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Journal of Food Science and Technology logoLink to Journal of Food Science and Technology
. 2020 Aug 19;58(6):2283–2294. doi: 10.1007/s13197-020-04739-1

Effect of different roasting methods on the bioactive properties, phenolic compounds and fatty acid compositions of pomegranate (Punica granatum L. cv. Hicaz) seed and oils

Mehmet Musa Özcan 1,✉, Mohammed Saeed Alkaltham 2,✉, Nurhan Uslu 1, Ahmad Salamatullah 2
PMCID: PMC8076372  PMID: 33967325

Abstract

In this study, whole and ground pomegranate (cv. Hicaz) seeds using conventional and microwave ovens were investigated under different parameter. The results show that the total phenolic contents of whole and ground seeds roasted in oven at (150 °C) and microwave at (720 W) for 10 and 20 min, and 5 and 7.5 min, respectively, were found to be slightly higher than those of the control group. In addition, the same roasting method of microwave at (720 W), ground seed oils showed greater fatty acids contents than those of whole seed oils. According to achieved results, roasting techniques used caused noticeable fluctuations of phenolic and fatty acids contents and that depending on which counterparts of pomegranate seeds treated. In addition, a caution recommended when using microwave oven in roasting pomegranate seeds to prevent undesirable alteration or losing of bioactive properties of this value-added product.

Keywords: Pomegranate seed, Roasting, Oil, Hicaz, Total phenol, Antioxidant activity, Phenolic compounds, Fatty acids

Introduction

Pomegranate (Punica granatum L.) belongs to the Punicaceae family and is cultivated in areas with arid and semi-arid climates. The regions favorable for growing pomegranates in Turkey are the Aegean, Mediterranean, and Southeastern Anatolia (Özgüven and Yılmaz 2000). The production of pomegranate in the world is led by India and Iran, followed by Turkey in the third position (Özgüven and Yılmaz 2000). The market consumption of pomegranates and its value-added products have spurred an increase in the production of this fruit. Pomegranate seeds are a major by-product remaining after juice extraction, which known to be a rich source of health promoting compounds (Eikani et al. 2012). Growing interest in natural preservation in the food industry has led to various applications of pomegranate seeds with high antioxidant activity, which were otherwise discarded as waste products (Naveena et al. 2008). A considerable amount of phenolic compounds can be extracted from pomegranate seeds (Özgen et al. 2008; Tehranifar et al. 2010). These bioactive compounds in pomegranate seeds reduce the risk of inflammation that causes chronic diseases such as diabetes and cancer (Lansky and Newman 2007; Sun et al. 2019; Baradaran Rahimi et al. 2020). The fatty acids contents of the pomegranate seed oil have been reported by El-Shaarawy and Nahapetian (1983). Among the polyunsaturated fatty acids found in pomegranate seed oil, the highest percentage is that of punicic acid (~70%). Punica fatty acid has attracted attention recently because of its health benefits and protective properties against oxidation, carcinogens, and inflammation (Fadavi et al. 2006). Heating food affects the characteristics of bioactive compounds and leads to chemical transformation and degradation, which can change its physicochemical properties. Oven heating is traditionally used to dry food for manufacturing and consuming proposes. Microwaves are a relatively recent technology to be used for this purpose and may be relied on more in the future owing to advantages such as high energy efficiency, rapid drying time, and high quality of final products (Zhang et al. 2006, 2019; Puligundla et al. 2013). Many studies have investigated the influence of factors (temperature, power, time, etc.) that lead to the development of different quality response in bioactive compounds of such products (Arjmandi et al. 2017; Gaikwad et al. 2017; Al-Juhaimi et al. 2018). In this study, the physicochemical and bioactive properties of whole and ground pomegranate (cv. Hicaz) seed and oils roasted in an oven and a microwave at different temperatures and powers were analyzed.

Material and methods

Material

Pomegranate (Punica granatum L. cv. Hicaz) fruits were picked from pomegranate trees cultivated in the Mediterranean region in Turkey. These fruits (~ 20 kg) were picked at the maturity stage and transferred to a laboratory in a cool bag for analysis on the same day. The fruits were manually peeled and the arils were removed. After pressing the arils, the seeds and pulps remained on the surface of the plate. The seeds were washed and dried at room temperature, and stored at 4 °C until used for the experiments.

Methods

Heating process

The pomegranate seeds (whole and ground) were spread on stainless steel trays and transferred to a hot-air oven and also placed on the turntable in a microwave oven. The heating process was conducted separately for both whole and ground samples. The samples were heated in an oven at 150 °C for 10, 20, and 30 min or in a microwave oven at 720 W for 5, 7.5, and 10 min, respectively. Finally, fresh and roasted samples were analyzed for different parameters.

