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Journal of Food Science and Technology logoLink to Journal of Food Science and Technology
. 2017 May 6;54(8):2230–2240. doi: 10.1007/s13197-017-2658-9

Effect of harvest time on physico-chemical properties and bioactive compounds of pulp and seeds of grape varieties

Mehmet Musa Özcan 1,✉, Fahad Al Juhaimi 2, Mehmet Gülcü 3, Nurhan Uslu 1, Ümit Geçgel 4, Kashif Ghafoor 2, Nesim Dursun 5
PMCID: PMC5502012  PMID: 28740279

Abstract

In this study, physicochemical properties and bioactive compounds of three grape varieties (Cardinal, Müşküle and Razaki) harvested at the three different harvest times (on time, one and two weeks earlier) were investigated. The highest antioxidant activity, total phenolic and flavonoid contents were observed in Razaki pulp and these were 82.854%, 127.422 mg/100 g, 3.873 mg/g, respectively. The contents of bioactive compounds in grape seeds were found higher than those in pulps. Similarly, seed of Razaki had higher antioxidant activity (91.267%) and total phenolic content (477.500 mg/100 g) when compared to results of other varieties. The key phenolic compounds of all grape variety and seeds were gallic acid, 3,4-dihydroxybenzoic acid, (+)-catechin ve 1,2-dihydroxybenzene. The oil content of grape seeds ranged from 8.50% (Razaki harvested one week ago) to 19.024% (Müşküle harvested one week ago). The main fatty acids of grapeseed oils were linoleic, oleic and palmitic acids. In addition, the oil of Razaki seeds was rich in tocopherols when compared to the other varieties.

Keywords: Grape, Bioactive compounds, Antioxidant, Fatty acid composition, Harvest time

Introduction

Harvest at the most appropriate stage of ripening is crucial for optimum quality of grape with respect to some physicochemical and sensory properties, and maturity of grape begins at the moment of veraison and continues until the harvest (Piazzolla et al. 2015). Some changes such as accumulation of secondary metabolites occur in fruit during the ripening process. The optimum proportion of sugar-acid shows pulp maturity. Skin maturity is provided with the maximum level of some aroma components and phenolic compounds (Pena-Neira et al. 2004). Grapes (Vitis vinifera L.) are significant sources of natural antioxidants such as phenolic compounds. Environmental and geographical factors, and variety affect on the amounts of phenolics of grape fruits (Yang et al. 2009). In recent years, determination of natural antioxidants has been drawn attention because of free radical damage (Nawaz et al. 2006; Shaker, 2006; Yalcin et al. 2016). Grapes, contain a great quantity of phenolic substances in skins, pulp and seeds. Therefore, grapes have the importance for health protective effects (Yılmaz et al. 2014). The aim of present work was to determine and compare the effect of both variety and harvest time on several physicochemical properties (oBrix, titratable acidity, maturation index, total dry matter, mineral content) and bioactive compounds (antioxidant activity, total phenolic and flavonoid contents, phenolic compounds, fatty acid composition and tocopherol content) of grape pulp and seeds.

Materials and methods

Material

The grape fruits used for the experiment were freshly harvested from vineyard garden of Viticulture Research Institute of Tekirdağ in Turkey. The experiment consisted of two factors like maturity stages and different postharvest treatments. The experiment was conducted in the laboratories of the Department of Food Engineering, Faculty of Agriculture, Selçuk University. Pulp and seeds of table grapes were obtained from Viticulture Research Institute of Tekirdağ in Turkey. 3 kg of random grape samples were harvested at three different harvest date. Grapes were brought to the laboratory in cool bag and cut from middle using knife. Pulp + skin (seedless parts) and seeds were separated manually. Cleaned grape seeds were dried in an oven at 40°C until constant weight. Seeds were stored at +4 °C; parts of pulp and skin were frozen at −80 °C until analysis.

Methods

Sample extraction

Phenolic compounds and antioxidants were extracted according to Gomez-Alonso et al. (2007) with some modifications. 2 g of ground samples were added to 15 ml mixture of methanol: water: formic acid (5:4.85:1.5, v/v). The mixture was homogenised using a blender for 2 min and kept in rinsing water-bath for 1 h, followed by centrifugation at 4500 rpm for 15 min. and then the supernatant was collected, and injected. Prior to injection, the extract was filtered through a 0.45 µm nylon filter. All analyses were carried out in triplicate.

Physico-chemical analysis

0Brix, titratable acidity, maturation index and total dry matter were analysed according to Cemeroğlu (1992).Percent dry matter content of the grape pulp was calculated from the data obtained during moisture estimation using the following formula: % dry matter = 100 − % moisture content.

Total phenolic content

Total phenol contents of extracts were determined by using the Folin–Ciocalteu (FC) method as reported by Yoo et al. (2004). 1 ml of FC reagent was added and mixed for 5 min. Afterwards, 10 ml of Na2CO3 was added into mix, the final volume was completed to 25 ml with distilled water. After 1 h, sample was measured in 750 nm in spectrophotometer. The results were given as mg GAE/100 g.

Antioxidant activity

The antioxidant activity values of grape pulp and seed extracts were determined using DPPH (1,1-diphenyl-2-picrylhydrazyl) method according to Lee et al. (1998). The extract was mixed with 2 ml methanolic DPPH solution, and the mixture was shaken, and kept at room temperature for 30 min. The absorbance was measured at 517 nm by using a spectrophotometer. All determinations were performed in triplicate.

Determination of phenolic compounds

Phenolic compounds were determined by Shimadzu-HPLC equipped with PDA detector and Inertsil ODS-3 (5 µm; 4.6 × 250 mm) column. As mobile phases, 0.05% acetic acid in water (A) and acetonitrile (B) mixture were used. The flow rate of the mobile phase and the injection volume were 1 ml/min at 30 °C and 20 µl, respectively. The peak records were carried out at 280 and 330 nm. The total running time for each sample was 60 min. The analysis was carried out according to gradient elution program in order to determine the profile of phenolic substances.

HPLC Conditions are as shown below,

  • Colonm: ODS-3 (5 µm; 4.6 × 250 mm)

  • Flow rate: 1 ml/min.

