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近日,中科院大连化学物理研究所赵宗保研究员领导的生物质高效转化研究组(1816组)在生物质能源研究中,首次实现葡萄糖和木糖同步利用生产油脂。这一重要研究成果于近日正式发表在《生物燃料生物技术》(Biotechnology for Biofuels,Hu et al., Biotechnology for Biofuels, 2011, 4: 25)上。生物质主要由纤维素、半纤维素和木质素组成,其水解产物具有葡萄糖和木糖并存的基本特点。将生物质水解产物转化为液体燃料面临的共性难点问题之一是葡萄糖和木糖并存的原料难以被微生物高效利用。生物柴油是重要的液体生物燃料,其规模化应用的瓶颈问题是油脂原料供应不足。微生物油脂具有与动植物油脂相近的脂肪酸组成,可用于制备生物柴油。大连化物所生物质高效转化研究组多年来致力于将生物质转化为生物柴油的研究。通过筛选发现,部分产油酵母可同步利用葡萄糖和木糖,在胞内积累油脂,菌体油脂含量达到59%。直接利用玉米秸秆水解液培养该产油酵母,菌体油脂含量达到39%。该研究成果对发展混合糖同步生物转化技术、降低微生物油脂生产原料成本、拓展生物柴油产业原料,均具有重要意义。http://www.bioon.com/biology/UploadFiles/201109/2011092710581567.jpgdoi:10.1186/1754-6834-4-25PMC:PMID:Simultaneous utilization of glucose and xylose for lipid production by Trichosporon cutaneumCuimin Hu, Siguo Wu, Qian Wang, Guojie Jin, Hongwei Shen and Zongbao K Zhao Background Biochemical conversion of lignocellulose hydrolysates remains challenging, largely because most microbial processes have markedly reduced efficiency in the presence of both hexoses and pentoses. Thus, identification of microorganisms capable of efficient and simultaneous utilization of both glucose and xylose is pivotal to improving this process. Results In this study, we found that the oleaginous yeast strain Trichosporon cutaneum AS 2.571 assimilated glucose and xylose simultaneously, and accumulated intracellular lipid up to 59 wt% with a lipid coefficient up to 0.17 g/g sugar, upon cultivation on a 2:1 glucose/xylose mixture in a 3-liter stirred-tank bioreactor. In addition, no classic pattern of diauxic growth behavior was seen; the microbial cell mass increased during the whole culture process without any lag periods. In shake-flask cultures with different initial glucose:xylose ratios, glucose and xylose were consumed simultaneously at rates roughly proportional to their individual concentrations in the medium, leading to complete utilization of both sugars at the same time. Simultaneous utilization of glucose and xylose was also seen during fermentation of corn-stover hydrolysate with a lipid content and coefficient of 39.2% and 0.15 g/g sugar, respectively. The lipid produced had a fatty-acid compositional profile similar to those of conventional vegetable oil, indicating that it could have potential as a raw material for biodiesel production. Conclusion Efficient lipid production with simultaneous consumption of glucose and xylose was achieved in this study. This process provides an exciting opportunity to transform lignocellulosic materials into biofuel molecules, and should also encourage further study to elucidate this unique sugar-assimilation mechanism.
[img]http://www.instrument.com.cn/bbs/images/affix.gif[/img][url=http://www.instrument.com.cn/bbs/download.asp?ID=103248]大黄中大黄酚-8-O-β-D-吡喃葡萄糖苷的提取、纯化及含量测定方法的研究[/url]
木糖醇,即戊五醇,为糖醇的一种,是一种可以作为蔗糖替代物的五碳糖醇,是木糖代谢的产物,木糖广泛存在于各种植物中,但由于含量低,提取成本高,故食品生产过程中通过木糖的加氢还原得到木糖醇。木糖醇的甜度与蔗糖相当,但热量比蔗糖低很多。木糖醇在体内的代谢途径与一般糖类不同,不需要胰岛素的参与,大部分分解成二氧化碳从肺部经过呼吸排出体外,不会升高血糖,因此木糖醇常被作为糖尿病人的甜味剂,木糖醇食品:添加有木糖醇的休闲食品都可称为木糖醇食品。看来木糖醇替代白糖是有科学依据的。同时糖尿病人需要注意的是无糖食品,并不是绝对的“无糖”无糖食品:根据国家标准《预包装特殊膳食用食品标签通则》规定,"无糖"的要求是指固体或液体食品中每100克或100毫升的含糖量不高于0.5克。无糖食品里面,可能含有淀粉水解物类作为甜味来源,也就是淀粉糖浆、果葡糖浆、麦芽糖之类。这些糖浆升高血糖、变成能量的效率,未必会比蔗糖慢。曾见过这样的产品,添加了葡萄糖浆或淀粉糖浆,还号称无糖食品。而这些配料,升高血糖的速度甚至可能快于白糖。其次,中国大部分无糖产品都用的是高效甜味剂,特别是合成甜味剂,比如安塞蜜、甜蜜素、糖精、阿斯巴甜等。但是,这些东西的甜度是蔗糖的几百倍。那么如原来的配方中,100克产品要加40克蔗糖,现在只需加零点几克甜味剂就够了,用什么来凑体积呢?一般来说,用来做填充的大都是淀粉、淀粉水解物或糊精之类。所以糖尿病人千万不能被无糖二字蒙蔽哦!