Moisture content

The moisture content of seed samples was measured at 105 °C in an oven (Nüve FN055, Ankara, Turkey) until a constant weight was obtained.

Oil content

Following the AOAC (1990) method, the oil contents of the samples were measured using petroleum benzine as an extraction solvent in a Soxhlet apparatus. The pomegranate seed oil was extracted and then the solvent was removed with a rotary vacuum evaporator at 50 ºC.

Extraction procedure

Polyphenols and antioxidant compounds were extracted according to the method described by Madrigal-Carballo et al. (2009) with some modifications. Samples (0.5 g) were added to 20 mL of methanol:water (50:50) mixture. The mixture was sonicated in an ultrasonic bath for 15 h and centrifuged at 6,000 rpm for 10 min. The supernatant was collected and filtered through a 0.45 µm nylon filter prior to injection.

Antioxidant activity

1,1-Diphenyl-2-picrylhydrazyl (DPPH) was used to determine the free radical scavenging activity of samples according to the method described by Lee et al. (1998). The methanolic solution of DPPH (2 mL) was added to the extract. The mixture was shaken vigorously and incubated at room temperature for 30 min, after which absorbance was recorded at 517 nm using a spectrophotometer.

Total phenolic content

The total phenolic contents of the extracts were determined using the Folin-Ciocalteu (FC) reagent, as described by Yoo et al. (2004) with some modifications. The FC reagent (1 mL) was added to the extracts and mixed for 5 min, followed by the addition of 10 mL of 7.5% Na2CO3. The solution in the test tubes was mixed again and the final volume was adjusted to 25 mL with deionized water. At the end of 1 h, the total phenolic content was determined at a wavelength of 750 nm in a spectrophotometer (Shimadzu UV-Vıs spectrophotometer, UV mini 1240). A calibration curve was set up using gallic acid (0–200 mg/mL) as a standard. All determinations were performed in triplicate. The results are given as mg gallic acid equivalent (GAE)/100 g of fresh weight.

Determination of phenolic compounds

Phenolic compounds of extracts were performed using a Shimadzu-HPLC equipped with a PDA detector and an Inertsil ODS-3 (5 µm; 4.6 × 250 mm) column. The mobile phase was a mixture of 0.05% acetic acid in water (A) and acetonitrile (B). Injection volume was 20 µL and the flow rate of the mobile phase was 1 mL/min at 30 °C. The peaks were recorded at 280 nm and 330 nm using the PDA detector. The gradient program was as follows: 0–0.10 min, 8% B; 0.10–2 min, 10% B; 2–27 min, 30% B; 27–37 min, 56% B; 37–37.10 min, 8% B; 37.10–45 min, 8% B. The total running time per sample was 60 min.

Fatty acid composition

Pomegranate seed oil was esterified according to the ISO-5509 (1978) method. A gas chromatograph (Shimadzu GC-2010) equipped with flame-ionization detector (FID) and capillary column (Tecnocroma TR-CN100, 60 m × 0.25 mm, film thickness = 0.20 µm) was used to analyze the fatty acid methyl esters. The temperatures of the injection block and detector were set to 260 ºC. The flow rate of nitrogen as a mobile phase was 1.51 mL/min. The total flow rate was 80 mL/min and split rate was 1/40. Column temperature was set at 120 ºC for 5 min, then increased to 240 ºC at 4 ºC/min, and maintained at this temperature for 25 min.

Statistical analyses

A complete randomized split plot block design was used, and JMP version 9.0 (SAS Inst. Inc., Cary, NC, USA) was used to conduct analysis of variance (ANOVA). All analyses were carried out in triplicate and the results are reported as mean ± standard deviation (MSTAT C) of independent pomegranate seed and heating methods (Püskülcü and İkiz 1989).