  • Wave length: 278 nm

  • Control system: SCL-10A VP- SHIMADZU

  • Dedector: SPD-M10Avp diode arrray dedectör -SHIMADZU

  • Degazör: DGU-14A- SHIMADZU

  • Colonm oven: CTO-10 AVP-SHIMADZU

  • Program: Class-VP, 5.0 (Software)

Total flavonoid content

Total flavonoid content of samples was determined using colorimetric method (Hogan et al. 2009). Methanol extracts were properly diluted with distilled water. 5% NaNO2 solution was added to each test tube; after 5 min, 10% AlCl3 solution was added and then after 6 min 1.0 M NaOH was added. Finally total volume was filled up to 5 ml with water and the test tubes were mixed well. Absorbance of the resulting pink-colored solution was measured at 510 nm versus blank.

Mineral content

Grape pulp and seed samples were dried at 70 °C in a drying cabinet with air-circulation until they reached constant weight. Later, about 0.5 g dried and ground sample was digested by using 5 ml of 65% HNO3 and 2 ml of 35% H2O2 in a closed microwave system (Cem-MARS Xpress) at 200 °C. The volumes of the digested samples were completed to 20 ml with ultra-deionized water and mineral concentrations were determined by inductively coupled plasma-optical emission spectroscopy (ICP-AES; (Varian-Vista, Australia). The heavy metal contents of the samples were quantified against standard solutions of known concentrations which were analysed concurrently (Skujins 1998).

Working conditions of ICP-AES

Instrument is ICP-AES (Varian-Vista), and its RF Power is 0.7–1.5 kw (1.2–1.3 kw for axial). Plasma and Auxilary gas flow rates (Ar) are 10.5–15 l/min. (radial) 15 “(axial) and 1.5”, respectively. Viewing height is 5–12 mm. Reading and Copy times are 1–5 s (max. 60 s) and 3 s (max. 100 s), respectively.

Oil content

Oil contents of grape seed samples were determined according to AOAC (1990) method. Total oil content of grape seed was extracted with petroleum benzine in Soxhlet Apparatus for 5 h and the solvent was removed with a rotary vacuum evaporator at 50 °C.

Fatty acid composition

Fatty acid methyl esters of Grape seed oil esterificated according to ISO-5509 (ISO 1978) method were analysed using gas chromatography (Shimadzu GC-2010) equipped with flame-ionization detector (FID) andcapillarycolumn (Tecnocroma TR-CN100, 60 m × 0.25 mm, film thickness: 0.20 µm). The temperature of injection block and detector was 260 °C. Mobile phase was nitrogen with 1.51 ml/min flow rate. Total flow rate was 80 ml/min and split rate was also 1/40. Column temperature was programmed 120 °C for 5 min and increased 240 °C at 4 °C/min and held 25 min at 240 °C. Commercial mixtures of fatty acid methyl esters were used as reference data for the relative retention times (AOAC 1990).

Tocopherol content

Tocopherol content of grape seed oil was performed according to Spika et al. (2015). 0.1 g of oil was dissolved in 10 ml of n-hexane and filtered through a 0.45 µm nylon fitler. HPLC analyses of tocopherols were determined using Shimadzu-HPLC equipped with PDA detector and LiChroCART Silica 60 (4.6 × 250 mm, 5µ; Merck, Darmstadt, Germany) column. Tocopherols were separated by isocratic chromatography using a mobile phase of 0.7% propan-2-ol in n-hexane. The flow rate of the mobile phase was 0.9 ml/min, and the injection volume was 20 µl. The peaks were recorded at 295 and 330 nm with PDA detector. The total running time per sample was 30 min. Standard solutions of tocopherols (α, β, γ and δ-tocopherol) were constructed in the concentrations of 0–100 mg/l (Balz et al. 1992).

Statistical analyses

A complete randomized split plot block design was used. Analysis of variance (ANOVA) test was performed using JMP software, version 9.0 (SAS Inst. Inc., Cary, N.C.U.S.A). The results are mean ± standard deviation (MSTAT C) of three independent grape samples (Püskülcü and İkiz 1989).

Results and discussion

Physico-chemical properties (0Brix of pulp, total dry matter of seed, titratable acidity, maturation index and harvest date) of grape varieties are given in Table 1. The highest 0Brix content was found in Razaki (19.70%). 0Brix of samples, harvested early, was lower than samples harvested on time. The results of titratable acidity ranged from 4.10 to 7.80 g/l. The highest titratable acidity was determined for Razaki (harvested two weeks ago, while the minimum value was found in Müşküle (harvested on time). The titratable acidity, which was higher in samples harvested early, showed a decrease as the harvest time approached. Maturation index of grape varieties in harvest time varied from 18.10 (in Cardinal) to 44.40 (in Müşküle). Maturation indexs of Cardinal, Müşküle and Razaki varieties which harvested early were 24.30, 30.60 and 25.10 (harvested one week earlier); 18.10, 24.80 ve 19.20 (harvested two weeks earlier), respectively. While the highest dry matter is found in Razaki (66.18%), the lowest dry matter was determined in Cardinal (46.84%) variety. A decrease was observed in total dry matter contents of grape seeds with early harvest, similar to 0Brix content of grape varieties. There were statistically significant differences between 0Brix values of grape varieties depending on harvesting time. While the titrable acidity of the samples increased, the ripening index and the total dry matter content decreased and statistically significant differences were detected between variety and harvesting time (p < 0.05).

Table 1.

Some properties of grape varieties

Grape varieties Harvest date Brix (pulp, %) Titratable acidity (g/l) Maturation index Total dry matter (seed, %)
Cardinal* 17.08.15 15.20 ± 0.56****a 5.30 ± 0.45c 29.00 ± 1.28a 51.55 ± 1.17a
Cardinal** 10.08.15 14.20 ± 0.98b***** 5.90 ± 0.87b 24.30 ± 1.33b 49.03 ± 0.98b
Cardinal*** 03.08.15 13.20 ± 1.13c 7.30 ± 0.58a 18.10 ± 1.56c 46.84 ± 0.75c
Müşküle* 29.09.15 18.30 ± 1.21a 4.10 ± 0.64c 44.40 ± 2.45a 64.83 ± 0.58a
Müşküle** 21.09.15 16.50 ± 0.67b 5.40 ± 0.71b 30.60 ± 3.69b 63.38 ± 0.73b
Müşküle*** 14.09.15 15.60 ± 0.93c 6.30 ± 0.83a 24.80 ± 2.17c 61.25 ± 0.84c
Razaki* 01.09.15 19.70 ± 0.69a 5.90 ± 0.88c 33.70 ± 1.18a 66.18 ± 0.58a
Razaki** 24.08.15 17.60 ± 0.71b 7.00 ± 0.61b 25.10 ± 1.23b 59.48 ± 0.47b
Razaki*** 17.08.15 15.00 ± 0.88c 7.80 ± 0.92a 19.20 ± 1.56c 54.21 ± 0.65c
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* Harvest; ** harvested one week ago; *** harvested two weeks ago; **** each value is expressed as mean ± standard deviation; ***** values in each column with different letters are significantly different (p < 0.05)

