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25
Journal of Oleo Science
Copyright ©2025 by Japan Oil Chemists’ Society
doi : 10.5650/jos.ess24152
J. Oleo Sci. 74, (1) 25-34 (2025)
The Role of Microwave and Oven Roasting on Oil
Contents, Bioactive Properties, Phenolic
Components, Fatty Acids and Mineral Contents of
Grape (Vitis spp.) Seeds
Isam A. Mohamed Ahmed1, Fahad AlJuhaimi1, Mehmet Musa Özcan2＊, Nurhan Uslu2,
and Zainab Albakry3
1 College of Food and Agricultural Sciences, Department of Food Science & Nutrition, King Saud University, Riyadh-SAUDI ARABIA
2 Selcuk University, Faculty of Agriculture, Department of Food Engineering, 42031 Konya, TURKEY
3 Jimei University, College of Ocean Food and Biological Engineering, Xiamen 361021, CHINA
1 Introduction
Grape（Vitis vinifera）is widely grown in all regions of
Turkey due to changing climatic conditions1−3）
. Grape pulp,
skin and seed constitute approximately 20％ of the pro-
cessed fruit. Approximately 9 million tons of pulp are re-
leased as process waste annually worldwide. Turkey ranks
6th in the world with an annual fresh grape production of
approximately 4 million tons. 49.8％ of the grapes pro-
duced in Turkey are for table use, 38.4％ for drying and
11.8％ for wine4, 5）
. However, since their water solubility is
low before use, grape skins and seeds must be subjected to
＊Correspondence to: Mehmet Musa Özcan, Selcuk University, Faculty of Agriculture, Department of Food Engineering, 42031
Konya, TURKEY
E-mail: mozcan@selcuk.edu.tr
Accepted September 18, 2024 (received for review July 1, 2024)
Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online
https://www.jstage.jst.go.jp/browse/jos/ https://mc.manuscriptcentral.com/jjocs
size reduction after drying6）
. Grape marc, which is the re-
maining pulp after processing grapes, consists of 50％ skin,
25％ seed and 25％ grape stem. As a result of growers not
being able to utilize the marc released during processing, it
accumulates in significant amounts at production points
and is thrown away because it cannot be used, which can
cause environmental pollution to a considerable extent7）
. It
was determined that the use of grape seed flour and oil did
not cause any negative results on the moisture, pH, color
and texture values of the sausages. However, when sensory
values were examined, it was seen that the group in which
Abstract: In this study, the role of roasting on the total phenol, antioxidant capacity, phenolic constituents
and fatty acid profile of the grape seeds was investigated. Total phenolic and flavonoid quantities of the
grape seeds roasted in microwave (MW) and conventional oven (CO) systems were recorded between 673.57
(control) and 713.57 (MW) to 7121.67 (MW) and 7791.67 mg/100 g (CO), respectively. Antioxidant activities
of the grape seeds varied between 6.57 (MW) and 7.24 mmol/kg (control). Catechin and rutin quantities of
the grape seeds were recorded to be between 435.30 (CO) and 581.57 (control) to 94.94 (CO) and 110.53
mg/100 g (MW), respectively. While gallic acid amounts of the seed samples are established between 21.06
(control) and 101.79 (MW), quercetin values of the grape seeds were assigned to be between 56.59 (control)
and 77.81 mg/100 g (CO). In addition, p-coumaric acid and resveratrol quantities of the grape seeds were
recorded between 15.43 (control) and 22.98 (CO) to 12.50 (CO) and 29.57 mg/100 g (MW), respectively. The
main fatty acids in oil samples were linoleic, oleic, palmitic and stearic acids in decreasing order. Linoleic
and oleic acid values of the oils provided from grape seeds were recorded to be between 72.75 (control) and
73.33% (MW) to 14.79 (CO) and 14.87% (MW), respectively. It was observed that the element results
related to the grape seed differed based on the roasting type when compared to the control. The most
abundant elements in the grape seed were K, P, Mg, S, Na, Fe, Ca, Zn, and K and P amounts of the grape
seeds were reported to be between 6706.93 (MW) and 7089.33 (control) to 2764.27 (CO) and 2927.97 mg/kg
(control), respectively. It is thought that it would be beneficial to add grape seeds to foods as an ingredient
by taking into account these phytochemical components as a result of the applied heat treatment.
