Polymorphic transformations in sn-1, 3-distearoyl-2-ricinoleyl-glycerol

Polymorphic transformations of sn-1,3-distearoyl-2-ricinoleyl-glycerol (SRS) have been studied with differential scanning calorimetry, X-ray powder diffraction (XRD), synchrotron radiation X-ray diffraction, and Fourier transform infrared spectroscopy (FTIR) techniques by using a 99.8% pure sample. Four polymorphs, α, γ, β′₂, and β′₁, were isolated. The thermal behavior of the four forms showed that the fusion of α at 25.8°C was followed by the crystallization of γ which melts at 40.6°C, and β′₂ and β′₁ revealed melting peaks at 44.3 and 48.0°C, respectively. No β form was observed, even when the two β′ forms were annealed around their melting points over one week. The XRD long spacing indicates that α packs into a double chain-length structure; however, γ and the two β′ phases pack into a triple chain-length structure. The polarized and nonpolarized FTIR spectra in methylene scissoring and methylene rocking regions indicated a parallel subcell packing in γ, and a mixture of orthorhombic perpendicular and parallel or hexagonal subcells in the β′₂ and β′₁ phases. Consequently, SRS exhibits quite a unique polymorphic behavior, compared to tristearoyl glycerol and sn-1,3-distearoyl-2-oleoyl-glycerol.     

Binary Phase Behavior of 1,3-Dipalmitoyl-2-oleoyl-<Emphasis Type="Italic">sn</Emphasis>-glycerol and 1,2-Dioleoyl-3-palmitoyl-<Emphasis Type="Italic">rac</Emphasis>-glycerol

1,3-Dipalmitoyl-2-oleoyl-sn-glycerol (POP) and 1,2-dioleoyl-3-palmitoyl-rac-glycerol (OOP) are two major molecular species that account for roughly half of the total triacylglycerols in palm oil. The binary phase behavior of a POP/OOP mixture plays an important role in the crystallization of palm oil. We conducted thermodynamic and kinetic studies of OOP and its mixtures with POP using differential scanning calorimetry and X-ray diffraction with a conventional generator and synchrotron radiation. We found that OOP has two polymorphs, α as a metastable form and β′ as the most stable form, and that the two forms are stacked in a triple-chain-length structure. The POP/OOP mixtures exhibited immiscible eutectic natures in both their metastable and their most stable states, in contrast to POP/1,2-dipalmitoyl-3-oleoyl-rac-glycerol and POP/1,3-dioleoyl-2-palmitoyl-sn-glycerol mixtures, in which molecular compounds of a double-chain-length structure were formed. A time-resolved synchrotron radiation X-ray diffraction study undertaken during the cooling and heating processes indicated that the α and β′ forms of the POP and OOP fractions crystallized and melted in separate manners, and that crystallization of the β′ form and the polymorphic transformation from α to β′ of POP and OOP are promoted in the presence of another component. The absence of molecular compound crystals in the binary mixtures of POP/OOP is explained by taking into account the molecular interactions of acyl chain packing, glycerol conformation, and methyl end stacking, among which glycerol conformation appeared to be most influential.     

Polymorphic transformation of 1,3-distearoyl-sn-2-linoleoyl-glycerol

Polymorphic transformation behavior of sub-α₁, sub-α₂, α, and γ in 1,3-distearoyl-sn-2-linoleoyl-glycerol (SLS) has been studied with X-ray diffraction, differential scanning caloremetry, and Fourier-transform infrared spectroscopy. Synchrotron radiation X-ray beam was employed to observe rapid transformation processes from the sub-α and α forms to the γ form. The chain length structures were double in sub-α₁, sub-α₂, and α, whereas γ was of triple chain-length structure. The subcell packing was pseudohexagonal for the two sub-α forms, hexagonal for the α form, and parallel type for the γ form. In comparison with 1,3-distearoyl-sn-2-oleoyl-glycerol (SOS), the occurrence behavior of sub-α, α, and γ of SLS was the same as that of SOS. However, the absence of β′ and β was unique for SLS. The chain-chain interactions between the linoleoyl moieties may stabilize the γ form, prohibiting the transformation into β′ and β forms. The presence of two cis double bonds may cause this stabilization, revealing the disordered chain conformation of the unsaturated chains.     

