Ultrasound pretreatment combined with supercritical CO2 extraction of Iberis amara seed oil
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.
Section snippets
Plant material
I. amara seeds were collected in October 2016 from a commercial farm in Guangzhou, Guangdong Province, China. The plant materials were identified by Professor Guangzhi Wang, College of Pharmacy, Chengdu University of Traditional Chinese Medicine, Chengdu, China. The moisture content of seeds was 8.17 ± 0.37 % after oven-drying. The seeds were smashed using a disintegrator (FW100, Taisite, Tianjin, China) and particles were characterized by size classification in a standard sieve with several
Effect of USP on IASO yield
Effect of ultrasound pretreatment on IASO yield for SCE was studied for seeds subjected to different ultrasonic durations and UEDs. The yields were compared with these obtained from untreated seeds using traditional SCE and SE. The IASO yields obtained by SE and SCE combined with and without ultrasound exposure are summarized in Table 1. The USP used prior to SCE impacted markedly on IASO yield. Compared to the IASO yield acquired by SCE from untreated seeds, the IASO yield increased 11 %–28 %
Conclusions
In this study, an improved process utilizing ultrasonic pretreatment combined with supercritical CO2 extraction to obtain oil from I. amara seeds. USP of the seeds before SCE resulted in higher IASO yield. The highest IASO yield by SCE was after USP was more than 25 %. It was comparable with the yield obtained by SE using n-hexane. Furthermore, USP + SCE improved the selectivity of SCE on MUFA composition, the extractability of active phytocompounds from I. amara seeds, as well as the
Declaration of Competing Interest
The authors declare no conflicts of interest.
Acknowledgements
The authors gratefully acknowledge Professor Guangzhi Wang for identification of the plant material. The project was supported by grants from Chongqing Science and Technology Commission (cstc2013kjrc-ljrccj10003), National “111 Plan’’ Base (B06023) and the Key Projects of Basic Science and Advanced Technology Research of Chongqing City (cstc2015jcyjBX0125).
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