Oil extraction from seeds of Nettle and evaluation of its qualitative properties during storage

Abstract

Abstract Background: Fats and oils are one of the main ingredients in the food formulation. Today, the global demand for vegetable oils has increased, and as a result, findings and research on oils extracted from vegetable seeds have been taken to find new oil seeds. Roman nettle (Urtica pilulifera L.) is an annual plant whose seeds are rich in oil and valuable phytochemicals. Due to the prevalence of Roman nettle plant in the region and its widespread use of seeds in medicine and limited information on its oil and the effect of moisture adjustment on Roman nettle seed oil. Therefore, the aim of this study was to evaluate the effect of the seed moisture content on oil recovery, and to assess the oil composition and quality during storage at room temperature. Materials and Methods: After preparing the oil seeds to find the optimal moisture to increase the oil extraction efficiency, the Urtica pilulifera L. seeds were divided into five parts and their moisture content was adjusted to 0, 2.5, 5, 7.5 and 10%, respectively, and then under extraction. The oil was extracted by cold pressing and then the samples were stored at room temperature (25°C) for 3 months and its quality characteristics (acid value, peroxide value, fatty acid content, oxidative stability by rancimet test and Schaal test, total phenolic compounds, phytosterol and tocopherol content) were evaluated. Results & Conclusion: The highest oil yield (31.5%) was found in the seeds containing 5% moisture. Acid and peroxide values increased with both moisture content increase and during storage. Moreover, an increase in seed moisture content decreased the oxidative stability (from 8.1 to 6.3 h), carotenoids (from 25 to 14 mg/kg), chlorophylls (from 742 to 486 mg/kg), and phenolic contents (from 134 to 97 (mg caffeic acid/kg oil)) of the extracted oils. Fatty acid profile and phytosterols were not significantly influenced by the moisture content of the seeds and storage. Total phenol contents and γ-tocopherol levels increased during storage, but carotenoids, chlorophylls and α-tocopherol levels decreased. Based on results, Also, adjustment of the moisture content of the seeds prior to extraction improves the oil yield. Thus, it can be concluded that Roman nettle seed oil is a good source of phytochemicals and essential fatty acids, so due to its oxidative stability, it can be used as salad and cooking oils as well as in blended with other oils.

Keywords: Roman nettle, Urtica pilulifera, Seed oil, Fatty acids, Cold-press, Tocopherols, Storage