Vegetable oils: do they have antioxidant activity?

Abstract

The main aim of this paper is to start the discussion about the potential antioxidant activities of oil extracts and oils from various vegetable raw materials. Many publications reported that the seed oils and essential oils possess the high antioxidant activities. In our opinion it is not so. We want to share the results of own investigations and our view at this topic. We tested: a) oils extracts from seeds of apricot, grape, peach, pumpkin, fenugreek, white bryony, sea buckthorn and rosehip; b) walnut oils (eight samples of oil); c) essential oils from needles of juniper and pine. Antioxidant activities of oils and oil extracts were appreciated by two spectrophotometric methods: method based on model oxidation reaction of Ν,-diphenyl-nphenylenediamine by azo-bis-(isobutyronitrile) as the initiator of free radicals; and procedure of DPPH free radicals scavenging. Trolox was used as standard antioxidant. Tested oil extracts from seeds did not show antioxidant capacities; on the contrary, they took part in reaction enhancing of free radical oxidation. Walnut oils demonstrated a neutral effect against free radicals. They did not enhance and did not reduce oxidative processes. Thus, the antioxidant capacities of walnut oils also were not identified. Freshly obtained essential oils from needles of juniper and pine possessed the antioxidant activity, which decreased by 2-8 times during one mount of storage. The oil extracts, vegetable and essential oils have others nutritional values and should not be considered as antioxidant. Moreover, to extend shelf-life they need to be fortified by antioxidants.