SOME ASPECTS OF THE STRUCTURE AND FUNCTION OF THE YEAST PLASMA MEMBRANE

The permeation of many compounds into the yeast cell is largely regulated by the plasma membrane according to their lipid solubility and degree of dissociation. Thus the permeation rate of the fatty acids and α-keto acids is proportional to their relative lipid solubility. The highly dissociated and poorly lipid-soluble di- and tri-carboxylic acids and halogenated acetic acids permeate only very slowly; the impermeable α-ketoglutaric acid becomes easily permeable when made lipid-soluble by esterification. The lipid composition of the plasma membrane can thus be of decisive importance in regulating the movement of different compounds into and out of the yeast cell. Lipid analyses revealed that anaerobiosis clearly affected the neutral lipid composition of the plasma membrane. The aerobic membrane contained more unsaturated fatty acids, mainly palmitoleic and oleic acids, more total sterol, much more ergosterol and much less squalene. The principal sterol in the aerobic membrane, ergosterol, was mainly in the free form, whereas zymosterol and other minor sterols were predominantly esterified. In contrast, the anaerobic membrane contained small amounts of biosynthetic sterol precursors of ergosterol, and was clearly richer in saturated fatty acids having a greater variation in chain length. Both plasma membranes contained a considerable amount of triacylglycerols.     

EFFECTS OF LINOLEIC ACID SUPPLEMENTS ON THE SYNTHESIS BY YEAST OF LIPIDS AND ACETATE ESTERS

The concentrations of acetate esters in beer were reduced by up to 85% by addition of linoleic acid to the fermentation or by pitching with yeast previously enriched with this unsaturated fatty acid. Linoleic acid was rapidly incorporated into yeast lipids and was effective in reducing the rate of ethyl acetate formation within 2 h. Addition of linoleic acid altered the pattern of synthesis of fatty acids by yeast, causing a shift from medium toward long chain acids. Secondly, the amount of squalene in yeast was reduced by up to 70% whereas that of lanosterol was increased threefold. Since total yeast lipid synthesis was reduced by up to 40%, we conclude that less acetylCoA is synthesized in the presence of linoleic acid. Further, high concentrations of linoleic acid decreased the proportion of acetylCoA consumed by the synthesis of acetate esters. Therefore linoleic acid may directly decrease acetate ester synthesis in addition to its effect via reduction of acetylCoA availability.     

The Effects of Linoleic Acid Supplementation of Cropped Yeast on its Subsequent Fermentation Performance and Acetate Ester Synthesis

For beer wort fermentation the addition of unsaturated fatty acids has sometimes been suggested as an alternative to wort oxygenation. This can however negatively affect the synthesis of acetate esters and consequently beer flavour. This work investigates the effect of supplementing a cropped yeast with an unsaturated fatty acid on the fermentation performance of the pitching yeast. Cropped yeast is in a different physiological state to yeast pitched in unfermented wort. Using a synthetic medium for the fermentations, it was found that the incubation of cropped yeast with linoleic acid resulted in two important changes in the yeasts composition: (1) the ratio of unsaturated fatty acids to total fatty acids increased from 0.53 to 0.66 and (2) the ratio of trehalose to glycogen increased from 0.17 to 0.49. The performance of this yeast in subsequent fermentations was compared to unsupplemented yeast under three conditions: medium pre‐aeration, de‐aerated medium and de‐aerated medium with newly added unsaturated fatty acid. It was found that the supplemented pitching yeast showed growth, attenuation and ethanol formation profiles similar to those obtained with unsupplemented yeast in pre‐aerated medium, which simulated the normal brewing practice. Compared to fermentations with unsaturated fatty acids added to the medium, the supplemented cropped yeast did not induce a reduction in acetate ester synthesis. Results indicated that the supplementation of cropped yeast with unsaturated fatty acids could be an interesting alternative to wort oxygenation to restore the optimal membrane fluidity of the yeast.     

