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           Meri-Rastilantie 3 B, FI-00980        Journal of Food, Agriculture & Environment Vol.7 (2) : 50-53. 2009              www.world-food.net
           Helsinki, Finland
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 The storage conditions impact on the oxidative stability and antioxidant properties of
                                    grape seed oil
                            Mariana-Atena Poiana *, Calin Jianu, Ionel Jianu and Alexandru Rinovetz
               Banat’s University of Agricultural Sciences and Veterinary Medicine, Food Technology Department
          Calea Aradului 119, 300645 - Timisoara, Romania. *e-mail: atenapoiana@yahoo.com, calin.jianu@gmail.com,
                                                   alexandrurino@yahoo.com

Received 7 February 2009, accepted 10 April 2009.


                                                                       Abstract
The unrefined grape (Vitis vinifera) seed oil of two grape varieties, Merlot and Italian Riesling, was evaluated in terms of quality properties including
free fatty acid content, iodine value, saponification number, relative density, refractive index, non-saponifiable substances, peroxide value and
antioxidant properties including polyphenol content and total antioxidant capacity. The effect of different storage conditions on oxidative stability
and antioxidant properties versus time was also followed. In the case of Merlot grape seed oil exposed to daylight for 3 months at room temperature,
peroxide value was O2 20.84 meq kg-1 and after 7 months it reached 31.12 meq kg-1. For Italian Riesling grape seed oil exposed to daylight for 2 months
the peroxide value was 20.07 meq kg-1 and after 7 months 36.54 meq kg-1. After the storage of grape seed oil for 7 months at 10°C in darkness and
in artificial diffuzed light peroxide value was < 20 meq kg-1, so the upper limit of peroxide value for unrefined oil was not reached during experimental
period. The oxidation is retarded if proper storage conditions are chosen and as long as antioxidants are present. The best antioxidant properties were
displayed by the Merlot grape seed oil: total antioxidant capacity was 4.68 mM Fe2+ L-1 and polyphenol content 2.23 mM gallic acid L-1. The
oxidation process in the first months of storage was more affected by daylight than by temperature. The Merlot grape seed oil was more stable of
oxidation than Italian Riesling grape seed oil. We explain these results by retarded oxidation due to antioxidant compounds present in Merlot grape
seed oil. These compounds are able to postpone the oxidation process, depending on storage conditions, until these antioxidants are oxidized and lose
their antioxidant potential.

Key words: Grape seed oil, storage conditions, oxidative stability, antioxidant properties.




                             Introduction
Grape pomace is one of the most attractive residual sources of                stress, reducing the risk of chronic diseases, prevent LDL
valuable bioactive compounds, although it is still underutilized or           modification, inhibited the proliferation of cancer cells and
only used as agricultural conditioner. Grape seeds weigh no more              significantly reduce the serum triglycerides and cholesterol 4, 5.
than 2-3% of the fresh fruits, but amounted to 20-26% of the                  Grape seed oil is excellent for frying because of its remarkable
pomace. Therefore, the seeds could be utilized as a potential source          heat stability and the desirable butter taste imparted to fried foods.
of edible oil on an industrial scale. Grape seed oil, noticed GSO, is         It is one of the most stable cooking oils known. Phenolic
a by-product of the elaboration of wine which possesses various               compounds are present in unrefined vegetable oils, which is very
natural liposoluble antioxidants. GSO is a rich natural source of             important for the oxidative stability of polyunsaturated fatty acids
polyphenolics with strong antioxidant activity and also an excellent          of these oils. Thus, the oils examined may be used in different
source of essential fatty acids necessary for normal cell                     food and cosmetics applications to provide nutrition and health
metabolism. Grape seed oil from crushed seeds contains much                   benefits 16. The beneficial effects of a diet richer in unprocessed
unsaturated fatty acids such as linoleic acid (62-75%), oleic acid            vegetable oil may be defined by the unique antioxidant properties
and alpha-linolenic acid. Among all oils and foods, it has the                of its phenolic compounds 14, 15. To date there are only few
highest content of linoleic acid. GSO is used in cosmeceuticals               researches on the antioxidant characteristics and oxidative stability
and skincare products for many perceived health benefits. Grape               of grape seed oil stored under different conditions. The main
seed oil contains phytosterols, tocopherols, that act as free radical         parameters that determine the stability of oils toward oxidation
scavengers, which hinder the oxidizing process. Grape seed oil is             are the triglyceride composition and the presence of antioxidant
considered to be a drying oil with high vitamin E content and to              compounds 2, 8, 11, 12.
have a good effect on human health 4, 7, 18. The composition varies              Due to high content of unsaturated fatty acids in grape seed
with the grape cultivar, origin and agrotechnical measures applied            oils, their oxidative stability should be an important factor. To
in grape production 7, 18. The natural antioxidants from unrefined            better understand the beneficial effects of antioxidant compounds
grape seeds display inhibitory activities against several diseases,           in vegetable oils, it is important to investigate the storage
including cancer, heart failure and other disorders of oxidative              conditions which maintain the antioxidant properties of these oils.