Binary phase behavior of 1,3-distearoyl-2-oleoyl-sn-glycerol (SOS) and 1,3-distearoyl-2-linoleoyl-sn-glycerol (SLS)

The binary phase behavior of SOS (1,3-distearoyl-2-oleoyl-sn-glycerol) and SLS (1,3-distearoyl-2-linoleoyl-sn-glycerol) was examined by using DSC and conventional and synchrotron radiation X-ray diffraction. The solid-solution phases were observed in the metastable α and γ forms in all concentration ranges. Results indicated that the miscible γ form did not transform to the β′ form when the mixtures were subjected to simple cooling from a high-temperature liquid to a low-temperature solid phase. However, and α-melt-mediated transformation into β′ and β₂ resulted in the formation of immiscible phases in concentration ranges of SLS below 30%. By contrast, at SLS concentration ranges above 30%, the α-melt-mediated transformation caused crystallization of only the γ form, and β′ and β₂ crystals did not appear. These results show that the specific interactions between SOS and SLS are operative in the phase behavior of the mixture states of SOS and SLS.     

Polymorphism of POP and SOS. I. occurrence and polymorphic transformation

The polymorphic modifications of POP and SOS were identified with X-ray diffraction (XRD), DSC and Raman spectroscopy by using pure samples (99.9%). In POP, six polymorphs, α,γ, pseudo-β′₂, pseudo-β′₁, β′₂ and β′₁, were obtained, whereas five polymorphs, α, γ, pseudo-β′, β₂ and β₁, were isolated in SOS. Thermodynamic stability increased from α to β₁ straightforwardly both in POP and SOS, because the polymorphic transformation went monotropically in the order described above. Additionally, the 99.2% sample of POP crystallized another form, δ, but the 99.9% sample did not, implying subtle influences of the impurity. The four forms, α, γ, β₂ and β₁, of POP, revealed XRD and DSC patterns identical to the four forms of SOS designated by the same symbols. The chain length structure was double inα and triple in the other three forms in both POP and SOS. Peculiarity of POP was revealed partly in the chain length structure of pseudo-β′₂ and pseudo-β′₁ which were double, whereas pseudo-β′ of SOS was triple. This apparently showed contrast to the facts that the three forms revealed rather similar XRD short spacing patterns. Another peculiarity of POP was revealed in enthalpy value of the melt crystallization of α: ΔH_c (α) = 68.1 kJ/mol which was much larger than that of SOS (47.7 kJ/mol), and also than AOA and BOB. These peculiarities mean that the double chain length structures of POP are more stabilized than the others. Raman bands of CH₂ scissoring mode of SOS indicated parallel packing in γ, β₂ and β₁, and orthorhombic perpendicular packing in pseudo-β′. The polymorphic transformation mechanisms were discussed based on the proposed polymorphic structure models. Presented at the AOCS annual meetings in New Orleans, Louisiana in May 1987 and Phoenix, Arizona in May 1988.     

Crystallization Behavior of Molecular Compound in Binary Mixture System of 1,3‐Dioleoyl‐2‐Palmitoyl‐sn‐Glycerol and 1,3‐Dipalmitoyl‐2‐Oleoyl‐sn‐Glycerol

Previous studies showed that the stable β‐form of molecular compound (MC) crystals having a double‐chain‐length structure is formed in a binary mixture system of 1,3‐dioleoyl‐2‐palmitoyl‐sn‐glycerol (OPO) and 1,3‐dipalmitoyl‐2‐oleoyl‐sn‐glycerol (POP) with a 1:1 concentration ratio of OPO and POP. The use of MC crystals made of POP and OPO for edible applications, such as margarine, is advantageous due to no‐trans, low‐saturated, and high‐oleic fats. Industrial manufacturing technology involves rapid cooling processes, and the kinetic properties of crystallization of MC of OPO and POP are required. In this study, we clarified the crystallization of MC of OPO and POP under rapid cooling at rates of 1–150 °C min^?1, using synchrotron radiation time‐resolved X‐ray diffraction and differential scanning calorimetry methods. The main results are as follows: (1) POP and OPO crystallized in separate manners without the formation of MC crystals under rapid cooling (>40 °C min^?1), while MC crystals started to form with decreasing rates of cooling in addition to the POP and OPO crystals (<30 °C min^?1); (2) metastable and stable forms sub‐α, α, β′, and β of POP and OPO were formed, whereas the MC crystals of β were formed during the cooling processes; and (3) the heating processes after crystallization by rapid cooling caused separate melting of the metastable and stable forms of POP and OPO crystals and the formation of MC crystals of β made of POP and OPO, as well as melting of the MC crystals alone.     

