Oxidative stability of structured lipids produced from sunflower oil and caprylic acid

Traditional sunflower oil (SO), randomized lipid (RL) and specific structured lipid (SL), both produced from SO and tricaprylin/caprylic acid, respectively, were stored for up to 12 wk to compare their oxidative stabilities by chemical and sensory analyses. Furthermore, the effect of adding a commercial antioxidant blend Grindox 117 (propyl gallate/ citric acid/ascorbyl palmitate) or gallic acid to the SL was investigated. The lipid type affected the oxidative stability: SL was less stable than SO and RL. The reduced stability was most likely caused by both the structure of the lipid and differences in production/ purification, which caused lower tocopherol content and higher initial levels of primary and secondary oxidation products in SL compared with RL and SO. Grindox 117 and gallic acid did not exert a distinct antioxidative effect in the SL oil samples during storage.     

Oxidative stability during storage of structured lipids produced from fish oil and caprylic acid

Structured lipids produced by enzymatic or chemical methods for different applications have been receiving considerable attention. The oxidative stability of a randomized structured lipid (RFO), produced by chemical interesterification from fish oil (FO) and tricaprylin, and a specific structured lipid (SFO), produced by enzymatic interesterification from the same oil and caprylic acid, was compared with the stability of FO. Oils were stored at 2°C for 11 wk followed by storage at 20°C for 6 wk. In addition, the antioxidative effect of adding the metal chelators EDTA or citric acid to SFO was investigated. FO contained the largest amount of PUFA and RFO the lowest. However, SFO had a higher PV initially and during storage at 2°C, whereas the PV of FO was highest during storage at 20°C. The level of volatile oxidation products was highest in SFO during the entire storage period, and off-flavors were more pronounced in SFO. The lower oxidative stability of SFO was probably related to the initially lower quality (regarding oxidation products), which is apparently a result of the long production procedure required. Addition of metal chelators did not reduce the oxidation of the SFO.     

Oxidative stability of mayonnaise containing structured lipids produced from sunflower oil and caprylic acid

Mayonnaise based on enzymatically produced specific structured lipid (SL) from sunflower oil and caprylic acid was compared with mayonnaise based on traditional sunflower oil (SO) or chemically randomized lipid (RL) with respect to their oxidative stability, sensory and rheological properties. Furthermore, the potential antioxidative effect of adding lactoferrin, propyl gallate or EDTA to the mayonnaise with SL was also investigated. Mayonnaise based on SL oxidized faster than mayonnaise based on RL or SO. The reduced oxidative stability in the SL mayonnaise could not be ascribed to a single factor, but was most likely influenced by the structure of the lipid, the lower tocopherol content and the higher initial levels of lipid hydroperoxides and secondary volatile oxidation compounds in the SL itself compared with the RL and traditional sunflower oil employed. EDTA was a strong antioxidant, while propyl gallate and lactoferrin did not exert any antioxidative effect in the SL mayonnaise.     

Characterization of enzymatically synthesized structured lipids containing eicosapentaenoic, docosahexaenoic, and caprylic acids

Structured lipids (SL) containing n-3 polyunsaturated (eicosapentaenoic or docosahexaenoic) and mediumchain (caprylic) fatty acids were synthesized in gram quantities and characterized. Tricaprylin was mixed with n-3-rich polyunsaturated fatty acids in a 1:2 molar ratio and transesterified by incubating at 55°C in hexane with SP 435 lipase (10% by wt of total substrates) in a 125-mL Erlenmeyer flask as the bioreactor. After several batches of reaction, the products were pooled and hexane was evaporated. Short-path distillation was used for purification of synthesized SL. The distillation conditions were 1.1 Torr and 170°C at a feed flow rate of 3 mL/min. Up to 240 g of SL was isolated and deacidified by alkaline extraction or ethanol-water solvents. The fatty acid profile, free fatty acid value, saponification number, iodine value, peroxide value, thiobarbituric acid, and conjugated diene contents were determined. Oxidation stability, with α-tocopherol as antioxidant, and the oxidative stability index were also determined.     

