Optimized simultaneous extraction of flaxseed lignan and oil from its processing byproducts using subcritical biphasic solvent systems

Flaxseed dehulling generates substantial waste rich in valuable phytonutrients. This study developed a sustainable subcritical biphasic solvent extraction (SBE) using n-butane/ethanol to simultaneously recover lignans and oil from this byproduct. Optimization via Box-Behnken design achieved a total phenolic content (TPC) of 22.76 mg GAE/g DW under optimal conditions (69°C, 2 h, and 200 mL ethanol). The predominant phenolic was identified as secoisolariciresinol diglucoside (SDG), which demonstrated significant antioxidant activity compared to ascorbic acid. Furthermore, Hansen solubility parameters modeling theoretically validated the high dissolution efficiency of the solvent system for SDG. The co-extracted oil exhibited a quality comparable to commercial flaxseed oil. Importantly, the SBE process showed negligible interference on the subsequent polysaccharide extraction, yielding 18.19 g/100 g compared to conventional hot water extraction (18.73 g/100 g) from raw dehulling waste. This work establishes SBE as an efficient and integrated strategy for the comprehensive valorization of flaxseed processing waste, maximizing resource utilization and economic value.