Key words: grape seed, oil, roasting, bioactive properties, polyphenols, fatty acid profiles, nutrients
I. A. Mohamed Ahmed, F. AlJuhaimi, M. M. Özcan et al.
J. Oleo Sci. 74, (1) 25-34 (2025)
26
grape seed oil was used instead of animal fat in the sausage
formulation was less preferred8）
. The parts of grapes
（leaves, seeds, peel and pulp）have different phenolic con-
stituents related to their antioxidant activity9−12）
. In addi-
tion to phenolic compounds, grape seed has important ad-
vantages for human health due to its mineral, oil,
polyunsaturated fatty acids and tocopherol contents13−16）
.
It is important to dispose of large amounts of wastes such
as fruit seeds, representing approximately 50-60％ of
fruits, and convert them into value-added bioproducts17, 18）
.
Grape seed oil is generally used in salad dressings, frying,
baking, massage oils and hand creams14, 19）
. It has been
stated that grape skins, pulp and seeds have protective
effects on grape health due to the presence of a large
amount of phenolic substances20）
. Grape, which is rich in
hydroxycinnamic and hydroxybenzoic acids, is processed
into various products such as boiled fruit juice, wine and
fruit juice. Grape seed, which is released as a by-product in
the production of these products, is rich in phenolic com-
pounds21, 22）
. Grape seeds, which have very important
effects on human health, have 10-20％ oil rich in vitamin
E16, 17, 23）
. Grape seeds produced as waste from the process-
ing of wine, vinegar, boiled fruit juice, grape juice and other
grape products pose a problem for the environment. In
order to solve this problem, it is noteworthy that grape
seed has been used as a food supplement in various foods
in recent years. Grape pulp emerges as a potential raw ma-
terial for industries such as pharmaceuticals and cosmetics
as well as for food, thanks to its rich bioactive components
such as fatty acids, polyphenols, proanthocyanidins, and
sterols24, 25）
. Phenolic compounds of grape seeds consist of
flavonoids（anthocyanin, flavonol and flavanols）and pheno-
lic acids（catechin, proanthocyanidin）known for their
strong biological effects26）
. The pharmacological benefits
and nutritiveness of grape seed from the free radical scav-
enging capacity of the polyphenols it contains27）
. Grape
seed has the potential to be used as a food additive and
supplement with the compounds it contains and its physio-
logical effects28, 29）
. Considering the inadequacy of the
worlds raw material resources, the importance of the eval-
uation of the grape pomace is understood once again. The
food and beverage industry in the world, like all other in-
dustries, attaches importance to waste reduction and recy-
cling. If the wastes generated by the nature of the targeted
product or the process used are used as input for any other
food, the amount of use of other resources required for the
production of the product may decrease. Utilizing waste as
input also reflects on the profitability of organizations and
makes this type of work attractive. During the processing
of food, the waste generated due to the nature of the final
products must be evaluated separately. It is seen that ap-
proximately 30％ of the waste, which is the by-product of
the grape juice and winemaking industry, consists of grape
seeds. Grape seeds contain sugars, polysaccharides, oils,
organic acids, phenolic compounds, nitrogenous com-
pounds, minerals and vitamins5, 30）
. There are limited works
on the role of heating on the total phenol, antioxidant ca-
pacity, phenolic constituents and fatty acid profile of the
grape seeds. The objective of this research was to illustrate
effect of thermal processing on bioactive compounds and
antioxidant capacity and phenolic constituent and fatty
acid quantities of the grape seeds.
2 Material and Methods
2.1 Material
The grape（Merlot cv）seeds used in current study were
provided in Konya province in 2021. The air-dried seeds
were transferred to the laboratory for analysis. Grape seeds
were milled in a laboratory mill until they became powder.
2.2 Methods
2.2.1 Heat treatment
Cleaned and ground grape seeds were roasted in an oven
at 110℃ for 30 min; in a microwave oven at 720 W for 11
min.
2.2.2 Moisture quantity
The moisture of grape seeds were measured by the
KERN & SOHN GmbH infrared moisture analyser.
2.2.3 Oil content
After roasted and unroasted grape seed samples were
ground in the laboratory mill, seed powders were passed
through a 0.5 mesh sieve. After 10 g of powdered grape
seed powder, were weighed into cartridge, it was covered
with oil-free cotton. Then, the cartridge was put in the
Soxhlet extractor and extracted with petroleum ether for 5
h. After the solvent was evaporated with a rotary evapora-
tor at 50℃, the oil content was calculated by weighing31）
.