Lipase-catalyzed acidolysis of perilla oil with caprylic acid to produce structured lipids

Structured lipids were synthesized by acidolysis of perilla oil and caprylic acid using two lipases, Lipozyme RM IM from Rhizomucor miehei and Lipozyme TL IM from Thermomyces lanuginosa. Effects of molar ratio, reaction time, reaction temperature, enzyme load, and solvent content on acidolysis reactions were studied. The solvent content ranged from 0.0 (solvent-free) to 85.3%. The results showed that the incorporation increased in parallel with solvent content to 49.0% with Lipozyme RM IM and to 63.8% with Lipozyme TL IM. After 24 h incubation in n-hexane, caprylic acids were incorporated to 48.5 mol% with Lipozyme RM IM and to 51.4 mol% with Lipozyme TL IM, respectively, whereas linolenic acid content was reduced from 61.4 to 31.5 mol% with Lipozyme RM IM and to 28.4 mol% with Lipozyme TL IM, respectively. Lipozyme TL IM showed a higher acyl migration rate than Lipozyme RM IM when acidolysis was performed in the reaction system containing n-hexane as a solvent, whereas the difference in acyl migration between the two lipases in the solvent-free system was negligible.     

Solvent-free enzymatic synthesis of structured lipids from peanut oil and caprylic acid in a stirred tank batch reactor

Structured lipids were synthesized by transesterification of peanut oil and caprylic acid in a stirred-batch reactor. Different substrate molar ratios (1:1 to 1:4, peanut oil/caprylic acid) were used. The reaction was performed for 72 h at 50°C catalyzed by IM60 lipase from Rhizomucor miehei (10 g, 2% w/w substrate) in the absence of organic solvent. The highest incorporation of caprylic acid was obtained with a 1:2 molar ratio (peanut oil/caprylic acid) after 72 h reaction. With a 1:2 molar ratio, the incorporation increased by 28% from 1:1. On the other hand, a 1:4 molar ratio gave the lowest incorporation during the reaction. The effect of different mixing speeds (200, 640, or 750 rpm) on reaction was studied with a 1:2 substrate molar ratio for 24 h. A high incorporation of caprylic acid (14.3 mol%) was obtained at 640 rpm, while 200 rpm gave the lowest incorporation (2.2 mol%), suggesting that good mixing is essential in a stirred-batch reactor. After 24 h of reaction at different rpm, IM60 lipase was recovered, washed with hexane, and reacted with substrates to study its stability after reaction at different mixing speeds. The results showed that caprylic acid incorporation was similar (24.9, 24.3, 24.2 mol%) at 200, 640, and 750 rpm, respectively. When 20 g of IM60 lipase (4% w/w substrate) instead of 10 g was used in a 1:1 substrate molar ratio reaction, the incorporation of caprylic acid increased by 26% after 72 h. To study enzyme reuse, 10 g of IM60 lipase was used in a 1:1 substrate molar ratio for 24 h at 640 rpm. The incorporation of caprylic acid gradually decreased with increased number of reuses. During five times of reuse, 15, 13.9, 9.6, 6.7, and 9.7 mol% of caprylic acid were incorporated into peanut oil, respectively.     

Characterization and oxidative stability of enzymatically produced fish and canola oil-based structured lipids

Two-kilogram quantities of structured lipids (SL) of menhaden fish and canola oils containing caprylic acids (8∶0) were produced in a laboratory-scale packed-bed bioreactor by acidolysis catalyzed by an immobilized lipase, Lipozyme IM, from Rhizomucor miehei. SL were characterized and their oxidative stabilities investigated. The SL contained 29.5% 8∶0 for fish oil and 40.15 for canola oil. Polyunsaturated fatty acids (PUFA) of fish oil remained unchanged after the modification while PUFA of canola oil were reduced from 29.6 to 21.2%. Monoenes, especially 18∶1n−9, were completely replaced by 8∶0 in fish oil and reduced from 61.9 to 34.7% in canola oil. Downstream processing of enzymatically produced SL led to loss in natural total tocopherol contents of the fish and canola oils. The effects of antioxidants such as α-tocopherol (TOC), tert-butylhydroxyquinone (TBHQ), and combinations thereof on the oxidative stability of SL were investigated. SL were analyzed for oxidative stability index, peroxide value, conjugated diene content, free fatty acid content, iodine value, saponification number, and thiobarbituric acid value. Iodine value of unmodified fish oil (154.71) was reduced to 144.10 and that of canola oil (114.49) to 97.27 after modification. The SN increased from 183.72 to 242.63 for fish oil and from 172.50 to 227.90 for canola oil. TBHQ exhibited better antioxidant effects than TOC. A combination of TBHQ/TOC also proved to be an effective antioxidant for SL. We suggest the addition of antioxidants to enzymatically produced and purified SL.     

