Effect of Diacylglycerol Supplementation on Fasting Serum Triacylglycerol Concentration: a Meta-Analysis

Diacylglycerol (DAG) supplementation has been shown to be associated with the reduction of fasting serum triacylglycerol (TAG) concentration, although the extent of the association is uncertain. We quantitatively examined the effect of dietary DAG on fasting serum TAG concentration by conducting a meta-analysis of randomized controlled trials. Potential papers were searched from electronic databases of Medline, Embase and Cochrane Library. Information was extracted and the net change of fasting serum TAG concentration was used as the primary outcome to examine the effect of DAG in Review Manager 4.2. Six papers with seven independent studies (298 subjects) were included into the statistic pooling. Meta-analysis with random effect model showed that DAG did not reduce the fasting serum TAG concentration (WMD: −0.07 mmol/L; 95% CI: −0.21 to 0.08 mmol/L; P = 0.37). Sensitivity analysis indicated the robustness of overall results. Fail-safe number analysis indicated that 18 studies with positive effect were necessary to reverse the reported non-significant efficacy of DAG. Weight estimation analysis indicated that the effect of DAG was influenced to some extent by the initial fasting serum TAG concentration. In conclusion, DAG supplementation did not reduce the fasting serum TAG concentration significantly compared with TAG, but some effects were suggested in diabetic patients with hypertriglyceridemia.     

Effect of Interesterification of Palmitic Acid-rich Triacylglycerol on Postprandial Lipid and Factor VII Response

The process of interesterification results in changes in triacylglycerol (TAG) structure and is used to increase the melting point of dietary fats. The acute health effects of this process on palmitic acid-rich fats are uncertain with regard to postprandial lipemia, insulin and factor VII activated (FVIIa) concentrations. Two randomized crossover trials in healthy male subjects compared the effects of meals containing 50 g fat [interesterified palm oil (IPO) versus native palm oil (NPO); n = 20, and IPO versus high-oleic sunflower oil (HOS); n = 18], on postprandial changes in lipids, glucose, insulin, chylomicron composition and FVIIa. Compared with NPO, IPO decreased postprandial TAG and insulin concentrations. Both NPO and IPO increased FVIIa concentrations postprandially; mean increases at 6 h were 21 and 19%, respectively. Compared with HOS, IPO decreased postprandial TAG (47% lower incremental area under the curve) and reduced the postprandial increase in FVIIa concentration by 64% at 6 h; no significant differences in hepatic and total lipase activities or insulin concentrations were noted. All three test meals increased postprandial leukocyte counts (average 26% at 6 h). The fatty acid composition of the chylomicron TAG was similar to the test fats following all test meals. It is concluded that interesterification of palm oil does not result in adverse changes in postprandial lipids, insulin or FVIIa compared to high oleate and native palm oils. George J. Miller: Deceased August 2006.     

Working with Randy: The Diacylglycerol Acyltransferase Story

Vegetable oils are one of the main agricultural commodities. Demand has been increasing steadily over the last five decades and, with finite land available, it is vital that we increase productivity. My laboratory has focused on the regulation of plant lipid metabolism and, as part of this work, we identified diacylglycerol acyltransferase (DGAT) as important at regulating carbon flux during oil accumulation. This led to collaborations with Randy Weselake's research group when we quantified the importance of DGAT in oilseed rape by using flux control analysis. Later, with David Taylor, we showed that over-expression of DGAT boosted oil accumulation in field-grown crops by around 8%. These studies led to a multitude of experiments with different oil crops, such as oil palm and soybean, as well as many rewarding collaborations with Randy.     

A Fluorescence-Based Assay for Quantitative Analysis of Phospholipid:Diacylglycerol Acyltransferase Activity

Phospholipid:diacylglycerol acyltransferase (PDAT) catalyzes the acyl-CoA-independent triacylglycerol (TAG) biosynthesis in plants and oleaginous microorganisms and thus is a key target in lipid research. The conventional in vitro PDAT activity assay involves the use of radiolabeled substrates, which, however, are expensive and demand strict regulation. In this study, a reliable fluorescence-based method using nitrobenzoxadiazole-labeled diacylglycerol (NBD-DAG) as an alternative substrate was established and subsequently used to characterize the enzyme activity and kinetics of a recombinant Arabidopsis thaliana PDAT1 (AtPDAT1). We also demonstrate that the highly toxic benzene used in typical PDAT assays can be substituted with diethyl ether without affecting the formation rate of NBD-TAG. Overall, this method works well with a broad range of PDAT protein content and shows linear correlation with the conventional method with radiolabeled substrates, and thus may be applicable to PDAT from various plant and microorganism species.     

