Facile purification of tocopherols from soybean oil deodorizer distillate in high yield using lipase

Tocopherols have been purified from deodorizer distillate produced in the final deodorization step of vegetable oil refining by a process including molecular distillation. Deodorizer distillate contains mainly tocopherols, sterols, and free fatty acids (FFA); the presence of sterols hinders tocopherol purification in good yield. We found that Candida rugosa lipase recognized sterols as substrates but not tocopherols, and that esterification of sterols with FFA could be effected with negligible influence of water content. Enzymatic esterification of sterols with FFA was thus used as a step in tocopherol purification. High boiling point substances including steryl esters were removed from soybean oil deodorizer distillate by distillation, and the resulting distillate (soybean oil deodorizer distillate tocopherol concentrate; SODDTC) was used as a starting material for tocopherol purification. Several factors affecting esterification of sterols were investigated, and the reaction conditions were determined as follows: A mixture of SODDTC and water (4∶1, w/w) was stirred at 35°C for 24 h with 200 U of Candida lipase per 1 g of the reaction mixture. Under these conditions, approximately 80% of sterols was esterified, but tocopherols were not esterified. After the reaction, tocopherols and FFA were recovered as a distillate by molecular distillation of the oil layer. To enhance further removal of the remaining sterols, the lipase-catalyzed reaction was repeated on the distillate under the same reaction conditions. As a result, more than 95% of the sterols was esterified in total. The resulting reaction mixture was fractionated to four distillates and one residue. The main distillate fraction contained 65 wt% tocopherols with low contents of FFA and sterols. In addition, the residue fraction contained high-purity steryl esters. Because the process presented in this study includes only organic solvent-free enzymatic reaction and molecular distillation, it is feasible as a new industrial purification method of tocopherols. This work was presented at the Biocatalysis symposium in April 2000, held at the 91st Annual Meeting and Expo of the American Oil Chemists Society, San Diego, CA.     

Purification of tocopherols and phytosterols by a two-step <Emphasis Type="Italic">in situ</Emphasis> enzymatic reaction

The purification of tocopherols and phytosterols (referred to as sterols) from soybean oil deodorizer distillate (SODD) was attempted. Tocopherols and sterols in the SODD were first recovered by short-path distillation, which was named sODD tocopherol/sterol concentrate (SODDTSC). The SODD-TSC contained MAG, DAG, FFA, and unidentified hydrocarbons in addition to the two substances of interest. It was then treated with Candida rugosa lipase to convert sterols to FA steryl esters, acylglycerols to FFA, and FFA to FAME. Methanol (MeOH), however, inhibited esterification of the sterols. Hence, a two-step in situ reaction was conducted: SODDTSC was stirred with 20 wt% water and 200 U/g mixture of C. rugosa lipase at 30°C, and 2 moles of MeOH per mole of FFA was added to the reaction mixture after 16h. The lipase treatment for 40 h in total achieved 80% conversion of the initial sterols to FA steryl esters, complete hydrolysis of the acylglycerols, and a 78% decrease in the initial FFA content by methyl esterification. Tocopherols did not change throughout the process. To enhance the degree of steryl and methyl esterification, the reaction products, FA steryl esters and FAME, were removed by short-path distillation, and the resulting fraction containing tocopherols, sterols, and FFA was treated with the lipase again. Distillation of the reaction mixture purified tocopherols to 76.4% (recovery, 89.6%) and sterols to 97.2% as FA steryl esters (recovery, 86.3%).     

