ± 0.00 b	0.18 ± 0.01 a	0.04 ± 0.00 a	nd *	0.02 ± 0.00 a	0.06 ± 0.00 b	2.05 ± 0.09 b	4.92 ± 0.37 b

Means in a column with a common superscript letter (a–c) differ (p < 0.05) as determined by Duncan’s test. Values with the same letter are not significantly different according to Duncan’s test (p < 0.05). * nd—not detected.

The results obtained from the analyses of the polyphenolic profile of pomegranate peels were in accordance with previously reported data by other authors. Gallic acid, ellagic acid and punicalagin were found to be the most abundant phenolic compounds in the pomegranate peel extract analyzed with concentrations of 9.01, 1.73, and 0.28 mg/100 g, respectively [34]. Balaban et al. [35] tested different extraction methods for bioactive compounds of pomegranate peels and reported that the ethanol acid extract had the highest level of ellagic acid. Kumar et al. [36] examined different solvents for extraction of polyphenolic compounds from pomegranate peels and confirmed that methanol and ethanol were more efficient for extracting higher amounts of ellagitannins. Contrary to our study, EI-Hamamsy and EI-Khamisi [37] reported that the hot-water extract of pomegranate peels contained about a three times higher quantity of ellagic acid than the ethanolic extract and about two times higher content than cold-water extract. It should be noted here that the differences in phenolic composition established in our and other studies may be due to the use of different solvents, extraction methods, pomegranate cultivars, climatic and geographical conditions used to grow the pomegranates, etc.

The identified ellagitannins (pedunculagin and punicalagin) in pomegranate peel extracts are known to possess valuable biological activities such as anticancer, antioxidant, antimicrobial, anti-inflammatory, antiviral, angiogenesis-stimulating, hepatoprotective, antihypertensive, gastroprotective and skin-protective properties, which are of great importance to the pharmaceutical and cosmetic sectors [38,39]. In certain conditions, pedunculagin can be hydrolyzed to punicalin and ellagic acid, and punicalin can be further hydrolyzed to ellagic acid [40]. This phenolic compound has also demonstrated many biological activities, such as antioxidant, antimicrobial, antiviral, anti-inflammatory, antimutagenic, anticarcinogenic, antiproliferative, neuroprotective, hepatoprotective, nephroprotective, cardioprotective, skin-protecting and wound-healing properties. In addition, ellagic acid has shown a protective effect against the toxicity of heavy metals and metalloids, pesticides, synthetic and natural toxins [41].

Mphahlele et al. [4] found that fresh and dried pomegranate peels contained 2135 to 4666.03 mg/kg rutin (depending on the temperature treatment method used), while hesperidin was found in significantly lower amounts (1.77–16.45 mg/kg). Contrary to our results, Kumar et al. 2022 [36] reported that methanolic extracts obtained by different drying methods of two pomegranate peel varieties contained the highest quantity of quercetin (between 0.46 and 2.51 mg/g, and 0.10 and 0.53 mg/g, respectively), followed by ethanolic and aqueous ones. Saeed et al. 2020 [42] detected quercetin only in the methanolic pomegranate peel extract, while the ethanolic extract was the richest in kaempferol. Elzaher et al. [43] also determined hesperidin, rutin, quercetin, kaempferol, and apigenin in ethanolic and aqueous extracts of pomegranate peels, but in different quantities than those in our study. The flavonoids presented in pomegranate peels are known to exhibit a broad spectrum of useful biological activities, such as antioxidant, antimicrobial, hepatoprotective, anticancer, anti-inflammatory, and other properties [44].

3.3. HPLC Analysis of Organic Acids and Sugars of Pomegranate Peel Extracts

HPLC analysis of organic acids revealed the presence of malic, ascorbic, citric and fumaric acid, as the citric acid was the most abundant (4.43 mg/g dw). HPLC analysis of carbohydrates demonstrated the presence of two sugars—glucose (60.51 mg/g dw) and fructose (54.70 mg/g dw) (

Table 7. Results from the HPLC analysis of organic acids and sugars of the pomegranate peels (aqueous extract).

Compounds	Amount, mg/g dw
Organic acids
Mallic	2.23 ± 0.03
Ascorbic	1.69 ± 0.02
Citric	4.43 ± 0.03
Fumaric	2.02 ± 0.02
Sugars
Fructose	54.70 ± 0.43
Glucose	60.51 ± 0.59

).