13C cross-polarization and magic-angle spinning nuclear magnetic resonance of polymorphic forms of three triacylglycerols

The cross-polarization and magic-angle spinning nuclear magnetic resonance (CP/MAS-NMR) technique has been used to analyze the polymorphic forms of three triacylglycerols, 1,3-dipalmitoyl-2-oleoyl glycerol (POP), 1, 3-racpalmitoyl-stearoyl-2-oleoyl glycerol (POS), and 1,3-distearoyl-2-oleoyl glycerol (SOS). Specific attention has been paid to glycerol, carbonyl, olefinic, and methyl end carbon resonances. Many distinct differences were observed in each polymorphic form of SOS. In the α form, the saturated and unsaturated acyl chains exhibit liquid state-like conformations. However, olefinic conformations of the γ and β′ forms were asymmetric with respect to thecis double bond. Spectral difference between β₂ and β₁ was observed only for the methylene carbon, and not in the other regions. Spectra of corresponding polymorphic forms of POP and POS were almost identical to those of SOS. However, some spectral differences were observed in the glycerol and methyl regions of γ and β′. From the chemical shifts of the methylene carbons, the crystal structures of the polymorphic form have been discussed, particularly in terms of the subcell structures.     

Polymorphism of pos. I. occurrence and polymorphic transformation

Polymorphic behavior of 1,3-rac-palmitoyl-stearoy 1-2-oleoylglycerol, 99.9% purity (POS) was examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), solubility measurements and optical microscopy in comparison with 1,3-dipalmitoyl-2-oleoylglycerol (POP) and 1,3-distearoyl-2-oleoylglycerol (SOS). Melt crystallization and solvent crystallization were examined for the occurrence of metastable and stable polymorphs. The number of independent polymorphs was four; α,δ, pseudoβ′ andβ. The lowest melting form, α, was identical to that commonly observed in POP and SOS lowest melting forms. As to the highest melting form,β, the XRD shortspacing pattern was identical toβ ₁ of POP and SOS. This is consistent with crystal habit:β single crystals of POS showed the same shape as those of β₁ of POP and SOS. However, the melting point ofβ (POS), 35.9°C, was lower than those ofβ ₁ of POP, 36.7°C, and of SOS, 43.0°C. Correspondingly, solubility ofβ of POS was lower than that of β₁ of POP below about 13°C, but higher above 13°C. POS did not possessβ ₂ , which is the second stable form in POP and SOS. Two forms of6 and pseudoβ′ occurred, the latter being more stable. The structural properties ofδ showed thatδ is not identical toγ previously observed in POP and SOS. Transformation behavior from the metastable to stable polymorphs of POS showed some differences from those of POP and SOS. Presented at the AOCS annual meeting in Cincinnati, Ohio, in May 1989.     

Synchrotron radiation X-ray diffraction study on phase behavior of PPP-POP binary mixtures

The phase behavior of thesn-1,3-dipalmitoyl-2-oleoylglycerol (PPP-POP) binary mixture system was studied by powder X-ray diffraction with synchrotron radiation and by differential scanning calorimetry. The results showed that the immiscible phases were observed in metastable and in the most stable forms. In particular, synchrotron X-ray diffraction enabled us to reveal the monotectic nature of α as a kinetic phase behavior. The equilibrium phase diagram of the PPP-POP mixture is divided into two regions. In POP concentration ratios below 40%, solid-state transformation from α to β was observed, indicating that the α-β transition of PPP was promoted in the presence of POP. By contrast, the polymorphic transition proceeds from α to β through the occurrence of the intermediate β′ form at POP concentration ratios above 50%.     

Phase Equilibrium and Optimization Tools: Application for Enhanced Structured Lipids for Foods

Solid–liquid phase equilibrium modeling of triacylglycerol mixtures is essential for lipids design. Considering the α polymorphism and liquid phase as ideal, the Margules 2-suffix excess Gibbs energy model with predictive binary parameter correlations describes the non ideal β and β′ solid polymorphs. Solving by direct optimization of the Gibbs free energy enables one to predict from a bulk mixture composition the phases composition at a given temperature and thus the SFC curve, the melting profile and the Differential Scanning Calorimetry (DSC) curve that are related to end-user lipid properties. Phase diagram, SFC and DSC curve experimental data are qualitatively and quantitatively well predicted for the binary mixture 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP) and 1,2,3-tripalmitoyl-sn-glycerol (PPP), the ternary mixture 1,3-dimyristoyl-2-palmitoyl-sn-glycerol (MPM), 1,2-distearoyl-3-oleoyl-sn-glycerol (SSO) and 1,2,3-trioleoyl-sn-glycerol (OOO), for palm oil and cocoa butter. Then, addition to palm oil of Medium-Long-Medium type structured lipids is evaluated, using caprylic acid as medium chain and long chain fatty acids (EPA-eicosapentaenoic acid, DHA-docosahexaenoic acid, γ-linolenic-octadecatrienoic acid and AA-arachidonic acid), as sn-2 substitutes. EPA, DHA and AA increase the melting range on both the fusion and crystallization side. γ-linolenic shifts the melting range upwards. This predictive tool is useful for the pre-screening of lipids matching desired properties set a priori.     

