Triglyceride composition of ewe,cow, and goat milk fat

The separation and identification of the components in milk fat, which are mainly triglycerides, is a challenge due to its complex composition. A reverse-phase high-performance liquid chromatography (HPLC) method with gradient elution and light-scattering detection is described in this paper for the triglyceride analysis in ewes’ milk fat. Triglyceride identification was carried out by combining HPLC, gas-liquid chromatography (GLC), and the calculated equivalent carbon numbers of several triglyceride standards. Quantitation of partially resolved peaks in the HPLC chromatogram was accomplished by applying a peak deconvolution program. Forty-four fatty acids were identified by GLC analysis, but only 19 were used for the following prediction of triglyceride molecular species; 181 triglycerides were identified, some of which were grouped at the same peak and needed application of the deconvolution program. Consequently, coefficients of variation were close to or lower than 5%. Moreover, the triglyceride composition of ewe, cow, and goat milk fat were compared by using these methods. These results show that ewe milk fat is richer in short- and medium-chain triglycerides, and cow milk fat is richer in long-chain and unsaturated triglycerides.     

Lipid domains in the milk fat globule membrane: Specific role of sphingomyelin

Lipids are secreted in milk in the form of unique colloidal assemblies, the milk fat globules, which are surrounded by a biological membrane, the milk fat globule membrane (MFGM). Recent confocal laser scanning microscopy experiments showed heterogeneities in the composition and structure of the MFGM. For the first time, we revealed the phase separation of polar lipids in the plane of the MFGM with the lateral segregation of sphingomyelin and cholesterol in rigid liquid‐ordered (L_o) domains surrounded by the fluid matrix of glycerophospholipids in the liquid‐disordered (L_d) phase. The MFGM is a unique and highly dynamic biophysical system, the functional and nutritional properties of which need to be further studied for health benefits.     

Separation of milk fat triacylglycerols by argentation thin-layer chromatography

Argentation thin-layer chromatography was investigated as a method of obtaining detailed compositional information about milk fat. A modified argentation thin-layer chromatography procedure, developed to optimize the separation of the complex mixture of total milk fat triacylglycerols, provided nine different groups of triacylglycerols, based on both the degree of unsaturation and the total length of fatty acid groups. Fatty acid methyl ester (FAME) analysis was performed to determine the composition of each band. Separation on the basis of chainlength was most pronounced among the fully saturated triacylglycerol groups, as evidenced by the high level of C_4:0 and C_6:0 in bands 7 and 8, respectively. For the cis-monoenoic triacylglycerols, the separation of C_4:0 and C_6:0 was less distinct. The cis,cis dienes and other dienoic, trienoic, or tetraenoic species were principally observed in two bands of retention factor <0.08 on the chromatography plate. Minimal cross-contamination of bands was observed, with the exception of the lowest of the trisaturate bands, band 7, in which trans-monoenes were found to be present. Three samples from different points of the New Zealand dairy season were separated by argentation thin-layer chromatography, and their FAME distributions were measured. In addition to differences in the masses of band extracts from these samples, levels of C_10:0 and C_12:0 in all bands, and levels of monounsaturates in the dienoic and trienoic bands, were found to differ. These changes were generally consistent with a pattern of decreasing fat hardness over the November to March period of a typical dairy season.     

Membrane phospholipids and sterols in microfiltered milk fat globules

Native milk fat globules of various mean diameters, ranging from d₄₃ = 2.3 µm to 8.0 µm, were obtained using microfiltration of raw whole milk. After milk fat globule washing, the milk fat globule membrane (MFGM) was separated by manual churning. After total lipid extraction and separation of polar lipids, their phospholipid (PL) and sterol composition was measured using thin‐layer chromatography, methyl ester analyses by gas chromatography, and gas chromatography coupled to mass spectrometry. The main PL species were phosphatidylethanolamine, phosphatidylcholine and sphingomyelin. The respective fatty acid composition of each PL species was measured. Many different minor bioactive sterols were detected in the MFGM, e.g. lanosterol, lathosterol, desmosterol, stigmasterol and β‐sitosterol. No significant differences in the PL and sterol profile were found between MFGM extracted from small and large milk fat globule fractions.     

