代谢副产物对L-苏氨酸发酵的影响及应对措施

研究了L-苏氨酸的发酵过程,通过高效液相色谱和氨基酸分析仪测定了L-苏氨酸发酵液中的主要副产物为乙酸、乳酸、缬氨酸、天冬氨酸、丙氨酸等。利用外源添加实验研究了各种代谢副产物对L-苏氨酸发酵的影响。结果表明乙酸浓度高于2 g/L、乳酸浓度高于10 g/L时对L-苏氨酸生产菌的生长和产酸有抑制作用,采用提高溶解氧和葡萄糖限制性脉冲流加措施将乙酸、乳酸的浓度控制在0.5 g/L以下,L-苏氨酸产量明显提高。     

L-苏氨酸发酵过程中乙酸的控制

大肠杆菌是表达外源基因常用的宿主菌,然而在培养过程中容易发生副产物乙酸的积累,不仅造成碳源的浪费,而且严重抑制菌体生长及外源基因的表达.本研究利用一株自主构建的大肠杆菌基因工程菌(MHZ0200-2)发酵生产L-苏氨酸.通过选择合适的发酵条件来控制其副产物乙酸的生成,从而提高L-苏氨酸的产量.L-苏氨酸的初始产量是0.09g/L,培养条件优化后产量提高到2.06g/L.     

调整葡萄糖转运系统提高大肠杆菌L-苏氨酸产量

葡萄糖的有效利用是提高大肠杆菌合成L-苏氨酸能力的关键,作者通过优化葡萄糖转运来提高大肠杆菌L-苏氨酸合成能力。利用CRISPR基因编辑技术在大肠杆菌TWF001中分别敲除了PTS系统关键基因ptsH和ptsG,并在30 g/L葡萄糖质量浓度下进行了摇瓶发酵。与对照菌株TWF001相比,TWF001ΔptsH和TWF001ΔptsG合成L-苏氨酸能力均有明显改善;TWF001ΔptsH L-苏氨酸产量提升38.02%。在TWF001ΔptsH基因组上用trc启动子过表达galP基因,构建了TWF001ΔptsH,Ptrc：：PgalP。对3株突变菌在40、50、60 g/L葡萄糖质量浓度下进行了摇瓶发酵;36 h后TWF001ΔptsH,Ptrc：：PgalP在40 g/L葡萄糖质量浓度时,L-苏氨酸产量达到26.16 g/L,糖酸转化率为0.65 g/g,L-苏氨酸产量提升幅度达42.12%。研究结果说明优化葡萄糖转运可以有效提高大肠杆菌L-苏氨酸合成能力。     

碳源对L-苏氨酸发酵的影响

以L-苏氨酸生产菌TRFC为供试菌株,研究了碳源对L-苏氨酸发酵的产量和糖酸转化率的影响。采用补料分批发酵工艺生产L-苏氨酸,利用氨基酸分析仪测定发酵液中L-苏氨酸的产量。确定了发酵的最佳碳源及其补料方式,通过10L罐补料分批发酵36h,产酸可达118.9 g/L,糖酸转化率为47.6%。     

增强乙醛酸循环对大肠杆菌合成L-苏氨酸的影响

L-苏氨酸是人类必需氨基酸,在医药、食品、饲料领域有广泛的应用。在L-苏氨酸发酵生产过程中,乙醛酸循环起到部分回补途径的功能。本实验利用Red重组技术,以L-苏氨酸生产菌Escherichia coli THRD为出发菌株,构建了icl R基因缺失菌株THRDΔicl R以及不同强度启动子替换ace BAK启动子的菌株THRD P1和THRD P2。通过实时荧光定量PCR检测表明,苹果酸合酶基因(ace B)的表达量分别是原菌的1.89倍、2.11倍以及2.96倍。摇瓶发酵结果显示,THRDΔicl R的L-苏氨酸产量及糖酸转化率分别为42.60±1.23 g/L和32.77 g/g,较原菌THRD(35.32±1.07 g/L和27.17 g/g)分别提高20.61%和20.70%。THRD P1 L-苏氨酸产量及糖酸转化率分别为36.50±1.42 g/L和28.08 g/g,较原菌THRD(35.32±1.07 g/L和27.17 g/g)分别提高3.34%和3.39%。而THRD P2 8 h后菌体生长停滞,L-苏氨酸产量及糖酸转化率分别为8.31±1.31 g/L和20.78 g/g,较原菌THRD(35.32±1.07 g/L和27.17 g/g)分别降低了76.47%和23.52%。综上所述,适当增强乙醛酸循环有利于L-苏氨酸的积累,而过强的乙醛酸循环影响菌体的正常代谢。     