Effect of Triacylglycerol Compositions and Physical Properties on the Granular Crystal Formation of Fat Blends

The effect of triacylglycerol (TAG) compositions and physical properties related to solid fat content (SFC) on the behavior of granular crystal formation was investigated. Four fat blends involving different 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP) and 1-palmitoyl-2,3-dioleoyl-sn-glycerol (POO) compositions or SFC were prepared, and crystallization was investigated using polarizing microscopy, X-ray diffraction, SFC, whereas hardness was determined using a texture analyzer. Samples containing a higher saturated fatty-acid content from palm and higher SFC showed higher β-type crystals in the initial period, yielding a number of small-sized crystals, with no growth occurring afterward. Growth of the granular crystals as a function of time was observed in the samples, transforming from the β’- to β-type polymorph gradually. Large granular crystals at the initial stage were observed in the sample with a higher POO content and lowest SFC. These results suggested that POO promotes the rate of the crystals’ polymorphic transformation, resulting in the growth of granular crystals. In contrast, excess high-melting-point TAG content, such as tripalmitin and POP, retarded granular crystal growth regardless of the increased β’ to β transition rate. We concluded that the behavior of the growth of granular crystals is influenced by the combined effect of TAG composition and SFC.     

A Novel Assay of DGAT Activity Based on High Temperature GC/MS of Triacylglycerol

Diacylglycerol acyltransferase (DGAT) catalyzes the final step in the acyl-CoA-dependent biosynthesis of triacylglycerol (TAG), a high-energy compound composed of three fatty acids esterified to a glycerol backbone. In vitro DGAT assays, which are usually conducted with radiolabeled substrate using microsomal fractions, have been useful in identifying compounds and genetic modifications that affect DGAT activity. Here, we describe a high-temperature gas chromatography (GC)/mass spectrometry (MS)-based method for monitoring molecular species of TAG produced by the catalytic action of microsomal DGAT. This method circumvents the need for radiolabeled or modified substrates, and only requires a simple lipid extraction prior to GC. The utility of the method is demonstrated using a recombinant type-1 Brassica napus DGAT produced in a strain of Saccharomyces cerevisae that is deficient in TAG synthesis. The GC/MS-based assay of DGAT activity was strongly correlated with the typical in vitro assay of the enzyme using [1-¹⁴C] acyl-CoA as an acyl donor. In addition to determining DGAT activity, the method is also useful for determining substrate specificity and selectivity properties of the enzyme.     

Effect of Addition of Purified Diglycerol Linoleic Acid Esters on the Crystallization Behavior of Diacylglycerol Oils

Liquid oils containing high‐melting diacylglycerols (DAGs) are more likely to cause precipitation than triacylglycerol‐based oils during long‐term storage, which is not desired for consumer products. Therefore, we attempted to retard the crystallization of high‐melting DAGs by adding emulsifiers, diglycerol esters of fatty acids (DGEs), which were synthesized by esterification of diglycerol and linoleic acid using Novozym 435. The reaction product was isolated by silica gel column chromatography to obtain pure mono‐, di‐, and triesters of diglycerol, and the composition was analyzed by HPLC and ESI‐MS. Further structural analysis of the purified products was performed by ¹H‐ and ¹³C‐NMR. The retardation effect of DGEs with a different esterification degree on the crystallization of DAGs was investigated using solid fat content, differential scanning calorimetry, polarized light microscopy, and X‐ray diffraction. The results reveal that addition of 0.5 % (w/w) DGEs could effectively retard the crystallization of high‐melting DAGs by inhibiting the nucleation process and delaying the crystal growth, but their addition did not alter the crystal forms of DAGs. Moreover, the retardation effect was enhanced as the esterification degree of DGE decreased.     