Results and discussion

Effect of roasting on physicochemical and functional of pomegranate seeds

Some physicochemical and functional characteristics of whole and ground pomegranate (cv. Hicaz) seeds roasted in an oven and microwave at different temperatures and powers are presented in Table 1. The moisture contents of the whole and ground seeds treated by both roasting methods were found to be lower than those of the control group. The moisture content of pomegranate seeds roasted at 150 °C for 30 min in the oven was lower than those of whole and ground seeds roasted in the microwave for 10 min. While the moisture contents of whole seeds roasted at 150 °C ranged between 5.43% (30 min) and 8.95% (10 min), those of whole seeds roasted at 720 W varied between 7.90% (7.5 min) and 9.25% (5 min) depending on the roasting time. The oil contents of the seeds roasted in both ovens were more (except for 150 °C for 20 and 30 min, and 720 W for 7.5 and 10 min) than that of the control. The oil contents of whole seeds roasted at 150 °C varied between 6.70% (30 min) and 13.80% (10 min) while those of whole seeds roasted in the microwave oven (720 W) ranged between 11.49% (5 min) and 12.70% (10 min) depending on the roasting time. While the oil contents of ground pomegranate seeds roasted in the oven (150 °C) were between 1.40% (30 min) and 12.80% (10 min), those of ground seeds roasted in the microwave varied between 5.00% (10 min) and 12.84% (5 min) depending on the roasting time. The antioxidant activity values of whole pomegranate seeds roasted in the oven ranged between 86.78% (20 min) and 88.78% (30 min) while those of whole seeds roasted in the microwave were 86.33% (10 min) and 89.33% (5 min) as compared to the control group (84.38%) depending on the roasting time. The antioxidant activity values of oven-roasted ground seeds ranged between 75.86% (30 min) to 86.88% (10 min), while those of microwave-roasted ground seeds ranged between 64.40% (10 min) and 89.23% (7.5 min). The total phenol contents of whole and ground pomegranate seeds roasted in the oven (150 °C) varied from 548.89 mg GAE/100 g (30 min) and 958.33 mg GAE/100 g (20 min) to 381.67 mg GAE/100 g (20 min) and 647.78 mg GAE/100 g (10 min) as compared to the control group (417.78 mg GAE/100 g). The total phenol contents of whole and ground pomegranate seeds roasted in the microwave (720 W) for 10 min were 419.17 mg GAE/100 g and 533.06 mg GAE/100 g, respectively. Statistically significant differences were observed among total phenol, antioxidant activity, and oil contents of whole and ground pomegranate seed extracts roasted in oven and microwaves (p < 0.05). Decrease in the oil contents of the seeds for all roasting times at the high oven temperature and microwave power may be attributed to the partial burning of the seeds during roasting. The antioxidant capacity values and total phenol contents of whole seeds roasted in both oven and microwave oven for all the treatment times were found to be higher than that of the control group. However, some antioxidant capacity values and total phenol contents of ground seeds roasted in both oven and microwave were lower as compared to that of the control group. In general, the antioxidant capacity values of the seeds roasted in both oven and microwave were partly higher than those of ground seeds. Al-Juhaimi et al. (2017) reported that the total phenol contents and antioxidant activity values of pomegranate seeds varied between 23.6 and 28.8 mg GAE/g and between 17.6% and 22.9%, respectively. Elfalleh et al. (2012) reported that the antioxidant capacity and total phenol values of methanolic extract of pomegranate seeds were 21.00 µg/mL and 11.84 mg GAE/g, respectively. The total phenol content of pomegranate seed extract was determined as 77.93 µg GAE/mg (Manasathien et al. 2012). The pomegranate seed was found to be rich in total phenol content and had a high free radical scavenging potential (He et al. 2011). According to a previous report, the total phenolic content of pomegranate seeds ranged between 1.29 and 2.17 mg GAE/g (Jing et al. 2012) Basiri (2015). used different solvents to determine the total phenol contents of pomegranate seed extract and these were 22.61, 27.93, 3.41, 0.57, 0.37, and 0.29 mg/L in water, methanol, acetone, butanol, ethyl acetate, and Hexane, respectively. The radical scavenging capacity of the seed extracts could be attributed to the substitution of hydroxyl groups in the aromatic rings of phenolic compounds, thus contributing to their hydrogen donating ability (Brand-Williams et al. 1995). Derakhshan et al. (2018) reported that the total flavonoid content and total phenolic content positively correlated with antioxidant activity value of Natanz, Shahreza, and Doorak pomegranate seed extracts.

Table 1.

Some chemical and bioactive properties of pomegranate seeds

Temperature Time Moisture (%) Oil (%) Antioxidant activity (%) Total phenolic content (mg GAE/100 g)
Control 11.85 ±  0.52a 10.79 ± 0.54d 84.38 ± 0.00e 417.78 ± 0.001e
Whole 150 °C 10 min 8.95 ± 0.45*b 13.80 ± 0.64a   87.88 ± 0.00b  632.50 ± 0.11c
150 °C 20 min 8.23 ± 0.23c** 13.50 ±  0.68b 86.78 ± 0.00d 958.33 ± 0.01a
150 °C 30 min 5.43 ± 0.01f 6.70 ±  0.29e 88.78 ± 0.00a 548.89 ± 0.08d
Ground 150 °C 10 min 8.15 ± 0.19d 12.80 ±  0.64c 86.88 ± 0.00c 647.78 ± 0.03b
150 °C 20 min 8.00 ± 0.50e 2.00 ±  0.10f 76.36 ± 0.01f 381.67 ± 0.04f
150 °C 30 min 5.96 ± 0.01 g 1.40 ±  0.07 g 75.86 ± 0.01g 408.06 ± 0.04e
Whole 720 W 5 min 9.25 ± 0.25c 11.49 ± 0.58e 89.33 ± 0.00a 665.56 ± 0.07a
720 W 7.5 min 7.90 ± 0.47f 12.23 ± 0.48d  89.23 ± 0.00b 636.67 ± 0.06b
720 W 10 min 7.98 ± 1.02e 12.70 ± 0.46c 86.33 ± 0.01c 419.17 ± 0.02d
Ground 720 W 5 min 10.39 ± 0.44b 12.84 ± 0.61b 76.06 ± 0.00d 349.72 ± 0.02f
720 W 7.5 min 7.45 ± 0.01g 5.60 ± 0.28f 89.23 ± 0.00b 533.06 ± 0.03c
720 W 10 min 8.33 ± 0.00d 5.00 ± 0.25g 64.40 ± 0.01e 304.44 ± 0.02g
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*Standard deviation; **values in each column followed by different letters are significantly different at p < 0.05

