Enhancement of both reaction yield and rate of synthesis of structured triacylglycerol containing eicosapentaenoic acid under vacuum with water activity control

Synthesis of structured lipids by lipase-catalyzed interesterification of triacetin with camellia oil methyl esters and preliminary evaluation of their plasma lipid-lowering effect in mice

Structured lipids (SLCTs triacylglycerols with short- and long-chain acyl residues) were synthesized by interesterification of triacetin and fatty acid methyl esters (FAMEs) from camellia oil, followed by molecular distillation for purification. Different commercial immobilized lipases (Lipozyme RM IM and Novozyme 435), the substrate molar ratios of FAMEs to triacetin, the reaction temperatures and the lipase amounts were studied for their efficiency in producing SLCTs. Results showed that Novozyme 435 was more suitable for this reaction system. Moreover, the optimal reaction conditions for the highest conversion of FAMEs and the highest LLS-TAGs (triacylglycerols with one short- and two long-chain acyl residues) yields were achieved at a molar ratio of FAMEs to triacetin of 3:1, 50 °C of reaction temperature and a lipase amount of 4% (w/v). Scale-up was conducted based on the optimized reaction conditions. Results showed that after 24 h of reaction , the conversion rate of FAMEs was 82.4% and the rate of disubstituted triacetin was 52.4 mol%. The final product yield rate was 94.6%. The effects of the synthesized SLCTs on the plasma lipid level of fasting mice were also studied. The SLCTs could effectively lessen the total triacylglycerol levels in plasma compared to the triacylglycerol group in fasting NIH mice. It suggested that this type of structured lipid might be beneficial for human health, especially for the prevention of obesity.

Acidolysis between triolein and short-chain fatty acid by lipase in organic solvents

Ten kinds of lipases were examined as biocatalysts for the incorporation of short-chain fatty acids (acetic, propionic, and butyric acids) into triolein in order to produce one kind of reduced-calorie structured lipids. Trans-esterification (acidolysis) was successfully done in n-hexane by several microbial lipases. Among them, lipase from Aspergillus oryzae was used to investigate the effects of incubation time, substrate molar ratio, and water content on acidolysis. Finally, more than 80% of triolein was incorporated by butyric acid (molar ratio of triolein to butyric acid, 1:10) in the dried n-hexane at 52 degrees C for 72 h. More than 90% of the products was monosubstituent, which was esterified with this short chain fatty acid at the 1-position of the glycerol moiety of triolein. These results suggest that A. oryzae lipase would be a powerful biocatalyst for the synthesis of low caloric oil, such as triacylglycerol containing a mixture of long- and short-chain aliphatic acids.

Off-line coupling of non-aqueous reversed-phase and silver ion high-performance liquid chromatography–mass spectrometry for the characterization of rice oil triacylglycerol positional isomers

The determination of the triacylglycerol (TAG) profile in real world matrices is rather difficult as these compounds present a complex composition and are characterized by similar physico-chemical properties. This investigation is based on the high-performance liquid chromatography (HPLC) multidimensional determination of the TAG profile in terms of TAG species and positional isomers in a rice oil sample. The off-line bi-dimensional system was attained through the coupling of non-aqueous reversed-phase HPLC and silver ion (Ag)-HPLC. The primary column eluate was fractionated and the fractions of interest were then injected onto the secondary column, allowing the separation of several TAG positional isomers, unresolved in the first dimension. Peak assignment was carried out by combining retention data with atmospheric pressure chemical ionisation (APCI) MS spectra information. The fatty acid distribution along the glycerol backbone, determined by Ag-HPLC, was confirmed through diglyceride ion ratios derived from APCI-MS analysis. Method validation, where both precision and accuracy were measured, was carried out in preliminary applications on standard compounds. The analytical results obtained show that rice oil TAGs follow a distribution which can be considered typical for vegetable oils.

Detailed analysis and group-type separation of natural fats and oils using comprehensive two-dimensional gas chromatography

Comprehensive gas chromatography (GC x GC) is an adequate methodology for the separation and identification of very complex samples. It is based on the coupling of two capillary columns that each give a different but substantial contribution to the unprecedented resolving power of this technique. The 2D space chromatograms that derive from GC x GC analysis have great potential for identification. This is due to the fact that the contour plot positions, pinpointed by two retention time coordinates, give characteristic patterns for specific families of compounds that can be mathematically translated. This investigation concerned the application of this principle to fatty acid methyl esters that were grouped on an equal double bond number basis. The ester samples were derived from various lipids and all underwent bidimensional analysis on two sets of columns. Peak attribution was supported by mass spectra, linear retention indices and information reported in the literature.

Behavior of silica aerogel networks as highly porous solid solvent media for lipases in a model transesterification reaction

Highly porous silica aerogels with differing balances of hydrophobic and hydrophilic functionalities were studied as a new immobilization medium for enzymes. Two types of lipases from Candida rugosa and Burkholderia cepacia were homogeneously dispersed in wet gel precursors before gelation. The materials obtained were compared in a simple model reaction: transesterification of vinyl laurate by 1-octanol. To allow a better comparison of the hydrophobic/hydrophilic action of the solid, very open aerogel networks with traditional organic hydrophobic/hydrophilic liquid solvents, this reaction was studied in mixtures containing different proportions of 2-methyl-2-butanol, isooctane, and water. The results are discussed in relation to the porous and hydrophobic nature of aerogels, characterized by nitrogen adsorption. It was found that silica aerogels can be considered as "solid" solvents for the enzymes, able to provide hydrophobic/hydrophilic characteristics different from those prevailing in the liquid surrounding the aerogels. A simple mechanism of action for these aerogel networks is proposed.

