The storage conditions impact on the oxidative stability and antioxidant properties of grape seed oil

Author: Mariana-Atena Poiana *, Călin Jianu, Ionel Jianu and Alexandru Rinovetz

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.