解淀粉乳酸细菌在L-乳酸发酵生产中的应用

对解淀粉乳酸细菌及其产生的淀粉酶和发酵工艺等方面的国内外研究现状进行了综述。解淀粉乳酸细菌具有分泌淀粉酶的能力,可免去原料水解处理工序直接发酵淀粉质原料生产乳酸,可以简化生产工艺,并可节约设备投资,进而降低生产成本。解淀粉乳酸细菌主要分离自传统发酵食品,也可从有机废弃物和厨余垃圾中分离得到。介绍了解淀粉乳酸细菌直接利用淀粉质原料的机理,比较了解淀粉乳酸菌发酵生产L-乳酸的工艺。提出通过诱变育种和基因工程育种等方法获得更加高效的解淀粉乳酸细菌,并结合先进的发酵、分离技术来提高乳酸生产效率。     

L-乳酸发酵的研究

本文报导了L-乳酸产生菌筛选、发酵条件以及发酵产物鉴定的结果。从56株根霉中筛选出10株产L-乳酸较高的菌株,其中根霉R47产L-乳酸最高,产酸稳定。发酵条件试验结果表明,该菌最适发酵培养基组成(％)：葡萄糖15,尿素0．2,KH 2PO40．02,MgSO4·7H2O0．025,ZnSO4·7H2 0 0．0044,CaCO3,6,7;pH6．7。在摇瓶培养条件下,35℃48小时,产L-乳酸达11．84 g／100 ml,对糖的重量转化率达78,9％。发酵液经离子交换等方法纯化,得到无色或微黄色透明糖浆状液体。经纸层析、比旋光度测定、紫外光谱和红外光谱分析证明确系L-乳酸。     

L-乳酸发酵菌株的选育

以初筛得到的 1株干酪乳杆菌鼠李糖亚种突变株R2 (Lactobcilluscaseisubsp .rhamnosusR2 )为出发菌株 ,经紫外线、硫酸二乙酯、复合诱变处理 ,筛选出 1株产乳酸较高的突变株ZY ,L 乳酸含量达 93.9%。以正交试验为基础对发酵培养基进行优化 ,采用优化后的培养基发酵 4d ,残糖降至 0 .1 %以下 ,L 乳酸产量达9.5 7g/ 2 0 0mL ,对糖的转化率达 96 .3%。     

L-乳酸的发酵生产和聚L-乳酸的化学加工

L-乳酸广泛应用于食品、医药、日化和工业等各个领域。近年来随着石化资源的不断紧缺,众多化学合成的高分子材料的生产受到了限制。以生物质资源为基础的L-乳酸因此被大量用于加工生产成聚L-乳酸等环境友好型生物可降解材料。正是由于L-乳酸需求量的增大,如何高效低成本地生产L-乳酸显得尤为重要。系统综述了L-乳酸生产菌株的选育,用于L-乳酸发酵生产的廉价资源的开发利用,L-乳酸的发酵生产和L-乳酸的分离纯化等方面的研究进展。目前研究的热点和难点正是基于上述四个部分:菌种方面,以可以高效代谢利用廉价底物,且营养需求低的选育目标获得了多个优良的生产菌种,然而具备综合代谢优势的菌种还有待进一步选育;发酵底物方面,已开发利用多种廉价,来源丰富且易于菌种代谢并高效转化成乳酸的底物,但是对这些底物工业规模应用还有待进一步研究;发酵工艺方面,建立了环境友好型,劳动强度低的发酵工艺,然而实际应用中仍然存在成本高的问题;后提取方面,通过选育低营养需求的生产菌种和采用新型发酵工艺有效地简化了后提取过程,但是实际应用方面仍受发酵工艺成本高的制约。最后对聚L-乳酸的化学加工以及聚L-乳酸的生物降解进行了探讨并提出了一些建议。     

基因工程菌发酵生产L-乳酸研究进展

乳酸是重要的工业平台化学品。随着聚乳酸产业的兴起,对高质量L-乳酸的需求量也不断增加。为了进一步降低L-乳酸发酵成本,提高菌株的工业适应性,各种现代生物技术已经应用到L-乳酸发酵菌种的改造上来。文中简要综述了近年来使用乳酸菌、酵母、大肠杆菌及米根霉等基因工程菌株发酵生产L-乳酸的技术进展。     

产L-乳酸凝结芽孢杆菌发酵条件的初步研究

对经N+离子注入筛选到的L-乳酸高产菌株BacilluscoagulansRS12-6的发酵条件进行了初步研究。主要研究了 通气量、温度及pH值等培养条件对菌体生长及产酸的影响。确定最佳培养条件及最佳碳源、氮源配比。     