50                                                                                 Journal of Food, Agriculture & Environment, Vol.7 (2), April 2009
                      Material and Methods                               were: Folin-Ciocalteu phenol reagent solution 1:10 (v/v) in distilled
Material: Grape seeds were collected from the pomace of two              water; 7.5% Na2CO3 solution; standard solution of 10 mM gallic
grape varieties, Merlot and Italian Riesling (vintage 2005),             acid (1.8755 g acid gallic in 1000 mL of 4:1 (v:v) methanol-distilled
harvested in Recas vineyard in the Western part of Romania. The          water mixture. For calibration curve preparation, 0.5 mL aliquot of
pomace of the Italian Riesling variety used for white wine               0.05-0.6 mM gallic acid solution was mixed with 2.5 mL Folin-
production was immediately separated from the must after                 Ciocalteu reagent and 2.0 mL Na2CO3 solution. Calibration curve
pressing, whereas pomace from Merlot variety was obtained after          equation was Y = -0.10149 + 1.7869X and the correlation coefficient
pressing and subsequent fermentation. The grape seeds were all           R = 0.9991. For total polyphenol content determination the
subjected to air-drying. The grape seed oil was obtained after           supernatant obtained previously was used in the case of total
pressing the dried and milled grape seeds. In our study, the oil         antioxidant capacity investigation; 0.5 mL aliquot of diluted
obtained from Merlot grape seeds was noticed M-GSO and the oil           supernatant 1:5 (v:v) with mixture methanol-distilled water 4:1 (v:v)
obtained from Italian Riesling grape seeds IR-GSO, respectively.         was mixed with the reagents described above and absorbance
The mixture obtained by pressing was filtered, and before the            was read at λ = 750 nm after 2 h. Blank solution included 0.5 mL
analysis the oil was held in darkness at 10°C for 2 weeks.               mixture methanol-distilled water 4:1 (v:v), 2.5 mL Folin-Ciocalteu
                                                                         reagent and 2.0 mL Na2CO3 solution.
Storage conditions: Oil samples were transferred to sealed
transparent glass bottles (50 mL). These were closed and subjected                              Results and Discussion
to different storage conditions: I room temperature with exposure        Physical and chemical characteristics of M-GSO and IR-GSO are
to daylight; II room temperature in darkness; III 10°C with exposure     presented in Table 1. The oil contained 0.83-0.97% of free fatty
to artificial diffused light and IV 10°C in darkness. The unrefined      acids that were probably formed by the hydrolytic activity of
oil samples were analyzed fresh, noticed 0, and after 1, 2, 3, 4, 5, 6   lipolytic enzymes during the preparation of seeds for processing.
and 7 months of storage in mentioned conditions. Periodically,           Unrefined oils can have up to 2.0% of free fatty acids, according
the oil from each bottle stored in conditions I-IV was subjected to      to the regulations for such oils. The relative density at 20°C for
determination of the peroxide value, total antioxidant capacity          M-GSO (0.9251) was higher than for IR-GSO (0.9243), but in accord
and total polyphenols. The oil samples exposed to daylight were          with other data for this unrefined oils. Higher density is quite
placed in the distance of approximately 2 m from window, not             understandable bearing in mind that the density of oil increases
exposed to direct sunlight. The room temperature was between 20          as the degree of unsaturation increases. The refractive index of
and 25°C.                                                                GSO was higher than the values for some unrefined vegetable
                                                                         oils, such as coconut oil (1.448), cottonseed oil (1.458) and palm