Antioxidant activity, total phenol and flavonoid contents of grape pulp and seed samples are presented in Table 2. Antioxidant activity of samples varied between 38.658 and 82.854%. According to harvest time, the highest antioxidant activity was observed in Razaki when harvested one week earlier (82.854%), followed by Müşküle (harvested two weeks earlier) (70.554%) and Cardinal (harvested one week ago) (61.342%). According to results of total phenolic contents of grape samples, Razaki variety, harvested one week earlier, had the highest total phenolic content (127.422 mg GAE/100 g), followed by Müşküle, harvested two weeks ago (93.516 mg GAE/100 g). The results revealed that early harvest caused a change in total phenolic contents of samples. The changes were similar to antioxidant activity of grape samples. Total flavonoid contents of grape varieties ranged from 0.854 to 3.873 mg/g. The increase and decrease in flavonoid contents were closed each other and in accordance with total phenolic content and antioxidant contents of grape samples. In addition to pulp of grapes, antioxidant activity, total phenolic and total flavonoid contents of grape seeds were determined and are shown in Table 2. Antioxidant activities of seeds were determined between 84.878 and 91.267%, and these values were found higher than results of grape pulp. Razaki (harvested one week ago) and Cardinal (harvested two weeks ago) varieties had the greatest amount of antioxidant activities, with the proportion of 91.267 and 91.054%, respectively. Total phenolic contents of grape seeds ranged from 456.563 to 477.500 mg GAE/100 g and were higher than 400 mg GAE/100 g in all of seed varieties. Total flavonoid contents of grape seeds were considerably high compared the pulp of grapes and found between 91.984 and 161.706 mg/g. Razaki and Cardinal were significant source of flavonoids with maximum contents. Therefore, grape seeds had rich bioactive substance and were good for health. Antioxidant activity, total phenol and flavonoid (except seed) values of grape pulp were found to be statistically significant differences depending on harvesting time. Statistically significant differences were found between naringenin and kaempferol contents of rape pulp harvested one and second week ago (p < 0.06). In the experiments reported by Obreque-Slier et al. (2010), total phenolic contents of Carmenere and Cabernet Sauvignon grape skins ranged from 110 to 290 mg GAE/100 g; from 80 to 180 mg GAE/100 g, respectively. Total phenolic contents of grape seeds varied from 1000 to 2250 mg GAE/100 g; from 850 to 2040 mg GAE/100 g, respectively. Total phenolic content increased with early harvest. According to study of Anjelkovic et al. (2013), the maximum radical scavenging activity was determined in seed (from 77.73 to 82.22%), followed by skin (from 49.04 to 68.12%) and pulp (from 21.96 to 36.24%). Antioxidant activity of seeds and pulp increased during ripening period and the highest radical scavenging activity was observed at 40th day after veraison. In addition, total phenolic content of grape seed and pulp showed increase during grape maturity and also reduced relatively from 40th day after veraison. According to the oil contents of grape seeds, the highest oil content was determined in Müşküle variety (17.719–19.024%), while seeds of Razaki variety (8.500–11.100%) had the lowest oil content. Oil content was effected from harvest time as other results. The maximum oil contents of Müşküle and Cardinal varieties were observed in samples harvested one week earlier. In Razaki variety, oil content was higher in samples harvested two weeks earlier.

Table 2.

Antioxidant activity, total phenolic and total flavonoid contents of grape pulp and seeds

Grape varieties (pulp) Antioxidant activity (%) Total phenolic content (mg/100 g) Total flavonoid content (mg/g)
Razaki* 60.011 ± 0.015****c 80.313 ± 0.015b 1.723 ± 0.002b
Razaki** 82.854 ± 0.004a***** 127.422 ± 0.014a 3.873 ± 0.003a
Razaki*** 63.525 ± 0.002b 79.766 ± 0.005c 1.798 ± 0.002b
Müşküle* 68.850 ± 0.006b 89.375 ± 0.017b 2.235 ± 0.002a
Müşküle** 48.190 ± 0.002c 59.844 ± 0.027c 1.148 ± 0.001b
Müşküle*** 70.554 ± 0.003a 93.516 ± 0.027a 2.454 ± 0.002a
Cardinal* 38.658 ± 0.009c 50.000 ± 0.018c 0.854 ± 0.001c
Cardinal** 61.342 ± 0.005a 80.156 ± 0.022a 2.248 ± 0.002a
Cardinal*** 53.727 ± 0.006b 72.266 ± 0.017b 1.666 ± 0.003b
Grape seed varieties Antioxidant activity (%) Total phenolic content (mg/100 g) Total flavonoid content (mg/g) Oil content (%)
Razaki* 89.830 ± 0.0000c 474.063 ± 0.037b 155.873 ± 0.020b 10.800 ± 0.200b
Razaki** 91.267 ± 0.001a 477.500 ± 0.026a 152.123 ± 0.004c 8.500 ± 0.100c
Razaki*** 90.522 ± 0.002b 456.563 ± 0.036c 161.706 ± 0.001a 11.100 ± 0.500a
Müşküle* 85.836 ± 0.004b 470.000 ± 0.034b 91.984 ± 0.002c 18.970 ± 0.830b
Müşküle** 88.019 ± 0.001a 475.300 ± 0.022a 96.984 ± 0.002b 19.024 ± 0.024a
Müşküle*** 84.878 ± 0.003c 460.313 ± 0.024c 99.761 ± 0.009a 17.719 ± 0.119c
Cardinal* 90.948 ± 0.000b 464.063 ± 0.029b 155.956 ± 0.014a 14.784 ± 0.584b
Cardinal** 90.149 ± 0.000b 473.750 ± 0.012a 138.095 ± 0.006c 15.347 ± 0.747a
Cardinal*** 91.054 ± 0.001a 461.563 ± 0.021c 147.539 ± 0.003b 14.762 ± 0.362b
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* Harvest; ** harvested one week ago; *** harvested two weeks ago; **** each value is expressed as mean ± standard deviation; ***** values in each column with different letters are significantly different (p < 0.05)