Effect of roasting on phenolic composition of pomegranate seeds

The contents of phenolic compounds of pomegranate seeds roasted in an oven (150 °C) and microwave (720 W) are given in Table 2. Gallic acid, 3,4-dihydroxybenzoic acid, ( )-catechin, 1,2-dihydroxybenzene, and quercetin were the key phenolic constituents of roasted pomegranate seeds. While gallic acid contents of whole seeds roasted in oven range between 203.60 mg/100 g (30 min) to 2,212.54 mg/100 g (20 min), those of oven-roasted ground pomegranate seeds varied between 161.83 mg/100 g (10 min) and 189.66 mg/100 g (30 min) as compared to the control group (125.73 mg/100 g). The 3,4-dihydroxybenzoic acid contents of whole and ground seeds roasted in oven varied from 83.70 mg/100 g (30 min) and 202.77 mg/100 g (20 min) to 38.0 mg/100 g (30 min) and 80.32 mg/100 g (10 min), respectively, as compared to the control group (98.51 mg/100 g). The (+)-catechin contents of whole and ground oven-roasted pomegranate seeds varied from 95.39 mg/100 g (20 min) and 242.17 mg/100 g (30 min) to 140.63 mg/100 g (30 min) and 220.39 mg/100 g (20 min), respectively. Further, while the 1,2-dihydroxybenzene contents of whole seeds roasted in oven range between 36.95 mg/100 g (20 min) to 124.22 mg/100 g (30 min), those of oven-roasted ground seeds ranged between 87.18 mg/100 g (30 min) and 120.78 mg/100 g (20 min) as compared to the control group (171.75 mg/100 g). The quercetin contents of whole and ground seeds roasted in the oven varied from 20.25 mg/100 g (20 min) and 115.15 mg/100 g (10 min) to 16.76 mg/100 g (20 min) and 43.24 mg/100 g (10 min), respectively, depending on the roasting times and in comparison to the control group (51.26 mg/100 g). In the case of oven-roasted seeds, the isorhamnetin contents of whole and ground seeds ranged between 24.76 mg/100 g (30 min) and 68.47 mg/100 g (10 min), and between 17.81 mg/100 g (30 min) and 30.18 mg/100 g (10 min), respectively. The observed decline in the contents of phenolic compounds partly depended on the roasting times. The contents of some constituents such as p-coumaric acids in whole and ground seeds increased for all roasting times. While gallic acid contents of the microwave-roasted whole seeds range between 137.45 mg/100 g (5 min) to 199.23 mg/100 g (7.5 min), those of ground seeds varied between 49.59 mg/100 g (5 min) and 177.21 mg/100 g (10 min). 3,4-Dihydroxybenzoic acid contents of microwave-roasted whole and ground pomegranate seeds ranged from 44.94 mg/100 g (5 min) and 156.98 mg/100 g (7.5 min) to 8.99 mg/100 g (7.5 min) and 85.27 mg/100 g (5 min), respectively. In addition, while the (+)-catechin contents of whole seeds roasted in the microwave varied between 91.47 mg/100 g (7.5 min) and 213.72 mg/100 g (10 min), those of ground seeds were found to be between 161.14 mg/100 g (10 min) and 262.18 mg/100 g (7.5 min). Further, the 1,2-dihydroxybenzene contents of whole and ground seeds roasted in the microwave ranged from 20.26 mg/100 g (5 min) and 33.06 mg/100 g (10 min) to 13.25 mg/100 g (5 min) and 24.61 mg/100 g (7.5 min), respectively. In addition, the quercetin contents of whole seeds roasted in the microwave changed between 10.02 mg/100 g (5 min) and 53.58 mg/100 g (7.5 min) while those of microwave-roasted whole seeds vary between 32.65 mg/100 g (10 min) and 59.17 mg/100 g (5 min). The caffeic acid contents of whole and ground pomegranate seeds varied from 15.20 mg/100 g (5 min) and 41.65 mg/100 g (10 min) to 30.0 mg/100 g (10 min) and 50.59 mg/100 g (5 min), respectively. Statistically significant differences were observed among the phenolic compounds of whole and ground pomegranate seed extracts roasted in a conventional oven and microwave oven (p < 0.05). Russo et al. (2018) reported that the pomegranate pulp (aril and seed) contained 20.8–11.1 mg/kg gallic acid and 15.4–238.4 mg/kg catechin. In general, the contents of phenolic components in whole and ground pomegranate microwave-roasted seeds were slightly lower as compared to those in the oven-roasted seeds. Table 2 shows the fluctuations in the contents of phenolic components of the whole and ground pomegranate seeds depending on the roasting times. These differences may be attributed to the molecular structure of the phenolic compounds and the rate of chemical reactions during roasting. No kaempferol component was found during most of the treatment times of both roasting methods.