Triacylglycerol Estolides,a New Class of Mammalian Lipids,in the Paracloacal Gland of the Brushtail Possum (Trichosurus vulpecula)

The paracloacal glands are the most prevalent scent glands in marsupials, and previous investigation of their secretions in the brushtail possum (Trichosurus vulpecula) has identified many odorous compounds together with large amounts of neutral lipids. We have examined the lipids by LC–MS, generating ammonium adducts of acylglycerols by electrospray ionisation. Chromatograms showed a complex mixture of coeluting acylglycerols, with m/z from about 404 to 1048. Plots of single [M + NH₄]⁺ ions showed three groups of lipids clearly separated by retention time. MS–MS enabled triacylglycerols and diacylglycerol ethers to be identified from neutral losses and formation of diacylglycerols and other product ions. The earliest‐eluting lipids were found to be triacylglycerol estolides, in which a fourth fatty acid forms an ester link with a hydroxy fatty acid attached to the glycerol chain. This is the first report of triacylglycerol estolides in animals. They form a complex mixture with the triacylglycerols and diacylglycerol ethers of lipids with short‐ and long‐chain fatty acids with varying degrees of unsaturation. This complexity suggests a functional role, possibly in social communication.     

Effect of Dietary Cholesterol and Fat on Cell Cholesterol Transfer to Postprandial Plasma in Hyperlipidemic Men

Postprandial chylomicrons are potent ultimate acceptors of cell membrane cholesterol and are believed to accelerate reverse cholesterol transport (RCT). We compared the effects of meals rich in polyunsaturated fat (PUFA) and either high (605 mg) or low (151 mg) in cholesterol and a meal rich in dairy fat (DF) in the form of cream on net in vitro transport of red blood cell (RBC) membrane cholesterol to 4 and 6 h postprandial plasma in eight normotriglyceridemic (NTG-H) and eight hypertriglyceridemic (HTG-H) men with mild to moderate hypercholesterolemia. In HTG-H men, cell cholesterol accumulation in 6-h postprandial plasma was significantly (P = 0.02) less after the PUFA-HC meal compared with the other meals. The significant (P < 0.001) increase in cell plus endogenous cholesterol accumulation in the triglyceride-rich lipoprotein (TRL) fraction of 4 h postprandial plasma incubated with RBC was significantly (P = 0.007) higher after the PUFA-HC meal compared with DF meal in HTG-H men. In NTG-H men, cholesterol accumulation in plasma and plasma lipoproteins in the presence and absence of RBC was not significantly affected by the type of meal ingested. These data suggest that addition of large amounts of cholesterol to a PUFA meal may impair diffusion-mediated transport of cell membrane cholesterol to postprandial plasma and that replacing DF with PUFA in a meal increases postprandial lipemia and may potentially increase cholesterol accumulation in atherogenic postprandial TRL in HTG-H men.     

化学剂组分浓度对聚合物凝胶成胶性能影响研究

为了更好的揭示聚合物凝胶体系的成胶规律,利用布氏粘度仪对不同化学剂浓度下聚合物凝胶体系成胶粘度及成胶时间进行表征。研究结果表明:凝胶体系随着聚合物以及铬交联剂浓度的增加成胶时间下降、成胶强度增加,硫脲作为稳定可以有效的延缓成胶时间而对成胶强度影响较小。综合考虑成胶时间及成胶强度,最佳的聚合物凝胶体系配方为浓度为2 500 mg/L的聚合物+质量分数为为0.3%的铬交联剂醋酸铬+质量分数分别为0.03%的硫脲。     

Contribution of lignite in the Greek electricity generation: Review and future prospects

In the present study, a review of the lignite-based electricity generation in Greece is presented. By using real, long-term data concerning the national electricity generation and an appropriate mathematical model developed from first principles, it is expected that the lignite’s depletion time shall vary from 25 to 50 years. Acknowledging its finite character, an investigation is carried out in order to assess the future prospects of lignite in the national electricity status. For this purpose, emphasis is also given on the impacts entailed by the former exploitation for electricity purposes on both the local environment and the national economy.     

Synthesis of flexible heat exchanger networks:A review

Dealing with uncertainty is one of practical issues in design and operation of heat exchanger networks(HENs), arising the problem of flexible HEN synthesis. This paper addresses the state-of-the-art methods for flexible HEN synthesis based on sensitivity analysis, resilience analysis, flexibility analysis and multiperiod synthesis techniques as well. Each of these methods is summarized by presenting their general procedures and recent developments on modeling, solving strategies and applications. Some current topics related to flexible process synthesis have been briefly presented to provide several future research possibilities.     