Enzymatic synthesis of structured lipids from single cell oil of high docosahexaenoic acid content

The lipase-catalyzed acidolysis of a single-cell oil (SCO) containing docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA) with caprylic acid (CA) was investigated. The targeted products were structured lipids containing CA residues at the sn-1 and -3 positions and a DHA or DPA residue at the sn-2 position of glycerol. Rhizomucor miehei lipase (RML) and Pseudomonas sp. KWI-56 lipase (PSL) were used as the biocatalysts. When PSL was used > 60 mol% of total SCO fatty acids (FA) were exchanged with CA, with DHA and DPA as well as the other saturated FA being exchanged. The content of the triacylglycerols (TG) containing two CA and one DHA or DPA (number of carbon atoms = 41, i.e., C₄₁) residue was high (36%), and the isomer with the desired configuration (unsaturated FA residue at the sn-2 position) represented 77–78% of C₄₁. In the case of RML, CA content reached only 23 mol% in the TG. A large amount of DHA and DPA residues remained unexchanged with RML, so that the resulting oil was rich in TG species containing two or three DHA or DPA residues (46%). TG C₄₁ amounted to 22%, almost all of which had the desired configuration. This result suggested that the difference in the degree of acidolysis by the two enzymes was due to their different selectivity toward DHA and DPA, as well as the difference in their positional specificities.     

Solvent-free enzymatic synthesis of structured lipids containing CLA from coconut oil and tricaprylin

Lipase-catalyzed acidolysis of different TAG with CLA was performed to produce structured lipids (SL) containing CLA. An immobilized lipase from Mucor miehei (Lipozyme IM, Novo Nordisk Inc., Franklinton, NC) was used as the biocatalyst in a solvent-free system. Conconut oil and tricaprylin, which are sources of medium-chain FA, were the starting substrates, and a mixture of FFA (MFFA) containing 73% CLA was the donor of the acyl groups. For each TAG, four different ratios of TAG/MFFA were blended to prepare about 500 g of mixture containing 10, 20, 30, and 40% CLA (w/w). Each blend was reacted with 5% lipase at 65°C for 48 h under nitrogen. Over the range of TAG/MFFA ratios examined, CLA was incorporated effectively by the enzyme. Lipozyme IM exhibited no special preference for any particular FA, since the incorporation of FA was proportional to their concentration in the system. FFA, PV, p-anisidine value (p-AV), iodine value (IV), and saponification number (SN) were evaluated for all the SL. FFA, PV, and p-AV depended on the purification process and showed no significant deterioration of SL with respect to the original TAG, whereas IV and SN depended on the composition of the SL, mainly the CLA content.     

Enzymatic synthesis of structured lipids: Transesterification of triolein and caprylic acid ethyl ester

Structured lipids were successfully synthesized by lipase-catalyzed transesterification (ester interchange) of caprylic acid ethyl ester and triolein. The transesterification reaction was carried out in organic solvent as reaction media. Eight commercially-available lipases (10% w/w substrates) were screened for their ability to synthesize structured lipid by incubating with 100 mg triolein and 78.0 mg caprylic acid ethyl ester in 3 mL hexane at 45°C for 24 h. The products were analyzed by reverse-phase high-performance liquid chromatography with evaporative light-scattering detector. Immobilized lipase IM60 fromRhizomucor miehei converted most triolein into structured lipids (41.7% dicapryloolein, 46.0% monocapryloolein, and 12.3% unreacted triolein). However, lipase SP435 fromCandida antarctica had a higher activity at higher temperature. The reaction catalyzed by lipase SP435 yielded 62.0% dicapryloolein, 33.5% monocapryloolein, and 4.5% unreacted triolein at 55°C. Time course, incubation media, added water, and substrate concentration were also investigated in this study. The results suggest that lipase-catalyzed transesterification of long-chain triglycerides and medium-chain fatty acid ethyl ester is feasible to synthesize structured lipids.     