Table 2.

Phenolic compounds present in pomegranate seeds

mg/100 g Control 150 °C (whole) 150 °C (ground)
10 min 20 min 30 min 10 min 20 min 30 min
Gallic Acid 125.73 ± 1.76*g 428.57 ± 32.91b 2212.54± 6.96a 203.60 ± 2.19c 161.83 ± 0.79f 168.94 ± 1.70e 189.66 ± 1.23d
3.4-Dihydroxybenzoic acid 98.51 ± 0.15c** 169.36 ± 1.85b 202.77 ± 2.49a 83.70 ± 0.48d 80.32 ± 0.09e 61.51 ± 1.66f 38.00 ± 1.76 g
(+)-Catechin 179.14 ± 2.64c 137.76 ± 0.12f 2.49a ± 1.41 g 242.17 ± 1.46a 177.39 ± 1.62d 220.39 ± 0.17b 140.63 ±  4.25e
1,2-Dihydroxybenzene 171.75 ± 4.77a 84.83 ± 0.51f 95.39 ± 1.05 g 124.22 ± 5.74b 99.01 ± 0.68d 120.78 ± 0.36c 87.18 ± 1.27e
Syringic acid 30.90 ± 0.35b 26.49 ± 0.77c 12.66 ± 0.47 g 53.91 ± 3.27a 24.12 ± 0.74d 22.11 ± 0.84e 17.36 ± 1.31f
Caffeic acid 37.58 ± 0.79c 36.08 ± 0.64d 13.68 ± 0.14f 44.12 ± 2.45a 37.87 ± 0.88c  34.68 ± 0.34e 43.91 ± 2.63b
Rutin trihydrate 28.98 ± 0.58b 28.27 ± 1.56c 12.57 ± 0.71 g 29.84 ± 1.43a 15.41 ± 1.05f 18.71 ± 0.86e 25.22 ± 1.66d
p-Coumaric acid 4.21 ± 0.15b 3.98 ± 0.05d 2.07 ± 0.11 g 4.39 ± 0.26c 4.51 ± 0.16a 2.84 ± 0.04f 3.60 ± 0.23e
trans-Ferulic acid 35.43 ± 1.00a 15.09 ± 0.26e 5.89 ± 0.33 g 22.46 ± 0.41b 14.21 ± 0.41f 20.09 ± 1.14c 16.52 ± 1.32d
Apigenin 7-glucoside 26.37 ± 0.50a 21.85 ± 0.70b 12.14 ± 0.71f 18.96 ± 0.59d 14.44 ± 0.76e 14.69 ± 0.42e 20.45 ± 1.36c
Resveratrol 12.25 ± 0.14a 10.05 ± 0.32b 6.51 ± 0.38c 10.07 ± 0.40b 5.15 ± 0.36f 6.35 ± 0.34d 5.78 ± 0.27e
Quercetin 51.26 ± 0.44b 115.15 ± 0.83a 20.25 ± 0.21e 38.14 ± 2.06d 43.24 ± 3.65c 16.76 ± 0.88 g 19.68 ± 0.94f
trans-Cinnamic acid 10.10 ± 0.49b 10.38 ± 0.32a 7.08 ± 0.39c 4.91 ± 0.23e 4.54 ± 0.20f 5.48 ± 0.34d 4.33 ± 0.22 g
Naringenin 38.18 ± 0.50a 33.03 ± 0.89b 14.50 ± 0.00e 15.29 ± 0.35d 18.63 ± 0.77c 9.98 ± 0.22f 15.31 ± 0.17 g
Kaempferol 55.63 ± 1.63a *** 13.63 ± 0.00b 7.51 ± 1.05e – – –