Efficient Production of 1,3-Dioleoyl-2-Palmitoylglycerol through Rhodococcus opacus Fermentation

1,3-Dioleoyl-2-palmitoylglycerol (OPO) is the main triacylglycerol species in human milk-fat substitute. The production of OPO is of considerable research interest. In this study, a new strategy for producing OPO by fermentation with R. opacus is proposed. Chemically Interesterified fat (high oleic acid sunflower oil/hydrogenated palm oil 1.73:1 w/w), or a mixture of ethyl oleate/ethyl palmitate 2:1 (w/w) as a starting material. The highest biomass and oil content obtained were 3.3 g L⁻¹ and 40.2% (dry cell weight), respectively. The yield of OPO was 0.62 g L⁻¹. The fatty acid composition of produced OPO was 55.7–59.7% 18:1 and 28.3–29.8% 16:0, and the sn-2 position was predominantly 16:0 (64.7–74.5%). ¹³C-nuclear magnetic resonance analysis showed that the sn-1,3 and sn-2 positions were predominately esterified by 18:1 and 16:0, respectively. OPO (47.1%), OPL (13.9%), PPO (13.1%), and PPoO (16:0–16:1–18:1) (10.3%) were the most abundant triacylglycerol species.     

Polymorphism of POP and SOS. II. kinetics of melt crystallization

Melt crystallization of the polymorphs of SOS, α,γ, pseudo-β′, β₂ and β₁. and of POP, α,γ, pseudo-β′₂ pseudo-β ₁, β₂andβ ₁was examined using pure samples (99.9%). Induction time τ for newly occurring crystals in the melt phase was measured with a polarizing microscope equipped with a temperature-controlled growth cell. Rate of crystallization, 1/τ, was obtained for each polymorph of POP and SOS whose identification was done with X-ray diffraction and differential scanning calorimetry (DSC). Two modes of crystallization, melt-cooling and melt-mediation, yielded approximately the same results for POP and SOS: (a) The rates of crystallization were always higher in less stable than in more stable forms,β ₂only crystallized via a γ-melt mediation, butβ ₁did not occur by the melt crystallization; (b) the rate of meltmediated crystallization was always higher than the simple melt-cooling as examined at the same crystallization temperature; (c) the occurrence behavior of the polymorphs differed between the simple-cooling and meltmediation. The results were related to the solidification behavior of the polymorphs of cocoa butter. Presented at the AOCS Annual Meeting in Phoenix, Arizona in May 1988.     

On the formation of granular crystals in fat blends containing palm oil

The use of palm oil for plastic fats has encountered serious difficulty due to its crystallization properties, one of which is the formation of granular crystals. The granular crystals cause sandy teste and inhomogeneity of fat crystal morphology of end products. In the present study, we analyzed the formation process of these granular crystals. Chemical and physical analyses for triacylglycerol (TAG) compositions, polymorphism and melting points of the granular crystals led to the conclusion that the granular crystals are of the most stable polymorph, β₁, of POP (1,3-dipalmitoyl 2-oleoyl glycerol) with triple chainlength fat blend consisting of POP and reapeseed oil. The following characteristics of β₁ polymorph of POP contribute to the formation of granular crystals in fat blends containing palm oil: (i) β₁ reveals well-defined plate-like crystal morphology, which grows easily into the bulky granular from; (ii) the triple chainlength structure of POP has a tendency to segregate and does not from a solid solution together with other TAGs.     