Computer simulation study on the shear-induced phase separation in semidilute polymer solutions in 3-dimensional space

We investigated the shear-induced phase separation and/or concentration fluctuation phenomena in semidilute polymer solution by using computer simulation in 3-dimensional space with Doi-Onuki theory. The enhancement of the concentration fluctuations occurs under shear flow and the scattering function in q_x-q_z plane exhibits the so-called butterfly pattern as observed experimentally, where q_x and q_z are the components of the scattering vector for flow direction and neutral direction, respectively. The time changes in the peak position and the intensity at peak position in the scattering function in q_x-q_z plane can be divided into two regions: the peak position becomes smaller and the peak intensity increases with t, and then the peak position and intensity become constant and the system reaches its steady state. These agree with the experimental results qualitatively. However, the computer simulation results indicate that the peak position at the steady state is almost independent of the shear rate, while the decrease in the peak position at steady state with shear rate has been observed experimentally. This disagreement originates from the use of the simplest constitutive equation in the computer simulation.     

Liquid and supercritical CO2 extraction of fat from rendered materials

The separation of fat from rendered materials has potential for value-added products, fuels and feed sources for animals. Current industrial processes utilize continuous screw pressing to extract fat from rendered materials, but the ability to minimize residual fat content is limited. In this work, liquid and supercritical CO₂ were used to extract the remaining fat from rendered poultry meal. CO₂ extraction offers high extraction yields with potential ecological and economic benefits for the rendering industry. A semi-batch extraction unit was used to investigate the effect of pressure (69–345 bar), temperature (25 °C, 40 °C and 50 °C), flow rate, and mass of CO₂ on the extraction yield and the fat solubility. Maximum extraction yields between 87% and 97% were obtained which produced a remaining fat content of 1.0 ± 0.3 wt% in the extracted poultry meal. Fat solubility increased with pressure but decreased with temperature, providing liquid CO₂ with the highest fat solubility (6.47 g/L) at 25 °C and 345 bar. The Chrastil model successfully correlated the solubility data as a function of density and temperature, obtaining an AARD value of 5.56%. Gas chromatography was used to analyze the composition of fatty acids, obtaining similar results with those reported in the literature. It can be concluded that high fat extraction yields can be obtained using CO₂ and that liquid CO₂ is more effective than supercritical CO₂ for the extraction of rendered fats under the conditions tested.     

Electrochemistry and determination of epinephrine using a mesoporous Al-incorporated SiO2 modified electrode

The potential application of Al-incorporated mesoporous SiO₂ (denoted as Al-MCM-41) in electrochemistry as a novel electrode material was investigated. The peak currents of K₃[Fe(CN)₆] remarkably increase and the peak potential separation obviously decreases at the mesoporous Al-MCM-41 modified carbon paste electrode (CPE). These phenomena suggest that the mesoporous Al-MCM-41 modified CPE possesses larger electrode area and electron transfer rate constant. Furthermore, the electrochemical behavior of epinephrine (EP) was investigated in different supporting electrolytes such as 0.01 mol L⁻¹ HClO₄ and pH 7.0 phosphate buffer. It is found that the mesoporous Al-MCM-41 modified CPE exhibits catalytic ability to the oxidation of EP due to remarkable peak current enhancement and negative shift of peak potential. The electrochemical oxidation mechanism was also discussed. Finally, a novel electrochemical method was proposed for the determination of EP, which used to determine EP in urine samples.     

On the Multiplicity of Resolution Equations in the Chromatographic Literature

Abstract

It is shown that, in spite of the multiplicity of resolution equations in the literature, there are only three basic relations: the Purnell, Knox, and Said equations of resolution.

The Giddings equation for peak capacity in its differential form may also be extended to include resolution, leading to an alternative definition for it in which the width log mean average is used instead of the width arithmetic average. This definition is based on the continuity of peak width variation along the column and leads to numerical answers practically identical with those based on the original definition.

This new definition of resolution, which is not an approximation of the original one but stands on its own merits, gives strength to an already deduced and simple peak capacity equation, which was thought to be approximate, as being exact. This eliminates the necessity of lengthy algebraic derivations leading to complicated equations which give no more than the results obtained by the simple peak capacity equation.

Alternate resolution equations which are simple and exact were derived and a chart for the separation efficiency _1:1 as a function of the number of theoretical plates N and the separation factor α was prepared. The resolution R_s can be read on an extra scale in the plot. This chart may be used as a substitute for the controversial Glueckauf chart.