Kinetics of lipase‐catalysed interesterification of triolein and caprylic acid to produce structured lipids

The influence of the molar ratio caprylic acid/triolein, enzyme concentration and water content on the kinetics of the interesterification reaction of triolein (TO) and caprylic acid (CA) were studied. The enzyme used was the 1,3‐specific Rhizomucor miehei lipase. Data modelling was based on a simple scheme in which the acid was only incorporated in positions 1 and 3 of the glyceride backbone. In addition, it was assumed that positions 1 and 3 of the triglycerides were equivalent and that the events at position 1 did not depend on the nature of the fatty acid in position 3 and vice versa. Monoglycerides and diglycerides were not detected during the experiments. This was attributed to the low water content of the immobilised enzyme particles. The value of the equilibrium constant, K, for the exchange of caprylic and oleic acids was 2.7, which indicated that the incorporation of caprylic acid into triglycerides was favoured compared with the incorporation of oleic acid. Simple first order kinetics could describe the interesterification reaction. Using this model and the calculated equilibrium constant, the apparent kinetic constants were calculated. The model fitted all the experimental data except for the CA/TO molar ratios larger than 6. Moreover, the interesterification reaction rate had a maximum value at CA/TO molar ratios of 4–6 mol mol^?1. Copyright © 2003 Society of Chemical Industry     

Impact of high-intensity ultrasound on physical properties and degree of oxidation of lipase modified menhaden oil with caprylic acid and/or stearic acid

The purpose of this research was to determine the effect of high-intensity ultrasound (HIU) on physical properties, degree of oxidation, and oxidative stability of structured lipids (SLs). Caprylic acid (C) and stearic acid (S) were incorporated into menhaden oil using Lipozyme® 435 lipase to obtain five samples: (1) LC 20 (menhaden oil with 20% of C), (2) LC 30 (menhaden oil with 30% C), (3) LS 20 (menhaden oil with 20% S), (4) LS 30 (menhaden oil with 30% S), and (5) Blend C (menhaden oil with 16.24% C and 13.04% S). Samples were crystallized for 90 min at the following temperatures: (1) LC 20 at 15.5°C, (2) LC 30 at 17.5°C, (3) LS 20 at 24°C, (4) LS 30 at 30°C, and (5) Blend C at 18.0°C, and HIU was applied at the onset of crystallization. Physical properties, degree of oxidation, and oxidative stability were evaluated in sonicated and nonsonicated samples. All SLs had statistically higher G′ after sonication. Sonicated LS 30, LC 30, and Blend C had a higher melting enthalpy than the nonsonicated ones, while enthalpy values in sonicated LS 20 and LC 20 samples were not statistically different than the nonsonicated ones. No significant difference between sonicated and nonsonicated samples was observed in peroxide values (1.2 ± 0.1 meq/kg, p > 0.05) and in the oxidative stability index (6.3 ± 0.2 h, p > 0.05). These results showed that HIU was effective at changing physical properties without affecting the oxidation of the samples.     

Synthesis, purification, and characterization of structured lipids produced from chicken fat

