Total oil and fatty acid composition of the seed of 16 grape genotypes with different skin colors and ripening times

Abstract

BACKGROUND:

Grapes, which have gained prominence in recent years due to their positive contributions to human health, are considered a functional food due to the oil content in their seeds. Although the oil content and fatty acid composition of commonly grown grape varieties have been the subject of many studies, these characteristics of local varieties haven’t been sufficiently examined.

OBJECTIVE:

This study was carried out to determine the usability of grape varieties grown in Southeastern Anatolia (Turkey) in grape seed oil production and identify potential parent candidates that could be used in the breeding of grape varieties with high-quality seed oil.

METHODS:

The effects of genotypes, berry skin color, ripening time, and the climatic characteristics of the cultivation season on the oil content and fatty acid composition of seeds from 16 different grape (Vitis vinifera L.) varieties were investigated. Grape seed oils were extracted by soxhlet device and major, minor, and essential fatty acid compositions were determined by gas chromatography.

RESULTS:

According to the findings, the oil content of the grape seeds varied only depending on the genotype and ranged from 9.78% to 18.50% w/w. Moreover, 13–15 fatty acids were detected in the grape seed oils, with linoleic acid (56.13% –69.36%) and oleic acid (15.99% –30.97%) being the most common in all varieties. Only palmitic acid and stearic acid showed variation depending on the skin color; the other fatty acids weren’t affected. Cultivation season didn’t affect the fatty acid composition, but the major and minor fatty acid composition varied depending on ripening time.

CONCLUSIONS:

In cases where it isn’t possible to separate the seeds of grape varieties on a variety basis, classifying them according to the ripening time of the berries may be helpful in predicting the amounts of major, minor fatty acids and partially essential fatty acids in the seeds.

Keywords

Berry skin color seasonal variation seed oil major fatty acids

1 Introduction

Grapes, which are one of the most commonly cultivated fruit species around the world, have many varieties [1]. According to FAO data, a total of 73,524,196 tons of grapes were produced on 6,729,198 hectares of land worldwide in 2021 [2]. Although grapes are a fruit specie that could be utilized in multiple ways, approximately 60% of the grapes produced each year in the world are used as wine grapes, which are used in the production of wine, fruit juice, and related products [3]. Wine, which has the highest production share in these products, generates a significant amount of organic waste during its production [4]. Grape pomace is one of the waste materials involved. According to Garcia-Lomillo and Gonzalez-SanJose [5], grape pomace is generated in an amount equal to approximately 20% of the annual production of grapes used for wine production, or about 8.8 million tons. The amount of pomace left by the wine industry alone is not economically storable, and other industries in which pomace is generated (such as food, vinegar, liqueur, and other alcoholic beverages) are operating today. Therefore, research is being conducted to find ways to recover pomace for economic benefit [6 –11].

Pomace, which is the main waste product of wine production, consists of grape skins, seeds, stems, pulp, and other organic compounds [12, 13]. Grape skins and seeds, which account for 50% and 25% of pomace, respectively, are considered to have positive contributions to health due to their rich composition of phenolic acids, anthocyanins, anthocyanidins, stilbenes, flavonoids, and antioxidants [14 –20]. Some of the positive health effects of grape seeds identified by research include repairing DNA damage, reducing oxidative stress, lowering high blood pressure, strengthening the central nervous system, and healing dermal wounds [21 –29]. Additionally, grape seeds have attracted the attention of researchers due to their high protein and oil content [30 –32]. Some researchers have stated that adding grape seeds to animal feed would increase the quantity and quality of animal products obtained [33 –37]. In addition, it has been reported that the oil found in grape seeds is rich in unsaturated fatty acids and contains phenolic compounds, phytosterols, and tocopherols in its structure, making it suitable for use in the food, cosmetics, and medical pharmacology industries [38 –43].

Researchers who have studied grape seeds generally agree that they are an important source of oil and contain high amounts of linoleic acid and oleic acid [44 –48]. However, not all varieties of the genus Vitis, which has a wide variety and population, contain the same amount of oil in their seeds [49 –51]. Moreover, the amounts of the two main fatty acids found in grape oils can also vary depending on the grape variety from which they are obtained. For example, the linoleic acid content of grape seed oil was found to range from 58.9% to 63.0% in varieties of Vitis labrusca [52], from 67.7% to 72.3% in varieties of Vitis muscadinia [53], and from 49.0% to 91.4% in varieties of Vitis vinifera L. [52, 54]. Furthermore, research on Vitis vinifera L. varieties has shown that the oil content and fatty acid composition of grape seeds can be influenced by the ecological characteristics of the region where they are grown [55 –57], altitude [58, 59], climatic conditions during the cultivation season [60], rootstocks used in the vineyard [61], and the maturity level of the grapes [62]. Additionally, the method used to extract the oil from grape seeds can also affect the amount and composition of the oil obtained [49 , 63–65]. However, the changes in the amount of oil and fatty acid composition in grape seeds according to the berry skin color and the ripening time of the grapes have not been sufficiently studied. Genotypic differences and environmental effects that have been previously identified could lead to problems in meeting the increasing demand for grape seed oil in various industries in the near future. Therefore, factors that may affect the fatty acid composition of grape seed oil should be examined in more detail, and the seed oil contents and fatty acid compositions of local grape varieties that are not well known should be determined to reveal their commercial potential. Taking into account all of these reasons, in the present study conducted in Southeast Anatolia (Turkey), which has a very wide grapevine genetic source, changes in the oil content and fatty acid composition of 16 different grape varieties’ seeds were examined with respect to berry skin color, ripening time of grapes, and the season in which they were grown.

2 Materials and methods

2.1 Sampling of grape varieties

A total of 16 local and standard grape (Vitis vinifera L.) varieties grown in the province of Şanlıurfa, in Southeast Anatolia, Turkey, were examined in two consecutive cultivation seasons (2014 and 2015). The grapevines of the varieties whose seeds were examined were grown under similar cultivation conditions in local producers’ vineyards, on their own roots, and without irrigation. The geographical locations of the vineyards are presented in Table 1.