Phenolic compounds of grape pulp and seed are shown in Table 3. Generally, dominant phenolic compounds of all varieties harvested on time were gallic acid, 3,4-dihydroxybenzoic acid, (+)-catechin and 1,2-dihydroxybenzene. Early harvest of Razaki, Müşküle and Cardinal varieties caused some changes in phenolic compounds. The results demonsrated that early harvest (one week) in Razaki variety provided an increase in (+)-catechin content, but caused a decrease in 1,2-dihydroxybenzene content. There was an increase in gallic acid, (+)-catechin and ferullic acid contents when samples were harvested two weeks earlier. In Müşküle variety, early harvest (one week) was significantly decreased the dominant phenolics. In Cardinal variety, an increase in gallic acid, (+)-catechin and 1,2-dihydroxybenzene contents was observed, while a decrease in content of 3,4-dihydroxybenzoic acid is found with early harvest.

Table 3.

Phenolic compounds of grape pulp

Phenolic compounds of pulp (mg/100 g) Razaki* Razaki** Razaki*** Müşküle* Müşküle**
Gallic Acid 38.828 ± 0.295****b 37.715 ± 0.627c 48.951 ± 1.020a 43.352 ± 1.115b 12.554 ± 0.324c
3.4-Dihydroxybenzoic acid 45.806 ± 0.102b***** 54.681 ± 0.066a 35.830 ± 0.747c 47.454 ± 0.840b 5.741 ± 0.479c
(+)-Catechin 56.056 ± 1.430c 76.081 ± 0.588a 61.075 ± 1.466b 63.767 ± 0.150a 3.535 ± 0.330c
1.2-Dihydroxybenzene 58.547 ± 2.116a 32.918 ± 0.592c 53.921 ± 0.143b 47.227 ± 0.704a 3.878 ± 0.215c
Syringic acid 15.726 ± 0.092c 17.307 ± 0.861b 18.399 ± 0.381a 17.426 ± 0.151a 0.914 ± 0.081b
Caffeic acid 12.712 ± 0.049b 10.125 ± 0.082c 13.173 ± 0.049a 16.278 ± 0.115a 1.855 ± 0.218b
Rutin trihidrate 16.926 ± 0.034a 14.521 ± 0.227b 16.636 ± 0.488a 9.638 ± 0.420a 0.967 ± 0.090c
p-Coumaric acid 1.323 ± 0.021c 1.874 ± 0.091b 1.906 ± 0.073a 1.234 ± 0.085a 0.205 ± 0.011b
trans-Ferulic acid 9.724 ± 0.256b 6.324 ± 0.143c 20.304 ± 0.349a 6.854 ± 0.410a 1.160 ± 0.063c
Apigenin 7 glukozid 9.573 ± 0.317c 11.904 ± 0.158b 12.223 ± 0.086a 13.561 ± 0.214a 0.706 ± 0.045c
Resveratrol 3.973 ± 0.152a 3.975 ± 0.084a 3.840 ± 0.122b 2.885 ± 0.191a 1.180 ± 0.018b
Quercetin 12.765 ± 0.045b 11.787 ± 0.412c 13.137 ± 0.033a 10.247 ± 0.683a 6.963 ± 0.064b
trans-Sinnamic acid 2.618 ± 0.165a 2.175 ± 0.060c 2.481 ± 0.150b 2.118 ± 0.167c 2.365 ± 0.042b
Naringenin 3.871 ± 0.000a 2.774 ± 0.237b 2.158 ± 0.000b 0.922 ± 0.000c 10.997 ± 0.222a
Kaempferol 12.149 ± 0.035a 6.703 ± 0.026b 6.682 ± 0.096b 5.882 ± 0.500a 5.867 ± 0.000a
Isorhamnetin 25.293 ± 0.236a 21.629 ± 0.582c 23.579 ± 0.347b 9.336 ± 0.107a 5.906 ± 0.101c
Müşküle*** Cardinal* Cardinal** Cardinal***
Gallic Acid 56.747 ± 1.323a 24.670 ± 1.066c 35.029 ± 3.657b 53.524 ± 0.150a
3.4-Dihydroxybenzoic acid 49.656 ± 0.929a 80.693 ± 0.216a 38.052 ± 2.375b 26.254 ± 0.884c
(+)-Catechin 13.669 ± 0.844b 3.139 ± 0.212c 23.553 ± 2.123a 18.733 ± 1.012b
1.2-Dihydroxybenzene 12.098 ± 0.892b 2.860 ± 0.012c 15.009 ± 1.125a 12.033 ± 0.208b
syringic acid 0.899 ± 0.038c 1.860 ± 0.020b 2.409 ± 0.006a 0.603 ± 0.023c
Caffeic acid 1.045 ± 0.021c 1.212 ± 0.089b 5.822 ± 0.880a 0.772 ± 0.039c
Rutin trihidrate 2.710 ± 0.389b 1.511 ± 0.081b 4.027 ± 0.624a 0.946 ± 0.071c
p-Coumaric acid 0.234 ± 0.022b 1.341 ± 0.210b 1.829 ± 0.284a 0.275 ± 0.012c
trans-Ferulic acid 1.242 ± 0.080b 6.759 ± 1.161a 6.295 ± 0.974b 0.869 ± 0.062c
Apigenin 7 glukozid 0.800 ± 0.066b 0.539 ± 0.028c 9.382 ± 1.346a 0.900 ± 0.058b
Resveratrol 1.114 ± 0.034c 3.706 ± 0.453a 2.874 ± 0.362b 1.343 ± 0.043c
Quercetin 3.565 ± 0.130c 5.805 ± 0.169c 6.766 ± 0.403a 6.432 ± 0.175b
trans-Sinnamic acid 2.738 ± 0.049a 3.496 ± 0.106a 3.505 ± 0.121a 2.730 ± 0.025b
Naringenin 8.673 ± 0.056b 9.008 ± 0.005b 8.981 ± 0.221c 9.227 ± 0.044a
Kaempferol –# – –
Isorhamnetin 8.368 ± 0.159b 9.603 ± 0.252a 6.970 ± 0.090c 7.475 ± 0.016b
Phenolic compounds of seeds (mg/100 g) Razaki* Razaki** Razaki*** Müşküle* Müşküle**
Gallic acid 29.096 ± 1.505b 22.337 ± 0.478c 40.496 ± 0.899a 59.336 ± 2.384a 47.703 ± 2.734b
3.4-Dihydroxybenzoic acid 147.250 ± 0.430b 186.374 ± 0.735a 159.431 ± 2.434c 130.701 ± 0.366a 79.841 ± 0.162b
(+)-Catechin 761.568 ± 4.363b 243.382 ± 2.720c 768.751 ± 21.390a 85.457 ± 3.324a 71.663 ± 0.710b
