Sensory evaluation


   
 

276 

 

Journal homepage: www.fia.usv.ro/fiajournal 

Journal of Faculty of Food Engineering,  

Ştefan cel Mare University of Suceava, Romania  

Volume XVII, Issue 4-2017, pag. 276  - 281 

 

 

ANTIOXIDANT ACTIVITY AND TOTAL PHENOLIC CONTENT OF  

GRAPE SEEDS AND PEELS FROM ROMANIAN VARIETIES 

 

Mădălina IUGA
1
, Sorina ROPCIUC

1
, Silvia MIRONEASA*

1
 

 
1Faculty of Food Engineering, Stefan cel Mare University, Suceava,  

Universitatii str. 13, Suceava, Romania, silviam@fia.usv.ro 

*Corresponding author 

Received 19th October 2017, accepted 8th December 2017 

 

 

Abstract: Grape seeds and peels are valuable by-products from wine production industry that can be 

valorized in food production. Both grape seeds and peels have a great amount of antioxidants and 
polyphenolic compounds. The aim of this study was to investigate the total phenolic content of red and 

white grape seeds and peels and to establish the optimal solvent concentration for highest extraction 

yield. For this purpose, Folin Ciocâlteu method was used to achieve the phenols content and the 

antioxidant activity was estimated using 2,2 – diphenyl-1-1picrylhydrazyl (DPPH) reagent. The total 
phenolic content ranged from 81.13 mg GAE/g for red peels, 93.47 mg GAE/g for white peels, to 

128.47 mg GAE/g for red seeds and 164.70 mg GAE/g for white seeds. The One-Way ANOVA method 

was used to see if there are differences between the antioxidant activities depending on the solvent 
concentration. The results showed that the methanol concentration significantly (p < 0.05) influences 

the antioxidants extraction. The inhibition percent IC50 ranged from 0,24 to 4,37 μg/mL for white 

peels, from 3,12 to 6,29 μg/mL for red peels, from 5,53 to 5,90 μg/mL for white seeds and from 4,59 to 

6,14 μg/mL for red seeds. This study highlighted the possibility to use grape seeds and peels as food 
ingredients or natural antioxidant to extend the shelf life of food, especial of lipids and lipid-

containing foods because of their high antioxidant activity and total phenolic content. 

 

Key words: grape seeds, grape peels, antioxidant activity, total phenolic content. 

 

 

1. Introduction 

 

Grapes, one of the most cultivated fruits in 

the world, are used in high proportion 

(80%) in wine-making production [1]. 

Wine industry has an adverse 

environmental impact because of residual 

phenols of by-products resulted from 

grapes processing. Relative high amounts 

of phenolic compounds in waste are a 

problem for flora and fauna from discharge 

zones due to their inhibition of germination 

properties [2].  

Grape pomace generated in wine- making 

process is a valuable by-product for oil 

extraction and some active compounds, 

such as dietary fiber, polyphenols, 

anthocyanins, flavonols and resveratrol [3, 

4]. The wine-making grape pomace 

includes as main components peels and 

seeds. The polyphenols and other 

compounds with antioxidant activity are 

present in grape peels and seeds. The 

quantitative and qualitative distribution of 

polyphenolic compounds in grape peels 

and seeds depends on grape variety, 

harvesting conditions, geographic location 

of the culture, soil, vinicultural techniques, 

winemaking process, etc. [5]. 

Many studies showed that the phenolic 

profile is related to the fruit maturity level: 

it increases with the ripening level increase 

[6]. During the winemaking process, part 

of the phenolic compounds in grapes is 

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Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XVI, Issue 4  – 2017 

 

 
Mădălina IUGA, Sorina ROPCIUC, Silvia MIRONEASA, Antioxidant activity and total phenolic content of grape seeds 
and peels from Romanian varieties, Volume XVI, Issue 4 – 2017, pag. 276 – 281 
 

277 

 

transferred to wine, but a high amount still 

remains in the grape by-products, mainly 

in the grape pomace. More than 70% of 

phenols from grapes rest in pomace [5].  

The phenolic compounds are present in 

plants and have many biological functions. 

The researchers revealed hundreds of 

polyphenols in edible plants [7]. In wine 

pomace there are flavonoid compounds 

such as anthocyanins, flavonols, flavan-3-

ol, tannins and non-flavonoid substances, 

especially resveratrol [8] and phenolic 

acids [9]. In red pomace there are many 

antochianyns, while in white pomace the 

flavonols are in higher quantity [10]. The 

total polyphenolic content of grape pomace 

can be influenced by the differences 

between white and red wine making 

processes [11].  

In grape peels there are elagic acid, 

resveratrol, myricetin, quercetin, 

kaempferol, epigalocatechine. The results 

showed by many researches revealed the 

fact that the phenolic content is higher in 

red peels than in white peels because the 

monomeric anthocyanins are absent from 

white peels [10].  