GC-MS定量检测谷氨酸发酵产酸期细胞膜脂肪酸

采用气相色谱质谱连用法(GC-MS)分析了谷氨酸棒状杆菌的细胞膜中脂肪酸的组分,并用选择离子检测方式(SIM)测定产酸期前后细胞膜脂肪酸含量的变化。结果表明:谷氨酸棒状杆菌细胞膜主要含有肉豆蔻酸、棕榈油酸、棕榈酸、硬脂酸和油酸等5种脂肪酸,其中棕榈酸含量最高,棕榈油酸含量最低;另外,在谷氨酸发酵过程中,随着产酸的启动,细胞膜中饱和脂肪酸与不饱和脂肪酸比率呈下降趋势,说明细胞膜中饱和脂肪酸与不饱和脂肪酸的比率与谷氨酸的分泌可能存在一定的关联性。     

发酵条件对发酵性丝孢酵母脂肪酸组成的影响

通过摇瓶发酵，研究了温度、摇瓶转速、碳源种类和浓度对发酵性丝孢酵母（Trichosporom fermentans）脂肪酸组成的影响。气相色谱法分析结果表明，较高发酵温度能提高菌体油脂的脂肪酸饱和程度，此条件下饱和脂肪酸含量占脂肪酸总量的49．1％：摇瓶转速高有利于菌体油脂不饱和脂肪酸的生成；木糖浓度为100g／L时菌体油脂中饱和脂肪酸含量最高，占脂肪酸总量的50．4％；木糖比葡萄糖更容易被转化生成饱和脂肪酸含量较多的油脂。菌体脂肪酸组成包括肉豆蔻酸、棕榈酸、棕榈油酸、硬脂酸、油酸和亚油酸，其中棕榈酸和油酸含量较高。     

STEROL SYNTHESIS IN RELATION TO GROWTH AND FERMENTATION BY BREWING YEASTS INOCULATED AT DIFFERENT CONCENTRATIONS

The sterol contents of brewing yeasts harvested from an anaerobic fermentation and inoculated into air-saturated wort rise rapidly from ca. 1 mg/g dry yeast to ca. 10 mg/g and remain at this level until the oxygen is absorbed. After all oxygen is removed from the medium, sterol synthesis ceases and the concentration in the cells declines as growth occurs until a limiting value is reached, when reproductive growth ceases. In the presence of oxygen, sterols are present primarily as sterol esters; free sterols accumulate after oxygen uptake is complete. The total quantity of sterol which is synthesized in the presence of oxygen determines the extent of subsequent yeast growth. It is shown that the magnitude of sterol synthesis in the yeast population as a whole is influenced by the pitching rate.     

8种枣核油脂肪酸组成及含量分析与比较

对8种枣核(贡枣、晋枣、骨头枣、北樱枣、秤砣枣、敦煌大枣、滩枣、鸡心枣)油的脂肪酸组成与含量进行分析。结果表明:8种枣核油共检出24种脂肪酸,包括13种饱和脂肪酸、11种不饱和脂肪酸;饱和脂肪酸主要为棕榈酸、硬脂酸,不饱和脂肪酸主要为亚油酸、油酸、棕榈油酸;秤砣枣核油不饱和脂肪酸含量最高,达到84.55%;北樱枣核油、秤砣枣核油、滩枣核油和鸡心枣核油中油酸和亚油酸含量较高;贡枣核油、晋枣核油、骨头枣核油和敦煌大枣核油的棕榈酸含量较高;贡枣核油中亚麻酸含量最高,达到3.57%。采用聚类分析、主成分分析及线性判别分析,通过枣核油脂肪酸组成和含量可以实现8种枣核油的有效分类与区分,为不同品种大枣的分类判别与枣种质资源研究提供了新方法。     

DETERMINATION OF SOME LIPID CONSTITUENTS OF BAKER'S YEAST

Lipid was extracted from whole yeast cells with difficulty because of the limited porosity of the cell wall and its sensitivity to dehydrating solvents. Extraction from mechanically broken cells was rapid and complete. Metabolic alteration of lipid when cells were disintegrated was minimized by first heating a yeast suspension briefly at 90°C. Details are given for the routine analysis of yeast phospholipids by quantitative paper chromatography and of neutral lipids by column chromatography. Lysophosphatides were found in some types of yeast after drying, but not in pressed commercial yeast or in yeast grown on synthetic media. They were formed when yeast was suspended in methanol-water, as yeast phospholipase A was activated and split palmitoleic acid from lecithin and phosphatidyl ethanolamine. Phosphatidyl inositol in baker's yeast contained a higher proportion of saturated fatty acids than other phospholipids. Sterols were present free and as esters with palmitoleic and oleic acids. Phospholipid content was affected by growth conditions. A high level of inositol in the growth medium reduced the formation of neutral lipid but did not affect the content of yeast phospholipid.     

