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.