Isorhamnetin 46.11 ± 1.96b 68.47 ± .03a 44.18 ± 3.26c 24.76 ± 1.05e 30.18 ± 0.67d 17.83 ± 0.76f 17.81 ± 0.56f
mg/100 g 720 W (whole) 720 W (ground)
5 min 7.5 min 10 min 5 min 7.5 min 10 min
Gallic Acid 137.45 ± 1.91*e 199.23 ± 0.69a 192.77 ± 0.98b 49.59 ± 0.56f 166.19 ± 0.12d 177.21 ± 2.60c
3,4-Dihydroxybenzoic acid 44.94 ±  1.85e** 156.98 ± 3.34a 88.79 ± 1.19b 85.27 ± 0.76c 8.99 ± 0.27f 62.85 ± 0.34d
(+)-Catechin 174.31 ±  3.41d 91.47 ± 3.70f 213.72 ± 2.14c 244.97 ± 0.68b 262.18 ± 1.01a 161.14 ± 0.05e
1,2-Dihydroxybenzene 20.26 ±  0.97f 62.42 ± 3.47d 121.73 ± 3.55b 243.71 ± 5.53a 27.75 ± 0.73e 113.97 ± 3.19c
Syringic acid 13.60 ± 0.85e 18.73 ± 1.58c 33.06 ± 1.32b 13.25 ± 0.42e 24.61 ± 0.28a 16.30 ± 1.32d
Caffeic acid 15.20 ±  0.42f 36.88 ± 2.08d 41.65 ± 1.75b 50.59 ± 0.45a 38.78 ± 1.03c 30.00 ± 1.44e
Rutin trihydrate 15.47 ± 1.50e 29.75 ± 0.99b 22.01 ± 1.17c 30.43 ± 0.97a 21.76 ± 0.83d 11.97 ± 0.11f
p-Coumaric acid 1.69 ±  0.18f 2.19 ± 0.08e 5.46 ± 0.30c 6.92 ± 0.17a 6.24 ± 0.14b 2.36 ± 0.14d
trans-Ferulic acid 7.56 ±  0.63f 25.17 ± 1.50b 14.23 ± 0.83e 19.80 ± 0.44d 64.98 ± 0.12a 22.31 ± 1.45c
Apigenin 7-glucoside 4.38 ±  0.43f 21.29 ± 0.61c 23.43 ± 1.39b 19.49 ± 0.32d 23.52 ± 0.59a 12.65 ± 0.75e
Resveratrol 2.36 ±  0.24f 9.87 ± 0.18c 9.17 ± 0.51d 10.48 ± 0.06b 11.88 ± 0.24a 8.19 ± 0.37e
Quercetin 10.02 ±  0.86f 53.58 ± 2.63b 42.61 ± 3.08d 59.17 ± 1.30a 47.37 ± 1.48c 32.65 ± 1.94e
trans-Cinnamic acid 3.28 ±  0.17f 5.23 ± 0.11b 3.52 ± 0.13d 3.86 ± 0.09c 6.96 ± 0.36a 3.42 ± 0.04e
Naringenin 11.02 ±  0.28f 15.68 ± 0.05d 15.41 ±  0.52e 15.94 ± 0.40c 21.00 ± 0.12a 18.52 ± 0.57b
Kaempferol *** - - - - 11.36 ± 0.14
Isorhamnetin 14.54 ±  0.24f 23.17 ± 0.22b 21.76 ± 0.49c 19.58 ± 0.81d 28.02 ± 1.17a 16.36 ± 0.35e
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*Standard deviation; **values in each row followed by different letters are significantly different at p < 0.05; ***Nonidentified

