Integrated Utilization Strategy for Soybean Oil Deodorizer Distillate: Synergically Synthesizing Biodiesel and Recovering Bioactive Compounds by a Combined Enzymatic Process and Molecular Distillation

Abstract

Soybean oil deodorizer distillate (SODD) is well recognized as a good source of both biodiesel and high-value bioactive compounds of tocopherols, squalene, and phytosterols. To achieve a one-step synthesis of biodiesel and recovery of bioactive compounds from SODD, four commercial immobilized enzymes (Novozym 435, Lipozyme TLIM, Lipozyme RMIM, and Lipozyme RM) and one self-prepared immobilized lipase MAS1-H108A were compared. The results showed that immobilized lipase MAS1-H108A due to the better methanol tolerance and higher catalytic activity gave the highest biodiesel yield of 97.08% under the optimized conditions: molar ratio of 1:2 (oil/methanol), temperature of 35 °C, and enzyme loading of 35 U/g SODD, even after 10 persistent cycles without significant decrease of activity. Simultaneously, there was no loss of tocopherols and squalene in SODD during the enzymatic reaction. Pure biodiesel (characterized by fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR)) and a high concentration of bioactive compounds could be successfully separated by molecular distillation at 100 °C. In a word, this work provides an interesting idea to achieve environmentally friendly treatment of SODD by combining an enzymatic process and molecular distillation, and it is suitable for industrial production.

Figure 1

Chromatogram of bioactive components analyzed by HPLC at 205 nm (A) and 296 nm (B). Chromatogram of FAME analyzed by as chromatography-mass spectrometry (GC-MS) (C). Peak order of each component was δ-tocopherol (1), γ-tocopherol (2), α-tocopherol (3), β-sitosterol (4), squalene (5), methyl palmitate (6), methyl seventeen alkanoate (internal standard) (7), methyl oleate (8), methyl linoleate (9), and methyl stearate (10).

Figure 2

Effect of the five immobilized lipases on the FAME yield and bioactive component contents in the process of catalysis. Yield of FAME (A); content of α-tocopherols (B); content of δ-tocopherols (C); content of γ-tocopherols (D); content of squalene (E); and content of β-sitosterol (F). The reaction was performed at a molar ratio of 1:1 (oil/methanol), a temperature of 35 °C, and enzyme loading of 25 U/g SODD for 24 h. Methanol was added at the beginning of the reaction by one-step.

Figure 3

Effect of molar ratio (oil/methanol) on the FAME yield and bioactive component contents in the process of immobilized MAS1-H108A catalysis. Yield of FAME (A); content of α-tocopherols (B); content of δ-tocopherols (C); content of γ-tocopherols (D); content of squalene (E); and content of β-sitosterol (F). The reaction was performed at an enzyme loading of 25 U/g SODD and the temperature of 35 °C. Methanol was added in 3 steps at 0, 2, and 4 h.

Figure 4

Effect of temperature on the FAME yield and bioactive component contents in the process of immobilized MAS1-H108A catalysis. The yield of FAME (A); content of α-tocopherols (B); content of δ-tocopherols (C); content of γ-tocopherols (D); content of squalene (E); and content of β-sitosterol (F). The reaction was performed at a molar ratio of 1:2 (oil/methanol) and an enzyme loading of 25 U/g SODD. Methanol was added in 3 steps at 0, 2, and 4 h.

Figure 5

Effect of enzyme loading on FAME yield and bioactive components contents in the process of immobilized MAS1-H108A catalysis. The yield of FAME (A); content of α-tocopherols (B); content of δ-tocopherols (C); content of γ-tocopherols (D); content of squalene (E); content of β-sitosterol (F). The reaction was performed at a molar ratio of 1:2 (oil/methanol) and a temperature of 35 °C. Methanol was added in 3 steps at 0, 2, and 4 h.

Figure 6

Reusability of immobilized lipase MAS1-H108A. Reaction conditions: molar ratio of 1:2 (oil/methanol), enzyme loading of 35 U/g SODD, and a temperature of 35 °C.

Figure 7

FT-IR spectrum of FAME and SODD (A). ¹H NMR spectrum of FAME and SODD (B). ¹³C NMR spectrum of FAME and SODD (C).