2.2.4 Extraction procedure
After 2 g of the grape seed powder was mixed with 20 ml
of methanol, the solution was shaken in a water bath for 1
hour. After the mixture was centrifuged at 6000 rpm for 10
minutes, the resulting supernatant was filtered through a
0.45 µm membrane filter. 15 mL n-hexane was added and
the mixture was mixed by vortex for 2 minutes. After pre-
treatments, the extracts were dissolved in 10 ml metha-
nol32）
.
2.2.5 Total phenolic content
Total phenolic quantities of the grape seed extracts were
established by using the Folin-Ciocalteu chemical accord-
ing to the study stated by Yoo et al.33）
. The absorbance ob-
tained was determined at 750 nm by the spectrophotome-
ter（Shimadzu UV mini 1240, Japan）. The findings obtained
are stated as mg GAE）100 g（dw）.
2.2.6 Total flavonoid quantity
After 0.3 ml of NaNO2, 0.3 ml of AlCl3 and 2 ml of NaOH
was added to the grape seed extract（1 mL）, respectively, it
Phytochemical and Fatty Acid Composition of Grape Seeds
J. Oleo Sci. 74, (1) 25-34 (2025)
27
was vigorously mixed with vortex. After preprocessing, the
absorbance was assigned at 510 nm. The findings are dis-
played as mg QE/100 g（dw）
34）
.
2.2.7 Antioxidant capacity
DPPH（1.1-diphenyl-2-picrylhydrazyl）was used for the
antioxidant capacity of extracts with some modifications35）
.
The absorbance was depicted at 517 nm. The findings are
stated as mmol trolox（TE）/kg.
2.2.8 Determination of phenolic compounds
Chromatographic separation of phenolic compounds
found in roasted and unroasted grape seed extracts were
carried out by HPLC（Shimadzu）equipped with a PDA de-
tector and an Inertsil ODS-3（5µm; 4.6×250 mm）column.
As injection volume, 20 µL injected to HPLC. The peaks
were taken at 280 using a PDA detector.
2.2.9 Fatty acid composition
Gas chromatography（Shimadzu GC-2010）equipped with
flame-ionization detector（FID）and capillary column（Tec-
nocroma TR-CN100, 60 m×0.25 mm, film thickness: 0.20
µm）was used for analysis of fatty acid methyl esters of
grape seed oils esterificated according to ISO-550936）
method.
2.3 Statistical analyses
Data of triplicate analyses were equated and carried out
analysis of variance. The significant changes among results
of the grape seed samples were established by Duncans
Multiple Range Test（p＜0.05）.
3 Results and Discussion
3.1 Physical and bioactive properties of unroasted and
roasted grape seeds
The oil quantity and bioactive properties of the grape
seeds roasted in microwave（MW）and conventional oven
（CO）are assigned in Table 1. The moisture and oil amounts
of the grape seeds were specified to be between 2.78％
（CO）and 8.26％（ control）to 12.36％（ control）and 13.72％
（MW）, respectively. In previous studies, grape seeds con-
tained 8.09％ - 19.6％ oil23, 37−40）
. Our findings were similar
to previous studies on the increase in oil content as a result
of roasting seeds23, 39−41）
. Also, total phenol and flavonoid
amounts of the extracts of the grape seeds roasted in MW
and CO systems were established to be between 673.57
（control）and 713.57 mg GAE/100 g（MW）to 7121.67（MW）
and 7791.67 mg/100 g（CO）. Antioxidant activities of the
grape seeds varied between 6.57 mmol/kg（MW）and 7.24
mmol/kg（control）. Statistically significant changes were
observed among bioactive properties of the grape seeds
depending on unroasted and roasting types（p＜0.05）. The
results show that roasting is effective on the moisture, oil
amounts, bioactive properties of the grape seeds. While the
the total flavonoid quantities and antioxidant activities of
the grape seeds decreased with roasting, the oil and total
phenol contents of the grape seeds increased. However, it
was low when compared to grape seeds roasted in micro-
wave and CO. The increase in the total phenol value as a
result of the heat treatment is likely due to the decrease in
the moisture amount in the seeds as well as the biochemi-
cal reaction products such as the maillard reaction caused