Sensitivity analysis on a sequencing batch reactor model. II: Effect of stoichiometric and operating parameters

A previously developed model for sequencing batch reactors was used in this study to investigate the effect of some of the model stoichiometric and operating parameters on the performance of the system. With regard to the effluent chemical oxygen demand (COD) concentration, the model predictions were determined to be correct for the parameters Y_p, f_p and S_sf. However, the stoichiometric parameters α, Y_h and the operating parameter X_ao were determined to have significant effect on the effluent COD concentrations. The intermediate COD concentrations are affected by the parameters Y_p, Y_h, S_sf and X_ao. To use the model for design or control purposes, special attention should be given to the parameters that affect the effluent COD concentration. © 1999 Society of Chemical Industry     

不同浓度二元复合体系对驱油效果的影响

近年来,水驱开发效果较差。油藏一般采取"调驱+水驱"方式取得了较好增油降水效果,但也存在药剂费用投入较高和配注工艺复杂等问题。对于强碱或者弱碱三元的复合体系中普遍存在采出液乳化和结垢的问题,优先选用聚合物和表面活性剂复合而成的二元体系,并采用室内物理模拟的方法,对比不同浓度聚/表二元体系的界面张力、黏度、驱油效果进行研究,发现聚/表二元体系可以实现超低界面张力的要求,而且聚/表二元体系的黏度也比较大,通过室内非均质岩心物理模拟实验研究,表明不同浓度的聚/表二元体系对驱油效果的影响效果差异较大。     

硫酸浓度对流动注射仪测定总氮的影响

用流动注射仪测定总氮水样,发现用不同的硫酸浓度保存总氮样品时,对其测定结果有一定的影响,并与过硫酸钾氧化-紫外分光光度法进行比对和分析.     

用水量与初始测长时间对减缩剂性能评价的影响

目前混凝土减缩剂性能评价方法没有统一的标准,影响减缩剂性能评价因素的研究也鲜有报道.本文对影响减缩剂性能评价的两个重要因素即掺减缩剂的砂浆用水量和砂浆试件初始长度测试时间进行了探讨与试验研究.研究表明砂浆试件的用水量应根据砂浆流动度为(180±5) mm来确定;减缩剂减缩率测试中砂浆试件初始长度应该从加水后24 h拆模就立即测试.     

A Comparison of Linear with Nonlinear Viscoelastic Solutions for Shear Stress Concentration in Double Lap Joints

The correspondence principle based on the Maxwell model and a nonlinear viscoelastic solution involving an iterative scheme are used to describe the time dependent variation of the adhesive maximum shear stress in adhesively bonded double lap joints. The results indicate that if the correspondence principle is applied, the use of Maxwell chain is necessary to approximate the continuous change in the relaxation time and to coincide with the results calculated using the nonlinear viscoelastic theory.     

A Comparison of Linear with Nonlinear Viscoelastic Solutions for Shear Stress Concentration in Double Lap Joints

The correspondence principle based on the Maxwell model and a nonlinear viscoelastic solution involving an iterative scheme are used to describe the time dependent variation of the adhesive maximum shear stress in adhesively bonded double lap joints. The results indicate that if the correspondence principle is applied, the use of Maxwell chain is necessary to approximate the continuous change in the relaxation time and to coincide with the results calculated using the nonlinear viscoelastic theory.     

Studying the Effect of Initiator Type and Concentration on the Setting Time of Acrylic Ester Anaerobic Adhesives

Anaerobic adhesives are polymerized and hardened rapidly through a free radical mechanism when placed between two metallic surfaces. The conducted investigations from 1960 have studied polymerization rate in the presence of different metallic ions, their breakdown speed using polarography techniques, and also the common use of cumene hydro-peroxide as an initiator. In order to investigate the effect of initiator type and concentration on the setting time of these adhesives, four different types of initiators in concentrations of 1–3 parts per hundred resin (phr) were incorporated into the monomer. The initiators were cumene hydroperoxide (CHP), methyl ethyl ketone peroxide, tert-butyl hydroperoxide, and benzoyl peroxide. The metal salt used was copper (II) saccharin. The obtained results indicated that the setting time in the methacrylate compositions depends not only on the initiator concentration, but also on its relative amount with respect to the metal ion, and some other factors such as monomer type, and stoichiometric relation between the metal ion and the accelerator—here, dimethyl p-toluidine, which was assumed to have an important role in the setting process. Finally, CHP was identified as the most appropriate initiator with an optimum value of 2 phr.