Separating and Enriching Natural Tocopherols from Soybean Oil Deodorizer Distillate via in-situ Formation of Deep Eutectic Solvents

Natural tocopherol products have attracted much attention in high value-added products because of its superiority in biological activity and dietary safety. Soybean oil deodorizer distillate (SODD), as soybean oil processing by-products, is the main source for extracting natural tocopherols. This study demonstrated a green and efficient method for the extraction of natural tocopherols (α, γ, δ) from SODD via the in-situ formation of a deep eutectic solvent (DES). The DES was formed directly within the SODD matrix through hydrogen bonding between tocopherols, acting as hydrogen bond donors, and tetrabutylammonium chloride (TBAC), the selected hydrogen bond acceptor. TBAC was identified as the optimal organic salt due to its strong hydrogen-bonding capability with tocopherols, influenced by its appropriate alkyl chain length and the chloride anion. Fourier-transform infrared spectroscopy confirmed hydrogen bond formation in the resulting TBAC-tocopherol DES. The extraction conditions were systematically optimized. Single factor experiments and response surface methodology revealed that the influence of operational parameters on the total tocopherol extraction yield followed the order: TBAC dosage > extraction time > extraction temperature. Under the optimized conditions (TBAC: SODD mass ratio of 2:1, n-hexane: TBAC mass ratio of 0.6:1, 40 °C, 3 h, and stirring at 1000 rpm), the extraction yields for α-, γ-, and δ-tocopherol reached 72.9%, 99.9%, and 95.0%, respectively, with a total tocopherol yield of 95.6%. Subsequent stripping and purification yielded a tocopherol product with 53.7% purity. This in-situ DES formation strategy provides an efficient and simplified alternative to conventional methods for the separation and enrichment of tocopherols from complex lipid byproducts. • Extraction natural tocopherols from SODD via in-situ formation of TBAC-tocopherol DES. • Performance of a green and rapid extraction strategy for natural tocopherols from SODD. • Offering an extraction strategy of natural tocopherols eliminating the need for pretreating SODD.