Table 1
Geographical locations of the vineyards where the grape varieties were grown

Variety Longitude Latitude Altitude

Tahannebi 36.9032 38.9201 384 m

Syrah 36.8887 38.9190 370 m

Çilorut 37.1507 38.4703 647 m

Hasani 37.7599 39.2879 759 m

Küllahi 37.2704 38.7751 676 m

Yediveren 36.9012 38.9173 385 m

Chardonnay 36.8887 38.9190 370 m

Kızıl Banki 37.7729 39.2971 768 m

Sergi Karası 37.1507 38.4703 647 m

Elma Üzümü 37.7729 39.2971 665 m

Horoz Karası 37.1638 38.8126 678 m

Hatun Parmağı 37.1549 38.2526 666 m

Azazi 37.1297 38.3792 600 m

Çiloreş 37.1835 38.4369 679 m

Hönüsü 37.5551 38.8092 599 m

Kabarcık 37.7589 39.2930 751 m

Variety	Longitude	Latitude	Altitude
Tahannebi	36.9032	38.9201	384 m
Syrah	36.8887	38.9190	370 m
Çilorut	37.1507	38.4703	647 m
Hasani	37.7599	39.2879	759 m
Küllahi	37.2704	38.7751	676 m
Yediveren	36.9012	38.9173	385 m
Chardonnay	36.8887	38.9190	370 m
Kızıl Banki	37.7729	39.2971	768 m
Sergi Karası	37.1507	38.4703	647 m
Elma Üzümü	37.7729	39.2971	665 m
Horoz Karası	37.1638	38.8126	678 m
Hatun Parmağı	37.1549	38.2526	666 m
Azazi	37.1297	38.3792	600 m
Çiloreş	37.1835	38.4369	679 m
Hönüsü	37.5551	38.8092	599 m
Kabarcık	37.7589	39.2930	751 m

The short ampelographic descriptions of the grape varieties from which seed samples were taken were created according to Gürsöz [66] and IPGRI et al. [67] and are presented in Table 2. Varieties with berry skin colors ranging from green to dark yellow (Tahannebi, Çilorut, Hasani, Küllahi, Chardonnay, Elma Üzümü, Hatun Parmağı, Azazi, Çiloreş, and Kabarcık) were defined as white, while varieties with colors ranging from red to black (Syrah, Yediveren, Kızıl Banki, Sergi Karası, Horoz Karası, and Hönüsü) were defined as colored, and comparisons based on skin color were made between these two groups. Each variety was recorded when they ripened, and the varieties were divided into three groups (early, mid-season, and late) according to their ripening times. Comparisons based on ripening time were made between these three groups.

Table 2

Some descriptive characteristics of the grape varieties

Variety	Berry Skin Color	Utilization	Sex of Flowers	Cluster Form	Berry Form	Seeds	Ripening Time
Tahannebi	Yellowish White	Table	Pistillate	Winged conical	Oblong	1-2	Early
Syrah	Black	Wine	Hermaphrodite	Winged cylindrical	Elliptic	2-3	Midseason
Çilorut	Green-Yellow	Table-Wine	Hermaphrodite	Branched conical	Obtuse-ovate	2-3	Midseason
Hasani	Green-Yellow	Table	Hermaphrodite	Winged conical	Round	2-3	Midseason
Küllahi	Green-Yellow	Table	Hermaphrodite	Shouldered branched	Round	2-3	Midseason
Yediveren	Red-Purple	Table	Hermaphrodite	Conical	Round	2-3	Midseason
Chardonnay	Amber Yellow	Wine	Hermaphrodite	Shouldered cylindrical	Round	1-2	Midseason
Kızıl Banki	Red	Table	Hermaphrodite	Shouldered branched	Oblong	2-3	Midseason
Sergi Karası	Black	Raisin	Hermaphrodite	Shouldered branched	Narrow elliptic	3-4	Midseason
Elma Üzümü	Green-Yellow	Table	Pistillate	Winged conical	Round	2-3	Midseason
Horoz Karası	Black	Table-Raisin	Hermaphrodite	Winged Conical	Narrow elliptic	3-4	Midseason
Hatun Parmağı	Green-Yellow	Table	Hermaphrodite	Shouldered branched	Narrow elliptic	2-3	Midseason
Azazi	Green-Yellow	Table-Wine	Hermaphrodite	Conical	Elliptic	2-3	Late
Çiloreş	Greenish Yellow	Table	Hermaphrodite	Conical	Oblong	1-3	Late
Hönüsü	Red-Violet	Table	Pistillate	Shouldered branched	Narrow elliptic	1-2	Late
Kabarcık	Green-Yellow	Table-Wine	Hermaphrodite	Conical shouldered	Round	2-3	Late

The seeds of each variety were extracted from ripe berries (16.5–18.5°Brix) using a scalpel. The seeds were then washed with pure water for 2 minutes to remove any remaining pulp and juice residues and dried with paper towels. Next, the seeds were dried at +24°C for 72 hours, packaged separately, and stored in a glass desiccator until analysis.

2.2 Climatic conditions and soil properties of the vineyards

Many years of climatic data for the region where the vineyards were located and it was observed that it had an average temperature of 19.0°C and total precipitation of 423.05 kg/m² per year and showed a continental climate. However, due to the irregular distribution of precipitation throughout the year and the relatively low total amount of precipitation, the region has a semi-arid climate. During 2014 and 2015, when the study was conducted, the annual temperature averages were 19.7°C and 19.2°C and the total precipitation was 406.1 kg/m² year and 389.8 kg/m² year, respectively. The monthly average temperature values and total precipitation amounts are presented in Fig. 1.