乳杆菌Lactobacillus sp.lxp发酵高产L-乳酸研究

筛选得到一株乳杆菌Laetobaeillus sp．,进行发酵生产高浓度L-乳酸的研究。考察了种龄、接种量、温度和不同pH调节剂对乳酸发酵的影响。结果表明：最佳种子培养时间为15h;最佳接种量为15％;最适培养温度为42℃;与氨水和氢氧化钠相比,碳酸钙更适于作为发酵过程的pH调节刺;以葡萄糖为碳源,添加豆粕水解液和玉米浆作为辅料,2L罐培养120h,L-乳酸质量浓度可达202 g/L,糖转化率91．3％,L-乳酸占发酵液中总酸含量98％以上。     

低能离子注入L-乳酸生产菌种选育与发酵条件初步优化

通过20keV氮离子注入L-乳酸生产菌(Bacillus coagulans)筛选到一株产量比出发菌株提高10％的高产菌株RS12-6C,经多次传代实验表明该菌遗传稳定性较好。并对其发酵条件如接种量、装液量、摇床转速、温度等进行初步优化,在含糖150g/L的摇瓶中发酵,其L-乳酸产量达到117g/L。     

聚合级L-乳酸的非粮生物质发酵研究进展

乳酸在化工、医药和食品加工等领域有着广泛的用途。随着聚乳酸产业的兴起,对聚合级L-乳酸的需求量也不断增加。开发低成本的非粮生物质乳酸发酵工艺、实现发酵-分离耦合是降低聚合级L-乳酸成本、摆脱原料价格不断上涨压力的技术趋势。文中简要综述了近2~3年使用非粮生物质发酵生产聚合级L-乳酸的技术进展,并对未来乳酸发酵工艺作了展望。     

d- and l-lactic acid production from fresh sweet potato through simultaneous saccharification and fermentation

The aim of this study was to develop a bioprocess for l- and d-lactic acid production from raw sweet potato through simultaneous saccharification and fermentation by Lactobacillus paracasei and Lactobacillus coryniformis, respectively. The effects of enzyme and nitrogen source concentrations as well as of the ratio of raw material to medium were investigated. At dried material concentrations of 136.36–219.51 g L⁻¹, yields of 90.13–91.17% (w/w) and productivities of 3.41–3.83 g L⁻¹ h⁻¹ were obtained with lactic acid concentrations as high as 198.32 g L⁻¹ for l-lactic acid production. In addition, d-lactic acid was produced with yields of 90.11–84.92% (w/w) and productivities of 2.55–3.11 g L⁻¹ h⁻¹ with a maximum concentration of 186.40 g L⁻¹ at the same concentrations of dried material. The simple and efficient process described in this study will benefit the tuber and root-based lactic acid industries without requiring alterations in plant equipment.     

Effects of intermittent addition of cellulase for production of L-lactic acid from wastewater sludge by simultaneous saccharification and fermentation

An attempt was made to create L-lactic acid, a precursor of poly-lactic acid, which is a biodegradable plastic, from wastewater sludge from the paper-manufacturing industry. The sludge contained a high percentage of cellulose and needed to be hydrolyzed to glucose by the action of the cellulase before being treating with lactic acid bacteria. Therefore, a method involving simultaneous saccharification and fermentation (SSF) was carried out. The optimum pH of the SSF for production of the lactic acid by the newly isolated lactic acid bacterium with a high selectively of L-lactic acid was found out to be around pH = 5.0, and the optimum temperature to be approximately 40 degrees C. On the basis of the measurement of the cell density changes in the lactic acid bacteria, it was ascertained that the bacterial activity could continue at a high level for a relatively long period of time, and that the L-lactic acid productivity was diminished by the rapid deactivation of the cellulase. With the intermittent addition of cellulase once daily for the sake of compensating for the cellulase deactivation, the L-lactic acid attained a maximum concentration of 16.9 g/L, i.e., a 72.2% yield based on the potential glucose contained in the sludge under optimum pH and temperature conditions.     

Product inhibition in simultaneous saccharification and fermentation of cellulose into lactic acid

The product, lactic acid, strongly inhibited microbial activity in lactic acid fermentation. The volumetric productivity declined from 1.19 g/l.h with zero lactic acid (control) to only 0.18 g/l.h when lactic acid reached 65 g/l. Lactic acid also inhibited cellulase activity but less severely than the inhibition on microbial activity as lactic acid above 90 g/l was needed for 50% inhibition. A gradual deterioration of the Simultaneous Saccharification and Fermentation (SSF) process occurred with the build-up of lactic acid and the rate-controlling step in SSF shifted from hydrolysis to fermentation as the bioprocess proceeded.     

Ethanol production from paper material using a simultaneous saccharification and fermentation system in a fed-batch basis

In this work, a recycled paper-derived feedstock was used to produce ethanol by the simultaneous saccharification and fermentation (SSF) process using the thermotolerant yeast Kluyveromyces marxianus CECT 10875. At standard SSF conditions, the highest yield (about 80% of theoretical) was obtained at low substrate concentration and high enzyme loading. With increasing substrate concentration, mixing difficulties appeared which prevented an adequate SSF process performance and limited ethanol production. An SSF fed-batch procedure was then used which permitted an increase in substrate concentrations while maintaining SSF yields similar to that obtained at standard SSF, thus allowing an increased final ethanol production (about 18 g/l).     

