Separation and Purification Technology 57 (2007) 17–24 Optimization of ethanol–water extraction of lignans from flaxseed Zhen-Shan Zhang a , Dong Li a,∗ , Li-Jun Wang b , Necati Ozkan c , Xiao Dong Chen a,d , Zhi-Huai Mao a , Hong-Zhi Yang a a College of Engineering, China Agricultural University, 17 Qinghua Donglu, Beijing 100083, PR China b College of Food Science and Nutritional Engineering, China Agricultural University, 17 Qinghua Donglu, Beijing 100083, PR China c Central Laboratory, Middle East Technical University, Ankara 06531, Turkey d Department of Chemical Engineering, Monash University, Clayton Campus, Victoria, Australia Received 30 January 2007; received in revised form 7 March 2007; accepted 7 March 2007 Abstract The optimal conditions for the extraction of lignans from flaxseed were determined. A second-order regression for rotation-orthogonal composite design was used to investigate the effects of three independent variables, namely ethanol concentration (%), extraction temperature ( ◦ C), and extraction time (h) on the response, the acquired ratio of lignans. The independent variables were coded at five levels and their actual values selected on the basis of results of single-factor experiment. The second-order regression for rotation-orthogonal composite design consisted of 23 experimental points and 9 replications at the central point. Data were analyzed using MATLAB software. The results indicated that acquired ratio of lignans might be beyond 8% at a probability of 95% in the range of ethanol concentration: 56.6–83.4%, extraction time: 26.7–27.9 h, extraction temperature: 38.7–40.1 ◦ C. And the optimal extraction conditions were ethanol concentration of 70%, extraction time of 28 h and extraction temperature of 40 ◦ C according to the analysis of response surface. In this condition, the experimental acquired ratio of lignans was 8.975% (w/w; lignans/defatted flaxseed powder), which is close to the predicted value (9.316%). © 2007 Elsevier B.V. All rights reserved. Keywords: Flaxseed; Acquired ratio of lignans; Response surface; Optimization; Ethanol–water extraction 1. Introduction Secoisolariciresinol diglycoside (SDG), a kind of phytoestro- gen, is the main component of flaxseed lignans [1]. SDG is the precursor of the major mammalian lignans enterodiol and enterolactone found in the urine and faeces of humans after flaxseed intake [2,3]. Previous researches indicated that SDG could prevent mammary, colonic, and prostate cancer [4–8] and have a beneficial effect on tumour [9,10] and atherosclerosis [11]. Positive results were also found on lupus nephritis [12,13], hypertension [14,15], diabetes [16,17] and other diseases after SDG intake. Although SDG can be found in many food prod- ucts, flaxseed appears to be the richest source, with values more than 100 times higher than those of the other foods. The content of SDG in flaxseed is 0.2–0.3%, and about 1–4% in defatted flaxseed powder [2,18,19]. ∗ Corresponding author at: College of Engineering, China Agricultural Uni- versity, P.O. Box 50, 17 Qinghua Donglu, Beijing 100083, PR China. Fax: +86 10 62737351. E-mail address: wlj@cau.edu.cn (D. Li). Flaxseeds are the seeds of the herb flax, which belong to flaxen section living one or more years. Flaxseeds are flat, oval, 4–6 mm long with a smooth, shiny surface, brown to light brown in color. Seed weight is about 5 ± 1 g/1000, and contains about 40% oil, 30% dietary fiber, 20% protein, 4% ash, and 6% mois- ture [20,21]. At present, flaxseed was mainly used to produce oil for a variety of industrial purposes (manufacturing of paints, varnishes, linoleum, printing inks, cosmetics, etc.) and oil-free meal for livestock [22,23]. Phytoestrogen-rich flaxseed is also a popular ingredient for use in various functional foods such as cereals, pancakes, muffins, pizza, and bread [24]. The first report of SDG occurring in flaxseed was done by Bakke and Klostermann [2]. Many extraction solvents have been utilized to extract flaxseed lignans from flaxseed. In 1956, Bakke and Kloster- mann described a laboratory process for extracting SDG from defatted flaxseed powder (DFP) using equal parts of 95% ethanol and 1,4-dioxane [18]. Degenhardt and Charlet obtained flaxseed lignans using methanol–water in their experiments [3,25]. And a solvent comprising acetone and water was adopted by Dob- binsan et al. in their American patent [18]. Complex solvent of 1383-5866/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2007.03.006