The average plate number N used in the resolution equation was studied when N ₁ # N ₂. The study leads to the conclusion that due to the large uncertainties in both the experimental and theoretical determination of N, any suggestion for N_av other than the simple arithmetic average cannot be justified.

Some erroneous equations and conclusions in the literature concerning resolution and peak capacity are pointed out.     

Lactation curves and effect of pup removal on milk fat of C57BI/6J mice fed different diet fats

Groups of C57BI/6J mice, fed either acis (C-Diet) ortrans diet (T-Diet) were milked without preconditioning at 6, 8, 10 and 12 dayspostpartum. On day 10, groups of mice were also milked 4, 6 and 18 h after separation of the pups. Except for the 18-h separation, all T-Diet fed animals produced milk of lower fat content than did the C-Diet animals (P<0.001) throughout the lactation period measured. In the C-Diet mice, the 6-h separation period resulted in a decrease (P<0.03) in fat, but the diet-depressed milk fat of T-Diet animals was not decreased further until the 18-h separation period. Milk volume increased as lactation progressed and was greatly increased as a result, of preconditioning (P<-0.001), even at 4 h of separation when fat was not reduced, and was always greater for T-Diet animals. Within diet groups, fatty acid composition was similar throughout the lactation period studied and was not affected by preconditioning, except in the 18-h separation period, whende novo fatty acids were significantly reduced (P≤0.05). The data are consistent with the hypothesis that preconditioning results in lowered milk fat values and that preconditioning techniques can explain discrepancies in literature values for murine milk fat. Based on a paper presented at the Symposium on Milk Lipids held at the AOCS Annual Meeting, Baltimore, MD, April, 1990.     

Determination of trace C6C8 aromatics in Iraqi natural gasoline by gas-liquid chromatography

The content of C₆C₈ aromatics in Iraqi natural gasoline and a benzene-free hexane fraction was determined quantitatively by gas-liquid chromatography using a 3 m column packed with 30% 1,2,3-tris(2-cyanoethoxy) propane on Diatomite S at 140 °C. The method employed gave more accurate results than standard methods for the samples used, as a result of the separation of the benzene peak after n-tridecane.     

Gas chromatographic analysis for alpha-olefin sulfonate

The separation and determination of alkene sulfonate and hydroxyalkane sulfonate, and the carbon chain distribution of the lipophilic groups of long chain alpha-olefin sulfonates (C₁₄ to C₁₈) were studied by means of gas chromatography. Samples were hydrogenated initially, and converted to sulfonyl chlorides for gas chromatographic analysis. Using a glass column, 4 mm i.d. and 2.5 m long, packed with Silicon SE-30, 3% on 60 to 80 mesh Chromosorb WAW treated with hexamethyldisilazane, a 0.3 to 0.6 μl sample, as 10% carbon tetrachloride solution, was injected directly on the column, and alkane and monochloroalkane sulfonyl chloride were determined as alkyl chloride and alkyl dichloride, respectively. Minimization of further decomposition, improvement of peak separation and reproducibility were accomplished by this procedure. The method was applied to alpha-olefin sulfonates produced commercially from C₁₄ to C₁₈ alpha-olefins.     

真空变压吸附沼气净化过程的仿真研究

真空变压吸附(VPSA)是一种气体分离技术,该技术运用在沼气净化过程还存在较多的问题,针对该过程吸附塔出口浓度出现的浓度峰问题,运用线性推动力模型(LDF)与Langmuir等温方程对其建立了数学模型,模拟分析了缓冲罐中杂质浓度对吸附步骤出口浓度的影响。结果表明:相同吸附时间下,随着吸附压的降低,二均降结束时会有更多的杂质进入缓冲罐,而缓冲罐中的杂质又会通过一均升步骤进入吸附塔,最终使得吸附步骤出口浓度曲线出现波峰,从而影响了吸附塔出口CH₄含量。通过模型的分析,吸附时间随着吸附压不断降低而缩短,可以有效控制杂质进入缓冲罐,从而使吸附塔出口CH₄含量提高。     

Lipase-catalyzed randomization of fats and oils in flowing supercritical carbon dioxide