In grape seeds catechin, epicatechin, malic 

acid and galocatechin are the most 

important phenols. The phenolic content of 

grape seeds is greater than of grape peels 

[12]. 

The most important operation for phenols 

recovery from grape seeds and peels is the 

extraction. Various solvents including 

ethanol, methanol, ethyl ether, etc. were 

used by researchers for the phenols 

extraction. Also, various techniques, such 

as ultra-sonication, stirring and shaking 

were applied. The most used solvent is 

methanol or methanol/water mixtures [13]. 

A higher total phenolic content gives a 

better antioxidant activity [14, 15]. The 

inclusion of antioxidants is a method to 

prolong shelf life of food products while 

they add extra health benefits. 

Polyphenolic compounds exhibits health 

benefits due to its cardioprotective and 

anti-inflammatory effects, anti-ulcer and 

anti-carcinogenic activity [16]. 

There are many researches about the 

phenolic compounds and antioxidant 

activity from grape peels and seeds, but 

there are very few reports that compare the 

total phenolic content distribution between 

peels and seeds among different varieties. 

The aim of this study was to determine the 

antioxidant activity and the total phenolic 

content of grape seeds and peels from two 

wine pomace varieties, red and white. This 

study wants to underline the importance of 

grape seeds and peels with respect their 

potential as a source of natural antioxidants 

and as an alternative to the reuse of by-

products from winemaking process.  

 

 

2. Materials and methods 

 

2.1. Materials 

Grape seeds and peels from red and white 

wine grape pomace provided by the 

viticulture center Jaristea, Odobesti 

ecosystem were used in this study. Grape 

seeds and peels were separated manually 

from dried grape pomace and ground in a 

speed grinder to obtain grape seeds and 

grape peels flours.  

As reagents of analytical grade, standards 

of gallic acid, ascorbic acid, methanol, 

calcium carbonate, 2,2 – diphenyl-1-

1picrylhydrazyl (DPPH) reagent and  

Folin-Ciocâlteu phenol reagent purchased 

from Sigma-Aldrich and Merck were used. 

 

2.2. Methods 

2.2.1. Antioxidant activity 

The antioxidant activity was achieved by 

DPPH method. The extracts were prepared 

according to Xuetao and collaborators 

method [17], with some modifications. 4 g 

of sample was extracted with 15 mL of 

solvent (methanol: distillated water, 0:100, 

60:40, 70:30 and 80:20). For this purpose, 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XVI, Issue 4  – 2017 

 

 
Mădălina IUGA, Sorina ROPCIUC, Silvia MIRONEASA, Antioxidant activity and total phenolic content of grape seeds 
and peels from Romanian varieties, Volume XVI, Issue 4 – 2017, pag. 276 – 281 
 

278 

 

the mixes were ultra-sonicated at 40 ºC, at 

25 Hz for 30 minutes. Then, they were 

centrifuged at 3000 rpm for 5 minutes. The 

supernatant was collected and the residue 

was mixed with 15 mL solvent and 

centrifuged again. This operation was 

repeated 3 times. The supernatants were 

collected and used for analysis.  

Each extract was diluted to 50%, 40%, 

30%, 20% and 10% with the 

corresponding solvent (methanol: 

distillated water, 0:100, 60:40, 70:30 and 

80:20). 2 mL of sample was mixed with 1 

mL of DPPH reagent and the absorbance at 

517 nm wavelength was read immediately 

by using UV-Vis-NIR spectrophotometer 

(Shimadzu Corporation, Japan). A blank 

sample was prepared for each solvent.  

The free radicals inhibition percent IC50 

was calculated using Eq.1 [18]: 

 

IC50 = [1-(A517sample-A517 blank] x 100    (1) 

 

where A517 blank is the absorbance value of 

the control sample and A517sample is the 

absorbance value in the presence of the 

extract sample and standard. 

 

2.2.2. Total phenolic content 

The phenolic content of grape seeds and 

peels were determined using the Folin 

Ciocâlteu method. 2 g of samples were 

mixed with 4 mL solvent (methanol: 

distillated water, 70:30) and shacked for 5 

minutes on the orbital shaker. Then, the 

mixes were centrifuged at 6000 rpm for 10 

minutes. The supernatant was collected 

and the residue was extracted again with 4 

mL solvent, as it is described above. The 

two supernatants were mixed and used for 

determination. 0.5 mL of extract was 

mixed with 0.5 mL of Folin Ciocâlteu 

reagent and 3 mL of Na2CO3 20%.  

The mixture was diluted with distillate 

water to final volume of 10 ml. The 

samples were allowed to stand for 30 

minutes and the absorbance was read at 

750 nm by using UV-Vis-NIR spectro-

photometer (Shimadzu Corporation, Japan). 

A blank sample was prepared with 

distillate water. Each determination was 

made in triplicate. The calibration curve 

was made with different gallic acid 

concentrations. The results were expressed 

as milligrams of gallic acid equivalents 

(GAE) per g of extract (mg GAE / g). 