by roasting. In addition, it was observed that the total fla-
vonoid structures of seeds were more damaged by micro-
wave roasting. The microwave roasting process significant-
ly increased the total phenolic quantities, while the total
flavonoid quantities of groundnut seed extracts decreased
with roasting time42）
. The flavonoid is broken down and de-
creased during the roasting process43）
. Our findings were
similar to the results of studies by Gülcü et al.44）
, Hu et
al.45）
and Dietrych-Szoctak and Oleszek43）
, which showed
that the flavonoid content decreased as a result of thermal
treatment. It was reported that the total phenolic amount
in fenugreek seeds increased with roasting46）
. The increase
in the total phenolic content during the roasting process is
probably due to the fact that the applied heat can partially
destroy the cell structure, causing the release of some
bound phenolic constituents that can become extractable
in the solvent47）
. In previous study, total phenolic amounts
of the grape seed varieties changed to be between 162.29
and 326.18 mg GAE/100 g20）
. Andelkovic et al.48）
deter-
mined 67.40 mg/g（dw）total phenolic, 1.89 mg/g（dw）flavo-
nols, 17.90 mg/g（dw）total anthocyanins and 1.160 EC50
（mg/mL; dw）antioxidant activity in Vranac wine pomace.
The flavonoid contents of Cabernet Sauvignon seeds were
Table 1 Some chemical and bioactive properties of grape seeds.
Process Moisture
content (%)
Oil content
(%)
Total phenolic
content (mg/100 g)
Total flavonoid
content (mg/100 g)
Total tannin
content (%)
Antioxidant
activity
(mmol/kg)
Control 8.26±0.31*a 12.36±1.03c 673.57±12.99c 7441.67±105.52a 7.00±0.62b 7.24±0.01a
Microwave 3.79±0.03b** 13.72±0.17a 713.57±23.30a 7121.67±177.45c 7.55±0.48a 6.57±0.18c
Conventional 2.78±0.02c 12.81±0.09b 700.24±24.31b 7791.67±186.90b 7.00±0.48b 6.97±0.01b
*Standard deviation,
**values within each column followed by different letters are significantly different at p < 0.05
I. A. Mohamed Ahmed, F. AlJuhaimi, M. M. Özcan et al.
J. Oleo Sci. 74, (1) 25-34 (2025)
28
specified between 0.349 and 1.004 g EQ/100 g49）
. Total
phenol content and antioxidant activity value of several
grape seeds were established as 4.66-5.12 mgGAE/100 g and
66.41-81.40％, respectively50）
. Antioxidant activities of grape
seeds ranged from 117.4 to 536.2 µmol Trolox/g（dw）
51）
. In
the experiments reported by Samoticha et al.52）
, the total
phenolic content of white grapes varied from 1974.9 to
3884.4 mg/100 g, while it ranged from 1037.0 to 5759.1
mg/100 g in red grapes. The results obtained regarding bio-
active properties of the grape seed were higher than the
results of previous studies49, 52）
. In general, climatic factors
such as grape variety, temperature, genetic structure, ma-
turity status, harvest time and cultural factors are thought
to be effective factors on some chemical and bioactive
characteristics of the grape seeds.
3.2 The phenolic compounds of raw and roasted grape
seeds
The phenolic quantitative values of the grape seeds
roasted in microwave and conventional oven are known in
Table 2. Table 2 shows that unroasted（control）and roasted
grape seeds are rich in phenolic components. The phenolic
compounds established in the highest quantities in grape
seeds were catechin, rutin, gallic acid, quercetin, and
3,4-dihydroxybenzoic acid, respectively. Catechin and rutin
values of the grape seeds were specified to be between
435.30（CO）and 581.57 mg/100 g（control）to 94.94（CO）
and 110.53 mg/100 g（MW）, respectively. While gallic acid
quantities of the seed samples are established between
21.06（control）and 101.79 mg/100 g（MW）, quercetin values
of the grape seeds were assigned to be between 56.59
（control）and 77.81 mg/100 g（CO）. In addition, p-coumaric
acid and resveratrol quantities of the grape seeds were
defined to be between 15.43（control）and 22.98 mg/100 g
（CO）to 12.50（CO）and 29.57 mg/100 g（MW）, respectively.
