无机盐渗透压对假丝酵母SK25.001发酵生产赤藓糖醇的影响

以假丝酵母SK25.001为生产菌,通过研究其发酵产赤藓糖醇的碳源、氮源、碳氮比以及NaCl、KCl对其发酵产赤藓糖醇的影响,来探索无机盐(NaCl,KCl)渗透压对赤藓糖醇发酵的影响。结果发现,葡萄糖、酵母粉分别是其最佳碳源和氮源,最佳碳氮比为20∶1,转化率达到了14.2%;向发酵培养基中添加不同浓度的KCl或NaCl后发现,菌体生长速度随着KCl或NaCl浓度增大而降低,在KCl浓度为0.4 mol/L或NaCl浓度为0.3 mol/L时赤藓糖醇产量达到最大,达到了18.4 g/L和17.4 g/L;将NaCl和KCl的浓度用渗透压表示发现赤藓糖醇的转化率随着渗透压的增大而升高,高渗透压抑制菌体的生长。     

丛梗孢酵母产赤藓糖醇的诱变选育

利用微波-硫酸二乙酯复合诱变对产赤藓糖醇丛梗孢酵母E54进行处理,以高渗平板和摇瓶发酵为筛选方法,得到遗传稳定的诱变高产株EW29;再采用氮离子注入对EW29进行诱变处理,摇瓶发酵筛选得到诱变株EN59,其90h发酵液中赤藓糖醇产量达到55.13g/L,较EW29提高20.3%,较E54提高36.9%,遗传稳定性较好。对突变株EN59的发酵培养基进行了优化,在优化培养基葡萄糖250g/L、酵母膏5g/L、KH2PO4 0.3g/L、MnSO4 ·4H2O 0.04g/L、CuSO4 ·5H2O 0.03g/L,初始pH4的条件下,90h发酵液中赤藓糖醇平均产量达到69.00g/L以上。在优化培养基的基础上进行5L罐发酵放大实验,发酵126h赤藓糖醇产量达到71.14g/L。     

Absorption and Metabolism of the Natural Sweeteners Erythritol and Xylitol in Humans: A Dose-Ranging Study

The natural sweeteners erythritol and xylitol might be helpful to reduce sugar consumption and therefore prevent obesity and diabetes. The aim of the present study was to determine the absorption and metabolization into erythronate of different concentrations of erythritol and xylitol. Seventeen healthy lean participants received intragastric solutions of 10, 25, or 50 g erythritol or 7, 17, or 35 g xylitol on three study days in a randomized order. The study was double blinded with respect to the doses administered. We assessed plasma concentrations of erythritol, xylitol, and erythronate at fixed time intervals after administration with gas chromatography-mass spectrometry. We found: (i) a dose-dependent and saturable absorption of erythritol, (ii) a very low absorption of xylitol, (iii) a dose-dependent metabolization of erythritol into erythronate, and (iv) no metabolization of xylitol into erythronate. The implications of the metabolization of erythritol into erythronate for human health remain to be determined and more research in this area is needed.     

基于响应面的零热量果冻粉配方优化

以具有零热量的赤藓糖醇为基础原料替代传统果冻中的砂糖,从而降低果冻的能量,开发零热量果冻粉。首先通过单因素优化了对果冻粉成型和口味影响较大的胶体、酸浓度和KCl的浓度。针对以上4因素,利用Box-Benhnken法进行3水平响应面优化设计实验确定最佳配方:赤藓糖醇77.70%,可溶性膳食纤维16.40%,魔芋胶1.54%,卡拉胶2.46%,柠檬酸1.30%,KCl 0.14%,食用色素0.03%,食用香精0.03%。经此果冻粉配方制备的果冻具有很好地弹性,口感爽滑,咀嚼度达到318.734 J,属于零热量食品。      

The Role of Hexokinase and Hexose Transporters in Preferential Use of Glucose over Fructose and Downstream Metabolic Pathways in the Yeast Yarrowia lipolytica

The development of efficient bioprocesses requires inexpensive and renewable substrates. Molasses, a by-product of the sugar industry, contains mostly sucrose, a disaccharide composed of glucose and fructose, both easily absorbed by microorganisms. Yarrowia lipolytica, a platform for the production of various chemicals, can be engineered for sucrose utilization by heterologous invertase expression, yet the problem of preferential use of glucose over fructose remains, as fructose consumption begins only after glucose depletion what significantly extends the bioprocesses. We investigated the role of hexose transporters and hexokinase (native and fructophilic) in this preference. Analysis of growth profiles and kinetics of monosaccharide utilization has proven that the glucose preference in Y. lipolytica depends primarily on the affinity of native hexokinase for glucose. Interestingly, combined overexpression of either hexokinase with hexose transporters significantly accelerated citric acid biosynthesis and enhanced pentose phosphate pathway leading to secretion of polyols (31.5 g/L vs. no polyols in the control strain). So far, polyol biosynthesis was efficient in glycerol-containing media. Moreover, overexpression of fructophilic hexokinase in combination with hexose transporters not only shortened this process to 48 h (84 h for the medium with glycerol) but also allowed to obtain 23% more polyols (40 g/L) compared to the glycerol medium (32.5 g/L).     

植物类异戊二烯合成途径的研究进展

类异戊二烯广泛分布于自然界中,是结构最复杂、功能最多的一类化合物,具有极其重要的生理生态作用及经济价值。植物体内的类异戊二烯化合物从异戊烯焦磷酸(IPP)合成,IPP的合成途径主要有两条:甲羟戊酸(MVA)途径和2-甲基-D-赤藓糖醇-4-磷酸(MEP)途径。     

Physical and Sensory Characteristics of Chiffon Cake Prepared with Erythritol as Replacement for Sucrose

ABSTRACT: The effects of erythritol on physical and sensory characteristics of chiffon cakes were studied. The results showed that chiffon cakes prepared with 25%, 50%, 75%, and 100% replacement of sucrose with erythritol were lighter in crust and crumb and less sweet in crumbs than those with sucrose. There were no differences in the specific gravity of cake batter, volume, and moisture content between cakes prepared with sucrose or erythritol. Results from sensory evaluation also showed no significant differences in crumb color, moistness, and tenderness for any cakes.     

低热值甜昧剂——赤藓糖醇

赤藓糖醇是一种多元醇类甜味剂,具有类似于蔗糖的口味,具有热量低、稳定性高、甜味协调、无吸湿性、无龋齿性、不发酵及不会引起肠胃不适等优点。文中简述了赤藓糖醇的物理化学特征、生理代谢特性、生产及应用情况。     

产赤酵母融合株RH-UV-L4-F9遗传学和生理学特征的研究

利用细胞融合技术获得了一株高产赤藓糖醇的融合株RH-UV-L4-F9,其发酵能力强,赤藓糖醇产量高。为进一步开发利用此菌株,对融合株及其亲本UV-L4和UV-F9进行细胞体积、生物量、遗传型、DNA含量的测定,又对融合株进行了糖发酵、耐高渗透压性能、遗传稳定性的测定。融合株细胞平均体积为19.960μm2;生物量780.6mg/500mL;可利用葡萄糖、麦芽糖、蔗糖、棉籽糖,不能利用果糖、乳糖,有耐高渗透性能,为双亲互补的原养型,DNA含量为3.11μg/cell×10-9。