 

2.2.3. Statistical analysis 

The results were expressed as the mean 

values  S.D. of three parallel 

measurements. One-way ANOVA method 

from Microsoft Excel 2007 was used to 

test the effect of variation factors – 

different samples on variable IC50. A 

difference was considered statistically 

significant at p  0.05. 

 

3. Results and discussion 

 

3.1. Antioxidant activity 

Figure 1 shows the total phenols content, 

measured as absorbance at 517 nm, for the 

white and red grape peels extracts in water 

and methanol mixture at different 

proportion and at various extracts 

concentration. Statistical analysis of the 

data shows that the extraction solvent had 

a positive effect (p < 0.05) on the 

antioxidant activity by increasing it with 

concentration increase. According to the 

results obtained, there were significant 

differences (p < 0.05) between the total 

phenolic content of each seed and peel 

extract. White grape pomace had higher 

solvent extraction yield than the red 

varieties. 

The total phenolic content for the white 

and red grape seeds extracts in water and 

methanol mixtures at different proportions 

(0:100, 60:40, 70:30 and 80:20, methanol: 

distillated water) and at various extracts 

concentration is showed in Figure 2.   
 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XVI, Issue 4  – 2017 

 

 
Mădălina IUGA, Sorina ROPCIUC, Silvia MIRONEASA, Antioxidant activity and total phenolic content of grape seeds 
and peels from Romanian varieties, Volume XVI, Issue 4 – 2017, pag. 276 – 281 
 

279 

 

 
a) 

 
b) 

Fig. 1. Absorbance curves for extracts 

diluted with aqueous methanol solutions 

(0:100, 60:40, 70:30 and 80:20, methanol: 

distillated water) from: a) white peels; b) red 

peels  

 

The results obtained highlight that the 

optimal mixture solvent for white grape 

peels and seeds is methanol/water in ratio 

80:20, while the antioxidants from red 

peels and seeds are best extracted in water 

(0:100).  

The parameter used to estimate the 

antioxidant activity is IC50 and it 

represents the antioxidant amount 

required to decrease the initial DPPH 

concentration by 50%. Low IC50 values 

indicated a high antioxidant activity [19].  

As it is shown in Figure 3, grape peels 

antioxidants are best extracted with lower 

methanol concentrations as compared to 

grape seeds.   

 
a) 

 
b) 

Fig. 2. Absorbance curves for extracts diluted 

with aqueous methanol solutions (0:100, 60:40, 

70:30 and 80:20, methanol: distillated water) 

from: a) white seeds; b) red seeds 

 

 
 

 
Fig. 3. IC50 values for grape seeds and peels 

extracts 

 

The fact that the aqueous extracts from 

white peels and white seeds had the 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XVI, Issue 4  – 2017 

 

 
Mădălina IUGA, Sorina ROPCIUC, Silvia MIRONEASA, Antioxidant activity and total phenolic content of grape seeds 
and peels from Romanian varieties, Volume XVI, Issue 4 – 2017, pag. 276 – 281 
 

280 

 

highest antioxidant activity underlines 

the possibility to use these by-products as 

natural additives in food products.  
 

3.2. Total phenolic content 

  

The variation of total phenolic contents 

of grape seeds and peels from white and 

red grape varieties are showed in Figure 

4. 

 

 
Fig.4. Total phenolics content in grape 

peels and seeds from red and  white varieties 
 

Regarding the total phenolic content, 

white peels have a higher amount of 

polyphenols than red peels, while white 

seeds have higher polyphenolic content 

than the red ones (Figure 3). The results 

revealed that grape seeds have more 

polyphenols than grape peels, in 

according to the results obtained in other 

studies [12, 20]. The main interest in 

phenolic compounds from grape by-

products lies in their antioxidant 

capacity. 

 

4. Conclusion 

  

Solvent concentration is an important 

parameter that influences significantly 

the antioxidants extraction and 

consequently the antioxidant activity. 

The results for total phenolic content of 

grape seeds and peels confirmed other 

specialist’s hypothesis: grape seeds are 

richer in polyphenols than grape peels.  

In conclusion, grape seeds and peels are 

a natural source of phenolic compounds 

with high antioxidant activity. These by-

products can be valorized in food 

industry as a source of natural phenols 

with the antioxidant power similar to that 

of synthetic antioxidants. 

  

5. Acknowledgements 

 

This work was supported by a grant of the 

Romanian National Authority for 

Scientific Research and Innovation, 

CNCS/CCCDI – UEFISCDI, project 

number PN-III-P2-2.1-BG-2016-0136, 

within PNCDI III. 

 

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Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XVI, Issue 4  – 2017 

 

 
Mădălina IUGA, Sorina ROPCIUC, Silvia MIRONEASA, Antioxidant activity and total phenolic content of grape seeds 
and peels from Romanian varieties, Volume XVI, Issue 4 – 2017, pag. 276 – 281 
 

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