Also, 3,4-dihydroxybenzoic acid quantities of the grape
seeds were stated between 34.59（CO）and 43.52 mg/100 g
（control）. Also, kaempferol values of the grape seeds were
established to be between 13.63（control）and 30.00 mg/100
g（MW）. The quantities of other phenolic constituents in
the control and unroasted grape seeds were found below
29.57 mg/100 g. The amounts of cinnamic acid in grape
seeds ranged from 3.90（control）to 7.95 mg/10 g（CO）. The
amounts of most of the phenolic compounds（gallic acid, p-
coumaric acid, quercetin, cinnamic acid and kaempferol）in
grape seeds increased with roasting. In addition, 3,4-dihy-
droxybenzoic acid, catechin, caffeic acid and syringic acid
values of the grape seed extracts decreased significantly
with roasting. While the rutin and resveratrol values of the
grape seeds roasted in the microwave were higher than
those roasted in control and CO, the phenolic acid amounts
were found to be lower. In general, the quantity of phenolic
constituents of the grape seeds roasted in the microwave
was higher than the ones roasted in the conventional oven.
Therefore, if the grape seeds will need to be roasted, it is
thought that it is important to roast the grape seeds in the
microwave because of these properties. It was reported by
Pastrana-Bonilla et al.53）
that phenolic components are dis-
persed at different rates in the peel, stem, leaf and seed of
the grapes. Gallic acid（7.22-161.74 mg/100 g）, catechin
（143.63-1067.0 mg/100 g）and epicatechin（89.21-371.65
mg/100 g）were found in extract of grape seeds54）
. Vanillic
acid, catechin, protacatechuic, coumarin, gallic, ferulic,
catechol, chlorogenic, synergic, pyrogallol and caffeic acid
contents of grape seeds were defined as 9.85, 1799.29,
210.00, 216.27, 2823.03, 33.42, 33.90, 3903.4, 19.50, 45.23
Table 2 Phenolic compounds of grape seeds.
Phenolic compounds (mg/100 g) Control Microwave Conventional
Gallic acid 21.06±0.68*c 101.79±0.16a 81.23±2.25b
3,4-Dihydroxybenzoic acid 43.52±0.15a** 42.20±1.54b 34.59±3.18c
Catechin 581.57±31.26a 445.21±28.09b 435.30±23.20c
Caffeic acid 23.46±2.74a 18.42±2.37b 12.42±1.18c
Syringic acid 26.08±1.28a 25.95±4.55b 24.10±0.91c
Rutin 107.89±13.60b 110.53±11.59a 94.94±9.49c
p-Coumaric acid 15.43±2.95c 20.37±1.53b 22.98±2.09a
Ferulic acid 21.21±2.66b 19.07±1.92c 26.55±3.21a
Resveratrol 21.04±2.57b 29.57±1.04a 12.50±2.00c
Quercetin 56.59±2.87c 66.96±9.52b 77.81±0.97a
Cinnamic acid 3.90±0.31a 7.90±1.04bc 7.95±0.98b
Kaempferol 13.63±1.52c 30.00±2.93a 23.74±3.31b
*Standard deviation,
**values within each row followed by different letters are significantly different at p < 0.05
Phytochemical and Fatty Acid Composition of Grape Seeds
J. Oleo Sci. 74, (1) 25-34 (2025)
29
and 5.33 mg/100 g, respectively15）
. Gallic acid, vanillic acid,
caffeic acid, syringic acid, protocatechuic acid, chlorogenic
acid, p-coumaric acid, quercetin hydrate contents of Pusa
Navarang and Merlot grape seeds were found as 1332 and
689.8, 3.4 and 2.8, 243.7 and 306.7, 44.0 and 52.6, 78.8 and
84.4, 1013.2 and 258.8, 341.3 and 212.2, 28.7 and 124.7 mg/
L, respectively55）
. In other study, Godevac et al.56）
reported
that some grape cultivars grown in Serbia contained 4.30
to 22.48 mg/100 g gallic acid, 0.78 to 2.44 mg/100 g proto-
catechuic acid, 0.81 to 7.04 mg/100 g caftaric acid and 0.24
to 1.43 mg/100 g p-hydroxybenzoic acids. Also, gallic acid,
（＋）-catechin, 3,4-dihydroxybenzoic acid, 1,2-dihydroxy-
benzene, caffeic acid, rutin-trihydrate, apigenin-7-gluco-
side, resveratrol quantities of grape seeds were identified
between 44.041-221.492, 56.423-480.509, 31.471-168.733,
82.626-556.198, 31.152-174.288, 64.207-231.542, 45.231-
194.638 and 12.0-197.508 mg/100 g, respectively52）
. The
results obtained regarding the phenolic components and
amounts of grape seed showed partial differences with the
results of last works. These changes can be likely due to
climatic factors and water57, 58）
. As a result, grape seeds will
be added to the components of foods due to the phyto-
chemical compounds it contains, leading to the production
of various functional food products. Therefore, the func-
tional characteristics of foods will be increased by adding
grape seed as a functional food supplement to the relevant
foods in certain proportions.