Sugars and organic acids determine the organoleptic properties and nutritional index of fruits. As mentioned above, the HPLC analysis of carbohydrates of pomegranate peel extracts revealed the presence of glucose and fructose. According to some authors, glucose and fructose were the main sugars found in the pomegranate peel, whereas other researchers have found that xylose and arabinose were predominant. It should be noted that those studies were performed for different purposes and therefore followed different procedures of analysis that might explain these differences [45,46]. A study conducted by Dafny-Yalin et al. [47] demonstrated that among 29 pomegranate cultivars grown in Israel, the major sugars were glucose (0.9–4.8 g/100 g) and fructose (0.9–6.6 g/100 g), which was consistent with our results. According to the same study, citric acid was the major one (11–390 mg/100 g). Besides citric acid, malic acid (1.5–32 mg/100 g) and succinic acid (2.5–14 mg/100 g) were also detected in the peel. Similarly to our results, citric acid was the predominant organic acid (507–1.678 mg/100 g) in the peels of six pomegranate cultivars grown in Georgia, followed by malic acid (93–116 mg/100 g) [48]. The organic acid content in pomegranate peels is highly variable and can be explained by the methods of extraction, genetic background, and fruit ripening stage at harvest time.

3.4. Antimicrobial Activity of the Pomegranate Peel Extracts

The purpose of the antimicrobial activity test was to evaluate whether the different pomegranate peel extracts could act as natural alternatives or supplements to synthetic preservatives, thereby reducing the need to apply chemical preservatives without compromising the safety and effectiveness of the cosmetic product.

The results presented in

Table 8. Antimicrobial activity of the pomegranate peel extracts.

Test Microorganisms	Inhibition Zones, mm
	Pomegranate Peel Extracts (100 mg/mL)				Controls (10 mg/mL)
	Aqueous	Ethanolic (70%)	Methanolic	DMSO	Kanamycin	Nystatin
B. subtilis ATCC 6633	15 ± 0.00 c	20 ± 0.00 b	20 ± 0.00 b	20 ± 0.00 b	22 ± 0.00 a	n.a.
B. cereus NCTC 11145	15 ± 0.71 d	18 ± 0.71 c	19 ± 0.71 b	18 ± 0.00 c	20 ± 0.00 a	n.a.
S. aureus ATCC 6538P	14 ± 0.00 d	20 ± 0.71 b	20 ± 0.00 b	19 ± 0.00 c	26 ± 0.00 a	n.a.
L. monocytogenes NBIMCC 8632	10 ± 0.00 c	16 ± 0.71 a	16 ± 0.00 a	15 ± 0.71 b	15 ± 0.00 b	n.a.
E. faecalis RC-21	10 ± 0.00 d	14 ± 0.00 c	14 ± 0.00 c	15 ± 0.71 b	20 ± 0.00 a	n.a.
S. typhimurium NBIMCC 1672	-	13 ± 0.00 a	14 ± 0.00 b	13 ± 0.00 a	22 ± 0.00 c	n.a.
K. pneumoniae RC-20	-	-	-	-	19 ± 0.00 a	n.a.
E. coli ATCC 25922	13 ± 0.00 b	15 ± 0.71 a	15 ± 0.00 a	15 ± 0.00 a	15 ± 0.00 a	n.a.
P. vulgaris ATCC 6380	13 ± 0.00 d	19 ± 0.71 b	19 ± 0.00 b	20 ± 0.00 a	16 ± 0.00 c	n.a.
P. aeruginosa ATCC 9027	14 ± 0.71 c	16 ± 0.71 b	16 ± 0.00 b	16 ± 0.00 b	17 ± 0.00 a	n.a.
C. albicans NBIMCC 74	-	12 ± 0.00 c	12 ± 0.00 c	13 ± 0.00 b	n.a.	17 ± 0.00 a
S. cerevisiae ATCC 9763	-	-	-	-	n.a.	18 ± 0.00 a
A. niger ATCC 1015	-	17 ± 0.00 a	14 ± 0.71 b	17 ± 0.71 a	n.a.	-
A. ochraceus	-	17 ± 0.71 a	14 ± 0.71 b	17 ± 0.00 a	n.a.	11 ± 0.00 c
A. flavus	10 ± 0.00 c	23 ± 0.71 a	21 ± 0.71 a	22 ± 0.00 a	n.a.	13 ± 0.00 b
P. chrysogenum	12 ± 0.71 b	18 ± 0.71 a	18 ± 0.00 a	18 ± 0.00 a	n.a.	11 ± 0.00 b
F. moniliforme ATCC 38932	-	-	-	-	n.a.	10 ± 0.00 a
F. oxysporum	-	-	-	-	n.a.	-
Rhizopus sp.	-	-	-	-	n.a.	-
Mucor sp.	-	20 ± 0.71 a	18 ± 0.71 b	18 ± 0.00 b	n.a.	10 ± 0.00 c