Enzymes can frequently impart more selectivity to a reaction than chemical catalysts. In addition, the use of enzymes can reduce side reactions and simplify post-reaction separation problems. In combination with an environmentally benign and safe medium, such as supercritical carbon dioxide (SC-CO₂), enzymatic catalysis makes supercritical fluids extremely attractive to the food industry. In this study, randomization of fats and oils was accomplished with an immobilized lipase in flowing SC-CO₂. Triglycerides, adsorbed onto Celite, are solubilized in CO₂ and carried over 1–10 g immobilized lipase derived from Candida antarctica. The degree of randomization and rate of triglyceride throughput could be controlled by CO₂ pressure and flow rate and quantity of enzyme used. The dropping points and solid fat indices of the resulting randomized oils were compared to oils that were randomized by conventional methods with sodium methoxide. Reversed-phase high-performance chromatography with flame-ionization detection was used to quantitate changes in triglyceride composition of various substrates, such as palm olein and high-stearate soybean oil. The resultant randomized oil mixtures have properties, e.g., solid fat index, that make them potential candidates for incorporation into traditional margarine formulations.     

Trace constituents in milk fat: Isolation and identification of oxofatty acids

Ca. 1% of the glycerides of milk fat contain oxofatty acids. The isolation, fractionation, and characterization of oxofatty acids were accomplished using the following sequence of steps: (A) transmethylation, (B) conversion into 2,4-dinitrophenylhydrazones, (C) adsorption of the 2,4-dinitrophenylhydrazones on magnesium oxide to eliminate the colorless lipid, (D) fractionation of the 2,4-dinitrophenylhydrazones into non-oxofatty acid and oxofatty acid fractions on alumina, (E) separation of the oxofatty acid 2,4-dinitrophenylhydrazones into saturated and unsaturated classes by argentation column chromatography, (F) separation of these classes by chain length using liquid-liquid column and thin layer partition chromatography, (G) resolution of positional isomers by thin layer chromatography, (H) regeneration of the positional isomer 2,4-dinitrophenylhydrazones, and (I) analysis of the parent oxofatty acids by gas liquid chromatographymass spectrometry. In this manner, 36 saturated and 11 unsaturated oxofatty acids were identified tentatively or positively. The saturated oxofatty acids ranged in chain length from C₁₀–C₂₄, predominantly C₁₈ and C₁₆, and generally contained an even number of carbon atoms. The unsaturated oxofatty acids ranged from C₁₄–C₁₈, with C₁₈ predominating.     

Effect of essential fatty acid deficiency on the size and distribution of rat plasma HDL

Rat plasma high density lipoproteins (HDL) are comprised of two major particle size subpopulations, HDL₁ (255 Å?140 Å) and HDL₂ (140 Å?84 Å), in which the proportion of arachidonate in fatty acids of cholesteryl esters is greater than 50%. To determine whether decreased availability of arachidonate for cholesterol esterification would alter the distribution and/or amounts of the HDL subpopulations, we compared HDL subpopulations in EFA-deficient and control rats. To separate the effects of EFA deficiency and fat deficiency and to evaluate effects of different saturated fats, we used EFA-deficient diets that were fat-free or that contained 5% saturated fat. The control diets were the EFA-deficient diets plus 1% safflower oil. The saturated fats were hydrogenated coconut oil, hydrogenated cottonseed oil and saturated medium-chain triglycerides. All EFA-deficient diets decreased the proportion of the HDL₁ subpopulation and the peak diameter of the HDL₂ subpopulation. These changes appeared after quite brief EFA depletion in young rats and may be related to the increased liver cholesteryl ester concentrations typical of EFA-deficient rats.     

Towards Monodisperse Semiconductor Clusters: Preparation and Characterization of ˜ 13-Å Thiophenolate-capped CdS Clusters

We report that two 10-Å [Cd₂₀S₁₃(SPh)₂₂]⁻⁸ clusters may be fused together to form a 13-Å CdS cluster, which shows a sharp absorption peak at 370 nm and a luminescence peak at 390 nm. This is supported by the concentration dependence of the absorption spectra, the luminescence-excitation spectra, the capillary zone electrophoresis separation, the electrochemical measurement, and the powder X-ray data. This cluster fusion process occurs naturally in solution at high concentrations of [Cd₂₀S₁₃(SPh)₂₂]⁻⁸. It can also be induced electrochemically by a two-electron oxidation process. We also show that capillary zone electrophoresis and electrochemical synthesis are two useful new techniques for obtaining monodisperse CdS clusters. Their potentials and limitations are discussed.     