3.3 Fatty acid composition of processed grape seed oils
The fatty acid profiles and their quantities of the oils
provided from unroasted（control）and roasted grape seeds
are assigned in Table 3. The fatty acids composition results
in grape seed oil showed partial differences based on the
roasting type when compared to the control. The most
abundant fatty acid in grape seed oil was linoleic（Fig. 1）.
Behenic acid was not found in the oil obtained from the
microwave-roasted grape seed. Linoleic and oleic acid
Table 3 Fatty acid composition of grape seed oils.
Fatty acids (%) Control Microwave Conventional Oven
Palmitic 7.27±0.02b 7.06±0.04c 7.38±0.06a
Stearic 4.33±0.01b 4.33±0.01b 4.36±0.00a
Oleic 14.84±0.04b 14.87±0.01a 14.79±0.00c
Linoleic 72.75±0.14bc 73.33±0.03a 72.96±0.03b
Arachidic 0.16±0.01b 0.16±0.00b 0.17±0.00a
Linolenic 0.41±0.00a 0.25±0.00b 0.24±0.00c
Behenic 0.06±0.00b ND* 0.19±0.00a
*Standard deviation;
** values within each row followed by different letters are significantly different at
p < 0.05
***ND: Not detected
C
ontrol
Oven
MW
10 20 30 40 50 mi
n
0.0
1.0
2.0
3.0
4.0
uV(x100,000)
Chromatogram
Palmitic
Stearic
Oleic
Linoleic
Arachidic
Linolenic
Behenic
10 20 30 40 50 mi
n
0.0
1.0
2.0
3.0
4.0uV(x100,000)
Chromatogram
Palmitic
Stearic
Oleic
Linoleic
Arachidic
Linolenic
10 20 30 40 50 mi
n
0.0
1.0
2.0
3.0
4.0uV(x100,000)
Chromatogram
Palmitic
Stearic
Oleic
Linoleic
Arachidic
Linolenic
Behenic
Fig. 1 Fatty acid chromatograms of the oils extracted
from grape seeds roasted in microwave and oven.
I. A. Mohamed Ahmed, F. AlJuhaimi, M. M. Özcan et al.
J. Oleo Sci. 74, (1) 25-34 (2025)
30
amounts of the oils provided from grape seeds were re-
corded to be between 72.75％（ control）and 73.33％（ MW）
to 14.79％（ CO）and 14.87％（ MW）, respectively. While pal-
mitic acid quantities of the grape seed oils change between
7.06（MW）and 7.38％（ CO）, stearic acid quantities of the
oils obtained from grape seeds were defined to be between
4.33（control and MW）and 4.36％（ CO0）. Statistically sig-
nificant changes were monitored among fatty acid compo-
sitions of the grape seed oils based on unroasted and roast-
ing types（p＜0.05）. The quantities of other fatty acids
established in grape seed oil have been stated below
0.41％. As seen in Table 3, the stearic, oleic, linoleic, ara-
chidic and behenic acid quantities of grape seed oils were
partially decreased. The palmitic acid amount of the oil ob-
tained from the microwave-roasted grape seed oil was de-
picted to be relatively low when compared to the palmitic
acid content of the unroasted（control）and CO-roasted
grape seed oil. Grape seed oils contained 66.69-72.50％ lin-
oleic acid, 13.13-18.50％ oleic acid and 6.87-9.56％ palmitic
acid40）
. Myristic, palmitic, stearic, arachidic, oleic, linoleic
and linolenic acid amounts of five grape seed oils changed
between 0.04-0.08％, 7.86-9.19％, 4.42-5.87％, 0.15-
0.21％, 16.07-24.88％, 60.94-69.16％ and 0.32-0.64％59）
.