The soil structure of the vineyards where the grape varieties studied were grown is generally slightly alkaline (pH 7.94), with low organic matter (1.43%), high lime (10.93%), and a clayey structure. However, the contents of N (0.056%), P₂O₅ (0.882 kg/ha), K₂O (16.15 kg/ha), Fe (3.25 ppm), and Zn (0.322 ppm) are low in the soils of the vineyards, but the contents of Ca (8417 ppm), Mg (1794 ppm), S (8.55 ppm), Mn (5.64 ppm), and Cu (1.75 ppm) are sufficient for optimum nutrition.

Fig. 1

Climatic data of the region where the vineyards were located.

2.3 Grape seed oil extraction

The seeds of the grape varieties studied were dried in a drying oven (Nüve FN400P, Turkey) at 65°C for 72 hours. After drying, the seeds were ground in a mill and 10 g of ground seed sample was subjected to n-hexane (Sigma-Aldrich CAS no: 110-54-3) extraction for 6 hours in a Soxhlet device (Gerhardt, Germany). Balloon flasks were used to separate the hexane from the oil/hexane mixture, which was left in a drying oven at 60°C for 24 hours [61]. The oil content of the grape seed varieties was determined as weight percentage (% w/w) [60]. After extraction, the grape seed oils were transferred to amber-colored tubes with screw caps and stored at +4°C until fatty acid analysis was performed.

2.4 Determination of fatty acid composition

The derivatization process was conducted according to Slover and Lanza [68]. Fatty acid analysis was performed using a Shimadzu Nexis GC-2030 (Kyoto, Japan) gas chromatography-mass spectrometer. An FID detector and a TR-CN100 (100 m×0.25 mm×0.20μm) (Barcelona, Spain) column were used. Readings were taken at an injection volume of 1μL and a flow rate of 1 mL min^–1 at a detector temperature of 240°C. Hydrogen was used as the carrier gas. Peaks were identified based on their retention times in the obtained chromatogram and the ratios of fatty acids were determined.

2.5 Statistical analysis

All analyses for determining the oil content of the grape seeds and the fatty acid composition of the seed oils were performed in triplicate. The data were presented as the mean±standard deviation (SD) of the years in which the study was conducted. One-way analysis of variance (ANOVA) was performed using Minitab (ver. 18) to evaluate significant differences in the means among the grape varieties, berry skin colors, ripening times, and cultivation seasons. Significant differences among the means (p < 0.05 and p < 0.01) were presented by grouping them according to the Tukey test.

3 Results and discussion

The grape varieties examined in the present study were significantly different from each other in terms of the total oil content of their seeds (p < 0.01) (Fig. 2). The variety with the highest oil content in its seeds was Yediveren (18.50±0.50% w/w), while the one with the smallest oil content was Horoz Karası (9.78±1.21% w/w). The amount of oil found in the seeds of the grape varieties we examined showed a range between the values reported by Sabir et al. [47] and Lachman et al. [60] for varieties of Vitis vinifera L. (3.91–24.76% w/w). However, the amounts of oil detected in the seeds of the Syrah, Hatun Parmağı, Chardonnay, and Çiloreş varieties were higher than those reported by Beveridge et al. [64], Odabaşıoğlu and Gürsöz [61], Al Juhaimi et al. [69], and Sağdıçoğlu [70] for these varieties, respectively. The amount of oil detected in the seeds of the Horoz Karası variety was low according to Tangolar et al. [71], but high according to Odabaşıoğlu and Gürsöz [61] and Sağdıçoğlu [70]. The minor variations observed between the studies in the literature and the present study regarding the oil content of seeds may have arisen from the differences in the ecological characteristics of the regions where the vineyards were located, the cultural practices applied in the vineyards, the use of rootstocks in the vineyards, and the differences in the methods and conditions applied during oil extraction.

Fig. 2

Total oil content in the seeds of the grape varieties (2014 and 2015 years’ average).

When the grape varieties we examined were classified according to their skin colors, there were similar oil contents in the seeds of the berry skin colors (Fig. 3a). Ovcharova et al. [72] reported that there was no difference between white and colored grape varieties in terms of the oil content of their seeds. Göktürk Baydar and Akkurt [50] also found a similar result, stating that there was no significant difference between wine grapes and table grapes in terms of the amount of oil in their seeds. However, the number of seeds in grapes may affect the oil content of the seeds. Indeed, previous studies have reported that the main factor affecting the oil content of grape seeds is genotypic variation [48 , 73–75]. Our findings also revealed that the amount of oil in grape seeds varies depending on the genotype.

Fig. 3

Seed oil content variation with berry skin color (a), ripening time (b), and cultivation season (c).

Ohnishi et al. [46] suggested that seed maturity, Rubio et al. [62] berry development stage, Özcan et al. [76] harvest time, and Göktürk Baydar and Akkurt [50] grape variety ripening time may affect the oil content of grape seeds. However, in our study, the effect of grape ripening time on the total oil content in the seeds was similar. Nonetheless, theearly ripening grape varieties had 13.50±1.50% w/w, while the seeds of medium and late ripening varieties had 14.17±2.94% w/w and 14.23±2.71% w/w average oil content in their seeds, respectively (Fig. 3b).

The amount of oil in the seeds of the varieties studied was similar depending on the season of cultivation (Fig. 3c). However, the fact that some more oil content was detected in seeds in 2014, when there was more precipitation during the vegetative development period of the grapevines, compared to 2015, indicates that there may be a relationship between the oil content of grape seeds and the amount of water uptake by the grapevines from the soil. Similar findings have also been reported by Lachman et al. [60] and Odabaşıoğlu and Gürsöz [61]. In various plant species (canola, sunflower, artichoke, and peanut), a positive correlation was found between seed oil content and the amount of water applied to the plants [77 –80].