Preparation of Infant Formula Fat Analog Containing Capric Acid and Enriched with DHA and ARA at the sn-2 Position

An infant formula fat analog with capric acid mostly esterified at the sn‐1,3 positions, and substantial amounts of palmitic, docosahexaenoic (DHA), and arachidonic (ARA) acids at the sn‐2 position, was prepared by physically blending enzymatically synthesized structured lipids (SL) with vegetable oils. The components of the blend included high sn‐2 palmitic acid SL enriched with capric acid (SL_CA), canola oil (CAO), corn oil (CO), high sn‐2 DHA (DHAO_m), and high sn‐2 ARA (ARAO_m) enzymatically modified oils. Each component was proportionally blended to match the fatty acid profile of commercial fat blends used for infant formula. The infant formula fat analog (IFFA₁) was characterized for total and positional fatty acids (FA), triacylglycerol (TAG) molecular species, thermal behavior, and tocopherol content. IFFA₁ contained 17.37 mol% total palmitic acid of which nearly 35 % was located at the sn‐2 position. The total capric acid content was 13.93 mol%. The content of DHA and ARA were 0.49 mol% (48.18 % at sn‐2) and 0.57 mol% (35.80 % at sn‐2), respectively. The predominant TAG were OPO (24.09 %), POP (15.70 %), OOO (11.53 %), and CLC (7.79 %). The melting completion and crystallization onset temperatures were 18.65 and ?2.19 °C, respectively. The total tocopherol content was 566.45 μg/g. This product might be suitable for commercial production of infant formulas.     

Structural investigations of β′ triacylglycerols: An x-ray diffraction and microscopic study of twinned β′ crystals

To reveal the structure ofβ′ triacylglycerols in detail, LML (C₁₂C₁₄C₁₂) was purified by a zone-melting procedure, and twinned crystals ofβ′ stable LML were obtained from a melt,β′ LML crystallizes in the monoclinic space group C₂, with eight molecules in the unit cell. A powder X-ray diffraction study of solid compounds of 1:1 mixtures of selected triacylglycerols led to the conclusion that the triacylglycerol molecules in theβ modification have a 1,2 chair-conformation (i.e., the fatty acid chains on glycerol positions 1 and 2 are adjacent, with the chain on the 3-position forming the back rest of the chair). Packing studies and the positions of two-fold axes and two-fold screw axes in the unit cell require that the molecules are bent at the glycerol site. The fatty acid chains make an angle of 25° with the long axis of the unit cell. Electron micrographs and precession photographs indicate that the twinning results from the stacking of a large number of thin crystalline platelets in two distinct orientations.     

Synthesis of the structured lipid 1,3-dioleoyl-2-palmitoylglycerol from palm oil

Human milk fat contains 20–25% palmitic acid (16∶0) and 30–35% oleic acid (18∶1). More than 60% of the plamitic acid occurs at the sn-2 position of the glycerol backbone. Palm oil is a rich source of both palmitic and oleic acids. The structured lipid 1,3-dioleyl-2-palmitoylglycerol (OPO) is an important ingredient in infant formula. OPO was synthesized from palm oil by a three-step method. In the first step, low-temperature fractionation was applied to palm oil FA, yielding a palmitic acid-rich fraction (87.8%) and an oleic acid-rich fraction (96%). The palmitic acid content was further increased to 98.3% by transforming palmitic acid into ethyl palmitate. In the second step, esterification of ethyl palmitate and glycerol catalyzed by lipase Novozym 435 under vacuum (40 mm Hg) was employed for the synthesis of tripalmitin. Finally, OPO was obtained by the reaction of tripalmitin. Finally, OPO was obtained by the reaction of tripalmitin with oleic acid catalyzed by Lipase IM 60. In this final step, the TAG content in the product acylglycerol mixture was 97%, and 66.1% oleic acid was incorporated into TAG. Analysis of the FA composition at the sn-2 position of TAG showed 90.7 mol% of palmitic acid and 9.3 mol% of oleic acid. OPO content in the product TAG was ca. 74 mol%. Thus, an efficient method was developed for the synthesis of OPO from palm oil.     

Contribution of triglycerides from cocoa butter to the physical properties of milkfat fractions

Milkfat was separated into major chainlength fractions by solid-phase extraction. The effect on thermal behavior and texture of replacing both saturated and monounsaturated long-chain triglycerides from milkfat by long-chain monounsaturated triglycerides with an unsaturated fatty acid in thesn-2 position is reported. Increasing proportions of cocoa butter were added to fractions of short-to medium-chain triglycerides (C₂₂−C₄₄) and medium- to long-chain triglycerides (C₃₆−C₄₈) isolated from milkfat. Thermal behavior and texture of the mixtures were measured. Results indicated that long-chain monounsaturated triglycerides from cocoa butter enhanced co-crystallization and co-operative melting and did not induce polymorphic transitions upon crystallization and melting of the fractions. At 4°C, they acted as texture builder if present in proportions of more than 30%, whereas below this level, they acted as texture softeners. The effect of the long-chain monounsaturated triglycerides on the texture of fractions that melt at low temperature could not be predicted from the proportion of solid fat at that temperature. Presented at the 1995 AOCS Annual Meeting & Expo, San Antonio, Texas, May 1995.     