Palmitic, stearic, oleic, linoleic and alpha-linolenic acids of
23 grape seed oils as a mean were 6.81％, 4.04％, 13.63％,
73.15％ and 0.42％14）
. Obtained data on fatty acids and
amounts of the present study found to be similar to most of
the last studies. Although there are some partial changes in
the quantitative values of fatty acids, they were found to be
within the tolerable limits14, 40, 59）
. However, partial changes
were monitored in the amount of fatty acids. The main
reason for these differences is probably the grape variety,
harvest time or maturity status, meteorological factors
such as climatic conditions, soil structure and agronomic
activities.
3.4 The element and protein quantities of unroasted and
roasted grape seeds
The mineral quantities of the grape seeds were demon-
strated in Table 4. It was observed that the elemental
results related to the grape seeds differed based on the
roasting type when compared to the control. The most
abundant elements in the grape seeds were K, P, Mg, S, Na,
Fe, Ca, Zn, and B. K and P amounts of grape seeds were
reported to be between 6706.93（MW）and 7089.33
（control）to 2764.27（CO）and 2927.97 mg/kg（control）, re-
spectively. Also, while Mg values of the grape seed samples
are measured to be between 274.25（CO）and 320.24 mg/kg
（MW）, S amounts of the seeds were reported between
255.73（CO）and 293.09 mg/kg（MW）. Ca amount of un-
roasted and roasted grape seeds were found at very low
levels. In addition, the amounts of Ca in grape seeds were
measured between 2.69（CO）and 3.10 mg/kg（MW）. Fe and
Zn amounts of unroasted（control）and roasted-grape seeds
were recorded to be between 9.54（CO）and 15.88 mg/kg
（control）to 2.36（CO）and 2.78 mg/kg（MW）, respectively.
Also, Cu values of grape seeds varied to be between 3.56
（CO）and 4.36 mg/kg（MW）. P, K and Na values of grape
seeds increased with roasting. In addition, the Ca, Mg, S,
Cu, Mn, Ni, Zn and B contents of the grape seeds roasted
in the microwave were higher than the results of the grape
seeds roasted in unroasted（control）and CO. When our
findings were compared with the results of last reports,
some fluctuations were monitored. These changes are
likely due to agricultural factors such as variety, soil struc-
ture, analytical conditions, type of solvent and extraction
method and fertilization. The importance of these elements
requires for cofactor of many enzymes60）
. Many of the
minor elements have been reported to contribute to bio-
logical processes62）
reported that different grape varieties
contained 1255-1750 K, 24-34 Ca, 53.75-102.5 Mg, 31.32-
53.30 Na, 97.20-168.2 P, 0.71-1.88 Fe, 0.8-2.5 Cu, 0.35-0.79
Zn and 0.49-1.45 mg/kg Mn. Zn, Fe, Mn and Cu amounts of
Razaki grape seeds were 12.29, 17.30, 11.33 and 9.29 mg/
kg, respectively63）
. Fe, Mn and Cu amounts of the grape
seeds detected in this study were found high compared
with result of Göktangolar et al.63）
. Ca, Mg, P and K were
elements found in significant amounts in grape seeds.
However, the Ca results were found to be considerably
lower than the results of Kamel et al.64）
. The range of con-
centrations of minerals showed some changes when com-
pared with the last published data. These changes can be
probably due to variety, soil fertilizer, climatic conditions,
color, maturation and environmental temperature.
Table 4 Macro and micro element contents of unroasted and roasted grape seeds（mg/kg）.