High antimicrobial activity: IZ ≥ 18 mm; moderate antimicrobial activity: IZ = 12–18 mm; low antimicrobial activity: IZ < 12 mm; “-”—no inhibition; “n.a.”—not applied. Means in a row with a common superscript letter (a–d) differ (p < 0.05) as determined by Duncan’s test. Values with the same letter are not significantly different according to Duncan’s test (p < 0.05).

revealed that the 70% ethanolic, methanolic and DMSO pomegranate peel extracts demonstrated higher antimicrobial activity against the test microorganisms used in the screening than the aqueous extract. As can be seen, the 70% ethanolic, methanolic and DMSO extracts exhibited high inhibitory activity against B. subtilis ATCC 6633, B. cereus NCTC 11145, S. aureus ATCC 6538P, P. vulgaris ATCC 6380, A. flavus, P. chrysogenum and Mucor sp. The aqueous extract showed a moderate inhibitory effect on the same test microorganisms, but did not inhibit the fungus Mucor sp. The 70% ethanolic, methanolic and DMSO extracts displayed moderate antimicrobial activity against L. monocytogenes NBIMCC 8632, E. faecalis RC-21, S. typhimurium NBIMCC 1672, E. coli ATCC 25922, P. aeruginosa ATCC 9027, C. albicans NBIMCC 74, A. niger ATCC 1015 and A. ochraceus. In contrast, the aqueous extract exhibited moderate to low inhibitory effects on the same bacteria and fungi (antimicrobial activity against S. typhimurium NBIMCC 1672, C. albicans NBIMCC 74, A. niger ATCC 1015 and A. ochraceus was not observed). None of the extracts inhibited the growth of K. pneumoniae RC-20, yeast S. cerevisiae ATCC 9763 and fungi F. moniliforme ATCC 38932, F. oxysporum and Rhizopus sp. Methanol used as a control did not show antimicrobial effect, while ethanol was vacuum-evaporated before the analysis.

The high antimicrobial potential of pomegranate peels is related to the presence of various phenolic compounds, especially tannins (punicalin, punicalagin and others) that exert their inhibitory effects through multiple mechanisms—interaction with the microbial cell wall, resulting in structural and functional disruptions, and loss of functions; inhibition of bacterial enzymes; reaction with sulfhydryl groups; nonspecific interactions with cell proteins and precipitation; removing metal cofactors due to the strong affinity for metal ions [49,50,51].

Selahvarzi et al. [49] determined that the antimicrobial activity of 70% ethanolic pomegranate peel extract against S. aureus was higher than that against E. coli with inhibition zones (IZs) of 13.04 mm and 10.50 mm, and minimum inhibitory concentration (MIC) values of 125 and 250 µg/mL, respectively. In a study performed by Nozohour et al. [52], 70% ethanolic pomegranate peel extract showed high inhibitory activity against S. aureus and P. aeruginosa. The concentration of 9 mg/disk led to the formation of IZs with diameters from 25.3 to 27.5 mm for two S. aureus strains, and 22.5 to 27.3 mm for two P. aeruginosa strains, which were higher as compared to our results for the ethanolic extract at the same concentration. According to Sweidan et al. [32], who examined six types of Jordanian pomegranate peel extracts, the ethanolic and methanolic extracts showed the highest inhibitory activity against the microbial strains used in the experiment. The ethanolic extract effectively inhibited Salmonella typhi, P. aeruginosa, K. pneumoniae, Micrococcus luteus and C. albicans, but failed to inhibit Streptococcus pyogenes and Candida krusei, whereas the methanolic extract did not inhibit S. typhi and C. krusei. Using the agar diffusion assay, Al-Zoreky [53] determined that 80% methanolic pomegranate peel extract inhibited the food-borne pathogens L. monocytogenes ATCC 7644, S. aureus ATCC 6538 and MRCA, B. subtilis ATCC 6633, E. coli ATCC 10536, P. aeruginosa ATCC 9027, K. pneumoniae ATCC 10031, and Yersinia enterocolitica ATCC 23715 (IZs from 13 to 20 mm). The author stated that the same extract had antifungal activity against Candida utilis Y-1084, S. cerevisae Y- 139, and A. niger (IZs from 12 to 18 mm). Foss et al. [54] confirmed that the 90% hydroalcoholic pomegranate peel extract and isolated tannin punicalagin were highly efficient against various dermatophytes causing nail, skin, and hair infections, such as Trichophyton mentagrophytes, T. rubrum, Microsporum canis and M. gypseum.

