Variation of lipid and tocopherol composition in three strains of channel catfish (Ictalurus punctatus)

Three strains of channel catfish (Ictalurus punctatus), which were designated as ‘AQUA’, ‘LSU’ and ‘MSU’, were examined for their lipid and tocopherol composition to delineate if genetic strains exhibited the potential to vary in their susceptibility to lipid oxidation. Since age, diet and environmental conditions were similar for all strains, growth and compositional differences were ascribed to genetic factors. Significant differences were noted between strains in their muscle tissue for triacylglycerol (TG) levels, fatty acid composition, and tocopherol levels. The largest quantity of TG was found in the LSU strain whereas the smallest quantity was found in the AQUA strain. Levels of polyunsaturated fatty acids (PUFA) in the TG and total lipid (TL) fraction were highest in the AQUA strain and lowest in the MSU strain. Similarly, a peroxidizability index, which took into account the differences in susceptibility of unsaturated fatty acids to oxidize, was highest in AQUA and lowest in MSU for the TG and TL fractions. The peroxidizability index for the phospholipid fraction did not vary between strains. Adopting a relative antioxidant effectiveness value of 0.31 for γ-tocopherol, the LSU, MSU and AQUA catfish strains were calculated to contain 37.72, 22.79 and 42.49 nmol of α-tocopherol equivalents, respectively. The MSU catfish strain exhibited the highest ratio (nmol PUFA/nmol α-tocopherol equivalents) suggesting that its tissue would be the least stable to oxidation.     

Lipase-catalyzed modification of borage oil: Incorporation of capric and eicosapentaenoic acids to form structured lipids

Two immobilized lipases, nonspecific SP435 from Candida antarctica and sn-1,3 specific IM60 from Rhizomucor miehei, were used as biocatalysts for the restructuring of borage oil (Borago officinalis L.) to incorporate capric acid (10:0, medium-chain fatty acid) and eicosapentaenoic acid (20:5n-3) with the free fatty acids as acyl donors. Transesterification (acidolysis) reactions were carried out in hexane, and the products were analyzed by gas-liquid chromatography. The fatty acid profiles of the modified borage oil were different from that of unmodified borage oil. Higher incorporation of 20:5n-3 (10.2%) and 10:0 (26.3%) was obtained with IM60 lipase, compared to 8.8 and 15.5%, respectively, with SP435 lipase. However, SP435 lipase was able to incorporate both 10:0 and 20:5n-3 fatty acids at the sn-2 position, but the IM60 lipase did not. Solvents with log P values between 3.5 and 4.5 supported the acidolysis reaction better than those with log P values between −0.33 and 3.0.     

Deterioration of diacylglycerol‐ and triacylglycerol‐rich oils during frying of potatoes

The stabilities of a commercial diacylglycerol‐rich oil (DAG) and a salad oil (TAG) that had been prepared from a mixture of rapeseed and soybean oils were compared while frying potatoes at 180 °C for 3 h. The representative chemical and physical characteristics of the oils were assessed before and after frying, together with the amount of volatile aldehydes in the exhaust of frying. Among the deterioration indications, the carbonyl value, polymer content, and residual polyunsaturated fatty acid content were similar and not significantly different between the TAG and DAG. On the other hand, the characteristics relating to free fatty acids, i.e. the acid value and emission of chemiluminescence at 100 °C, were greater and the smoke and flash points were lower in the DAG than in the TAG. An irritating odor was generated from the DAG after 1 h of frying and got stronger as frying continued. These results suggested that DAG more easily forms free fatty acids under frying conditions than TAG.     

Production of microparticles from milk fat products using the Supercritical Melt Micronization (ScMM) process

The ScMM (Supercritical Melt Micronization) process was applied for the production of microparticles from anhydrous milk fat (AMF) and a diacylglycerol-based modified milk fat (D-AMF). Both fats were able to dissolve ca. 30 wt% CO₂ in the studied pressure and temperature ranges, being the CO₂ amount slightly higher for AMF. A melting point depression was observed in both systems in the presence of CO₂. Two powder morphologies were obtained (spherical hollow particles and a mass sponge-like broken particles) depending on the ScMM process conditions. The concentration of CO₂ in the fat melt was the main process variable affecting the particle morphology, followed by the temperature of the melt. The small broken particles originated from the breakage of spherical fat particles that solidified before all CO₂ could escape from the atomized droplets. While the hollow spheres had a tendency to agglomerate, the broken microparticles constituted a free-flowing powder as long as they were stored at low temperatures (up to −18 °C). Both types of particles have a potential for being incorporated in refrigerated or frozen food products as a structuring agent.     