Mixing Phase Behavior of 1,3-Dipalmitoyl-2-Oleoyl-sn-Glycerol (POP) and 1,2-Dipalmitoyl-3-Oleoyl-rac-Glycerol (PPO) in n-Dodecane Solution

We examined the mixing phase behavior of 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP) and 1,2-dipalmitoyl-3-oleoyl-rac-glycerol (PPO) in organic solutions containing n-dodecane (C₁₂) as a solvent to confirm whether the molecular compound (MC) crystals of POP/PPO are formed as metastable and most stable forms in the dilute solution by using DSC and synchrotron radiation X-ray diffraction. The POP/PPO mixtures were prepared at different concentration ratios of POP and PPO with a 10 % increment in two solutions having weight concentration ratios of (POP+PPO):C₁₂ of 50:50 (50 % solution) and 20:80 (20 % solution). We found that MC crystals formed at a ratio of POP/PPO = 50/50 having the melting point of 23.1 and 20.6 °C in 50 and 20 % solution systems in stable states of incubated samples, respectively. The metastable (β′) and stable (β) forms of MC of POP/PPO = 50/50 having a double-chain-length structure were confirmed in kinetic behavior and thermodynamically stable states attained after long time incubation, in contrast to the triple-chain-length structure of stable forms of POP (β) and PPO (β′). In addition, we observed the formation of MC crystals of POP/PPO in diluted solutions having n-dodecane concentrations up to 98 % and conclude that molecular interactions between POP and PPO molecules to form MC crystals are not altered by solvent molecules in diluted solutions.     

The polymorphism of odd and even saturated single acid triglycerides,C8–C22

The polymorphism of single fatty acid odd triglycerides, C₁₁ through C₁₇ has been reinvestigated, with extension of the study to C₉, C₁₉ and C₂₁. With study of the even glycerides C₈, C₂₀ and C₂₂ it has been possible to review the whole series (odd and even) C₈ through C₂₂. The odd glycerides resemble the even in showing three distinct melting levels. Lowest melting forms are α. Stable forms are β except for C₉ and C₁₁ which show a different structure type. Intermediate melting β′ forms of odd glycerides are substantially more stable than their even counterparts as well illustrated by differential thermal analysis. There are no vitreous forms. Alternation in mp (between odd and even) is confirmed for stable phases and nonalternation for α and (within experimental error) for β′. Both β′ and β long spacings show alternation but not α. Alternation is evident in the short spacings of β′ and β forms. While short spacings of β′ forms of even triglycerides are much alike especially for C₁₄ through C₂₂, those of odd glycerides show a fortuitous 4-carbon cycle. This appears to involve no significant structural variation as chain length increases but simply an approximate 4-carbon cycle of variation in diffraction details derived from the presumed unvarying 0 ⊥ type subcell structure.     

Enzymatic synthesis of position-specific low-calorie structured lipids

An immobilized sn-1,3-specific lipase from Rhizomucor miehei (IM 60) was used to catalyze the interesterification of tristearin (C_18:0) and tricaprin (C_10:0) to produce low-calorie structured lipids (SL). Acceptable product yields were obtained from a 1:1 mole ratio of both triacylglycerols with 10% (w/w of reactants) of IM 60 in 3 mL hexane. The SL molecular species, based on total carbon number, were 44.2% C₄₁ and 40.5% C₄₉, with 3.8 and 11.5% unreacted tristearin C₅₇ and tricaprin C₂₇, respectively, remaining in the product mixture. The best yield of C₄₁ species (44.3%) was obtained with zero added water. Tricaprylin (C_8:0) was also successfully interesterified with tristearin in good yields at 1:1 mole ratio. Products were analyzed by reverse-phase high-performance liquid chromatography with an evaporative light-scattering detector. Reaction parameters, such as substrate mole ratio, enzyme load, time course, added water, reaction media, and enzyme reuse, were also investigated. Hydrolysis by pancreatic lipase revealed the specific fatty acids present at the sn-1,3 positions of SL. Biocatalysis Symposium Paper, presented at the AOCS Annual Meeting & Expo, Seattle, Washington. May 11–14, 1997.