1.2-Dihydroxybenzene 210.097 ± 0.961b 848.063 ± 1.512a 97.099 ± 6.327c 61.700 ± 0.669b 28.832 ± 0.085c
Syringic acid 38.321 ± 0.914c 56.325 ± 1.232a 45.453 ± 1.503b 27.295 ± 0.480c 31.177 ± 2.031
Caffeic acid 73.704 ± 1.493a 70.977 ± 0.984b 35.660 ± 1.145c 22.202 ± 0.762c 41.465 ± 1.973b
Rutin trihidrate 53.521 ± 0.458c 140.033 ± 0.309b 156.788 ± 0.324a 28.787 ± 0.648b 25.049 ± 0.291c
p-Coumaric acid 11.549 ± 0.026a 9.644 ± 0.393c 10.205 ± 0.361b 5.124 ± 0.038c 5.542 ± 0.169b
trans-Ferulic acid 54.140 ± 0.875c 111.639 ± 2.260a 69.097 ± 1.652b 47.425 ± 0.096a 41.073 ± 0.518b
Apigenin 7 glukozid 76.992 ± 3.330c 105.296 ± 2.579a 78.459 ± 1.668b 64.526 ± 2.015a 32.223 ± 0.814c
Resveratrol 12.245 ± 0.208b 9.866 ± 0.289c 14.422 ± 0.510a 10.918 ± 0.084a 10.661 ± 0.790a
Quercetin 9.951 ± 0.481c 25.410 ± 0.539b 28.349 ± 0.111a 23.693 ± 0.605b 45.030 ± 0.400a
trans-Sinnamic acid 1.347 ± 0.163c 4.345 ± 0.161a 2.902 ± 0.155b 3.372 ± 0.114b 2.230 ± 0.117c
Naringenin 4.884 ± 0.840c 10.931 ± 0.539a 10.085 ± 0.113b 9.204 ± 0.172a 7.991 ± 0.501c
Kaempferol 1.847 ± 0.027c 21.540 ± 0.407a 13.603 ± 0.526b 10.973 ± 0.533b 9.644 ± 0.661c
Isorhamnetin 1.842 ± 0.028c 19.753 ± 0.245a 16.551 ± 1.147b 11.508 ± 0.436b 7.707 ± 0.715c
Müşküle*** Cardinal* Cardinal** Cardinal***
Gallic acid 8.471 ± 0.545c 119.081 ± 1.451b 216.165 ± 0.551a 79.915 ± 4.628c
3.4-Dihydroxybenzoic acid 45.000 ± 0.320c 34.613 ± 3.713b 83.080 ± 0.124a 13.210 ± 0.807c
(+)-Catechin 66.348 ± 2.556c 48.445 ± 1.845c 67.826 ± 0.000b 154.031 ± 0.290a
1.2-Dihydroxybenzene 66.198 ± 0.720a 121.094 ± 3.467b 121.385 ± 0.000b 966.396 ± 7.258a
Syringic acid 85.365 ± 3.124a 15.076 ± 1.378c 188.310 ± 1.717a 55.719 ± 2.376b
Caffeic acid 123.506 ± 1.446a 37.710 ± 2.588c 41.353 ± 1.188b 200.934 ± 2.204a
Rutin trihidrate 33.070 ± 0.349a 38.999 ± 0.845c 51.107 ± 2.342a 44.646 ± 2.644b
p-Coumaric acid 7.379 ± 0.337a 13.640 ± 0.020a 9.985 ± 0.617c 11.534 ± 0.192b
trans-Ferulic acid 40.007 ± 1.548a 46.328 ± 0.780c 52.901 ± 0.106b 426.080 ± 1.803a
Apigenin 7 glukozid 48.219 ± 0.864b 164.161 ± 2.939a 113.338 ± 0.016b 97.803 ± 1.591c
Resveratrol 8.708 ± 0.427b 24.440 ± 0.394c 46.122 ± 1.253a 40.889 ± 0.424b
Quercetin 13.233 ± 0.140c 61.682 ± 1.604a 49.072 ± 0.423c 57.299 ± 1.526b
trans-Sinnamic acid 3.944 ± 0.072a 5.579 ± 0.205a 4.841 ± 0.155b 4.419 ± 0.188b
Naringenin 8.265 ± 0.104b 11.067 ± 0.570c 14.999 ± 0.261a 12.807 ± 0.072b
Kaempferol 14.627 ± 0.124a 17.371 ± 0.472a 13.687 ± 0.617b 13.807 ± 0.018b
Isorhamnetin 12.701 ± 0.127a 14.736 ± 1.031a 9.175 ± 0.279b 5.626 ± 0.199c
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# Not detected; * harvest; ** harvested one week ago; *** harvested two weeks ago; **** each value is expressed as mean ± standard deviation; **** values in each row with different letters are significantly different (p < 0.05)

Phenolic compounds of grape seeds were determined as significantly high in comparison with pulp of grapes. The highest gallic acid (40.496 mg/100 g) and (+)-catechin (768.751 mg/100 g) contents of Razaki seeds were found when harvested two weeks earlier, while gallic acid (59.336 mg/100 g) and (+)-catechin (85.457 mg/100 g) contents were determined the maximum in Müşküle seeds when harvested on time. In all grape varieties, Cardinal (harvested two weeks earlier) had the greatest gallic acid (216.165 mg/100 g) and trans-ferulic acid (426.080 mg/100 g) contents. Additionally, harvesting one week earlier significantly increased the amount of 1,2-dihydroxybenzene (848.063 mg/100 g). There were no statistically significant differences in trans-cinnamic acid and kaempferol contents of Cardinal grape seed harvested one and two weeks earlier. Phenolic compounds were considerably impressed from harvest time. Dominant phenolics of Carmenere and Cabernet Sauvignon grape varieties skins were gallic acid (2.1–3.4; 1.5–3.5 mg/kg), (+)-catechin (1.3–3.1; 0.5–5.1 mg/kg), syringic acid (1.0–3.1; 0.7–1.8 mg/kg) during ripening (Obreque-Slier et al. 2010). Gallic acid contents of grape seeds during ripening varied between 37.7 and 220 mg/kg; 36.9 and 113.2 mg/kg, respectively (Obreque-Slier et al. 2010).

