Evening primrose oil (EPO) quality changes dependent on storage temperature and storage time

Evening primrose (Oenothera biennis L.) is a seed drug plant and a rich source of γ-linolenic acid (GLA), an unusual fatty acid with proven value as a nutrient and prescription pharmaceutical. EPO contain high amount of unsaturated fatty acids, which makes it more susceptible to the oxidative deterioration. Therefore a suitable storage condition can improve the seed oil quality and delay it's spoliation (rancidity). Present trail was executed to clarify the effects of different storage temperatures (4°C, 21°C, 35°C) and storage time (0–4 months) on Oenothera biennis extracted crude oil and unextracted oil (seed) fatty acid composition and their stability during storage period. The results showed that the oil and protein content in the whole seed (unextracted oil) were significantly influenced by storage time. The lowest amount of seed oil content was observed at the last storage month (24,3% in compare to 26,0% in control). In contrast to that, the highest amount of protein content was measured in the last two months (15,4%) of storage. γ-linoleic acid and linolenic acid content were influenced by storage time both in unextracted oil and extracted crude oil. The amount of these two fatty acids shows a linear decrease during storage time. Free fatty acid was influenced by all treatment factors used for both oil samples. The highest amount of free fatty acid was observed when seeds were stored under high temperature during four months (3,4% FFA). The lowest free fatty acid content was observed in the low temperature. The content of oleic acid, linoleic acid and γ-linolenic acid of extracted oil did not change under different combination of light and temperature. According to the obtained results it can be concluded that extracted and unextracted oil compositions are more stable under cold temperature during a short time and extracted crude oil has more stability than unextracted oil.