Determination of physical and chemical characteristics:                  oil (1.455). The non-saponifiable substances for these oils were
Refractivity index was determined at 25°C with a Carl Zeiss Abbé         less than 1%, similarly with other unrefined edible oils. The iodine
refractometer 13. Density was determined pycnometrically at              value for M-GSO (I2 136.24 g 100 g-1) was higher than for IR-GSO
20°C 13. Free fatty acid content, iodine value and saponification        (I2 127.09 g 100 g-1) in accord with unsaturation degree of each oil.
value were determined according to AOAC methods. Oxidation
rate was followed by periodic determinations of peroxide value,          Table 1. The physico-chemical parameters of unrefined GSO.
noticed PV. Peroxide value was determined according to AOAC 13
and expressed as meq O2kg of oil-1.                                       Physical-chemical parameter               M-GSO          IR-GSO
   Total antioxidant capacity was evaluated by FRAP assay 3 by.           Free fatty acid content (% oleic acid)     0.83            0.97
                                                                          Iodine value (I2 g 100 g -1)              136.24          127.09
using 300 mM acetate buffer (pH 3.6); 10 mM TPTZ (2,4,6-                  Saponification number (KOH mg g-1)        193.01          184.52
tripyridyl-S-triazine) and 20 mM FeCl3. FRAP working solution             Relative density (20°C/water at 20°C)     0.9251          0.9243
included 25 mL acetate buffer, 2.5 mL TPTZ solution and 2.5 mL            Refractive index at 20°C                  1.4664          1.4656
FeCl3 solution. Standard solution included Mohr salt 1mM L-1.             Non-saponifiable substances (%)            0.79            0.88
Aqueous solutions of known Fe2+ concentration as Mohr salt                Peroxide value (O2 meq kg-1)               1.48            1.87
were used for calibration in a range of Fe2+ 0.05-0.4 mM L-1, and
0.5 mL aliquot of each solution was mixed with 2.5 mL FRAP                 The effect of storage conditions on the formation of oxidation
solution for calibration curve preparation. FRAP reagent was used        products, expressed as peroxide value versus time of storage is
as blank. Antioxidant compounds from oil were extracted by a             shown in Figs 1 and 2. At the beginning of experiment a peroxide
mixture of methanol-distilled water 4:1 (v:v) at 20°C for 1 hour. For    value for M-GSO oil was 1.48 and for IR-GSO 1.87 meq O2 kg-1 .
antioxidant capacity determination the supernatant obtained after        The obtained values for this parameter were considered as
centrifugation was used; 0.5 mL aliquot of supernatant, diluted          satisfactory according to the international regulations on edible
with a mixture of methanol-distilled water 1:5 (v:v), was mixed          oils. The peroxide value is used for monitoring peroxide formation
with the reagents described above. After 10 min, absorbance was          in the early stages of oxidation. In the case of M-GSO exposed to
read at λ = 593 nm using spectrophotometer Specord 205 ( Analytic        daylight for 3 months at ambient temperature, peroxide value was
Jena). Total antioxidant capacity (Fe2+mM L-1) was calculated.           20.84 meq O2 kg-1 and after 7 months it reached 31.12 meq kg-1. For
Calibration curve equation was Y = -0.025391+3.3917X and the             IR-GSO exposed to daylight for 2 months the peroxide value was
correlation coefficient was R = 0.9987.                                  20.07 and after 7 months 36.54 meq kg-1. Peroxide value of the
    Total polyphenol content was quantified in accord with               GSO stored in darkness did not show a remarkable increase after
Singleton and Rossi method 17 with Folin-Ciocalteau reagent using        the first three months of storage. The registered value did not
gallic acid for the preparation of a standard curve. Chemicals used      exceed 10 meq O2 kg-1 for the GSO stored for 7 months in darkness

