Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Microwave pretreatment as a promising strategy for increment of nutraceutical content and extraction yield of oil from milk thistle seed Bahram Fathi-Achachlouei a, ⁎ , Sodeif Azadmard-Damirchi b , Younes Zahedi a , Rezvan Shaddel a a Department of Food Science and Technology, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, P.O. Box 56199-11367, Ardabil, Iran b Department of Food Science and Technology, Faculty of Agriculture, University of Tabriz, P.O. Box 51666-16471, Tabriz, Iran ARTICLE INFO Keywords: Milk thistle oil Microwave pretreatment Physicochemical properties Nutraceuticals content ABSTRACT In this study, seeds of Milk thistle (Silybum marianum L.) as a biomedical plant were pretreated with microwaves (800 W) for 2 and 4 min, to evaluate the process of intensifying oil extraction efficiency, physicochemical properties, nutraceuticals content, and fatty acids profile of milk thistle seeds oil extracted from Iranian ecotype, Khoreslo. Results showed that microwave pretreatment of Milk thistle seed increased the oil extraction yield (by 6%), total phenolic content (by 12.2%), phytosterols (by 25%), and tocopherols (by 37.5%) of the oil obtained by solvent. Some physicochemical properties of seed oil such as chlorophyll content (0.55–1.73 mg pheophytin/ kg oil) and saponification value (179–187 mg KOH/g oil) increased, but acid value (4.24-2.16 mg KOH/g oil), peroxide value (5.11-2.09 meqO 2 /kg oil), iodine value (107-99 g I 2 /100 g oil), and the poly unsaturated to saturated fatty acids (PUFA/SFA) ratio of all samples decreased by treatment with microwaves. Moreover, the α, β, γ-, δ δ -tocopherols, and phytosterols content such as cholesterol, campesterol, stigmasterol, cleroesterol, β- sitosterol, and Δ7-sterol of milk thistle seed oils increased by microwaves treatment. In conclusion, the results indicated that microwave pretreatment is a promising strategy for amplification of oil extraction yield and the content of nutraceuticals in obtained oil from milk thistle seeds. 1. Introduction Silybum marianum L., commonly known as milk thistle (a member of the Astraceae family), is an annual or biennial flowering plant with acanaceous leaves and a milky sap. Milk thistle is known as a native species in the Mediterranean region of Europe; however, it is natur- alized in California and the eastern United States, and also grows in North Africa and the Middle East, especially in Iran (Hadolin et al., 2001; Pepping, 1999). Extract from the mature milk thistle seeds has been shown to have clinical utility in different liver disorders, containing hepatitis, cir- rhosis, and alcoholic liver disease (Pepping, 1999). The major active ingredients of milk thistle are flavonolignans; The bioactive flavonolignans are generally called silymarin found in the fruit, seeds, and leaves of the plant (Pepping, 1999; Talbott and Hughes, 2007). The seeds also contain trimethylglycine, essential fatty acids, and betaine which might be helpful for silymarin’s medicinal potentials (Subramaniam et al., 2008). Silymarin has strong antioxidant proper- ties and consists of three isomers namely silybin, silydianin, and sily- christin, with silybin being the most bioactive agent. Silymarin has shown cholesterol and blood pressure lowering activity, anti-pro- liferative activity against cancer cells, and chemo-protective activity (Pepping, 1999; Talbott and Hughes, 2007). Milk thistle seeds have a relatively high content of oil (26–31%). Considering this point, it is needed to remove the oil from seed before the extraction of silymarin. Actually, the oil is considered as a by-pro- duct of silymarin production (Fathi-Achachlouei and Azadmard- Damirchi, 2009). Milk thistle seed oil as a suitable edible oil contains long chain fatty acids (C16-C24), phytosterols such as campesterol, cleroesterol, stigmasterol, Δ-sterol and β-sitosterol, and it is also rich in vitamin E (Hadolin et al., 2001; Pepping, 1999; El-Mallah et al., 2003; Vojtisek et al., 1991). Many reports have represented pretreatment of oilseeds with sev- eral methods (microwave, ultrasonic baths, milling, rapid gas decom- pression, etc.) to amplify the extraction of valuable oilseed components and accessibility of favorable nutraceuticals, like tocopherols and phytosterols in the extracted oil, particularly microwave radiation of seeds which has been introduced as an impressive technique for en- hancement the oil extraction efficiency from seeds (Azadmard- Damirchi et al., 2010; Đurđević et al., 2017). The advantages of mi- crowave radiation are reducing the processing time and energy https://doi.org/10.1016/j.indcrop.2018.11.034 Received 7 September 2018; Received in revised form 12 November 2018; Accepted 13 November 2018 ⁎ Corresponding author. E-mail addresses: b_fathi@uma.ac.ir, bahram1356@yahoo.com (B. Fathi-Achachlouei). Industrial Crops & Products 128 (2019) 527–533 0926-6690/ © 2018 Elsevier B.V. All rights reserved. T