蛋黄甘油三酸酯的脂肪酸组成分析

采用毛细管气相色谱法分析酶法制备的蛋黄甘油三酸酯的脂肪改组成及相对含量，结果表明：其主要合有棕榈酸、油酸、硬脂酸、亚油酸、棕榈油酸，此外还含有微量的亚麻酸、花生四烯酸和二十二碳六烯酸。不饱和脂肪酸超过60％，是一种极具开发价值的营养保健油脂。     

Oxygen addition and sterol synthesis in Saccharomyces cerevisiae during enological fermentation

Under anaerobic conditions, yeast growth normally requires oxygen in order to favour the synthesis of sterols and unsaturated fatty acids. However, in such conditions, superfluous oxygen consumption by yeast cells is observed. The superfluous oxygen consumed by the yeast cells appears to be not related to classical respiration, but mainly to the operation of several alternative oxygen consumption pathways. In this study, the potential relationship between this superfluous oxygen consumption and the yeast sterol synthesis pathway was investigated during enological fermentation. Additions of small (7 mg l(-1)) and excess (37 mg l(-1)) amounts of oxygen at the end of cell growth phase were used as a method of comparing oxygen consumption by normal synthetic pathways with that by alternative respiration pathways. The superfluous oxygen consumption by yeast cells during fermentation seemed not to alter and strongly favoured fermentation kinetics and cell biomass formation. However, a marked decrease of the orderliness of the membrane phospholipids is observed, which is not related to the drop of cell viability. After oxygen additions, squalene contents of the cells decreased, while the relative proportions of ergosterol or its precursors in the total sterol fraction did not correlatively increase. It was further found that an oxygen-dependent sterol degradation occurred when oxygen was added in excess amounts with respect to the cellular requirements for sterol synthesis. At present, this modification of the sterol contents of yeast membranes has not been related to any physiological parameters.     

Changes in the lipid and fatty acid composition during maturation of seeds of white mustard (Sinapis alba)

The oil content of the seeds of white mustard (Sinapis alba) was determined 3 weeks after flowering and at weekly intervals until seeds were matured. Examination of the lipid classes by quantitative t.l.c. showed that triglycerides were the major components at all stages and were accompanied by sterol esters, diglycerides and polar lipids; monoglycerides were only detected in the first 2 samples. The fatty acid composition of the total oil and the mono-, di- and triglycerides and sterol esters was determined by g.l.c. The 7 major fatty acids, namely palmitic, stearic, oleic, linoleic, linolenic, eicosenoic and erucic acids were present at all stages of maturity. The fatty acid composition of the triglyceride fraction was similar to that of the total oil whereas the mono- and diglycerides and sterol esters contained a relatively higher proportion of saturated fatty acids. Erucic acid, the major acid of the oil from mature seeds did not become the major acid until 35 days after flowering. The results are discussed in relation to pathways of lipid synthesis in higher plants.     

Polar lipids of defatted chickpea (Cicer arietinum L.) flour and protein isolates

Polar lipid composition of defatted chickpea flour and protein isolates was studied. The main compounds were phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine. Other compounds, in lower amounts, were sterol glucosides, esterified sterol glucosides and digalactosyldiglycerides. Palmitic, oleic and linoleic acid were the main fatty acids in polar lipids. A reduction in the content of phosphatidylinositol and sterol glucosides in the protein isolates with respect to the defatted flour was observed, indicating that these compounds are more sensitive to the chemical treatment of the protein isolates. However, unsaturated fatty acids and unsaturated sterols content decreased in the protein isolates probably undergoing oxidative degradation.     

Influence of vacuum filtration of Viura must on the concentration of fatty acids and their utilization in fermentation

Fatty acids such as palmitoleic, oleic, linoleic and linolenic along with sterols constitute growth or survival factors for yeast. The objective of this work was to study the influence of vacuum filtration of Viura must on fatty acid contents and their use during fermentation. The results were compared with unclarified must, the control. Filtration drastically reduced the total fatty acid concentration (81.5%) and especially unsaturated fatty acids (97.1% of linoleic, and 100% of linolenic), as well as the minor saturated acids, arachidic and behenic. In the first half of fermentation, fatty acids were excreted in the filtered must (76.8%) whereas they were consumed in the control (46.8%). In the second half of fermentation, there was greater consumption in the control sample (74.5%) than in the filtered sample (37.4%).     