Fatty acid compositions of grape seed oil samples are shown in Table 4, and dominant fatty acids were linoleic, oleic, palmitic and stearic acids. It could be concluded that grape seeds are good source of essential fatty acids especially linoleic acid (64.532–73.571%). Oleic acid content ranged from 13.959 to 19.366%. The content of palmitic and stearic acids of grape seed oil changed between 6.233 and 9.797%; 3.558 and 5.435%, respectively. Besides, linolenic acid content of seed oil was determined below 1%. Fatty acid profile of Müşküle variety was not significantly affected by early harvest. However, early harvest (one week) caused a minor decrease in linoleic acid content and increase in oleic acid content of Razaki variety. Contrary to this, in Cardinal variety, it was found that linoleic acid content was higher and oleic acid content was also lower when samples were harvested early. There was no statistically significant difference between linoleic acid contents of Cardinal grape seed oil harvested one and two weeks earlier. In general, statistically significant differences were found between fatty acid composition of grape seed oil depending on the harvest time and variety.According to Yoo et al. (1984), grape seed oil was mainly composed of palmitic (6.7–9.1%), oleic (13.4–20.7%) and linoleic (68.1–78.1) acids. In previous study, Riccardo and Muratore (1993) found 65.9–62.2% linoleic, 18.6–16.9% oleic, 11.6–10.7% palmitic, 3.8–3.4% stearic and 3.5–2.8% myristic acid in seed oils of red and white Italian grapes, respectively. Won Young et al. (2000) reported that linoleic, oleic, palmitic and stearic acids were main components of grape seed oil, respectively. Uslu and Dardeniz (2009) reported that grape seed cultivars contained 8.40–6.51% palmitic, 16.1–11.62% oleic, 77.59–72.50% linoleic, 3.86–3.07% stearic acids. Özcan et al. (2010) determined 4.1% palmitic, 10.4% stearic, 16.4% oleic and 69.3% linoleic acids in grape seed oil. Results related to grape seed oils were quite similar to those in literature. There is some variation, among cultivars, in terms if their fatty acid composition. Also, grape seeds can be used as a source of edible vegetable oil. It is concluded that the seeds as a by-product of grape processing industries in Turkey could be benefited for mainly edible oil and the other functional components.

Table 4.

Fatty acid and tocopherol compositions of grape seeds

Fatty acids (%) Razaki* Razaki** Razaki*** Müşküle* Müşküle** Müşküle*** Cardinal* Cardinal** Cardinal***
Palmitic 8.965 ± 0.180****b 9.797 ± 0.028a 8.668 ± 0.072b 6.234 ± 0.082b 6.233 ± 0.078b 6.284 ± 0.007a 8.084 ± 0.035a 7.458 ± 0.010b 7.608 ± 0.048b
Stearic 4.754 ± 0.055c***** 4.757 ± 0.018b 4.787 ± 0.013a 5.435 ± 0.018a 5.253 ± 0.002a 4.995 ± 0.014b 3.832 ± 0.006a 3.626 ± 0.008b 3.558 ± 0.003c
Oleic 17.414 ± 0.206b 19.366 ± 0.009a 17.208 ± 0.015b 18.112 ± 0.028b 18.129 ± 0.019b 18.336 ± 0.023a 16.118 ± 0.018a 14.112 ± 0.013b 13.959 ± 0.002c
Linoleic 67.511 ± 0.118a 64.532 ± 0.065b 67.969 ± 0.037a 69.094 ± 0.033c 69.242 ± 0.051a 69.148 ± 0.040b 70.618 ± 0.053b 73.483 ± 0.008a 73.571 ± 0.038a
Arachidic 0.171 ± 0.008b 0.183 ± 0.003a 0.171 ± 0.002b 0.188 ± 0.002a 0.184 ± 0.001b 0.181 ± 0.000c 0.147 ± 0.000a 0.134 ± 0.001c 0.137 ± 0.001b
Linolenic 0.281 ± 0.137a 0.122 ± 0.008c 0.145 ± 0.009b 0.121 ± 0.001a 0.120 ± 0.003b 0.120 ± 0.001b 0.129 ± 0.003a 0.121 ± 0.000c 0.123 ± 0.003b
Tocopherols (mg/g) Razaki* Razaki** Razaki*** Müşküle* Müşküle** Müşküle*** Cardinal* Cardinal** Cardinal***
α-Tocopherol –# – 0.213 ± 0.574 0.176 ± 0.068a 0.138 ± 0.028c 0.148 ± 0.029b 0.140 ± 0.002c 0.150 ± 0.047b 0.179 ± 0.997a
β-Tocopherol 0.125 ± 0.042b 0.130 ± 0.102c 0.146 ± 0.667a – 0.119 ± 0.001b 0.145 ± 0.077a 0.191 ± 0.113b 0.116 ± 0.029b 0.157 ± 0.570a
γ-Tocopherol 0.110 ± 0.091b 0.107 ± 0.079c 0.121 ± 0.156a – 0.107 ± 0.035b 0.112 ± 0.165a 0.123 ± 0.066a 0.107 ± 0.058c 0.111 ± 0.030b
δ-Tocopherol 0.253 ± 0.311c 0.358 ± 0.099b 0.425 ± 0.811a – – – 0.288 ± 0.048b 0.409 ± 0.091a –
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# Not detected; * harvest; ** harvested one week ago; *** harvested two weeks ago; **** each value is expressed as mean ± standard deviation; ***** values in each rows with different letters are significantly different (p < 0.05)

The tocopherol compositions of seed oils are illustrated in Table 4. α- Tocopherol contents of seed oils ranged from 0.138 (Müşküle) to 0.213 mg/g (Razaki). The amounts of β- and γ- tocopherol were 0.116–0.191 mg/g; 0.107–0.123 mg/g, respectively. δ- tocopherol was not detected in Müşküle variety. Additionaly, Razaki variety exhibited the highest total tocopherol content, followed by Cardinal variety. Tocopherol contents of grape seed oils were found statistically significant depending on the variety and time (p < 0.05).