Determination of the conjugated linoleic acid-containing triacylglycerols in New Zealand bovine milk fat

Reversed-phase high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection at 233 nm was used to separate, quantify, and identify the triacylglycerols (TAG) of milk fat that contain conjugated linoleic acid (CLA). The absorbance at 233 nm was substantially due to CLA-TAG (chromatography of some representative TAG devoid of CLA, such as tripalmitin and triolein, showed poor responses at 233 nm, 1/800th that of CLA-TAG). A CLA molar extinction coefficient at 233 nm of 23 360 L mol⁻¹ cm⁻¹ and an HPLC UV response factor were obtained from a commercially available cis-9, trans-11-CLA standard. This molar extinction coefficient was only 86% reported literature values. Summation of all chromatographic peaks absorbing at 233 nm using the corrected response factor gave good agreement with independent determinations of total CLA by gas chromatography and UV spectrophotometry. This agreement allowed quantification of individual CLA-TAG peaks in the HPLC separation of a typical New Zealand bovine milk fat. Three CLA-containing TAG, CLA-dipalmitin, CLA-oleoyl-palmitin and CLA-diolein, were prepared by interesterification of tripalmitin with the respective fatty acid methyl esters and used to assign individual peaks in the reversed-phase chromatography of total milk fat, of which CLA-oleoyl-palmitin was coincident with the largest UV peak. Band fractions from argentation thin-layer chromatography of total milk fat were similarly employed to identify five predominant CLA-TAG groups in total milk fat: CLA-disaturates, CLA-oleoyl-saturates, CLA-vaccenyl-saturates, CLA-vaccenyl-olein, and CLA-diolein.     

Moderate Compared to Low Dietary Intake of trans-Fatty Acids Impairs Strength of Old and Aerobic Capacity of Young SAMP8 Mice in Both Sexes

The senescence accelerated SAMP8 mouse is a model for sarcopenia and provides an opportunity to study the effects of lifelong dietary composition on the loss of physical function with age. We studied the effects of trans-fatty acids (2 % of total energy, TFA diet) on the loss of strength and aerobic exercise capacity (VO₂peak) with age. SAMP8 mice were studied at two ages (young, 25 weeks; old, 60 weeks) and on two diets (control vs TFA). Body composition, grip strength, VO₂peak, blood metabolites, and biochemical parameters were assessed. Body weight, fat mass, and body fat percentage all increased with age (p < 0.05) but were not significantly impacted by diet. There was a significant age-related decline in total grip strength as well as that normalized to fat-free mass (FFM) (p < 0.05) with a further decrease at old age in these metrics of strength on the TFA diet vs control diet (p < 0.05). Total VO₂peak exhibited no change with age or diet, but when normalized to FFM, VO₂peak exhibited age and TFA-related declines (p < 0.05). Intramuscular triacylglycerol (p < 0.05) and collagen content (p < 0.05) significantly increased with age, while blood triacylglycerol was increased by the TFA diet (p < 0.05). These data further characterize the SAMP8 mouse as a model for sarcopenia and indicate that dietary fatty acid composition can impact the degree of this age-related loss of physical function.     

Crystallization behavior and IR structure of yttrium aluminosilicate glasses

The crystallization of four Y₂O₃-Al₂O₃-SiO₂ (YAS) glasses were investigated to prepare YAS glass ceramics precipitated singly/mainly Y₂Si₂O₇ or Y_4.67(SiO₄)₃O apatite, and to explore the crystallization difference between the stoichiometric parent glass (SPG) and non-stoichiometric parent glass (NSPG). The DSC results revealed that glass locating at the higher liquidus surface temperature has lower crystallization peak temperature, which indicating that the corresponding glass has higher crystallization potential to crystallize easily. Crystallization of the NSPG samples is along surface and caused by phase separation, while SPG sample is the surface crystallization at the first exothermic peak temperature and overall crystallization at the second exothermic peak temperature. Glass ceramics only containing y-Y₂Si₂O₇ or Y_4.67(SiO₄)₃O apatite are obtained successfully, and which are illustrated by fitting FTIR spectra. These results can provide technical guide for controlling the crystallization process and the types of precipitated crystals in YAS glass for different application potentials.