Structured Lipids-Novel Fats with Medical, Nutraceutical, and Food Applications

Generally, structured lipids (SLs) are triacylglycerols (TAGs) that have been modified to change the fatty acid composition and/or their positional distribution in glycerol backbone by chemically and/or enzymatically catalyzed reactions and/or genetic engineering. More specifically, SLs are modified TAGs with improved nutritional or functional properties. SLs provide an effective means for producing tailor-made lipids with desired physical characteristics, chemical properties, and/or nutritional benefits. The production, commercialization outlook, medical, and food applications of SLs are reviewed here. Physical property measurements for SL in food systems and future research needs for increased industrial acceptance are also included in this review.

Computer-aided real-time estimation of reaction conversion for lipase-catalyzed esterification in solvent-free systems

Real-time conversion estimation through macroscopic balancing was investigated for enzymatic esterification reactions in a solvent-free system. In principle, the conversion of ester synthesis can be determined from the amount of water produced by the reaction because water is formed as a by-product in the same molar ratio as the product. In this study, we show that the water production rate, and thereby the reaction conversion, can be estimated on-line from measurements of the relative humidity of the inlet and outlet air and the material balances of water in the system. In order to test the performance of the real-time conversion estimation method, the lipase-catalyzed esterification reaction of n-capric acid and n-decyl alcohol in solvent-free media was conducted while controlling the water activity at various values. When the reaction conversions estimated on-line were compared with those analyzed off-line by gas chromatography, good agreement was obtained: the average mean absolute error was +/- 2.4% of the reaction conversion despite the simplicity of the method. The on-line estimation method presented here requires no expensive or complicated analytical instruments and no sampling of reaction medium. It can be used for monitoring nonaqueous enzymatic reactions where water is produced or consumed during reaction.

Plant lipases: biocatalyst aqueous environment in relation to optimal catalytic activity in lipase-catalyzed synthesis reactions

Adsorption and desorption isotherms of two commercial enzyme preparations of papain and bromelain were determined with a Dynamic Vapor System. The Guggenheim-Anderson-deBoer (GAB) modeling of the obtained sorption isotherms allowed the definition of different levels of hydration of those samples. Afterward, these enzyme preparations were used as biocatalysts in water and solvent-free esterification and alcoholysis reactions. The evolution of the obtained fatty acid ester level as a function of the initial hydration level of the biocatalyst, i.e., thermodynamic water activity (a(w)) and water content, was studied. The results show an important correlation between the initial hydration level of the biocatalyst and its catalytic activity during the lipase-catalyzed synthesis reactions. Thus, the Carica papaya lipase (crude papain preparation) catalytic activity is highly dependent on the biocatalyst hydration state. The optimized synthesis reaction yield is obtained when the a(w) value of the enzyme preparation is stabilized at 0.22, which corresponds to 2% water content. This optimal level of hydration occurs on the linear part of the biocatalyst's sorption isotherm, where the water molecules can form a mono- or multiple layer with the protein network. The synthesis reaction yield decreases when the a(w) of the preparation is higher than 0.22, because the excess water molecules modify the system equilibrium leading to the reverse and competitive reaction, i.e., hydrolysis. These results show also that an optimal storage condition for the highly hydrophilic crude papain preparation is a relative humidity strictly lower than 70% to avoid an irreversible structural transition leading to a useless biocatalyst. Concerning the bromelain preparation, no effect of the hydration level on the catalytic activity during esterification reactions was observed. This biocatalyst has too weak a catalytic activity which makes it difficult to observe any differences. Furthermore, the bromelain preparation is far more hydrophobic as it adsorbs only 18 g of water per 100 g of dry material at a(w) around 0.90. No deliquescence of this enzymatic preparation is observed at this a(w) value.

Optical resolution of asymmetric triacylglycerols by chiral-phase high-performance liquid chromatography

A simple method for direct optical resolution of some asymmetric triacylglycerols (TGs) has been established. The method employs chiral-phase high-performance liquid chromatography (HPLC). An enantiomeric pair of TGs comprising 1-eicosapentaenoyl-2,3-dicapryroyl-sn-glycerol (ECC) and 1,2-dicapryroyl-3-eicosapentaenoyl-sn-glycerol (CCE) was resolved on a CHIRALCEL OF or on a CHIRALCEL OD column. The separation of another pair of asymmetric TGs, 1-docosahexaenoyl-2,3-dicapryroyl-sn-glycerol (DCC) and 1,2-dicapryroyl-3-docosahexaenoyl-sn-glycerol (CCD), was achieved with the CHIRALCEL OD column. The chiral-phase HPLC method in combination with silver-ion HPLC and high-temperature gas chromatography was used for monitoring two interesterification reactions, whose products were chiral TGs. Interesterification of tricapryloylglycerol with ethyleicosapentaenoate or with ethyldocosahexaenoate was performed using Rhizomucor miehei lipase as the catalyst. The products targeted were the asymmetric pair of TGs, ECC and CCE or DCC and CCD. The amounts of sn-1-substituted products (ECC or DCC) were greater than their sn-3-substituted counterparts (CCE or CCD) throughout the reaction period, suggesting that R. miehei lipase had a stereopreference towards the sn-1 position over the sn-3 position.