脂肪酸对酿酒酵母酒精耐性的影响

研究几种不同脂肪酸对酿酒酵母在存活率、生长速率和发酵方面的酒精耐性的影响。结果表明：培养基中添加两种不饱和脂肪酸（棕榈油酸和油酸）能显著增加酵母菌在酒精冲击下的存活率,其中棕榈油酸的效应更强。同时这些存活的酵母菌在含酒精培养基上的生长速率也比普通酵母菌更快,而两种饱和脂肪酸（棕榈酸和硬脂酸）在提高酵母菌存活率和生长速率方面几乎无贡献。同时在添加相同浓度不饱和脂肪酸的条件下,培养至稳定期的酵母菌比对数期酵母菌具有更高的存活率和更好的生长速率。但在发酵方面,添加短链脂肪酸（棕榈油酸和棕榈酸）能够使酵母菌发酵达到较高的酒精体积分数,这个结果与酵母菌生长耐酒精性的结果不一致,表明酵母菌生长和发酵的酒精耐性机制是不同的。     

金花葵籽油中不饱和脂肪酸的GC-MS测定

采用索氏提取法、石油醚浸泡法以及超声波提取法提取金花葵籽油,并对3种提取方法的含油率进行比较。利用GC-MS方法对金花葵籽油中不饱和脂肪酸的含量进行测定,并对气相的条件进行了优化。测定结果表明金花葵籽油含有亚油酸32.35%,油酸43.89%,棕榈油酸0.40%,不饱和脂肪酸占76.64%,含量较丰富。     

CHEMICAL CHARACTERIZATION AND STEREOSPECIFIC ANALYSIS OF LIPIDS SYNTHESIZED BY CERTAIN YEAST STRAINS

Fatty acid analysis of lipids from yeast strains, Apiotrichum curvatum ATCC 10567, Cryptococcus albidus ATCC 56297, Lipomyces starkeyi ATCC 12659, and Rhodosporidium toruloides ATCC 10788, grown on whey permeate revealed palmitic, stearic, oleic and linoleic acids as the predominant fatty acids in the triacylglycerol fractions. The phospholipid fractions were dominated by oleic and linoleic acids. The stereospecific distribution of fatty acids in the triacylglycerol fractions of lipids from two yeast strains, Apiotrichum curvatum ATCC 10567 and Lipomyces starkeyi ATCC 12659, was determined and revealed the presence of almost entirely unsaturated fatty acids at the sn-2 position (91.9% and 82.8%, respectively). The dominance of unsaturated fatty acids (in the range of 61.5 to 72.3%) at the sn-1 position was also observed. Oleic acid was the predominant fatty acid at positions sn-1 and sn-2 for both yeast strains. Position sn-3 had the greatest concentrations of saturated fatty acids, with palmitic acid as the predominant fatty acid.     

植物油中脂肪酸成分的调查与分析

通过对植物油中脂肪酸成分的调查,了解多种不同植物油中的脂肪酸含量及组成比,从而为研制符合国家推荐的脂肪酸比例的保健调和油提供数据参考。方法:取一定量的油脂样品,通过碱法甲酯化后用气相色谱分析。结果:实验结果显示,植物油中含有大量的不饱和脂肪酸,主要为油酸和亚油酸,同时还发现存在少量的共轭亚油酸,而饱和脂肪酸则以棕榈酸和硬脂酸为主。在不饱和脂肪酸中n-6/n-3的比值除了亚麻子油和精炼菜子油分别为0.44、2.84以外,其他植物油的比值均较高,从11.15到286.37不等。     

长柄扁桃油脂肪酸成分分析

长柄扁桃是一种新型的沙生木本油料植物。采用GC-MS法对长柄扁桃油的脂肪酸成分进行分析。结果表明,长柄扁桃种仁中油含量在55%以上,由棕榈酸、棕榈油酸、油酸、亚油酸、亚麻酸、花生烯酸和芥酸7种脂肪酸组成,其中不饱和脂肪酸高达98.1%,单不饱和脂肪酸与多不饱和脂肪酸的比例与橄榄油比例相似,芥酸含量仅为0.8%。表明长柄扁桃油是一种品质优良的食用油,具有广阔的开发前景。     

Changes in the fatty acid composition of dietetic ready-to-cook chicken meat products during frozen storage

A study was made on the fatty acid composition of dietetic ready-to-cook products of boneless chicken legs or breasts prepared by curing using several curing mixtures during frozen storage. Leg muscles were found to be richer in unsaturated fatty acids than breast muscles, substantial differences having been found in the contents of palmitoleic and linolenic acids. During frozen storage, the contents of unsaturated fatty acids were reduced, especially intensively in the leg muscle ready-to-cook products. The fastest changes occurred in linolenic and linolic acids and partly in palmitic acid. The level of oleic acid remained substantially unchanged throughout the storage period. Irrespective of the changes found, the ratio of unsaturated and saturated fatty acids in all the groups studied remained greater than 1 for both types of meat. The application of citrate in the curing mixture had a favourable effect on the changes, in that a minimum alteration in the contents of unsaturated fatty acids was achieved.