In the present study, the oils of the grape varieties examined contain different numbers of fatty acids (from 13 to 15), and 13 fatty acids are common. Indeed, Yi et al. [81] reported that up to 34 different fatty acids, including trans fatty acids and isomers, could be found in grape seed oils. Mattick and Rice [82], on the other hand, suggested that the fatty acid composition of grape seed oil was relatively constant regardless of species or variety. However, Fernandes et al. [48] and Tangolar et al. [71] found that the number and composition of essential fatty acids in grape varieties’ oils could differ from one another. The major fatty acids commonly found in all varieties of grape seed oils examined in this study were palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1n-9c), and linoleic acid (C18:2n-6c). The minor fatty acids commonly found in grape varieties’ seed oils are caproic acid (C6:0), myristic acid (C14:0), cis-10-heptadecanoic acid (C17:1), and docosahexaenoic acid (C22:6n-3c). Palmitoleic acid (C16:1), heptadecanoic acid (C17:0), linolenic acid (C18:3n-6c), eicosatrienoic acid (C20:3n-3c), and tricosenoic acid (C23:0) are essential fatty acids present in the oils of all 16 grape varieties examined in the present study in both years. In other studies examining seed oils of Vitis spp. varieties, all these fatty acids were detected [61, 83]. However, trace amounts of lauric acid (C12:0), trans-elaidic acid (C18:1n-9t), heneicosanoic acid (C21:0), erucic acid (C22:1n-9c), cis-13,16-docosadienoic acid (C22:2), and nervonic acid (C24:1) were detected in the oils of some grape varieties examined in our study. Of these essential fatty acids, only lauric acid (in the Azazi, Syrah, and Hasani varieties) and nervonic acid (in the Sergi Karası and Kabarcık varieties) were detected in some grape varieties’ oils in both years of analysis. Özcan et al. [84] reported the presence of lauric acid in the seed oil of the Alanya, Kış Üzümü, Köledoyuran, and Siyah Pekmezlik varieties. Özkaya et al. [83] found trace amounts of nervonic acid in the seed oil of the Besni (Peygamber) variety, and Yi et al. [81] reported the presence of nervonic acid isomers in the oils of the Cabernet Sauvignon and Royal Rouge varieties. Furthermore, Fernandes et al. [48] detected trans-elaidic acid in the seed oil of seven different Portuguese grape varieties, and Tangolar et al. [71] identified erucic acid in the seed oils of the Öküzgözü variety, as well as Cosmo 2 and Salt Creek grape rootstocks.

Linoleic acid was the most abundant fatty acid in the grape varieties’ oils. It was followed by oleic acid, palmitic acid, and stearic acid, respectively. Göktürk Baydar et al. [85], Akın and Altındişli [86], and Bada et al. [87] reported the same ranking of fatty acids based on their amounts in grape seed oil. The grape varieties examined in terms of the quantities of these four fatty acids showed significant differences from each other (Table 3). The highest linoleic acid content (69.36±0.13%) was in Elma Üzümü, the highest oleic acid content (30.97±0.20%) was in Küllahi, the highest palmitic acid content (13.07±0.62%) was in Horoz Karası, and the highest stearic acid content (3.46±0.74%) was in Hasani oil. The quantities of major fatty acid components found in the seed oils of the 16 grape varieties we examined varied within the range of upper and lower values reported by other researchers [47, 88]. Moreover, our findings are consistent with those of studies in the literature that indicate that the genotype is the main factor influencing the fatty acid composition of grape seed oil [47 , 89].

When the grape varieties were classified according to their berry skin color, stearic acid was more abundant in the seed oils of the white varieties, while palmitic acid was more abundant in the seed oils of the colored varieties (Table 3). Uslu and Dardeniz [90] reported that both fatty acids were more abundant in the seed oils of white grape varieties than in those of colored grape varieties. Odabaşıoğlu [91], on the other hand, suggested that the amounts of palmitic acid and linoleic acid in the seed oils varied depending on the berry skin color, with colored varieties having higher levels of these fatty acids. When the grape varieties in our study were classified according to the time of ripening of their berries, all the major fatty acids showed significant differences. Göktürk Baydar and Akkurt [50] reported that the fatty acid composition of grape seed oils showed limited variability across grape varieties. Rubio et al. [62] found that as the ripening level of Tempranillo grape variety berries increased, the amounts of stearic acid and oleic acid in the seed oil increased, while the amounts of palmitic acid and linoleic acid decreased. Özcan et al. [76] observed that changes in the fatty acid composition of grape seed oil associated with the ripening level of the berries varied depending on the grape variety examined.

Table 3

Composition of major fatty acids in the grape seed oils of the 16 grape genotypes

Variety	Palmitic Acid	Stearic Acid	Oleic Acid	Linoleic Acid
Tahannebi	12.03±0.66 abc^**	3.04±0.26 ab^**	15.99±1.28 g^**	66.87±2.00 ab^**
Syrah	9.33±0.15 ef	2.13±0.15 c	19.78±0.45 c-g	67.02±0.44 ab
Çilorut	10.79±0.92 b-e	2.58±0.11 bc	18.09±0.84 efg	66.44±1.65 abc
Hasani	10.24±0.29 c-f	3.46±0.74 a	19.54±1.35 c-g	65.24±2.20 a-d
Küllahi	8.38±0.13 f	2.66±0.37 abc	30.97±0.20 a	56.13±0.28 e
Yediveren	10.73±0.12 b-e	2.70±0.00 abc	22.17±0.86 bcd	62.81±0.91 bcd
Chardonnay	8.58±0.01 f	2.23±0.02 bc	19.08±2.81 c-g	68.25±2.81 a
Kızıl Banki	9.54±0.08 def	2.48±0.12 bc	20.48±1.11 c-f	66.16±1.28 abc
Sergi Karası	11.45±0.12 a-d	2.18±0.06 c	19.41±0.69 c-g	65.07±0.66 a-d
Elma Üzümü	9.54±0.11 def	2.61±0.07 bc	17.08±0.17 fg	69.36±0.13 a
Horoz Karası	13.07±0.62 a	2.22±0.16 bc	17.82±0.97 efg	65.01±0.12 a-d
Hatun Parmağı	10.03±0.01 c-f	2.02±0.02 c	21.10±1.57 cde	65.45±1.25 a-d
Azazi	10.93±1.62 b-e	2.64±0.18 abc	18.51±0.57 d-g	65.35±2.65 a-d
Çiloreş	11.02±0.62 a-e	2.26±0.06 bc	22.48±0.12 bc	62.51±0.50 bcd
Hönüsü	12.71±0.24 ab	2.40±0.04 bc	21.44±0.37 b-e	61.48±0.63 cd
Kabarcık	9.76±0.65 def	2.50±0.09 bc	25.18±1.10 b	60.22±2.06 de
White Var.	10.13±1.23 B^*	2.60±0.46 A^*	20.80±4.44^Ns	64.58±4.11^Ns
Colored Var.	11.14±1.49 A	2.35±0.22 B	20.19±1.60	64.59±2.06
Early Var.	12.03±0.66 A^**	3.04±0.26 A^*	16.00±1.28 B^**	66.87±2.00 A^**
Midseason Var.	10.15±0.03 B	2.48±0.16 B	20.50±0.27 A	65.18±0.32 AB
Late Var.	11.11±0.46 AB	2.45±0.02 B	21.90±0.01 A	62.39±0.43 B
2014	10.64±1.64^Ns	2.38±0.28^Ns	20.47±3.65^Ns	64.57±3.47^Ns
2015	10.37±1.28	2.63±0.53	20.68±3.87	64.60±3.81