A structured lipid (SL) was synthesized enzymatically from chicken fat by incorporating a medium-chain length fatty acid (caprylic acid) into chicken fat triacylglycerols. Carica papaya latex was used as the biocatalyst. The optimal substrate mole ratio found was 1∶2 (chicken fat fatty acids/caprylic acid). At this ratio of reactants, the incorporation of caprylic acid (C_8∶0) at 65°C was 23.4 mol%, whereas at 55°C the incorporation of caprylic acid was 17.6 mol%. A packed-bed column bioreactor was designed for the synthesis of SL from chicken fat. In using ground crude C. papaya latex (a _w <0.1), 7.1 mol% of caprylic acid was incorporated into the chicken fat triacylglycerols after 117 min of reactor residence time. After purification of the SL, the acyl positional distribution of fatty acids on the glycerol backbone was determined by ¹³C nuclear magnetic resonance (NMR) spectroscopy. From the NMR spectrum of the SL, it was determined that saturated fatty acyl residues at the 1,3-positions of the SL triacylglycerols increased to 62% over that of the starting chicken fat triacylglycerols, suggesting that caprylic acid was preferentially incorporated at the 1,3-positions. In addition, differential scanning calorimetry thermograms were obtained to compare the crystallization characteristics of the starting chicken fat with the SL prepared from it. 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.     

Enzymatic synthesis of high-purity structured lipids with caprylic acid at 1,3-positions and polyunsaturated fatty acid at 2-position

We attempted to synthesize high-purity structured triacylglycerols (TAG) with caprylic acid (CA) at the 1,3-positions and a polyunsaturated fatty acid (PUFA) at the 2-position by a two-step enzymatic method. The first step was synthesis of TAG of PUFA (TriP), and the second step was acidolysis of TriP with CA. Candida antarctica lipase was effective for the first reaction. When a reaction medium of PUFA/glycerol (3∶1, mol/mol) and 5% immobilized Candida lipase was mixed for 24 h at 40°C and 15 mm Hg, syntheses of TAG of γ-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic acids reached 89, 89, 88, and 83%, respectively. In these reactions, the lipase could be used for at least 10 cycles without significant loss of activity. In the second step, the resulting trieicosapentaenoin was acidolyzed at 30°C for 48h with 15 mol parts CA using 7% of immobilized Rhizopus delemar lipase. The CA content in the acylglycerol fraction reached 40 mol%. To increase the content further, the acylglycerols were extracted from the reaction mixture with n-hexane and were allowed to react again with CA under conditions similar to those of the first acidolysis. After three successive acidolysis reactions, the CA content reached 66 mol%. The content of dicapryloyl-eicosapentaenoyl-glycerol reached 86 wt% of acylglycerols, and the ratio of 1,3-dicapryloyl-2-eicosapentaenoyl-glycerol to 1(3),2-dicapryloyl-3(1)-eicosapentaenoyl-glycerol was 98∶2 (w/w). In this reaction, the lipase could be used for at least 20 cycles without significant loss of activity. Repeated acidolysis of the other TriP with CA under similar conditions synthesized 1,3-dicapryloyl-2-γ-linolenoyl-glycerol, 1,3-dicapryloyl-2-arachidonoyl-glycerol, and 1,3-dicapryloyl-2-docosahexaenoyl-glycerol in yields of 58, 87, and 19 wt%, respectively.     

Oxidative stability of soybean oil fatty acid methyl esters by oil stability index (OSI)

Biodiesel, an alternative diesel fuel derived from transesterification of vegetable oils or animal fats, is composed of saturated and unsaturated long-chain FA alkyl esters. During long-term storage, oxidation caused by contact with air (autoxidation) presents a legitimate concern with respect to monitoring and maintaining fuel quality. Extensive oxidative degradation may compromise quality by adversely affecting kinematic viscosity, acid value, or PV. This work examines the oil stability index (OSI) as a parameter for monitoring the oxidative stability of soybean oil FAME (SME). SME samples from five separate sources and with varying storage and handling histories were analyzed for OSI at 60°C using an oxidative stability instrument. Results showed that OSI may be used to measure relative oxidative stability of SME samples as well as to differentiate between samples from different producers. Although addition of α-tocopherol or TBHQ increased OSI, responses to these antioxidants varied with respect to SME sample. Variations in response to added antioxidant were attributed to aging and other effects that may have caused oxidative degradation in samples prior to acquisition for this study. Results showed that OSI was more sensitive than iodine value in detecting the effects of oxidative degradation in its early stages when monitoring SME during storage.     