Effect of roasting on fatty acid composition of pomegranate seed oil

The fatty acid compositions of pomegranate seed oils roasted by oven and microwave are shown in Table 3. Palmitic, stearic, oleic, linoleic, and punicic acids were the major fatty acids of the roasted pomegranate seed oils. While palmitic acid contents of whole seed oils roasted in the oven range between 2.47% (30 min) to 3.01% (20 min), those of ground seed oils vary between 15.68% (30 min) to 17.51% (20 min), as compared to the control group (3.33%). Stearic acid contents of whole and ground pomegranate seed oils roasted in the oven for different roasting times ranged from 1.655% (20 min) and 1.76% (30 min) to 1.81% (10 min) and 7.92% (20 min), respectively, as compared to the control group (1.71%). While the oleic acid contents of whole seed oils roasted in the ovenchange between 3.81% (30 min) and 5.32% (20 min), those of ground seed oils varied from 2.02% (20 min) to 12.86% (30 min), as compared to control group (5.26%). Further, linoleic acid contents of whole and ground seed oils roasted in the oven ranged from 4.08% (10 min) and 4.37% (20 min) to 12.71% (30 min) and 24.50% (20 min), respectively, as compared to the control sample (11.07%). In addition, while the punicic acid contents of oven-roasted whole seed oilschange between 49.48% (10 min) and 60.61% (20 min), those of oven-roasted ground seed oils ranged between 2.09% (30 min) and 52.33% (10 min), as compared to the control sample (57.73%). While palmitic acid contents of whole pomegranate seed oils roasted in the microwave are found between 2.48% (5 min) and 3.09% (7.5 min), those of microwave-roasted ground seed oils varied from 3.10% (5 min) to 8.75% (10 min). The stearic acid contents of microwave-roasted whole seed oils ranged between 1.63% (5 min) and 1.84% (7.5 min) while those of microwave-roasted ground seed oils are determine between 2.02% (5 min) and 3.05% (10 min). The oleic acid contents of microwave-roasted whole and ground pomegranate seed oils varied from 4.26% (5 min) and 6.26% (7.5 min) to 4.53% (5 min) and 10.95% (10 min), respectively. Additionally, while the linoleic acid contents of microwave-roasted whole seed oils range between 4.06% (5 min) and 4.86% (7.5 min), those of ground seed oils varied between 4.42% (5 min) to 48.56% (10 min). Punicic acid contents of microwave-roasted whole and ground pomegranate seed oils ranged from 51.63% (7.5 min) and 62.99% (5 min) to 14.53% (10 min) and 61.42% (7.5 min), respectively. Other fatty acids were found at low levels. Statistically significant differences were observed among the fatty acid compositions of whole and ground pomegranate seed extracts roasted in oven and microwave (p < 0.05). A unique punicic acid was found in the pomegranate seeds as a dominant fatty acid and its concentration varied between 71.17% (cv. Mayhoş) and 77.62% (cv. Hicaz) (Al Juhaimi et al. 2017). While the oleic acid contents of pomegranate seed oil change between 7.61% (cv. Hicaz) and 9.11% (cv. Silifke aşı), linoleic acid contents of the seed oils varied between 7.47% (cv. Hicaz) and 8.82% (cv. Silifke aşı) (Al Juhaimi et al. 2017). Rowayshed et al. (2013) determined that the oil of pomegranate seed contained 4.2% palmitic, 3.2% stearic, 6.5% oleic, 9.4% linoleic, and 59.4% punicic acid. Habibnia et al. (2012) determined 2.95–3.57% palmitic, 1.99–2.54% stearic, 5.71–7.48% oleic, 5.22–7.08% linoleic, and 78.25–82.40% punicic acid in pomegranate oils. Eikani et al. (2012) determined that pomegranate seed oil obtained by superheated Hexane, Soxhlet extraction, and cold pressing methods contained 4.85, 3.10, and 4.94% palmitic, 2.94, 1.91, and 3.19% stearic, 9.80, 5.80, and 10.50% oleic, 9.02, 5.70, and 8.95% linoleic, and 70.73, 81.69, and 69.79% punicic acids, respectively. The pomegranate seed oil contained ~ 80% punicic acid, according to El-Shaarawy and Nahapetian (1983). Behenic acid in ground seed oil roasted in microwave for 5 and 7.5 min was not identified. Further, the punicic acid content in the ground sample roasted in the microwave for 10 min was quite low (14.53%), while the linoleic acid content was significantly higher. In general, the fatty acid contents of ground seed oils roasted in the microwave were found to be higher than those of the microwave-roasted whole seed oils. Depending on the drying time and method, partial fluctuations were observed in the fatty acid contents of pomegranate seed oils. Any significant differences were likely a result of the alterations in the cell membrane during oven and microwave roasting.

Table 3.

Fatty acid compositions of pomegranate seed oils (%)