There is a significant difference (^*: p < 0.05; ^**: p < 0.01) between average values marked with different letters in the same column. Ns: non-significant.

Lachman et al. [60] in the Czech Republic found that a decrease in precipitation during the cultivation season resulted in an increase in palmitic acid and oleic acid and a decrease in stearic acid, linoleic acid, and α-linolenic acid in the seed oils of 23 different grape varieties. However, the change in stearic acid was not statistically significant. Odabaşıoğlu and Gürsöz [61] reported that changes in the composition of the major fatty acids of grape seed oil (excluding stearic acid) could be observed depending on the cultivation season and rootstocks used in the vineyard and that these changes were related to the uptake of water from the soil by the grapevines. However, in this study, the major fatty acid composition of grape seed oil was found to be similar between seasons (Table 3). The lack of significant changes in the composition of the major fatty acids in our study compared to previous studies, which found significant changes depending on seasonal variation, may have been due to the smaller difference in precipitation between 2014 and 2015.

The major fatty acids in grape seed oil varied depending on the ripening times. The period between blooming and harvest is longer in grape varieties that ripen in the mid-season and late season compared to early-ripening varieties [92, 93]. Although previous studies [94, 95] have shown that drought in early spring limits growth and productivity in grapevines more than in other periods, partial drought stress could occur in in mid-season and late-season ripening grape varieties grown without irrigation in semi-arid ecologies during the period between blooming and harvest. Early varieties could overcome this because their blooming-harvest period was too short than mid-season and late-season varieties. As the period between blooming and harvest lengthens, changes in the composition of the major fatty acids in grape seeds may be a phenotypic reflection of the physiological response of grapevines to this stress factor. Indeed, similar changes have been observed in the seeds of safflower [96], sunflower [97, 98], black cumin [99] and canola [100] in response to drought stress.

The minor fatty acids in the grape seed oils were ranked in terms of their quantity in the following order: caproic acid > cis-10-heptadecanoic acid > docosahexaenoic acid > myristic acid (Table 4). A similar ranking was reported by Odabaşıoğlu and Gürsöz [61]. The grape varieties examined showed significant differences (p < 0.01) in the amount of minor fatty acids in their seeds. The Azazi variety contained the highest amounts of caproic acid, myristic acid, and cis-10-heptadecanoic acid, while the Hasani variety contained the highest amount of docosahexaenoic acid. The color of the berry skin and the season in which grapevines were grown did not effect on the amount of minor fatty acids in the grape seed oil. However, the ripening time of the grape varieties had a significant effect on the amounts of caproic acid (p < 0.01), myristic acid (p < 0.05), and docosahexaenoic acid (p < 0.05) in the seed oil. The changes observed in caproic acid, myristic acid, and docosahexaenoic acid depending on the ripening time indicate that there may be changes in the amount of minor fatty acids in grape varieties due to accumulative intrinsic water shortage related to the time lengthening in blooming to ripening.

Table 4

Composition of minor fatty acids in the grape seed oils of the 16 grape genotypes

Variety	Caproic	Myristic	cis-10-heptadecanoic	Docosahexaenoic
	Acid	Acid	Acid	Acid
Tahannebi	0.88±0.07 ab^**	0.18±0.03 ab^**	0.38±0.09 ab^**	0.16±0.04 cd^**
Syrah	0.69±0.02 abc	0.15±0.01 a-d	0.27±0.04 ab	0.14±0.01 d
Çilorut	0.87±0.11 abc	0.17±0.01 abc	0.35±0.07 ab	0.27±0.02 abc
Hasani	0.56±0.08 bc	0.11±0.01 cd	0.16±0.05 b	0.33±0.05 a
Küllahi	0.76±0.04 abc	0.14±0.02 a-d	0.31±0.06 ab	0.18±0.05 bcd
Yediveren	0.66±0.07 abc	0.14±0.02 a-d	0.21±0.03 b	0.20±0.05 a-d
Chardonnay	0.67±0.01 abc	0.11±0.00 cd	0.34±0.02 ab	0.25±0.05 a-d
Kızıl Banki	0.53±0.04 c	0.10±0.00 cd	0.15±0.01 b	0.27±0.06 abc
Sergi Karası	0.79±0.07 abc	0.18±0.01 ab	0.26±0.05 b	0.23±0.01 a-d
Elma Üzümü	0.53±0.06 c	0.09±0.01 d	0.17±0.04 b	0.31±0.01 ab
Horoz Karası	0.66±0.25 abc	0.18±0.05 ab	0.27±0.17 ab	0.25±0.01 a-d
Hatun Parmağı	0.53±0.12 bc	0.13±0.02 bcd	0.17±0.06 b	0.20±0.03 a-d
Azazi	0.92±0.09 a	0.19±0.00 a	0.53±0.06 a	0.24±0.01 a-d
Çiloreş	0.75±0.17 abc	0.13±0.00 a-d	0.25±0.08 b	0.20±0.04 a-d
Hönüsü	0.79±0.02 abc	0.15±0.01 a-d	0.32±0.01 ab	0.28±0.07 abc
Kabarcık	1.01±0.09 a	0.19±0.03 ab	0.27±0.13 ab	0.22±0.03 a-d
White Var.	0.75±0.18^Ns	0.14±0.04^Ns	0.29±0.13^Ns	0.24±0.06^Ns
Colored Var.	0.69±0.13	0.15±0.03	0.25±0.08	0.23±0.06
Early Var.	0.88±0.07 A^**	0.18±0.03 A^*	0.38±0.09^Ns	0.16±0.04 B^*
Midseason Var.	0.66±0.04 B	0.14±0.01 B	0.24±0.04	0.24±0.00 A
Late Var.	0.87±0.04 A	0.17±0.00 AB	0.34±0.04	0.24±0.00 A
2014	0.75±0.17^Ns	0.15±0.04^Ns	0.30±0.14^Ns	0.24±0.05^Ns
2015	0.70±0.18	0.14±0.03	0.25±0.11	0.23±0.08