A comparative study of mayonnaise and italian dressing prepared with lipase-catalyzed transesterified olive oil and caprylic acid

Viscoelastic properties of mayonnaise and Italian salad dressing prepared with olive oil and enzymatically synthesized structured lipid (SL) from caprylic acid and olive oil were studied using an SR5000 dynamic stress rheometer. Storage modulus (G′) and loss modulus (G″) were determined as functions of frequency, temperature, and stress. Frequency sweeps did not show significant differences between dressings prepared with olive oil or SL. For all mechanical spectra, G′ values were consistently higher than G″ values. Both Italian dressing and mayonnaise samples displayed similar gel-like characteristics. Mayonnaise and Italian dressings made with olive oil separated when they were brought to room temperature from refrigeration temperatures. SL-based mayonnaise did not separate. Only minor separation was observed in SL-based Italian dressing. A change in the crystallization properties of the two oils was probably responsible for the differences observed after refrigeration. Both SL-based and unmodified olive oil-based mayonnaise and Italian dressing samples had similar viscoelastic character.     

Lipase‐catalyzed synthesis of structured lipids with fatty acids fractionated from saponified chicken fat and menhaden oil

In this study, free fatty acids (FFA) of chicken fat and menhaden oil, which were obtained by saponification, were dry‐fractionated and solvent fractionated. Using these fractionation processes, FFA fractions enriched in monounsaturated (MUFA) and polyunsaturated fatty acids were obtained. Chicken fat FFA fractions enriched in MUFA were modified further by lipase‐catalyzed esterification with the starting fat to produce structured lipids of high MUFA content.     

Effects of alkylamines and PC on the oxidative stability of soybean oil TAG in milk casein emulsions

The effects of alkylamines and PC on the coppercatalyzed oxidation of soybean oil TAG were studied in milk casein emulsions. Stearylamine showed an antioxidant effect in casein emulsions in the presence of PC, whereas dicetylphosphate acted as a prooxidant. The antioxidant or prooxidant effect could be explained by the electrostatic repulsion or attraction between positively charged stearylamine or negatively charged dicetylphosophate and positively charged copper ion at the interface, respectively. On the other hand, these effects were not observed in the absence of PC, suggesting the importance of PC for charged components to show their activities at the interface. Other types of alkylamines—spermine, spermidine, and putrescine—also inhibited the oxidation of soybean oil TAG emulsified with casein in the presence of PC. The antioxidant effects of these natural polyamines were higher than that of stearylamine. PC molecular species also affected soybean oil TAG oxidation in emulsion. The oxidative stability of soybean oil TAG increased in the emulsion with PC containing oleic acid.     

Production of structured lipids containing essential fatty acids by immobilizedRhizopus delemar lipase

An attempt was made to produce structured lipids containing essential fatty acid by acidolysis with 1,3-positional specificRhizopus delemar lipase. The lipase was immobilized on a ceramic carrier by coprecipitation with acetone and then was activated by shaking for 2 d at 30°C in a mixture of 5 g safflower or linseed oil, 10 g caprylic acid, 0.3 g water and 0.6 g of the immobilized enzyme. The activated enzyme was transferred into the same amount of oil/caprylic acid mixture without water, and the mixture was shaken under the same conditions as for the activation. By this reaction, 45–50 mol% of the fatty acids in oils were exchanged for caprylic acid, and the immobilized enzyme could be reused 45 and 55 times for safflower and linseed oils, respectively, without any significant loss of activity. The triglycerides were extracted withn-hexane after the acidolysis and then were allowed to react again with caprylic acid under the same conditions as mentioned above. When acidolysis was repeated three times with safflower oil as a starting material, the only products obtained were 1,3-capryloyl-2-linoleoylglycerol and 1,3-capryloyl-2-oleoyl-glycerol, with a ratio of 86∶14 (w/w). Equally, the products from linseed oil were 1,3-capryloyl-2-α-linolenoyl-glycerol, 1,3-caprylol-2-linoleoyl-glycerol, and 1,3-capryloyl-2-oleoly-glycerol (60∶22∶18, w/w/w). All fatty acids at the 1,3-positions in the original oils were exchanged for caprylic acid by the repeated acidolyses, and the positional specificity ofRhizopus lipase was also confirmed to be strict.