Fatty acids Control 150 °C (whole) 150 °C (ground)
10 min 20 min 30 min 10 min 20 min 30 min
Palmitic 3.33 ± 0.16*d 2.63 ± 0.40f 3.01 ± 0.25e 2.47 ± 0.15 g 3.96 ± 0.12c 17.51 ± 1.67a 15.68 ± 1.92b
Stearic 1.71 ± 0.04d** 1.66 ± 0.06f 1.65 ± 0.05f 1.76 ± 0.00e 1.81 ± 0.00c 7.92 ± 0.18a 6.13 ± 0.20b
Oleic 5.26 ± 0.13d 4.97 ± 0.27e 5.32 ± 0.01c 3.81 ± 0.03f 6.58 ± 0.00b 2.02 ± 0.03 g 12.86 ± 0.01a
Elaidic *** - - - - 21.37 ± 0.17a 12.09 ± 0.02b
Linolelaidic 0.19 ± 0.01f 0.21 ± 0.02d 0.20 ± 0.00e 0.22 ± 0.00c 0.18 ± 0.01 g 0.84 ± 0.05b 12.84 ± 0.02a
Linoleic 11.07 ± 0.30d 4.08 ± 0.23d 4.37 ± 0.16e 4.18 ± 0.07f 18.97 ± 0.03b 24.50 ± 0.14a 12.71 ± 0.05c
Arachidic 0.34 ± 0.00 g 0.38 ± 0.01c 0.37 ± 0.00d 0.41 ± 0.01b 0.36 ± 0.00e 0.35 ± 0.01f 0.66 ± 0.05a
Linolenic 0.27 ± 0.33f 0.58 ± 0.02c 0.52 ± 0.01d 0.60 ± 0.01b 0.49 ± 0.01e 0.02 ± 0.00 g 1.00 ± 0.01a
Behenic 0.08 ± 0.01 g 0.10 ± 0.02f 0.12 ± 0.00d 0.11 ± 0.02e 0.16 ± 0.01c 0.94 ± 0.00b 1.28 ± 0.01a
Arachidonic 0.25 ± 0.02e 0.24 ± 0.01f 0.24 ± 0.01f 0.27 ± 0.01d 0.28 ± 0.01c 1.87 ± 0.03a 1.28 ± 0.09b
Punicic 57.73 ± 0.06b 49.48 ± 0.18e 60.61 ± 0.27a 54.69 ± 0.25c 52.33 ± 0.05d 9.35 ± 0.17f 2.09 ± 0.01 g
720 W (whole) 720 W (ground)
5 min 7.5 min 10 min 5 min 7.5 min 10 min
Palmitic 2.48 ± 0.19*d 3.09 ±  0.41c 2.75 ± 0.01e 3.10 ± 0.14c 4.13 ± 0.06b 8.75 ± 0.07a
Stearic 1.63 ± 0.04f** 1.84 ± 0.06d 1.76 ± 0.01e 2.02 ± 0.00c 2.26 ± 0.04b 3.05 ± 0.00a
Oleic 4.26 ± 0.11e 6.26 ± 0.28b 4.59 ± 0.02c 4.53 ± 0.02d 6.29 ± 0.02b 10.95 ± 0.01a
Elaidic 0.45 ± 0.02f 0.52 ± 0.02c 0.48 ± 0.00d 0.47 ± 0.01e 0.61 ± 0.05b 1.03 ± 0.00a
Linolelaidic 0.20 ± 0.01e 0.21 ± 0.01d 0.23 ± 0.00c 0.23 ± 0.00c 0.28 ± 0.01a 0.27 ± 0.01b
Linoleic 4.06 ± 0.14f 4.86 ± 0.28c 4.57 ± 0.03d 4.42 ± 0.01e 6.47 ± 0.05b 48.56 ± 0.05a
Arachidic 0.38 ± 0.01e 0.43 ± 0.02c 0.42 ± 0.00d 0.37 ± 0.00f 0.49 ± 0.07b 0.55 ± 0.01a
Linolenic 0.54 ± 0.02d 0.57 ± 0.05c 0.61 ± 0.03b 0.54 ± 0.00d 0.66 ± 0.01a 0.30 ± 0.00e
Behenic 0.07 ± 0.03d 0.14 ± 0.05b 0.09 ± 0.00c *** – 0.17 ± 0.00a
Arachidonic 0.20 ± 0.11f 0.33 ± 0.03c 0.26 ± 0.01d 0.22 ± 0.02e 0.43 ± 0.01b 0.52 ± 0.02a
Punicic 62.99 ± 0.02a 51.63 ± 0.45e 59.13 ± 0.01c 54.01 ± 0.22d 61.42 ± 0.17b 14.53 ± 0.04f
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*Standard deviation; **values in each row followed by different letters are significantly different at p < 0.05; ***nonidentified

Conclusion

This study provides valuable information for the cultivar selection and value-added utilization of pomegranate seeds or seed fractions as nutraceuticals. Extracts of pomegranate seed contain phenolic compounds in high amount that responsible for high antioxidant capacities. Whole seeds roasted in both conventional and microwave ovens found to be higher in their antioxidant activity values compared to the control group. A lower content of phenolic components in the whole and ground pomegranate seeds roasted in a microwave were determined compared to those roasted in the oven. When using a microwave oven, a higher fatty acids contents of seed oils observed, while the same roasting treatment have lower effect on fatty acids content of whole seed oils. Thus, to prevent undesirable alteration or losing of bioactive properties of pomegranate seed, a mild condition such as time of roasting, temperature, and power applied seems to be favorable to preserve it.

Fig. 1.

Fig. 1

Fig. 1

Fig. 1

Fig. 1

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Chromatograms of whole and ground pomegranate seed extracts roasted in an oven and a microwave

Acknowledgments

The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group no. RG-1441-426

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Contributor Information

Mehmet Musa Özcan, Email: mozcan@selcuk.edu.tr.

Mohammed Saeed Alkaltham, Email: malkaltham@ksu.edu.sa.

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