Purification of steryl esters from soybean oil deodorizer distillate

Soybean oil deodorizer distillate (SODD) contains steryl esters in addition to tocopherols and sterols. Tocopherols and sterols have been industrially purified from SODD but no purification process for steryl esters has been developed. SODD was efficiently separated to low b.p. substances (including tocopherols and sterols) and high b.p. substances (including 11.2 wt% DAG, 32.1 wt% TAG, and 45.4 wt% steryl esters) by molecular distillation. The high b.p. fraction is referred to as soybean oil deodorizer distillate steryl ester concentrate (SODDSEC). We attempted to purify steryl esters after a lipase-catalyzed hydrolysis of acylglycerols in SODDSEC. Screening of industrially available lipases indicated that Candida rugosa lipase was most effective. Based on the study of several factors affecting hydrolysis, the reaction conditions were determined as follows: ratio of SODDSEC/water, 1∶1 (w/w); lipase amount, 15 U/g reaction mixture; temperature, 30°C. When SODDSEC was agitated for 24 h under these conditions, acylglycerols were almost completely hydrolyzed and the content of steryl esters did not change. However, study with a mixture of steryl oleate/trilinolein (1∶1, w/w) indicated that about 20% of constituent FA in steryl esters were exchanged with constituent FA in acylglycerols. Steryl esters in the oil layer obtained by the SODDSEC treatment with lipase were successfully purified by molecular distillation (purity, 97.3%; recovery, 87.7%).     

Isolation of tocopherol and sterol concentrate from sunflower oil deodorizer distillate

The isolation of tocopherols and sterols together as a concentrate from sunflower oil deodorizer distillate was investigated. The sunflower oil deodorizer distillate was composed of 24.9% unsaponifiable matter with 4.8% tocopherols and 9.7% sterols, 28.8% free fatty acid (FFA) and 46.3% neutral glycerides. The isolation technology included process steps such as biohydrolysis, bioesterification and fractional distillation. The neutral glycerides of the deodorizer distillates were hydrolyzed byCandida cylindracea lipase. The total fatty acids (initial FFA plus FFA from neutral glycerides) were converted into butyl esters withMucor miehei lipase. The esterified product was then fractionally distilled in a Claisen-vigreux flask. The first fraction, which was collected at 180–230°C at 1.00 mm of Hg for 45 min, contained mainly butyl esters, hydrocarbons, oxidized products and some amount of free fatty acids. The fraction collected at 230–260°C at 1.00 mm Hg for 15 min was rich in tocopherols (about 30%) and sterols (about 36%). The overall recovery of tocopherols and sterols after hydrolysis, esterification and distillation were around 70% and 42%, respectively, of the original content in sunflower oil deodorizer distillate.     

Enzymatic pretreatment of deodorizer distillate for concentration of sterols and tocopherols

Separation of sterols and tocopherols from fatty acids in deodorizer distillate was facilitated through lipase-catalyzed modification of fatty acids in canola, mixed and soya deodorizer distillates. The fatty acid esterification with methanol catalyzed by SP-382 (an immobilized nonspecific lipase) proceeded rapidly, with conversion of fatty acid to methyl ester in 5 h being 96.5, 83.5 and 89.4%, respectively. A model mixture of pure oleic acid and dl-α-tocopherol was used to study any potential side reactions that may lower the tocopherol content during the esterification reaction. Under the conditions employed, the loss of tocopherol was less than 5%. Simple vacuum distillation (1–2 mm Hg) was employed to remove the volatile fraction (methyl esters of fatty acids, some fatty acids and other volatiles) of the esterified deodorizer distillate, leaving behind sterols, sterol esters and tocopherols. Sterols and tocopherols were almost completely retained in the residue fraction with recoveries in the range of 95%. Overall recoveries of sterols and tocopherols after esterification and distillation were over 90% for all the deodorizer distillate samples.     

Influence of the vegetable oil refining process on free and esterified sterols

The influence of the refining process on the distribution of free and esterified phytosterols in corn, palm, and soybean oil was studied. Water degumming did not affect the phytosterol content or its composition. A slight increase in the content of free sterols was observed during acid degumming and bleaching due to acid-catalyzed hydrolysis of steryl esters. A significant reduction in the content of total sterols during neutralization was observed, which was attributed to a reduction in the free sterol fraction. Free sterols probably form micelles with soaps and are transferred into the soapstock. The steryl ester content remained constant during all neutralization experiments, indicating that hydrolysis of steryl esters did not take place during neutralization. During deodorization, free sterols are distilled from the oil, resulting in a gradual reduction in the total sterol content as a function of the deodorization temperature (220–260°C). A considerable increase in the steryl ester fraction was found during physical refining, probably owing to a heat-promoted esterification reaction between free sterols and FA.     