Table 5 shows the mineral content of pulp of grape varieties. The major minerals were potassium (K, 1584.038–2824.760 mg/kg), calcium (Ca, 174.465–329.947 mg/kg), phosphorus (P, 143.932–233.307 mg/kg), sulfur (S, 146.826–179.140 mg/kg), magnesium (Mg, 76.106–164.734 mg/kg) ve sodium (Na, 54.195–166.228 mg/kg). Other minerals, e.g. Fe, Al, B, Cu, Cd, Mo, Zn, Mn and Pb were found at lower levels. The highest potassium content was observed in Müşküle variety (2824.760 mg/kg), followed by Cardinal (2194.259 mg/kg) when harvested on time. Cardinal, harvested on time, contained the highest Ca contents (329.947 mg/kg), while Razaki variety, harvested one week earlier, had the maximum Mg (164.734 mg/kg). Cd element shows toxic effect and was found below 1%, while Ni and Cr elements were not detected in all varieties.

Table 5.

Mineral contents of grape samples (mg/kg)

Grape varieties (pulp) Al Mo Ca B Cd Cu Fe K
Razaki* 0.537 ± 0.016b**** – 257.360 ± 6.505c 7.132 ± 0.045c 0.263 ± 0.379a 1.006 ± 0.050a 5.337 ± 0.119a 1584.038 ± 10.530c
Razaki** 1.400 ± 0.020a***** 0.074 ± 0.008 286.343 ± 6.662a 7.182 ± 0.065b 0.037 ± 0.006b 0.742 ± 0.061b 4.171 ± 2.972b 2320.799 ± 8.008b
Razaki*** –****** – 235.200 ± 6.521b 7.334 ± 0.050a 0.022 ± 0.007c 0.751 ± 0.060b 3.336 ± 0.051c 2565.728 ± 7.113a
Müşküle* 0.992 ± 0.011c – 230.707 ± 2.526a 7.272 ± 0.045a 0.039 ± 0.012b 0.684 ± 0.070b 6.728 ± 0.135c 2824.760 ± 6.516a
Müşküle** 2.133 ± 0.029b – 174.465 ± 5.064c 4.909 ± 0.055c 0.034 ± 0.005c 0.652 ± 0.055c 10.765 ± 0.085b 1714.069 ± 7.001c
Müşküle*** 4.793 ± 1.667a – 206.518 ± 5.069b 5.556 ± 0.041b 0.054 ± 0.014a 0.783 ± 0.045a 14.034 ± 0.130a 2303.934 ± 7.564b
Cardinal* * 0.076 ± 0.006b 329.947 ± 8.615a 3.024 ± 0.058b 0.062 ± 0.016a 0.832 ± 0.052b 8.499 ± 0.090a 2194.259 ± 8.013a
Cardinal** 1.148 ± 0.027b 0.339 ± 0.017a 215.820 ± 2.024b 3.318 ± 0.056b 0.014 ± 0.005b 0.878 ± 0.045a 5.126 ± 0.060b 2137.085 ± 9.194b
Cardinal*** 1.323 ± 0.035a 0.012 ± 0.007c 191.166 ± 3.014c 4.123 ± 0.035a 0.052 ± 0.017a 0.370 ± 0.046c 5.855 ± 0.103b 2068.206 ± 7.009c
Grape varieties (pulp) Mg Mn Na P Pb S Zn
Razaki* 107.888 ± 3.169c 0.072 ± 0.017b 55.886 ± 3.172b 173.640 ± 5.039c – 179.140 ± 6.005b 9.960 ± 0.223a
Razaki** 164.734 ± 4.405a 0.217 ± 0.047a 54.195 ± 4.265c 233.307 ± 7.780a 0.282 ± 0.035a 183.720 ± 5.024a 1.938 ± 0.140b
Razaki*** 118.059 ± 2.912b – 67.257 ± 3.525a 184.987 ± 6.000b 0.028 ± 0.011b 151.750 ± 6.628c 1.114 ± 0.065b
Müşküle* 108.653 ± 7.505a 0.130 ± 0.036b 83.584 ± 5.502b 186.601 ± 5.503a – 155.064 ± 6.001c 1.431 ± 0.056c
Müşküle** 76.106 ± 4.552c – 68.349 ± 4.508c 143.932 ± 6.574c 0.358 ± 0.056a 162.095 ± 6.201a 3.130 ± 0.072a
Müşküle*** 93.918 ± 3.003b 0.190 ± 0.030a 105.575 ± 3.176a 173.283 ± 5.513b 0.287 ± 0.045b 161.550 ± 4.501b 2.461 ± 0.095b
Cardinal* 97.076 ± 4.609b 0.137 ± 0.031c 143.670 ± 4.510b 178.885 ± 6.003b – 174.972 ± 5.575a 3.659 ± 0.097a
Cardinal** 101.041 ± 5.557a 0.196 ± 0.031a 166.228 ± 5.520a 186.806 ± 4.531a 0.135 ± 0.031b 146.826 ± 5.009c 2.267 ± 0.055b
Cardinal*** 83.380 ± 5.504c 0.189 ± 0.030b 107.368 ± 5.505c 162.994 ± 6.556c 0.211 ± 0.045a 160.973 ± 6.564b 1.856 ± 0.070c
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* Harvest; ** harvested one week ago; *** harvested two weeks ago; **** each value is expressed as mean ± standard deviation; ***** values in each column with different letters are significantly different (p < 0.05); ****** nondetected