响应面法优化玉米秸秆同步酶解发酵产乙醇条件

对汽爆玉米秸秆同步酶解发酵生产乙醇的条件进行优化。首先利用Fractional Factorial设计法对影响乙醇产量的7个因素进行评价,筛选出具有显著效应的3个因素,即反应温度、酶添加量、总反应时间,再以Box—Behnken设计法及响应面分析法确定主要因素的最佳水平,即反应温度37℃,每g纤维素添加纤维素酶32u,反应时间87h,此时乙醇体积分数达到3．69％。新工艺条件实验结果表明,乙醇体积分数在87h可达到3．76％,和原工艺相比,反应时间缩短了9h,乙醇体积分数提高了13％。     

Direct lactic acid fermentation: Focus on simultaneous saccharification and lactic acid production

In the recent decades biotechnological production of lactic acid has gained a prime position in the industries as it is cost effective and eco-friendly. Lactic acid is a versatile chemical having a wide range of applications in food, pharmaceutical, leather and textile industries and as chemical feedstock for so many other chemicals. It also functions as the monomer for the biodegradable plastic. Biotechnological production is advantageous over chemical synthesis in that we can utilize cheap raw materials such as agro-industrial byproducts and can selectively produce the stereo isomers in an economic way. Simultaneous saccharification and fermentation can replace the classical double step fermentation by the saccharification of starchy or cellulosic biomass and conversion to lactic acid concurrently by adding inoculum along with the substrate degrading enzymes. It not only reduces the cost of production by avoiding high energy consuming biomass saccharification, but also provides the higher productivity than the single step conversion by the providing adequate sugar release.     

玉米芯稀酸水解及L-乳酸发酵研究

对玉米芯稀硫酸水解条件及糖化液发酵L-乳酸进行了初步研究。结果表明,玉米芯木聚糖最适水解条件为2%H2SO_4、120℃、30 min、固液比1:10,糖化液还原糖含量可达40.8 g/L,主要成分为木塘。细菌A-19可以利用水解液中的葡萄糖和木糖产酸,最适发酵条件为45℃、pH 6.5,从45℃～51℃、pH 5.5～pH 6.5产量均较高。用未浓缩的水解液发酵24 h,L-乳酸产量为30.6g/L,残糖为1.6 g/L,糖酸转化率为82.6%;用浓缩1倍的水解液发酵48 h,L-乳酸产量为41.4 g/L,残糖4.1g/L,糖酸转化率为68.2%,在发酵48 h后继续补料发酵至72 h(补料液为浓缩3倍的水解液),L-乳酸产量为50.9 g/L,残糖6.3 g/L,糖酸转化率为71.8%。该研究为利用木质纤维素生产L-乳酸奠定了一定基础。     

Effects of growth stage on enzymatic saccharification and simultaneous saccharification and fermentation of bamboo shoots for bioethanol production

Bamboo is a fast-growing renewable biomass that is widely distributed in Asia. Although bamboo is recognised as a useful resource, its utilization is limited and further development is required. Immature bamboo shoots harvested before branch spread were found to be a good biomass resource to achieve a high saccharification yield. The saccharification yield of the shoots increased (up to 98% for immature Phyllostachys bambusoides) when xylanase was used in addition to cellulase. Simultaneous saccharification and fermentation (SSF) processing converted immature shoots of P. bambusoides and Phyllostachys pubescens to ethanol with an ethanol yield of 169 and 139 g kg⁻¹, respectively (98% and 81%, respectively, of the theoretical yields based on hexose conversion) when 12 FPU g⁻¹ enzyme and the yeast Saccharomyces cerevisiae were used.     

Application of simultaneous saccharification and fermentation (SSF) from viscosity reducing of raw sweet potato for bioethanol production at laboratory, pilot and industrial scales

The aim of this work was to research a bioprocess for bioethanol production from raw sweet potato by Saccharomyces cerevisiae at laboratory, pilot and industrial scales. The fermentation mode, inoculum size and pressure from different gases were determined in laboratory. The maximum ethanol concentration, average ethanol productivity rate and yield of ethanol after fermentation in laboratory scale (128.51 g/L, 4.76 g/L/h and 91.4%) were satisfactory with small decrease at pilot scale (109.06 g/L, 4.89 g/L/h and 91.24%) and industrial scale (97.94 g/L, 4.19 g/L/h and 91.27%). When scaled up, the viscosity caused resistance to fermentation parameters, 1.56 AUG/g (sweet potato mash) of xylanase decreased the viscosity from approximately 30000 to 500 cp. Overall, sweet potato is a attractive feedstock for be bioethanol production from both the economic standpoints and environmentally friendly.