Application of short path distillation for recovery of polyphenols from deodorizer distillate

During physical refining of oil derived from ‘high temperature short time’ (HTST) pretreated rapeseeds, polyphenols are separated from the oil during deodorization and accumulate together with other high‐value minor compounds in the so‐called deodorizer distillate. For recovery of these compounds single‐stage and multistage short path distillations were carried out in a laboratory scale apparatus at evaporation temperatures between 110 and 170°C and pressures between 0.006 and 0.01 mbar. In addition, the removal of traces of pesticides from rapeseed deodorizer distillate was investigated. It was observed that these compounds can be separated from deodorizer distillate by means of short path distillation very effectively. On the basis of these experiments, a recovery process for polyphenols was proposed involving short path distillation, acid catalyzed esterification with methanol, solvent crystallization and solvent extraction processes. The final product was a polyphenol enriched extract containing about 14% of polyphenols. A polyphenol recovery of 50% is considered to be reachable and fractions rich in tocopherols and sterols may be obtained as by‐products.     

Analysis of free and esterified sterols in vegetable oils

In vegetable oils, phytosterols occur as free sterols or as steryl esters. Few analytical methods report the quantification of esterified and free sterols in vegetable oils. In this study, esterified and free sterols were separated by silica gel column chromatography upon elution with n-hexane/ethyl acetate (90∶10 vol/vol) followed by n-hexane/diethyl ether/ethanol (25∶25∶50 by vol). Both fractions were saponified separately and the phytosterol content was quantified by GC. The analytical method for the analysis of esterified and free sterols had a relative standard deviation of 1.16% and an accuracy of 93.6–94.1%, which was comparable to the reference method for the total sterol analysis. A large variation in the content and distribution of the sterol fraction between different vegetable oils can be observed. Corn and rapeseed oils were very rich in phytosterols, which mainly occurred as steryl esters (56–60%), whereas the majority of the other vegetable oils (soybean, sunflower, palm oil, etc.) contained a much lower esterified sterol content (25–40%). No difference in the relative proportion of the individual sterols among crude and refined vegetable oils was observed.     

菜籽油馏出物中维生素E的分子蒸馏工艺研究

介绍了菜籽油馏出物中维生素E的分子蒸馏工艺过程,考察了分子蒸馏各操作参数对维生素E的含量和收率的影响。研究结果表明:当操作压力为0.1Pa,蒸馏温度为180℃,进料流量250mL/h,进料温度170℃,刮膜速度150 r/min时,维生素E的一次收率可达65.38%,可得含量为51.72%的维生素E产品。利用分子蒸馏多级操作,可满足维生素E的进一步提纯要求。     

Large-scale purification of γ-linolenic acid by selective esterification using Rhizopus delemar lipase

γ-Linolenic acid (GLA) is a physiologically valuable fatty acid, and is desired as a medicine, but a useful method available for industrial purification has not been established. Thus, large-scale purification was attempted by a combination of enzymatic reactions and distillation. An oil containing 45% GLA (GLA45 oil) produced by selective hydrolysis of borage oil was used as a starting material. GLA45 oil was hydrolyzed at 35°C in a mixture containing 33% water and 250 U/g-reaction mixture of Pseudomonas sp. lipase; 91.5% hydrolysis was attained after 24 h. Film distillation of the dehydrated reaction mixture separated free fatty acids (FFA; acid value 199) with a recovery of 94.5%. The FFA were selectively esterified at 30°C for 16 h with two molar equivalents of lauryl alcohol and 50 U/g of Rhizopus delemar lipase in a mixture containing 20% water. The esterification extent was 52%, and the GLA content in the FFA fraction was raised to 89.5%. FFA and lauryl esters were not separated by film distillation, but the FFA-rich fraction contaminated with 18% lauryl esters was recovered by simple distillation. To further increase the GLA content, the FFA-rich fraction was selectively esterified again under similar conditions. As a result, the GLA content in the FFA fraction was raised to 97.3% at 15.2% esterification. After simple distillation of the reaction mixture, lauryl esters contaminating the FFA-rich fraction were completely eliminated by urea adduct fractionation. When 10 kg of GLA45 oil was used as a starting material, 2.07 kg of FFA with 98.6% GLA was obtained with a recovery of 49.4% of the initial content.     

