Ultrasound pretreatment combined with supercritical CO₂ extraction of Iberis amara seed oil

Highlights

• Iberis amara seed oil was obtained by ultrasound assisted supercritical CO₂.

• Ultrasound improved the yield and the quality of the oil.

• Ultrasound enhanced the contents of various phytochemicals in the oil.

• Ultrasound combined with supercritical CO₂ was efficient for oil extraction.

Abstract

Ultrasound pretreatment (USP) combined with supercritical CO₂ extraction (SCE) was carried out to obtain Iberis amara seed oil (IASO) in the present study. The maximal oil yield (25.28 ± 0.39 %, w/w, dry basis) acquired by SCE from ultrasound-treated seeds with ultrasonic energy density of 1.25 W/mL during 10 min, was 28 % higher than that obtained from the untreated seeds. Furthermore, the obtained oil samples were determined for physicochemical properties, fatty acid profile, contents of various phytocompounds and antioxidant activity. The results showed that USP + SCE resulted in better oil quality, slightly enhanced the selectivity of monounsaturated fatty acids in the obtained oil, as well as improved the contents of phytocompounds and antioxidant activity of IASO samples, when compared with traditional techniques. Our study revealed that ultrasound pretreatment combined with SCE can be considered efficient and environmentally-friendly for plant oil extraction at industrial scale. Furthermore, IASO has high nutritional value. Therefore, Iberis amara seeds can potentially be used as easily available sources of natural plant oil in the pharmaceutical, biodiesel and dietary supplement industries.

Introduction

Iberis amara, belongs to the Brassicaceae family and originates from southern Europe. It is cultivated worldwide as a popular aromatic ornamental bloomer and also used in commercial medicine for treatment of gastrointestinal disorders (Jehn, 1958). Iberis amara has been reported to possess significant anti-ulcerogenic, anti-inflammatory, anti-bacterial, anti-cancer, insecticidal and antioxidant activities, which are attributed to mustard oil glycosides, flavones, amines and cucurbitacines in the plant (Liu et al., 2019b). It also has good curative effects on asthma, dropsy and bronchitis (Schempp et al., 2003). Recent research on I. amara have focused primarily on cultivation techniques rather than on studying its active substances. To the best of our knowledge, no reports have been published on the variation of nutrients and fatty acid (FA) composition in I.amara seed oil (IASO).

Plant seeds are rich in oily substances that can be used in cosmetics, lubrication and biofuel as well as for edible purposes (Porto et al., 2016). The main components of plant oils are triglycerides, free FAs, phospholipids, glycolipid, tocopherols, waxes, carotenoids, chlorophylls, hydrocarbons, phenols and sterols (Dyer et al., 2008). FAs are rarely free in the cell but are primarily located in triglycerides (Dejoye et al., 2011). Plant oil usually contains abundant monounsaturated fatty acid that can reduce levels of total cholesterol and LDL cholesterol and improve insulin sensitivity (Gillingham et al., 2011). Furthermore, phospholipids and glycolipids support cell membrane structure and function, and also have antiangiogenic activity (Marcus and Schwarting, 1976). Tocopherols have prominent antioxidant, neuroprotective and cancer-preventive effects, and are essential components in the human diet (DellaPenna and Pogson, 2006). Carotenoids can effectively enhance the immune system (Elisabet et al., 2012) whereas phenols exhibits a wider range of biological activities, such as antineoplastic, antimitotic, antiviral and anti-inflammatory effects (Saladino et al., 2008). Sterols control membrane fluidity and permeability and have the ability to lower plasma cholesterol and LDL cholesterol (Piironen et al., 2000).

In order to acquire these lipids from plants, various extraction techniques have been developed. Extraction of plant oil is conventionally done by pressing and Soxhlet extraction (SE). These are straightforward and inexpensive techniques. However, pressing results in low oil yield and SE suffers from drawbacks such as toxicity and producing low quality products. Furthermore, the SE process requires large amounts of organic solvents, long duration, and degradation of thermosensitive substances occurs (Luque-Garcia and Castro, 2004). Supercritical CO₂ extraction (SCE) is emerging as a popular technique for recovery of diversified bioactive substances from plants. SCE was developed to overcome the limitations of the orthodox extraction techniques. It has many advantages, such as being eco-friendly, highly selective and lacking solvent residue in the extract (Yang and Wei, 2016). It is operated under relatively low pressures and moderate temperatures owning to the modest critical constants of CO₂ (Klejdus et al., 2010). CO₂ is a safe, cheap, readily available, non-toxic and non-inflammable gas. Supercritical CO₂ (SCO₂) has high solubility and mass transfer rate owing to low viscosity and high diffusivity (Yang and Wei, 2016). In addition, it is a Generally Recognized as Safe (GRAS) solvent and extracted products can be used for food and pharmaceutic applications (Bimakr et al., 2013). However, it has high running costs and it is difficult to apply mechanical vibrations during the extraction process due to the hyperbaric environment: This leads to slow extraction kinetics (Yang and Wei, 2016).

Efforts should be made to apply novel techniques to pretreat raw material prior to SCE to achieve superior performance with an economical and efficient extraction process. This will optimize the use of natural resources and economize the operating costs. Ultrasound is a safe technique producing high-frequent ultrasonic waves that can promote cavitation phenomena and enhance energy and mass transfer in liquid media. This may lead to rupture of plant cell walls, which will favor penetration of solvents (Chemat et al., 2017). However, ultrasound extraction is not selective to target compounds and the extract leaves a large amount of organic residue. Ultrasound pretreatment combined with SCE provides advantageous complementarities and superior extraction performance. Several studies on ultrasound assisted SCE have been reported. Santos et al. reported that capsaicinoids yield from malagueta pepper was increased by 77 % with the assistance of ultrasound compared to sole SCE (Santos et al., 2015). Our previous study showed that the cucurbitacin E yield from Iberis amara seeds was enhanced by 26.1 % after introduced ultrasound into SCE (Liu et al., 2020). Hu et al. reported that ultrasound-assisted SCE provided 14 % increase of total oil and coixenolide from adlay seed compared to SCE (Hu et al., 2007). Abovementioned findings indicate that yields of various target compounds for SCE can be significantly improved using ultrasound.

An improved SCE process by introducing ultrasound was proposed to obtain the oil product from Iberis amara seeds in this study. The aim of this study was to evaluate the effects of ultrasound pretreatment (USP) on SCE process of I. amara seeds, in terms of influence on oil yield and its physicochemical properties, fatty acid composition, contents of various phytocompounds and antioxidant activity. The extraction data were compared with traditional SE and SCE.