Identification of a triacylglycerol lipase gene family in Candida deformans: molecular cloning and functional expression

The yeast Candida deformans CBS 2071 produces an extracellular lipase which was shown to catalyse the production of various esters by the esterification of free fatty acids, even in the presence of a large molar excess of water. To clone the gene encoding this extracellular lipase, Saccharomyces cerevisiae was transformed with C. deformans genomic libraries and screened for lipolytic activity on a medium containing rapeseed oil emulsion and rhodamine B. Three members of a lipase gene family (CdLIP1, CdLIP2 and CdLIP3) were cloned and characterized. Each deduced lipase sequence has a Gly-His-Ser-Leu-Gly-(Gly/Ala)-Ala conserved motif, eight cysteine residues and encodes an N-terminal signal sequence. MALDI-TOF mass spectrometry analysis of a proteolytic digest of the lipase produced was used to obtain experimental evidence that the CdLIP1 gene encoded the extracellular lipase. Recombinant expression studies confirmed that the cloned genes encoded functional lipases. The three lipases are very similar to lipases from the related species Yarrowia lipolytica. Significant homologies were also found with several yeast and fungal lipases. As C. deformans CBS 2071 was previously considered to be synonymous with Y. lipolytica, the strains were compared for the extent of nucleotide divergence in the variable regions (D1/D2) at the 5'-end of the large-subunit (26S) ribosomal DNA (rDNA) gene. This rDNA region has diverged sufficiently to suggest that C. deformans is a separate species. The nucleotide sequences of the CdLIP1, CdLIP2 and CdLIP3 genes will appear in the EMBL nucleotide sequence database under Accession Nos AJ428393, AJ428394 and AJ428395, respectively.     

Effects of the degree of unsaturation of coexisting triacylglycerols on cholesterol oxidation

In order to evaluate the effects of the degree of unsaturation of triacylglycerols on cholesterol oxidation, mixtures of purified sardine oil triacylglycerols (iodine value, IV=182.6) and cholesterol; of partially hydrogenated sardine oil triacylglycerols (IV=174.5) and cholesterol; and of fully hydrogenated sardine oil triacylglycerols (IV=92.0) and cholesterol were incubated at 25°C in the dark. The oxidative stability of the samples decreased with increasing degree of unsaturation of the triacylglycerols in the sample mixtures; the induction period for peroxide values (PV) of the sardine oil triacylglycerols and cholesterol was shorter than that of the partially hydrogenated sardine oil triacylglycerols and cholesterol. Certain polyunsaturated fatty acids (PUFAs) in the constituent fatty acids of sardine oil triacylglycerols started to decrease after a shorter induction period compared with that of the partially hydrogenated triacylglycerols. The prominent cholesterol oxides accumulated in the samples were 7β-hydroxycholesterol, 7-ketocholesterol, β-epoxide and cholestane triol. The tendency for accumulation of cholesterol oxides in the time course coincided with the changes in PV as well as the decrease in PUFAs. Cholesterol was oxidized in conjunction with autoxidation of coexisting fish oil triacylglycerols. Although lowering the degree of unsaturation of fish oil triacylglycerols was effective in prolonging the induction period of cholesterol oxidation, the rate of cholesterol oxidation in the cholesterol oxides' formation phase after the induction period was not affected by the difference in the proportion of highly unsaturated fatty acids in the natural and partially hydrogenated triacylglycerols of fish oils.     

Crystallization kinetics of the pure triacylglycerols glycerol-1,3-dipalmitate-2-oleate,glycerol-1-palmitate-2-oleate-3-stearate,and glycerol-1,3-distearate-2-oleate

Crystallization kinetics of the three main components of cocoa butter, the triacylglycerols POP, POS, and SOS (where P, O, and S stand for palmitic, oleic, and stearic acids, respectively) were studied by combined differential scanning calorimetry and polarized light microscopy. The morphologies, nucleation kinetics, growth kinetics, and phases of the grains formed were identified with this system. The experimental data, as well as two different models to simulate crystallization and to predict behavior of the pure triacylglycerols, are presented. The first model is based on a macroscopical approach to solidification by using time-temperature-transformation (TTT) diagrams and the additivity principle. It allows prediction of the proportion of the different phases formed for any given thermal path imposed on the sample once the TTT diagram is known for the product. It is illustrated for SOS at constant cooling rates and is compared with experimental results. The second model directly simulates growth of the spherulites in the sample by using nucleation and growth rates that are determined experimentally. It provides a view of the structure as it would be observed with a microscope and shows evolution of the heat released in the sample. Isothermal solidification of POP at 15°C is displayed. The experiment and the model are in good agreement.     

Optimisation of tripalmitin‐rich fractionation from palm stearin by response surface methodology

BACKGROUND: Solvent fractionation is effective in improving separation at low temperature, resulting in higher yield and purity of the final product. Tripalmitin (PPP) is an important substrate for the synthesis of human milk fat substitute (HMFS). In this study a fraction rich in PPP was separated from palm stearin by solvent fractionation. RESULTS: The PPP‐rich fraction was concentrated from palm stearin by acetone fractionation. Response surface methodology (RSM) was employed to optimise PPP purity (Y₁, %) and PPP content (Y₂, g kg^?1 palm stearin) with the independent variables fractionation temperature (X₁, 25, 30 and 35 °C) and weight ratio of palm stearin to acetone (X₂, 1:3, 1:6 and 1:9). The predictive models for PPP purity and PPP content of the solid fraction were adequate and reproducible, with no significant lack of fit and satisfactory levels of R². PPP purity showed a positive correlation with temperature and acetone ratio, whereas PPP content exhibited a negative correlation. The optimised fractionation condition for a targeted PPP‐rich fraction with > 92% PPP purity and > 225 g kg^?1 PPP content from palm stearin was predicted. CONCLUSION: The RSM model for optimising PPP purity and PPP content in the PPP‐rich fraction from palm stearin by acetone fractionation was valid. The scaled‐up PPP‐rich fraction obtained can be used as a substrate for the synthesis of 1,3‐dioleoyl‐2‐palmitoylglycerol, which is a main component of HMFS in infant formulas. Copyright © 2010 Society of Chemical Industry