There is a significant difference (^*: p < 0.05; ^**: p < 0.01) between average values marked with different letters in the same column. Ns: non-significant.

As with the composition of major fatty acids, the fact that minor fatty acids were similar between cultivation seasons may be dependent on the low precipitation difference or stability of grape varieties’ genotypic character. Indeed, Zamorano et al. [101] reported that there is drought stress memory in grapevines that includes growth and physiological changes in response to repeated drought stress in consecutive cultivation seasons, and this increases the capacity to tolerate stress. However, grapevines cannot perform this physiological regulation to the same extent within a cultivation season and, as a result, they show significant changes in sugar, organic acid, color, aroma components, and other phytochemical syntheses, as well as a decrease in berry size [102, 103]. In the future, studies on the changes in fatty acid composition in grape seed oils of varieties grown under different water restrictions and drought levels may help to further clarify the findings of the present study.

The composition of essential fatty acids in grape varieties varies depending on the grape variety examined, as in the major and minor fatty acids found in grape seed oils (Table 5). Palmitoleic acid and eicosatrienoic acid were more abundant in the seed oil of the Kabarcık variety, heptadecanoic acid in the seed oil of the Azazi variety, and linolenic acid in the seed oil of the Chardonnay variety compared to other varieties examined. However, the Tahannebi and Azazi varieties were similar in terms of tricosenoic acid content in their seed oils. When the grape varieties were classified according to the color of the skin of the berries, the white varieties and colored varieties did not show significant differences in the amount of essential fatty acids in their seed oils. When the varieties examined were classified according to their ripening times, only palmitoleic acid and tricosenoic acid varied depending on the ripening time. The findings showed that the amount of palmitoleic acid in the seed oil increased with the lengthening of the time between blooming and harvest in grape varieties.

Table 5

Composition of essential fatty acids in the grape seed oils of the 16 grape genotypes

Variety	Palmitoleic	Heptadecanoic	Linolenic	Eicosatrienoic	Tricosenoic
	Acid	Acid	Acid	Acid	Acid
Tahannebi	0.06±0.01 c^**	0.10±0.02 ab^**	0.13±0.02 abc^*	0.05±0.02 ab^**	0.09±0.01 a^*
Syrah	0.14±0.01 b	0.09±0.01 ab	0.10±0.00 abc	0.03±0.00 abc	0.07±0.00 abc
Çilorut	0.12±0.01 bc	0.11±0.01 ab	0.08±0.01 abc	0.04±0.01 abc	0.09±0.02 abc
Hasani	0.09±0.01 bc	0.07±0.01 b	0.10±0.00 abc	0.02±0.00 bc	0.05±0.01 bc
Küllahi	0.09±0.01 bc	0.07±0.02 b	0.14±0.10 abc	0.03±0.00 abc	0.07±0.01 abc
Yediveren	0.09±0.01 bc	0.08±0.00 ab	0.09±0.00 abc	0.03±0.00 bc	0.09±0.01 abc
Chardonnay	0.08±0.02 bc	0.10±0.00 ab	0.17±0.05 a	0.04±0.01 abc	0.09±0.00 ab
Kızıl Banki	0.09±0.01 bc	0.06±0.03 b	0.06±0.01 c	0.02±0.00 c	0.05±0.00 c
Sergi Karası	0.07±0.01 c	0.08±0.02 ab	0.12±0.02 abc	0.04±0.01 abc	0.08±0.01 abc
Elma Üzümü	0.09±0.00 bc	0.07±0.01 ab	0.08±0.00 abc	0.03±0.00 bc	0.06±0.01 abc
Horoz Karası	0.14±0.02 b	0.09±0.04 ab	0.14±0.03 abc	0.03±0.02 abc	0.08±0.04 abc
Hatun Parmağı	0.10±0.01 bc	0.08±0.02 ab	0.08±0.03 abc	0.02±0.01 bc	0.06±0.02 abc
Azazi	0.13±0.03 b	0.13±0.01 a	0.07±0.01 bc	0.04±0.01 abc	0.10±0.00 a
Çiloreş	0.12±0.01 bc	0.09±0.02 ab	0.08±0.01 abc	0.04±0.01 abc	0.06±0.00 abc
Hönüsü	0.09±0.01 bc	0.09±0.00 ab	0.12±0.02 abc	0.04±0.00 abc	0.08±0.00 abc
Kabarcık	0.21±0.04 a	0.09±0.02 ab	0.16±0.01 ab	0.06±0.00 a	0.09±0.01 abc
White Var.	0.11±0.04^Ns	0.09±0.02^Ns	0.11±0.05^Ns	0.04±0.01^Ns	0.08±0.02^Ns
Colored Var.	0.10±0.03	0.08±0.02	0.11±0.03	0.03±0.01	0.08±0.02
Early Var.	0.06±0.01 B^**	0.10±0.02^Ns	0.13±0.02^Ns	0.05±0.02^Ns	0.09±0.01 A^**
Midseason Var.	0.10±0.00 AB	0.08±0.01	0.11±0.02	0.03±0.01	0.07±0.01 B
Late Var.	0.14±0.02 A	0.10±0.01	0.11±0.01	0.04±0.00	0.08±0.00 AB
2014	0.11±0.05^Ns	0.09±0.03^Ns	0.13±0.05 A^*	0.04±0.02^Ns	0.08±0.02^Ns
2015	0.10±0.03	0.08±0.02	0.09±0.03 B	0.03±0.01	0.07±0.02

There is a significant difference (^*: p < 0.05; ^**: p < 0.01) between average values marked with different letters in the same column. Ns: non-significant.

