Ultrasonic-Assisted Aqueous Two-Phase Extraction Combined with Macroporous Resin Enrichment of Lignans from Flaxseed Meal and Their Antioxidant Activities.

Abstract

Secoisolariciresinol diglucoside (SDG) is a natural antioxidant generally extracted from flaxseed, which is one of the most important oil crops in China, the by-product of the flaxseed oil, i.e., flaxseed meal still contains a lot of lignans. However, flaxseed meal is generally treated as waste, resulting in a huge waste of resources. To establish an efficient and convenient method for extraction and purification of lignans from flaxseed meal. First, we used response surface methodology (RSM) to optimize the extraction conditions of the ultrasonic-assisted (UA) aqueous two-phase system (ATPS), and we obtained the purified extracts by macroporous resin purification (MRP). Second, the antioxidant ability of the extracts was studied in vitro. The best extraction conditions obtained were as follows: 9.0% (w/w) sodium hydroxide; 30.0% (w/w) isopropanol; extraction time, 39 min; liquid-to-solid ratio, 52.0 mL/g; ultrasonic wave, 560 W; and extraction temperature, 40°C. Under the optimal conditions, the purity of crude extracts (SDG-APTS-C) reached 21.5%. The desorption conditions of MRP were as follows: eluting 3 BV with ultrapure water, and then eluting with 25% ethanol at 2 BV (bed volume)/h to collect eluents. The purified extracts (SDG-ATPS-P) had a purity quotient of 73.9%, which was 52.4% higher than that of SDG-ATPS-C. Additionally, experiments conducted revealed that SDG-ATPS-C and SDG-ATPS-P could effectively remove DPPH (2,2-Diphenyl-1-picrylhydrazyl), ABTS （2,-Azinobis-3-ethylbenzthiazoline-6-sulphonate）, and hydroxyl free radicals in vitro. The method was validated for extracting SDG from flaxseed meal, thus achieving the reuse of flaxseed meal. This research provides some references for the application of UAATPS combined with MRP in natural products.