3.5. Ultraviolet (UV) Protection of the Pomegranate Peel Extracts

The sun protection factor (SPF) values of the pomegranate peel extracts were calculated using the Mansur equation based on UV absorbance measurements. SPF indicates the level of protection a certain cosmetic product provides against sunburning rays. More specifically, SPF refers to how well cosmetic products reduce the sunburning effect on the skin.

The absorbance spectra, SPF values, critical wavelengths (λ_c) as well as UVA/UVB ratios are presented in

Table 9. SPF value, critical wavelength value (λ_c) and UVA/UVB ratio of pomegranate peel extracts in different solvents.

Pomegranate Peel Extracts	Concentration, mg/mL
	1	0.1
Aqueous
SPF value	22.00 ± 0.1	3.27 ± 0.01
λc, nm	385	380
UVA/UVB ratio	1.36 ± 0.01	0.94 ± 0.01
Ethanolic (70%)
SPF value	24.40 ± 0.02	5.30 ± 0.01
λc, nm	385	380
UVA/UVB ratio	1.56 ± 0.01	0.97 ± 0.01
Methanolic
SPF value	22.30 ± 0.01	3.40 ± 0.01
λc, nm	385	380
UVA/UVB ratio	1.32 ± 0.01	0.95 ± 0.01
DMSO
SPF value	25.80 ± 0.1	5.10 ± 0.01
λc, nm	385	380
UVA/UVB ratio	5.1 ± 0.01	1.14 ± 0.01

. The UV absorption spectra of four types of pomegranate peel extracts at concentrations of 1 mg/mL and 0.1 mg/mL are shown in Figure 2a,b, highlighting the differences in absorbance in both UVA and UVB regions.

The pomegranate peel extracts at a concentration of 1 mg/mL exhibited SPF values ranging from 22.00 (aqueous) to 25.80 (DMSO), whereas at a concentration of 0.1 mg/mL, the extracts demonstrated SPF values varying from 3.27 (aqueous) to 5.30 (70% ethanolic). The critical wavelength (λ_c), defined as the wavelength at which 90% of the total absorbance area from 290 to 400 nm is reached, ranged from 380 nm (0.1 mg/mL) to 385 nm (1 mg/mL) for all types of pomegranate peel extracts.

The Boots Star Rating System (Table 2), ranging from 0 to 5, indicates the percentage of UVA radiation that is absorbed by that particular sun protection, compared to UVB. The higher the star rating, the better the protection against UVA rays. According to the Boots Star Rating System, all pomegranate peel extracts demonstrated a UVA/UVB ratio above 0.8, corresponding to the maximum protection category (“****”).

3.6. Ultraviolet (UV) Protection of Cosmetic Emulsions

The cosmetic emulsions with the addition of ethanolic pomegranate peel extract at concentrations from 0.5 mg/g to 5 mg/g showed SPF values ranging from 13.59 to 50.65, whereas the control (without the addition of extract) demonstrated an SPF value of 4.62 (

Table 10. SPF value, critical wavelength value (λ_c) and UVA/UVB ratio of cosmetic emulsions with the addition of 70% ethanolic pomegranate peel extract.