Optimization of Phytosterols Recovery from Soybean Oil Deodorizer Distillate

A large amount of phytosterols in the bound form remains in the waste residue during the traditional process of recovering tocopherols and sterols from soybean oil deodorizer distillate (SODD). In order to avoid the loss of natural resources, we developed a process to recover the maximum amount of phytosterols from SODD. The process includes saponification, methyl esterification, and crystallization. The purpose of saponification and methyl esterification were to decompose the bound phytosterols and to esterify the fatty acids, respectively. The yield of sterols was dependent on saponification and solvent crystallization. The conditions of saponification and solvent crystallization were optimized by single-factor tests and response surface methodology, respectively. The sterol yield obtained under the optimized conditions was 6.64%. This value is much greater than 4.43% obtained by the traditional industrial process. The purity of the recovered sterols was 94.7%.     

Alteration of steryl ester content and positional distribution of fatty acids in triacylglycerols by chemical and enzymatic interesterification of plant oils

Steryl ester content of refined and interesterified corn, soybean, and rapeseed oils has been measured via clean-up on a short silica gel column, followed by high performance liquid chromatography with evaporative light-scattering mass detector. Chemical interesterification, catalyzed by sodium methoxide, led to random positional distribution of fatty acids in triacylglycerols and some increase in the steryl ester content of all three oils. Enzymatic interesterification, catalyzed by the immobilized lipase from Rhizomucor miehei (Lipozyme), resulted in a distinct reduction in steryl ester content, but essentially no alteration in positional distribution of fatty acids in triacylglycerols occurred. Formation of steryl esters during chemical and enzymatic interesterification was also examined by radioactive tracer technique with [4-¹⁴C]β-sitosterol added as marker to refined rapeseed oil and measurement of the radioactive steryl esters formed. Chemical interesterification of rapeseed oil resulted in moderate formation (10% of total radioactivity) of radioactive β-sitosteryl esters. Enzymatic interesterification of the oil, catalyzed by Lipozyme, led to little formation of radioactive β-sitosteryl esters, whereas with the lipase from Candida cylindracea high proportions (>90% of total radioactivity) of ¹⁴C-labeled β-sitosteryl esters were formed. Part of doctoral thesis of Roseli Ap. Ferrari to be submitted to Faculdade de Engenharia de Alimentos, Universidade de Campinas, Campinas, Brazil.     

Separation of squalene from olive oil deodorizer distillate using short-path molecular distillation

Squalene was recovered from an olive oil deodorizer distillate (OODD) containing 40% of squalene by a two-step process. The first step was to esterify the free fatty acids (FFAs) to make them less volatile. The second step was to separate the squalene by molecular distillation. The best esterification conditions were found to be 190°C and 360 min, where FFA content of the reaction mixture was reduced from 49.3% to 7.9%, however, an inevitable squalene loss (30%) was also observed due to a discontinuous operation. The remaining squalene (28%) in the esterified mixture was then distilled using a molecular distillation unit at elevated temperatures (190–230°C) and pressures (0.05–5 mmHg). When the temperature and vacuum during distillation increased, FFA content in the distillate reduced while distillate yield and squalene purity increased. The highest distillate yield (27.7%) and squalene purity (98.1%) were obtained at the highest applied temperature (230°C) under the lowest absolute pressure (0.05 mmHg), where FFA content of distillate was measured as 1.8%. High percentage of squalene (95%–98%) could be distilled at 230°C between 0.05 and 0.5 mmHg absolute pressures. The overall squalene recovery after all treatments was calculated as 68%.     