Journal of Food, Agriculture & Environment, Vol.7 (2), April 2009                                                                            51
                      40                                                         storage was more affected by daylight than by temperature. We
                      35
                                                                                 can observe that for both M-GSO and IR-GSO, the faster oxidation
                                                                                 occurred due to greater exposure to light.
                      30                                                           These observations are in accord with results about the oxidative
 PV (meq O2/kg oil)




                      25                                                         stability of unrefined oils 1, 6, 10, 12. In our study, the unrefined oils
                                                                                 from black grape seeds had more oxidative stability than oils from
                      20                                                         white grape seeds. We explain these results by two ways. Firstly,
                      15                                                         the oxidation process is retarded even in highly unsaturated oil if
                                                                                 antioxidant substances are present, and secondly, the oil
                      10                                                         proceeded from black grape seeds presents a higher content of
                       5                                                         polyphenols comparatively with oil from white grape seeds. PV of
                                                                                 20 meq O2kg-1, the upper limit for unrefined oils, was attained in 3
                       0
                                                                                 months in M-GSO exposed to daylight at ambient temperature
                           0   30   60     90 120 150 180 210                    and in 2 months in IR-GSO stored under same conditions. PV for
                                          Time (day)
                                         Time (day)
                                                                                 GSO stored for 7 months at 10°C both in darkness and in artificial
                               I - daylight, room temperature                    diffused light was less than 20 meq O2 kg-1, so the upper limit of
                               II - darkness, room temperature
                               III - artificial diffuzed light, 10°C             PV was not reached during investigated period. Thus, the oxidation
                               IV - darkness, 10°C                               process is retarded even in highly unsaturated GSO if proper
                                                                                 storage conditions are chosen and as long as antioxidants are
   Figure 1. Effect of light and temperature on the PV of M-GSO                  present.
   during storage.                                                                 The polyphenols are bioactive compounds with a considerable
                                                                                 antioxidant activity in oils. Many authors 5, 9, 11 have confirmed a
                                                                                 strong correlation between total phenolic content and oil stability
                                                                                 towards oxidation. The polyphenol contents are presented in
                      40
                                                                                 Table 2 and the total antioxidant capacity of GSO in Table 3. In
                      35                                                         advancement of oxidative process, monitored by peroxide value,
                                                                                 the polyphenols amount and antioxidant capacity were
                      30
 PV (meq O2/kg oil)




                                                                                 significantly reduced.
                      25                                                           The highest values of antioxidant capacity and polyphenols
                      20                                                         amount were obtained for the fresh unrefined GSO (total antioxidant
                                                                                 capacity Fe2+ 6.37 mM L-1 for M-GSO and 4.91 mM L-1 for IR-GSO;
                      15
                                                                                 polyphenol content gallic acid 2.23 mM L-1 for M-GSO and 1.92
                      10                                                         mM L-1 for IR-GSO). From obtained data it can be observed that in
                       5
                                                                                 all storage conditions M-GSO had higher antioxidant capacity
                                                                                 and amount of polyphenols than IR-GSO. In accordance with the
                       0                                                         time and storage conditions, antioxidant capacity and polyphenol
                           0   30   60    90 120 150 180 210                     content decreased. After 7 months, the highest antioxidant
                                         Time (day)
                                         Time (day)
                                                                                 capacity was registered for oil stored in darkness at 10°C (Fe2+
                               I - daylight, room temperature                    5.11 mM L-1 for M-GSO and 3.92 mM L-1 for IR-GSO). GSO contains
                               II - darkness, room temperature                   an appreciable amount of tocopherols and other bioactive
                               III - artificial diffuzed light, 10°C             compounds 4, 7. These compounds are able to postpone the
                               IV - darkness, 10°C                               oxidation process, depending on storage conditions, until these
      Figure 2. Effect of light and temperature on the PV of IR-GSO              antioxidants are oxidized and lose their antioxidant potential 2. By
      during storage.                                                            storage the antioxidant properties of GSO decreased because the
                                                                                 antioxidant compounds were lost in accordance with storage

at 10°C. The lower peroxide value of GSO was registered
for oil stored at 10°C in darkness (after 7 months PV was              Table 2. The storage time impact on the polyphenol content of unrefined
7.67 for M-GSO and 9.02 meq O2 kg-1 for IR-GSO). Higher                       GSO.
rate of increase in the peroxide value of these samples                Time of                     Polyphenol content (gallic acid mM L-1)
during the first months, but not later, can be at least                storage                   M-GSO                               IR-GSO
attributed to daylight and higher temperature. In the case              (day)          I       II      III     IV       I         II       III         IV
of M-GSO stored in darkness for 7 month at ambient                        0          2.23     2.23    2.23    2.23    1.92       1.92     1.92        1.92
temperature peroxide value increased to 21.08 meq kg-1                    30         1.62     1.94    2.07    2.16    1.45       1.66     1.81        1.85
                                                                          60         1.29     1.82    1.96    2.11    1.17       1.44     1.70        1.80
and for IR-GSO reached 26.19 meq kg-1. The PV in the                      90         1.34     1.71    1.87    1.94    1.08       1.38     1.55        1.72
case of storage in darkness at room temperature                          120         1.28     1.62    1.84    1.89    1.02       1.31     1.50         1.7
represented 67-70% of the values obtained in the case of                 150         1.21     1.58    1.75    1.84    0.91       1.19     1.43        1.63
storage in daylight at room temperature. These findings                  180         1.12     1.49    1.68    1.80    0.87       1.10     1.39        1.59
                                                                         210         1.05     1.34    1.59    1.77    0.73       1.07     1.30        1.51
show that the oxidation process in the first period of