When the fatty acids in the oils of grape varieties are classified according to their saturation status, they are obtained in the order of PUFA (polyunsaturated fatty acids)>MUFA (monounsaturated fatty acids > SFA (saturated fatty acids) (Table 6). The same ranking was also observed in previous studies examining different Vitis species [52 , 104] and grape varieties [105 –107] for their seed oils. In the present study, the grape varieties examined showed statistically significant differences (p < 0.01) from each other in terms of the amounts of SFA, MUFA, and PUFA and the PUFA/SFA ratio found in their seed oils. The variety with the highest amount of MUFA in the seed oil was Küllahi, while the variety with the highest PUFA/SFA ratio was Chardonnay. Tahannebi, Horoz Karası, and Hönüsü differed from the other varieties with their high SFA content, while Chardonnay and Elma Üzümü differed with their high PUFA content. The amounts of SFA, MUFA, and PUFA in grape seed oils that we observed were similar to the findings reported by Yi et al. [81], Akın and Altındişli [86], Demirtas et al. [88], and Yalcın et al. [108], while the PUFA/SFA ratio was similar to the findings reported by Tangolar et al. [71] and Fernandes et al. [48]. However, neither the cultivation season nor the color of the berry skin influenced the amounts of SFA, MUFA, or PUFA or the PUFA/SFA ratio. The ripening time of the grape varieties had a significant (p < 0.01) effect on these properties. Generally, as the ripening time of grape berries shifted towards the late season, MUFA increased but SFA and PUFA decreased in the seed oil. However, the highest PUFA/SFA ratio in grape seed oil was obtained from the average of the varieties that ripen in the midseason.

Table 6

SFA, MUFA, and PUFA compositions and PUFA/SFA ratio in the grape seed oils of the 16 grape genotypes

Variety	ΣSFA	ΣMUFA	ΣPUFA	PUFA/SFA
Tahannebi	16.32±0.52 a^**	16.44±1.38 f^**	67.20±1.93 abc^**	4.13±0.25 cd^**
Syrah	12.46±0.00 cde	20.19±0.43 c-f	67.29±0.43 ab	5.40±0.04 ab
Çilorut	14.61±0.88 abc	18.55±0.78 def	66.84±1.65 abc	4.60±0.39 bcd
Hasani	14.49±0.95 a-d	19.79±1.30 c-f	65.69±2.24 a-d	4.56±0.45 bcd
Küllahi	12.08±0.19 de	31.37±0.26 a	56.48±0.14 e	4.68±0.06 bcd
Yediveren	14.40±0.02 a-d	22.48±0.84 bc	63.13±0.86 bcd	4.38±0.07 bcd
Chardonnay	11.78±0.03 e	19.50±2.78 c-f	68.71±2.80 a	5.83±0.25 a
Kızıl Banki	12.77±0.11 b-e	20.72±1.12 cde	66.51±1.24 abc	5.21±0.14 ab
Sergi Karası	14.77±0.06 abc	19.75±0.64 c-f	65.46±0.70 a-d	4.43±0.07 bcd
Elma Üzümü	12.89±0.26 a-e	17.34±0.14 ef	69.77±0.13 a	5.42±0.12 ab
Horoz Karası	16.30±0.83 a	18.23±0.78 def	65.44±0.08 a-d	4.03±0.21 d
Hatun Parmağı	12.85±0.15 b-e	21.37±1.49 cd	65.76±1.32 a-d	5.12±0.05 abc
Azazi	14.92±1.90 ab	19.16±0.66 c-f	65.71±2.64 a-d	4.50±0.75 bcd
Çiloreş	14.31±0.38 a-d	22.84±0.06 bc	62.83±0.46 bcd	4.39±0.15 bcd
Hönüsü	16.23±0.31 a	21.85±0.37 bcd	61.92±0.68 cd	3.82±0.11 d
Kabarcık	13.63±0.88 b-e	25.65±1.18 b	60.66±2.09 de	4.48±0.44 bcd
White Var.	13.79±1.52^Ns	21.20±4.44^Ns	64.96±4.12^Ns	4.77±0.59^Ns
Colored Var.	14.49±1.57	20.54±1.56	64.96±2.02	4.55±0.60
Early Var.	16.32±0.52 A^**	16.44±1.38 B^**	67.20±1.93 A^**	4.13±0.25 B^**
Midseason Var.	13.58±0.13 B	20.85±0.23 A	65.55±0.35 AB	4.88±0.07 A
Late Var.	14.77±0.42 B	22.38±0.02 A	62.78±0.42 B	4.30±0.14 AB
2014	14.13±1.88^Ns	20.89±3.65^Ns	64.98±3.45^Ns	4.68±0.67^Ns
2015	14.02±1.40	21.04±3.89	64.95±3.83	4.68±0.60

There is a significant difference (^*: p < 0.05; ^**: p < 0.01) between average values marked with different letters in the same column. Ns: non-significant.