Mineral contents of grape seeds are given Table 6. Macro elements such as K, Ca, P, Mg, S and Na varied between 3950.714 and 7575.742 mg/kg, 3813.456 and 6190.063 mg/kg, 1627.718 and 2113.753 mg/kg, 923.203 and 1396.977 mg/kg, 761.623 and 984.442 mg/kg, 73.255 and 300.260 mg/kg, respectively. Mineral content of grape seed was higher than pulp of grape. Mineral contents of Razaki, Müşküle and Cardinal varieties showed a change according to harvest time. Generally, early harvest decreased the mineral contents of Razaki and Müşküle seeds. In addition, grape seeds did not contain Ni and Cr and Cd mineral and these werepresent (<1%)in grape pulp. It was ascertained that grape seed was a significant source of mineral.Mineral contents of grape seed and pulp differed according to harvest time and these differences were statistically significant (p < 0.05). According to Fazlo et al. (1982) mean values of Na, K and Ca contents of grape seeds were 4660, 124,000 and 271,000 mg/kg, respectively. The range of concentrations of minerals in grape seed and pulp as reported here differed from previous reports. The variations observed between the results of this work could be probabaly due to differences in climatic conditions, soil structure, genetic factor, variety and environmental temperature during maturation of grape seeds.

Table 6.

Mineral contents of grape seeds (mg/kg)

Grape seeds Al Mo Ca B Cd Cu Fe K
Razaki* 6.729 ± 0.112****b 0.222 ± 0.013a 4009.903 ± 9.039b 10.539 ± 0.044a 0.045 ± 0.005a 7.271 ± 0.026a 19.033 ± 0.152b 6008.179 ± 5.812a
Razaki** 3.169 ± 0.059c***** 0.182 ± 0.003b 4151.900 ± 1.853a 10.330 ± 0.043a 0.040 ± 0.010b 6.576 ± 0.068b 20.713 ± 0.030a 5313.065 ± 6.194b
Razaki*** 55.601 ± 0.102a – 3813.456 ± 13.438c 7.684 ± 0.104b 0.020 ± 0.001c 6.406 ± 0.109b 14.604 ± 0.350c 4796.281 ± 35.067c
Müşküle* 0.915 ± 0.014b 0.123 ± 0.015c 5145.905 ± 44.001a 11.351 ± 0.150a 0.021 ± 0.001b 7.715 ± 0.360a 21.473 ± 0.237b 4516.803 ± 10.229a
Müşküle** 0.401 ± 0.010c 0.138 ± 0.017b 4676.667 ± 7.638b 11.627 ± 0.142a 0.046 ± 0.005a 7.259 ± 0.151c 17.667 ± 0.551c 3950.714 ± 19.547b
Müşküle*** 1.449 ± 0.026a 0.142 ± 0.028a 3884.985 ± 5.000c 10.705 ± 0.208 0.018 ± 0.007c 7.599 ± 0.100b 28.911 ± 0.183a 3981.599 ± 6.502b
Cardinal* 1.885 ± 0.079c – 6190.063 ± 35.041a 9.544 ± 0.310a 0.046 ± 0.005b 8.421 ± 0.071b 26.220 ± 0.106c 6217.672 ± 24.110c
Cardinal** 3.228 ± 0.111b 0.523 ± 0.107a 6087.766 ± 2.657b 7.532 ± 0.207b 0.043 ± 0.006c 8.621 ± 0.071b 44.159 ± 0.122b 7123.793 ± 6.520b
Cardinal*** 28.038 ± 0.707a 0.193 ± 0.003b 6147.987 ± 107.636a 9.632 ± 0.767a 0.051 ± 0.002a 9.000 ± 0.315a 49.532 ± 0.759a 7575.742 ± 156.657a
Grape seeds Mg Mn Na P Pb S Zn
Razaki* 1089.706 ± 4.792a 8.093 ± 0.022a 129.828 ± 2.355c 1888.840 ± 10.618a 0.056 ± 0.006 958.034 ± 5.614a 11.252 ± 0.184b
Razaki** 1049.303 ± 1.478a 7.231 ± 0.114b 219.056 ± 3.676a 1749.547 ± 4.338b – 862.990 ± 4.341b 12.094 ± 0.092a
Razaki*** 923.203 ± 11.643b 5.164 ± 0.055c 133.117 ± 2.010b 1627.718 ± 10.753c – 761.623 ± 7.083c 8.672 ± 0.403c
Müşküle* 1357.151 ± 28.506a 9.815 ± 0.110a 130.542 ± 0.505c 2113.753 ± 7.120a 0.031 ± 0.002 984.442 ± 4.073a 7.055 ± 0.250a
Müşküle** 1250.040 ± 9.000b 9.153 ± 0.068b 175.854 ± 7.525a 1943.932 ± 4.606b – 900.973 ± 4.000b 7.636 ± 0.351a
Müşküle*** 1200.371 ± 11.019c 9.101 ± 0.100b 157.161 ± 2.019b 1752.920 ± 9.528c – 868.122 ± 16.737c 6.362 ± 0.251b
Cardinal* 1311.977 ± 12.533c 10.724 ± 0.120c 73.255 ± 2.536c 1836.637 ± 11.055c 0.404 ± 0.045b 944.436 ± 10.075a 11.827 ± 0.651a
Cardinal** 1330.758 ± 5.018b 12.185 ± 0.165b 300.260 ± 3.740a 1897.818 ± 15.06a7 – 916.420 ± 28.108b 10.166 ± 0.209b
Cardinal*** 1396.977 ± 31.837a 13.521 ± 0.410a 171.876 ± 1.736b 1882.020 ± 22.025b 0.428 ± 0.002a 946.590 ± 23.743a 9.616 ± 0.252c
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* Harvest; ** harvested one week ago; *** harvested two weeks ago; **** each value is expressed as mean ± standard deviation; ***** values in each column with different letters are significantly different (p < 0.05)

Conclusion

Both grape pulp and seeds are source of important compounds for health, such as antioxidants, phenolics and flavonoids. Grape seeds had higher bioactive compounds in comparison with pulp. The results of analysis showed a change in all varieties according to harvest date. The highest antioxidant activity, total phenolic and flavonoid contents were observed in Razaki variety when harvested one week ago. Early harvest caused a minor changes in fatty acid compositions of seed oils, while there were significant differences in mineral contents of pulp. Moreover, the tocopherol contents of seed oils increased with early harvest.

Acknowledgements

The authors extend their appreciation to the International Scientific Partnership Program ISPP at King Saud University for funding this research work through ISPP# 0015.

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