Brassica campestris var. Span: I. Fractionation of Rapeseed oil by molecular distillation and adsorption chromatography

Procedures for the large scale isolation of pure triglycerides and fractions rich in nontriglyceride components from Span rapeseed oil are described. Fractionation ofBrassica campestris var. Span rapeseed oil by molecular distillation yielded 4 triglyceride fractions, all of which contained traces of sterol esters. An additional triglyceride fraction rich in free and esterified sterols and other volatile components was obtained from the oil. Separation by adsorption chromatography of Span rapeseed oil yielded three fractions: A) a pure triglyceride fraction; B) a triglyceride fraction rich in sterol esters; and C) another fraction containing free sterols and other polar components. Contribution no. 559 Animal Research Institute.     

Enzymatic synthesis of steryl esters of polyunsaturated fatty acids

Steryl esters of long-chain fatty acids have water-holding properties, and polyunsaturated fatty acids (PUFA) have various physiological functions. Because steryl ester of PUFA can be expected to have both features, we attempted to synthesize steryl esters of PUFA by enzymatic methods. Among lipases used, Pseudomonas lipase was the most effective for the synthesis of cholesteryl docosahexaenoate. When a mixture of cholesterol/docosahexaenoic acid (3:1, mol/mol), 30% water, and 3000 units/g of lipase was stirred at 40°C for 24 h, the esterification extent attained 89.5%. Under the same reaction conditions, cholesterol, cholestanol, and sitosterol were also esterified efficiently with docosahexaenoic, eicosapentaenoic, arachidonic, and γ-linolenic acids.     

Production of phytosterol esters from soybean oil deodorizer distillates

Enzymatic esterification and supercritical fluid extraction was used to produce phytosterol esters from soybean oil deodorizer distillates. The raw material was first subjected to a two‐step enzymatic reaction; the product obtained mainly comprised fatty acid ethyl esters, tocopherols and phytosterol esters, together with minor amounts of squalene, free fatty acids, free sterols and triacylglycerols. The phytosterol esters were then purified from this mixture using supercritical carbon dioxide. Experimental extractions were carried out in an isothermal countercurrent column (without reflux), with pressures ranging from 200 to 280 bar, temperatures of 45–55 °C and solvent‐to‐feed ratios from 15 to 35 kg/kg. Using these extraction conditions, the fatty acid esters were completely extracted and, thus, the fractionation of tocopherols and phytosterol esters was studied. At 250 bar, 55 °C and a solvent‐to‐feed ratio of 35, the phytosterol esters were concentrated in the raffinate up to 82.4 wt‐% with satisfactory yield (72%).     

Steryl esters in a cell suspension culture of celery (Apium graveolens)

Arange of analytical techniques was used to investigate the composition of the steryl fatty acyl esters in a cell suspension culture of celery (Apium graveolens). Gas chromatography (GC) and GC-mass spectrometry (GC-MS), using electron ionization (EI) and negative ion chemical ionization (NICI), were employed to characterize the intact steryl esters. Assignments were supported by analysis of the sterol and fatty acid moieties released from the intact molecular species by alkaline hydrolysis. A selectivity for sterol esterification was noted, with the major free sterol, stigmasterol, occurring only in a very small amount in the esterified form. Instead, the precursors to Δ⁵-phytosterols, particularly cycloartenol, predominated in the ester fraction. The pentacyclic triterpene, β-amyrin, was also found as the palmitate and linoleate esters. Changes in composition and abundance of the steryl esters during the different growth phases of a celery cell suspension culture were investigated. The total amount of esterified sterols exceeded that of free sterols throughout the growth cycle. The changes observed during growth highlighted differences between the esters of precursor sterols and those of the 4-desmethyl-sterols, and it is postulated that the various steryl esters perform different functions in cell metabolism.     