Similar to the findings reported by Göktürk Baydar and Akkurt [50], there was no significant relationship between the amount of oil in the seeds of the grape varieties studied in our work and the composition of fatty acids. However, a negative correlation (r = –0.893, p < 0.01) was found between the amounts of linoleic acid and oleic acid in the grape seed oil (Table 7). Uslu and Dardeniz [90], Sabir et al. [47], and Yalcin et al. [108] also reported a negative correlation between these two fatty acids in grape seed oil. Myristic acid, eicosatrioenoic acid, tricosenoic acid, and caproic acid were the fatty acids most affected by changes in other fatty acids. However, stearic acid and docosahexaenoic acid were not affected by changes in other fatty acids in the grape seed oil. Göktürk Baydar and Akkurt [50] reported that stearic acid in grape seed oil was relatively stable. The amount of SFA in grape seed oil increased with an increase in palmitic acid, caproic acid, and myristic acid. PUFA showed a negative correlation with oleic acid (r = –0.895, p < 0.01) and a positive correlation with linoleic acid (r = 1.000, p < 0.01). In addition, a strong negative correlation (r = –0.901, p < 0.01) was found between PUFA and MUFA. SFA was not affected by changes in PUFA or MUFA.

Table 7

Pearson’s correlation coefficients of oil content and fatty acid compositions in grape seeds

		1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
1	Palmitic Acid	1.00
2	Stearic Acid	0.038	1.00
3	Oleic Acid	–0.340	0.005	1.00
4	Linoleic Acid	–0.093	–0.128	–0.893^**	1.00
5	Caproic Acid	0.231	–0.050	0.073	–0.273	1.00
6	Myristic Acid	0.506^**	–0.096	–0.048	–0.240	0.795^**	1.00
7	Palmitoleic Acid	0.044	–0.163	0.155	–0.202	0.348	0.307	1.00
8	Heptadecanoic Acid	0.271	–0.146	–0.261	0.078	0.712^**	0.605^**	0.164	1.00
9	cis-10-heptadecanoic Acid	0.240	–0.106	–0.107	–0.081	0.808^**	0.698^**	0.061	0.870^**	1.00
10	Linolenic Acid	–0.011	–0.205	0.236	–0.262	0.315	0.328	0.106	0.200	0.253	1.00
11	Eicosatrienoic Acid	0.230	–0.069	0.039	–0.227	0.892^**	0.715^**	0.352^*	0.669^**	0.725^**	0.449^**	1.00
12	Tricosenoic Acid	0.271	–0.114	–0.210	0.028	0.766^**	0.714^**	0.147	0.752^**	0.770^**	0.312	0.736^**	1.00
13	Docosahexaenoic Acid	0.103	0.075	–0.268	0.230	–0.222	–0.295	0.014	0.022	–0.137	–0.064	–0.171	–0.192	1.00
14	SFA	0.955^**	0.289	–0.309	–0.149	0.352^*	0.567^**	0.057	0.338	0.334	–0.021	0.327	0.346	0.078	1.00
15	MUFA	–0.331	–0.001	0.999^**	–0.900^**	0.106	–0.019	0.168	–0.229	–0.072	0.248	0.069	–0.182	–0.273	–0.297	1.00
16	PUFA	–0.090	–0.130	–0.895^**	1.000^**	–0.269	–0.238	–0.199	0.083	–0.077	–0.249	–0.220	0.031	0.247	–0.147	–0.901^**	1.00
17	PUFA/SFA	–0.831	–0.315	–0.138	0.563^**	–0.400^*	–0.574^**	–0.121	–0.215	–0.273	–0.060	–0.345	–0.247	0.046	–0.895^**	–0.150	0.562^**	1.00
18	Seed Oil Content	–0.131	–0.078	0.240	–0.185	–0.004	–0.230	–0.281	0.148	0.167	0.017	–0.012	0.035	–0.001	–0.146	0.242	–0.185	0.064	1.00

^*correlation is significant at the p < 0.05 level, ^**correlation is significant at the p < 0.01 level.

4 Conclusion

The amount of oil in grape seeds varies according to the grape variety examined, but when grape varieties are classified according to berry skin color or ripening time, this variation was not observed. The effect of precipitation differences between cultivation seasons on the oil content and major, minor, and essential fatty acid composition of seeds was found limited. However, the effects of irrigation levels applied to the grapevines on the oil content and fatty acid composition of the seeds should be re-examined with more comprehensive studies.

The composition of fatty acids in grape seed oils varied according to the genotype, but when classified according to berry skin color, the fatty acid composition, except for palmitic acid and stearic acid, did not differ. However, in cases where it is not possible to separate the seeds of grape varieties on a variety basis, classifying them according to the time of ripening of the berries may be helpful in predicting the amounts of major and minor fatty acids and partially essential fatty acids in the seed oil.

Yediveren and Küllahi, which have hermaphrodite flower types, 2- to 3-seeded berries, and higher oil content compared to the other varieties examined, are two varieties that stand out in terms of obtaining more grape seed oil from a unit vineyard area. Although the Hönüsü variety has high oil content in its seeds, it is not suitable for industrial-scale production of seed oil due to its pistillate flower type and 1- to 2-seeded berries. In new research, examination of the relationship between the number of grape seeds and the oil content of the seeds and whether the number of seeds in grapevines is a phenotypic marker for predicting the oil content and composition of the seeds can contribute to this area of study.

The composition of the seed oils of local grape varieties such as Elma Üzümü, Hatun Parmağı, and Kızıl Banki is quite similar in quality and PUFA/SFA ratio to the seed oils of standard grape varieties such as Chardonnay and Syrah, and they are identified as the most suitable oils for human consumption. Furthermore, the seed oil of the Küllahi variety can be stored for a long time without oxidative stability deterioration due to its 30.97% oleic acid content, and this feature can provide it with a more advantageous position in marketing compared to oils of other varieties. Eventually, the Küllahi grape variety was found to be the suitable parental candidate variety for breeding programs from this perspective.

Footnotes

Acknowledgments

The author would like to thank Dr. Aslı Polat for assisting in the collection of grape variety samples and Dr. Ceren Odabaşıoğlu for assisting in seed oil extraction.

Conflict of interest

The author states that there is no conflict of interest.

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