Parameter	Cosmetic Emulsions (Body Lotion)
	Control	0.5 mg/g	1 mg/g	2 mg/g	5 mg/g
SPF value	4.62 ± 0.1	13.59 ± 0.01	24.63 ± 0.01	41.15 ± 0.02	50.65 ± 0.02
λc, nm	345	375	380	380	380
UVA/UVB ratio	0.22 ± 0.01	1.33 ± 0.01	1.54 ± 0.01	1.59 ± 0.01	1.90 ± 0.01
UVA	3.08	24.49	52.03	81.67	124.48
UVB	13.89	18.46	32.65	52.90	65.43

). It is noteworthy that the SPF values, critical wavelength (λ_c) values, and UVA/UVB ratio increased proportionally with the concentration of pomegranate peel extract added to the cosmetic emulsion. The values of the critical wavelength (λ_c) ranged from 345 nm (the control) to 380 nm (5 mg/g). The UV absorption spectra of five types of cosmetic emulsions without the addition (the control) and with the addition of pomegranate peel extract (0.5–5 mg/g) are presented in Figure 3.

According to the Boots Star Rating System (Table 2), all cosmetic emulsions except the untreated sample (the control) demonstrated a UVA/UVB ratio above 0.8, which corresponded to the maximum protection category (“****”). Therefore, pomegranate peel extracts can be successfully applied in the development of cosmetic sunscreen products to enhance their sun-protective efficacy.

It has been found that some bioactive components and secondary metabolites of plants such as flavonoids (rutin, quercetin, luteolin, apigenin), stilbenes (resveratrol), ferulic acid, silymarin, pigments (curcumin), carotenoids, niacinamide (vitamin B3), ascorbic acid (vitamin C), vitamin E, and others possess UV-absorbing properties. By preventing the formation of UV-generated reactive oxygen species (ROS) and direct DNA molecule damage, they protect the plants from harmful UV radiation. The high antioxidant potential of these compounds also contributes to their UV protection capacity and beneficial effects on the skin [55]. In addition, the pomegranate extracts can be used for the treatment of UV-induced hyperpigmentation, decreased skin elasticity, and skin wrinkling [7].

Exposure to sunlight can hasten skin-related damage irrespective of the season. The aim of sunscreen technologies is to prevent UV-induced skin cancer by application of compounds with photoprotective activity that effectively absorb, disperse, or reflect UV rays. When administered topically, sunscreens protect the skin against harmful sunlight effects such as erythema or sunburn. Recent studies have revealed the sun protection activity of bioactive compounds of pomegranate peels and their potential application in sunscreen products. Faizatun et al. [56] investigated the possibilities for the utilization of red pomegranate peel extract in sunscreen lotions due to its protective activity against skin damage caused by UV radiation. The authors stated that the addition of 0.06%, 0.12%, and 0.24% in lotions showed SPF values of 13.11, 20.78 and 24.78, respectively. Chasanah et al. [57] examined the characteristics, antioxidant activity, and sun protection factor (SPF) sunscreen capacity of hydrogel preparations containing ethanolic extract of black pomegranate peel at concentrations of 0.5%, 1.0%, and 1.5%. The results showed that hydrogel containing extracts of 0.5%, 1.0%, and 1.5% demonstrated high antioxidant activity, but in contrast to our results, hydrogels exhibited low SPF values of 2.67, 4.36, and 6.65, respectively.

3.7. Stability of the Cosmetic Emulsions

The stability of cosmetic emulsions is an important criterion for determining and predicting their shelf life. The centrifugation test is based on the principle of separating two or more phases of different densities, such as oil-in-water (O/W) emulsions, by centrifugal force.

As can be seen in Figure 4, no phase separation was observed and all samples remained homogeneous after the centrifugation test, indicating that the designed cosmetic emulsions were stable (100% emulsion stability).

4. Conclusions

Since ancient times, herbal remedies have been used for treating dermatological problems in humans and animals due to their proven benefits on the skin. The results obtained in this study revealed that pomegranate peels represent a valuable by-product with promising potential for utilization in the fields of dermatology and cosmetology. Based on detailed results, we can conclude that pomegranate peels are a rich source of biologically active compounds (phenolic acids, flavonoids, anthocyanins and tannins) that possess strong antioxidant properties, high antimicrobial activity and remarkable photoprotective potential against UVA and UVB radiation. Therefore, pomegranate peels in the form of extracts can be successfully integrated into value-added skin health products for application on healthy and diseased skin.