不同地区茶叶籽油活性成分的比较分析

对浙江、云南、四川、江苏、湖南、湖北、福建、河南、贵州9个地区的茶叶籽油活性成分进行比较分析。结果表明,茶叶籽油中总酚含量以四川、贵州和云南最为突出,在900 mg/kg以上,其他地区差异不显著(400~660 mg/kg);VE含量以四川茶叶籽油最高,可达68.55 mg/100 g,而江苏茶叶籽油中生理活性最强的α-VE含量(31.94 mg/100 g)最多;角鲨烯、三萜类物质羽扇豆醇与4种甾醇类物质(菜油甾醇、豆甾醇、羊毛甾醇和谷甾醇)在所有地区茶叶籽油中均被检出;除湖南、湖北、福建外,其他几个地区茶叶籽油中都含有β-香树脂醇;此外,在所有地区的茶叶籽油中都检出1种类胡萝卜素——虾青素;四川和贵州的茶叶籽油中总甾醇含量最多,分别为5 710.4 mg/kg和5 539.3 mg/kg。综合分析,四川、贵州的茶叶籽油中活性成分含量最高,品质最好。     

高酸值米糠毛油碱炼脱酸工艺及条件的优化研究

以高酸值米糠毛油为原料,采用两次碱炼脱酸工艺,以碱炼得率、脱色率、谷维素损失率、甾醇损失率为考察指标,研究碱液质量分数对两次碱炼脱酸工艺中一次、二次碱炼效果的影响,并与一次碱炼脱酸工艺进行比较。结果表明:随碱液质量分数的增大,两次碱炼脱酸工艺中的一次、二次碱炼的碱炼得率变化不大,一次碱炼脱色率在14.24%时最大,二次碱炼脱色率呈起伏变化;两次碱炼脱酸工艺中二次碱炼时采用较低的碱液质量分数有利于甾醇和谷维素的保留;与一次碱炼脱酸工艺相比,两次碱炼脱酸工艺在相同碱液质量分数条件下,油脂碱炼得率平均提高4.89个百分点,谷维素损失率平均降低5.87个百分点;在碱液质量分数较低(8.07%~14.24%)时,脱色率平均提高9.25个百分点,甾醇损失率平均降低12.64个百分点。对于高酸值米糠毛油,采用两次碱炼脱酸工艺和质量分数为14.24%以下的碱液,对提高碱炼得率和脱色率以及减少谷维素和甾醇的损失都具有明显优势。     

Pleiotropic mutations in Saccharomyces cerevisiae affecting sterol uptake and metabolism

Sterol uptake control mutants (upc-) have been isolated via ethylmethanesulfonate mutagenesis from wild-type Saccharomyces cerevisiae. These mutants are heme and sterol competent but possess the ability to accumulate exogenous sterol(s) under aerobic conditions. Previous studies demonstrate sterol uptake only in a hem-, erg- background; however, the Upc- strains described here are Hem+ and do not require exogenous sterol for growth. We were unable to obtain viable hem+, erg-, upc+ recombinants; such combinations appear to be lethal. Isolates of Upc mutants demonstrated different levels of sterol uptake, and sterol analysis revealed a broad phenotypic range with regard to amounts and accumulation of ergosterol and non-ergosterol sterols. Assays of acyl CoA: ergosterol acyltransferase and sterol ester hydrolase showed no apparent difference in activity between Upc mutants and the wild type.     

LIPID COMPOSITION OF AEROBICALLY AND ANAEROBICALLY PROPAGATED BREWER'S BOTTOM YEAST

Aerobically grown pitching yeast is very rich in unsaturated fatty acids and sterol esters compared to traditional, anaerobic yeast. The principal fatty acids in aerobic yeast cells are unsaturated palmitoleic and oleic acids, whereas in anaerobic cells saturated palmitic acid predominates. The difference in fatty acid distribution between aerobic and anaerobic cells is most marked in the sterol esters. The fatty acids of phospho-lipids are more stable, although remarkable differences are observed. The sterols of aerobic cells are almost entirely in esterified form and zymosterol is the principal sterol. During the first hours of fermentation a rapid synthesis of palmitoleic acid is observed when anaerobic yeast is used for pitching and the wort is aerated. The synthesis of oleic acid requires more oxygen and time than is available under normal brewing conditions. When aerobic pitching yeast is used no more unsaturated fatty acids are synthesised and the lipid stores of pitching yeast are distributed among the daughter cells. The decrease in acetate ester production by aerobic pitching yeast is concluded to be due to a decrease in acetyl CoA synthesis, which may be caused by the high proportion of unsaturated fatty acids in membrane lipids.     