Process
Macro and micro elements
P K Ca Mg S Na Fe Cu Mn Ni Zn B
Control 2927.97
±83.33*a
7089.33
±480.95a
2.92
±0.42
302.12
±42.01b
283.09
±41.54b
69.57
±0.34c
15.88
±0.74a
3.98
±0.68b
4.87
±0.40
0.47
±0.02c
2.68
±0.44b
4.31
±0.63b
Microwave 2834.94
±149.34b**
6706.93
±173.90c
3.10
±0.24
320.24
±26.03a
293.09
±22.58a
71.57
±3.32b
14.11
±2.42b
4.36
±0.12a
5.03
±0.54
0.56
±0.03a
2.78
±0.28a
4.59
±0.28a
Conventional
oven
2764.27
±104.12c
6948.95
±128.05b
2.69
±0.16
274.25
±13.16c
255.73
±12.60c
82.96
±3.06a
9.54
±6.09c
3.56
±0.32
3.95
±0.08c
0.51
±0.04b
2.36
±0.09c
3.78
±0.33c
*Standard deviation;
**values within each roe followed by different letters are significantly different at p < 0.05
Phytochemical and Fatty Acid Composition of Grape Seeds
J. Oleo Sci. 74, (1) 25-34 (2025)
31
3.5 Principal component analysis（PCA）in phenolic
compounds
Principal component analysis was conducted to establish
the effect of heat treatment on phenolic constituents, total
phenol, total flavonoid amount, total tannin content and
antioxidant activity of the grape seeds, which are shown in
Fig. 2. PCA modeling showed about 57.985％ of explained
variance for PC1; 42.015％ of variance for PC2. PC1
showed positive correlation with quercetin（0.997）, cou-
maric acid（0.994）, cinnamic acid（0.901）, while it present-
ed negative correlation with caffeic acid（−0.993）,
catechin（−0.922）, 3,4-dihydroxybenzoic acid（−0.900）
and syringic acid（−0.863）. In addition, total tannin
content（0.998）and resveratrol（0.896）were the major vari-
ables on PC2（Table 5）. Grape seed applied microwave
heating was located in the positive area, while control
sample was located in negative area of both PC1 and PC2.
4 Conclusion
The results show that roasting is effective on the mois-
ture, oil quantity, bioactive properties of grape seeds. The
increase in the total phenol value as a result of the heat
treatment is likely due to the decrease in the moisture
amount in the seeds as well as the biochemical reaction
products such as the maillard reaction caused by roasting.
The phenolic compounds established in the highest quanti-
ties in grape seeds were catechin, rutin, gallic acid, querce-
tin, and 3,4-dihydroxybenzoic acid, respectively. The quan-
tities of the most phenolic constituents in grape seeds
increased with roasting. The fatty acids composition results
in grape seed oil showed partial differences based on the
roasting type when compared to the control. The main
fatty acids in grape seed oil were linoleic, oleic, palmitic
and stearic acids. Behenic acid was not found in the oil ob-
tained from the microwave-roasted grape seed. The pal-
mitic acid content of the oil extracted from the microwave-
roasted grape seed oil was determined to be relatively low
when compared to the palmitic acid content of the un-
roasted（control）and CO-roasted grape seed oil. The most
abundant elements in the grape seed were K, P, Mg, S, Na,
Fe, Ca, Zn and B. In addition, the Ca, Mg, S, Cu, Mn, Ni, Zn,
and B quantities of the grape seeds roasted in the micro-
wave were higher than the results of the grape seeds
roasted in unroasted（control）and CO. As a result, grape
seeds are very important for human health because of phy-
tochemicals in grape seeds. Further studies will be on the
determination of bioactive components and phytochemi-
cals at different ripening stages of grape seeds.
Acknowledgements
The authors extend their appreciation to Researchers
Supporting Project Number（RSPD2025R1074）, King Saud
University, Riyadh, Saudi Arabia.
Table 5 PCA results in relation to bioactive
properties of grape seeds.
PC1 PC2
Eigenvalue 9.278 6.723
Variability (%) 57.985 42.015
Cumulative % 57.985 100.00
Correlation
Gallic 0,761 0,649
Dihyd －0,900 0,436
Catechin －0,922 －0,388
Caffeic －0,993 0,115
Syringic －0,863 0,505
Rutin －0,734 0,680
Coumaric 0,994 0,111
Ferulic 0,645 －0,764
Resveratrol －0,443 0,896
Quercetin 0,997 －0,078
Cinnamic 0,901 0,433
Kaempferol 0,662 0,750
TPC 0,702 0,712
TFC 0,466 －0,885
TTC 0,065 0,998
AA －0,459 －0,888
Fig. 2 Biplot graph drawn with results of PCA.
I. A. Mohamed Ahmed, F. AlJuhaimi, M. M. Özcan et al.
J. Oleo Sci. 74, (1) 25-34 (2025)
32
Conflict of Interest
The author declares that he has no conflict of interest.
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