Enzymatic methylation of canola oil deodorizer distillate

Methylation of canola oil deodorizer distillate catalyzed by a nonspecific lipase was investigated. The conversion of fatty acids to methyl esters has been optimized by using a statistical design. Up to 96.5% conversion of fatty acids to their methyl esters has been achieved without the aid of vacuum or any water-removing agent. The effects of temperature, ratio of the reactants (methanol: fatty acids in the deodorizer distillate) and enzyme concentration on the equilibrium conversion were studied. The temperature and ratio of the reactants showed a significant effect on the conversion of fatty acids to methyl esters and they exhibited a strong interactive effect. Enzyme concentration in the range of 2.7% to 4.3% did not show a significant effect on the equilibrium conversion of fatty acids. Greater than 95% conversion of fatty acids to methyl esters was achieved at temperatures around 50°C and at a ratio of the reactants between 1.8 and 2.0. The inhibitory effect of hydrophilic methanol on the enzyme activity was largely reduced by working at the lower temperature range (around 50°C).     

Minor constituents of vegetable oils during industrial processing

We report the effects of individual steps of industrial refining, carried out in Brazil, on the alteration of selected minor constituents of oils, such as corn, soybean, and rapeseed oils. Total sterols, determined by capillary gas chromatography (GC), decreased by 18–36% in the fully refined oils, compared with the crude oils. The total steradienes, dehydration products of sterols, were determinedvia a simple clean-up on a short silica gel column, followed by high-performance liquid chromatography (HPLC) with ultraviolet detection. The level of steradienes, normally not present in crude oils, increased after each refining step, especially after deodorization. Thus, the content of steradienes increased after deodorization by about 15- to 20-fold in corn and soybean oils, and by about 2-fold in rapeseed oil. The total steryl esters were also determinedvia clean-up on a short silica gel column, followed by HPLC with evaporative light scattering mass detection. A minor decrease in the level of steryl esters was observed after complete refining. The individual tocopherols and tocotrienols were determined by HPLC with a fluorescence detector. The level of total tocopherols and tocotrienols decreased by about 2-fold after complete refining of corn oil and by about 1.5-fold in soybean and rapeseed oils. In all three cases, maximum reduction of tocopherols was observed after the deodorization step. The level of polymeric glycerides, determinedvia clean-up on a short silica gel column followed by size-exclusion HPLC, increased to some extent (0.4–1%) during refining. The level oftrans fatty acids, determined by capillary GC, also increased to a substantial extent (1–4%) after refining. Part of doctoral thesis of Roseli Ap. Ferrari to be submitted to Faculdade de Engenharia de Alimentos, Universidade de Campinas, Campinas, Brazil.     

Fractionation of urea-pretreated squid visceral oil ethyl esters

Ethyl esters of squid (Illex argentinus) visceral oil contained 11.8% eicosapentaenoic acid (EPA) and 14.9% docosahexaenoic acid (DHA). The esters were treated with urea to increase the contents of EPA and DHA. The non-urea complexing ethyl esters of squid visceral oil contained 28.2% EPA and 35.6% DHA. This mixture was fractionated by molecular distillation to further increase the EPA or DHA content. The fraction collected in the 110°C distillate had an EPA content of 39.0% with 0.26 g/100 g of cholesterol, while the 130°C distillate contained 65.6% DHA and 0.42 g/100 g of cholesterol. Ethyl esters prepared from visceral oil of squid Ommastrephes bartrami had 4.5% EPA and 12.7% DHA. After urea pretreatment, the EPA and DHA contents were raised to 10.1 and 30.0%, respectively. When this mixture was further fractionated by molecular distillation, 16.9% EPA with 0.35 g/100 g cholesterol was found in the 110°C distillate and 52.6% DHA with 0.70 g/100 g cholesterol was found in the 130°C distillate. Cholesterol in the squid visceral oil ethyl esters was concentrated in the final residue of molecular distillation when the polyunsaturated ethyl esters were enriched by the urea complexation method prior to molecular distillation. For example, the cholesterol content in the ethyl esters from O. bartrami squid visceral oil was 2.28 g/100 g originally. It was enriched to 64.15 g/100 g in the final residue from the molecular distillation.