Facile purification of tocopherols from soybean oil deodorizer distillate in high yield using lipase

Tocopherols have been purified from deodorizer distillate produced in the final deodorization step of vegetable oil refining by a process including molecular distillation. Deodorizer distillate contains mainly tocopherols, sterols, and free fatty acids (FFA); the presence of sterols hinders tocopherol purification in good yield. We found that Candida rugosa lipase recognized sterols as substrates but not tocopherols, and that esterification of sterols with FFA could be effected with negligible influence of water content. Enzymatic esterification of sterols with FFA was thus used as a step in tocopherol purification. High boiling point substances including steryl esters were removed from soybean oil deodorizer distillate by distillation, and the resulting distillate (soybean oil deodorizer distillate tocopherol concentrate; SODDTC) was used as a starting material for tocopherol purification. Several factors affecting esterification of sterols were investigated, and the reaction conditions were determined as follows: A mixture of SODDTC and water (4∶1, w/w) was stirred at 35°C for 24 h with 200 U of Candida lipase per 1 g of the reaction mixture. Under these conditions, approximately 80% of sterols was esterified, but tocopherols were not esterified. After the reaction, tocopherols and FFA were recovered as a distillate by molecular distillation of the oil layer. To enhance further removal of the remaining sterols, the lipase-catalyzed reaction was repeated on the distillate under the same reaction conditions. As a result, more than 95% of the sterols was esterified in total. The resulting reaction mixture was fractionated to four distillates and one residue. The main distillate fraction contained 65 wt% tocopherols with low contents of FFA and sterols. In addition, the residue fraction contained high-purity steryl esters. Because the process presented in this study includes only organic solvent-free enzymatic reaction and molecular distillation, it is feasible as a new industrial purification method of tocopherols. This work was presented at the Biocatalysis symposium in April 2000, held at the 91st Annual Meeting and Expo of the American Oil Chemists Society, San Diego, CA.     

The wide-ranging phenotypes of ergosterol biosynthesis mutants,and implications for microbial cell factories

Yeast strains have been used extensively as robust microbial cell factories for the production of bulk and fine chemicals, including biofuels (bioethanol), complex pharmaceuticals (antimalarial drug artemisinin and opioid pain killers), flavours, and fragrances (vanillin, nootkatone, and resveratrol). In many cases, it is of benefit to suppress or modify ergosterol biosynthesis during strain engineering, for example, to increase thermotolerance or to increase metabolic flux through an alternate pathway. However, the impact of modifying ergosterol biosynthesis on engineered strains is discussed sparsely in literature, and little attention has been paid to the implications of these modifications on the general health and well-being of yeast. Importantly, yeast with modified sterol content exhibit a wide range of phenotypes, including altered organization and dynamics of plasma membrane, altered susceptibility to chemical treatment, increased tolerance to high temperatures, and reduced tolerance to other stresses such as high ethanol, salt, and solute concentrations. Here, we review the wide-ranging phenotypes of viable Saccharomyces cerevisiae strains with altered sterol content and discuss the implications of these for yeast as microbial cell factories.     

Mutations in the nucleotide-binding domain of putative sterol importers Aus1 and Pdr11 selectively affect utilization of exogenous sterol species in yeast

Sterol uptake in the yeast Saccharomyces cerevisiae is mediated by two plasma membrane ATP-binding cassette transporters, Aus1 and Pdr11. Their expression is regulated by oxygen and is triggered by anaerobic growth conditions. Under these conditions, internal ergosterol synthesis is arrested and utilization of exogenous sterol is vital for yeast cells. Here, we demonstrate that Aus1 is the major importer of non–yeast sterols, mammalian cholesterol, and plant sterols under anaerobic conditions. In contrast, uptake of yeast native sterol, ergosterol, is relatively low. This uptake could not be enhanced by overexpression of either of the transporters. Interestingly, overexpression of the minor importer Pdr11 resulted in a substantial import of non–yeast sterols. We show that mutation of the conserved residue in one of the ABC characteristic motifs—the H-loop in Aus1 and Pdr11—lowered their ATPase activity. The residual activity was sufficient to import exogenous sterols and to preserve cell viability. Importantly, the reduction of sterol import was dramatic for mammalian cholesterol and plant sterols, whereas import of yeast ergosterol was decreased only slightly indicating substrate selectivity of the sterol utilization process.     

A comprehensive classification system for lipids

Lipids are produced, transported, and recognized by the concerted actions of numerous enzymes, binding proteins, and receptors. A comprehensive analysis of lipid molecules, “lipidomics,” in the context of genomics and proteomics is crucial to understanding cellular physiology and pathology; consequently, lipid biology has become a major research target of the postgenomic revolution and systems biology. To facilitate international communication about lipids, a comprehensive classification of lipids with a common platform that is compatible with informatics requirements has been developed to deal with the massive amounts of data that will be generated by our lipid community. As an initial step in this development, we divide lipids into eight categories (fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids, prenol lipids, saccharolipids, and polyketides) containing distinct classes and subclasses of molecules, devise a common manner of representing the chemical structures of individual lipids and their derivatives, and provide a 12 digit identifier for each unique lipid molecule. The lipid classification scheme is chemically based and driven by the distinct hydrophobic and hydrophilic elements that compose the lipid. This structured vocabulary will facilitate the systematization of lipid biology and enable the cataloging of lipids and their properties in a way that is compatible with other macromolecular databases.[Reprinted with copyright permission from the Journal of Lipid Research. 2005. 46: 839–861.]     

食品加工对植物甾醇的影响

血脂过高引起的心血管病已成为威胁人类健康的第一杀手，植物甾醇因其具有显著的降血脂作用而倍受关注。论述了植物甾醇的天然来源、存在形式及食品加工对其影响，以利于控制食品加工条件，最大限度地使甾醇得到保留。