1. Introduction
Sensitivity to oxidation of edible oils with higher unsaturation levels changes organoleptic properties and decreases the shelf life of the oil (Abdelazim et al., 2013). One of the practical strategies that can be used to increase oil oxidative stability during processing and storage is addition of antioxidant compounds. Edible oil industries use chemicals and synthetic antioxidants in preservation of oils. However, health risks of synthetic antioxidants and society’s growing demand for products that contribute to improving the quality of life has encouraged researchers to look for naturally-occurring alternatives antioxidants with comparable antioxidative properties and health benefits (Elaigwu et al., 2019; Farag et al., 2007; Iqbal & Bhanger, 2007; Ribeiro & Jorge, 2017). The popularity and desire to consumption of cold-pressed oils is continuously increasing among consumers. Recovery and preserving more bioactive compounds during the pressing process is the advantage of cold-pressed oils over refined oils. Lipid oxidation of oils can not only produce rancid odors, unpleasant flavors and discoloration, but can also decrease the nutritional quality and safety due to degradation products, resulting in harmful effects on human health when it is consumed (Böhm et al., 2013). In addition to fatty acid profile of oils, antioxidant polarity, structure, concentration, and mutual ratios influences oil oxidation mechanisms and rates (Choe & Min, 2006; Sielicka et al., 2014).
The sweet smell and good taste make sesame oil a natural and desirable salad or cooking oil, especially in Asian countries. Depends on variety, genetics, environment, and ecological factors, the oil content of sesame seed from different countries has been estimated to be 50.9 - 55% which contains 80% unsaturated fatty acids (such as oleic acid and linoleic acid) and less than 20% of saturated fatty acids (such as palmitic and stearic acids). Sesame oil also contains significant amounts of sesamol, sesamolin, and sesamin, which have antioxidant activities (Yermanos et al., 1972; Zanjani et al., 2020). For cold-pressed oils rich in polyunsaturated fatty acids (PUFAs), the effectiveness of antioxidants is of particular importance.
Antioxidants such as flavonoids, tannins, coumarins, curcumanoids, xanthons, phenolics, lignans and terpenoids are found in various plant parts (e.g. fruits, leaves, seeds and oils). For this reason, there is growing interest in separating these plant antioxidants and using them as natural antioxidants (Jeong et al., 2004). More than 90 species of the Senjed (Elaeagnus angustifolia L. ) are mainly distributed in subtropical regions of Asia, Europe and North America1 which are rich in terms of phytochemicals such as flavonoid compounds, sitosteroles, cardiac glycosides, terpenoids, coumarins, phenol carboxylic acids, saponins, carotenoids, vitamins, and tannins. Flavonoids which are mainly present in fruits and vegetables, due to their phenolic hydroxyl groups, are able to chelate metals, reduce lipid peroxidation and have shown a high antioxidant and free radical scavenging activities (Hamidpour et al., 2017; Saboonchian et al., 2014).
Despite studies on the antioxidant properties of various parts of Senjed fruit, literature review showed that the practical use of its extract as an antioxidant in edible oils is very limited. On the other hand, unexpectedly, the oxidative stability of sesame cold-pressed oils produced in Iran is lower (Farmani et al., 2019; Zanjani et al., 2020) than the national standard (INSO, 2016; INSO, 2013) recommendations (13 and 12 h for frying and blend oil, respectively). Therefore, given the presence of potentially useful bioactive compounds in Senjed and the interest in replacing synthetic antioxidants with natural ones, the main objective of this study was to evaluate the effectiveness of Senjed peel aqueous extract as a natural antioxidant at different concentration levels (0, 100, 200, 400, and 600 ppm) compared to widespread synthetic antioxidant TBHQ (200 ppm), on shelf life and oxidative properties of cold-pressed sesame oil.