52                                                                                    Journal of Food, Agriculture & Environment, Vol.7 (2), April 2009
Table 3. The storage time impact on the total antioxidant capacity of
       unrefined GSO.
Time of                     Total antioxidant capacity (Fe2+ mM L-1)
storage                  M-GSO                                  IR-GSO
 (day)          I       II       III      IV        I        II       III      IV
    0         6.37     6.37     6.37     6.37     5.12     4.91      4.91     4.91
   30         4.72     5.73     6.07     6.20     4.07     4.12      4.75     4.80
   60         4.16     5.17     5.94     6.12     3.14     3.81      4.60     4.57
   90         3.62     4.73     5.54     5.68     2.80     3.63      4.26     4.47
  120         3.36     4.51     5.42     5.58     2.64     3.50      4.21     4.35
  150         3.23     4.29     5.14     5.42     2.24     3.27      3.91     4.11
  180         2.87     2.92     5.06     5.24     2.12     2.98      3.74     4.05
  210         2.75     3.84     4.80     5.11     1.81     2.90      3.26     3.92


conditions. The most important factors that affected the oil stability            Winkelmann, W. 2006. Quantitation of the main constituents of some
are temperature, light and storage time.                                          authentic grape-seed oils of different origin. J. Agric. Food Chem.
                                                                                  54(17):6261-6265.
                                                                              8
                             Conclusions                                       Läubli, M.V. and Bruttel, P.A. 1986. Determination of the oxidative
                                                                                  stability of fats and oils. J. Am. Oil. Chem. Soc. 63:792-795.
The susceptibility to oxidation is affected by the storage                    9
                                                                               McDonald, S., Prenzler, P.D., Antolovich, M. and Robards, K. 2001.
conditions. In the first period of storage the oxidation process                  Phenolic content and antioxidant activity of olive extracts. Food
was more affected by daylight than temperature. The oil damage                    Chemistry 73:73-81.
was reached faster for storage in daylight at room temperature.               10
                                                                                 Monteleone, E., Caporale, G., Carlucci, A. and Pagliarini, E. 1998.
The rate of oxidation is higher in IR-GSO oil than in M-GSO because               Optimisation of extra virgin olive oil quality. J. Sci. Food Agric. 77:31-
the oil from black grape seeds has a higher content in polyphenol                 37.
                                                                              11
compounds than oil from white grape seeds. The oxidation                        Morello, J.R., Motilva, M.J., Tovar, M.J. and Romero, M.P. 2004.
process is retarded even in highly unsaturated oil if antioxidant                 Changes in commercial virgin olive oil during storage, with special
substances are present. The susceptibility to oxidation increased                 emphasis on the phenolic fraction. Food Chem. 85:357-364.
                                                                              12
                                                                                 Murkovic, M. and Pfannhauser, W. 2000. Stability of pumpkin seed
with time of storage because the antioxidant components present
                                                                                  oil. European Journal of Lipid Science and Technology 102(10):607-
in GSO were deteriorated, thus losing their antioxidant properties,               611.
and the oxidation products increased with storage time. The                   13
                                                                                 AOAC 1999.Official Methods of Analysis of AOAC. 16th edn. AOAC
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grape seed oil was influenced by storage conditions and grape                 14
                                                                                Okogeri, O. and Tasioula Margari, M. 2002. Changes occuring in phenolic
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                                                                              15
antioxidant properties of GSO. The oxidation is retarded if proper               Parry, J.W., Cheng, Z., Moore, J. and Yu, L. 2008. Fatty acid
storage conditions are chosen and as long as antioxidants are                     composition, antioxidant properties, and antiproliferative capacity of
                                                                                  selected cold-pressed seed flours. J. Am. Oil Chemists’ Soc. 85(5):457-
present. These data are important for the evaluation of the
                                                                                  464.
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                                                                                 Siger, A., Nogala-Kalucka, M. and Lampart-Szczapa, E. 2008. The
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                                                                              17
                                                                                 Singleton, V.L. and Rossi, J.A. 1965. Colorimetry of total phenolics
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Journal of Food, Agriculture & Environment, Vol.7 (2), April 2009                                                                                        53

								
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