黄色短杆菌B-003产L-精氨酸发酵条件的研究

目的通过对摇瓶发酵条件的研究,提高黄色短杆菌B-003 L-精氨酸的产量。方法在单因素实验的基础上,利用响应面法,以L-精氨酸的产量为响应值,研究L-精氨酸摇瓶发酵条件。结果 Plackett-Burman设计筛选出3个对L-精氨酸产量有显著影响的因素：葡萄糖、硫酸铵和磷酸二氢钾的浓度,通过Box-Behnken试验设计得出,葡萄糖的浓度为99.57 g/L,硫酸铵浓度为60.80 g/L,磷酸二氢钾浓度为2.18 g/L时L-精氨酸产量最高。结论在最佳培养条件下,L-精氨酸产量达24.10 g/L,与最初培养条件相比产量提高了58.55%。     

黄色短杆菌B．003产L-精氨酸发酵条件的研究

目的通过对摇瓶发酵条件的研究,提高黄色短杆菌B-003 L-精氨酸的产量。方法在单因素实验的基础上,利用响应面法,以L-精氨酸的产量为响应值,研究L-精氨酸摇瓶发酵条件。结果 Plackett-Burman设计筛选出3个对L-精氨酸产量有显著影响的因素：葡萄糖、硫酸铵和磷酸二氢钾的浓度,通过Box-Behnken试验设计得出,葡萄糖的浓度为99.57 g/L,硫酸铵浓度为60.80 g/L,磷酸二氢钾浓度为2.18 g/L时L-精氨酸产量最高。结论在最佳培养条件下,L-精氨酸产量达24.10 g/L,与最初培养条件相比产量提高了58.55%。     

提高L- 谷氨酸产量的后期发酵工艺参数研究

以谷氨酸生产菌S9114 为供试菌株,利用50m3 发酵罐研究了L- 谷氨酸的发酵过程,确定发酵后期产酸速率过低是影响L- 谷氨酸产量的主要原因。优化发酵工艺的参数以提高L- 谷氨酸后期发酵的比产酸速率,结果表明：采用溶氧控制的葡萄糖流加方式,控制发酵后期的pH 值,在发酵的适当时期流加一定量的生物素和KCl 等措施可有效提高L- 谷氨酸的后期产酸水平。在最优条件下,单罐最高产量可达148g/L,糖酸转化率为60.5%。     

谷氨酸棒状杆菌合成L-高丝氨酸的代谢改造与发酵条件探究

目的:本研究以谷氨酸棒状杆菌ATCC 13032为底盘细胞,构建1株L-高丝氨酸合成菌株并分析溶氧环境对其产物合成的影响。方法:首先通过外源添加0～40 g/L的L-高丝氨酸分析谷氨酸棒状杆菌的产物耐受性;随后,通过基因thrB敲除阻断L-高丝氨酸的降解途径,获得谷氨酸棒状杆菌重组菌H1;在此基础上利用挡板摇瓶进行细胞培养以增强发酵过程中氧气供给能力。结果:与大肠杆菌相比,谷氨酸棒状杆菌对L-高丝氨酸具有更强耐受性。研究中通过敲除基因thrB构建了L-苏氨酸缺陷型谷氨酸棒状杆菌重组菌H1,发现基础培养基中加入0.5 g/L的L-苏氨酸后,该重组菌生长恢复正常水平。挡板摇瓶条件下重组菌H1的L-高丝氨酸产量增加至836.7 mg/L,较普通摇瓶产量44.6 mg/L提高了17.76倍。结论:通过阻断L-苏氨酸的合成,成功构建L-高丝氨酸合成菌株谷氨酸棒状杆菌H1,并且发现利用挡板摇瓶增强发酵过程中供氧能力是促进谷氨酸棒状杆菌高效合成L-高丝氨酸的有效手段,为后续提高L-高丝氨酸发酵产量提供了参考。     

正交旋转组合优化L-苏氨酸发酵的氮源

利用旋转回归法研究氮源对L-苏氨酸产量的影响并拟合出回归方程,探索L-苏氨酸发酵的最佳氮源及其用量.经回归分析表明,培养基中硫酸铵、酵母粉的含量及其配比对L-苏氨酸产量有显著影响,通过岭脊分析寻优得出:硫酸铵最佳浓度为17.66g/L、酵母粉最佳浓度为2.51 g/L.在此优化条件用10L自动发酵罐补料分批发酵38h,L-苏氨酸产量可达119.7g/L,糖酸转化率为47.9%.     

Reliable identification of grapevine rootstock varieties using RAPD PCR on woody samples

Since grapevine ( Vitis spp .) rootstock material is being traded increasingly as disbudded woody material a lack of distinctive morphological features on such material necessitates an alternative and reliable means of identification. Methods described here were developed for rapid and efficient extraction of DNA from woody samples rich in phenolic compounds and polysaccharides, and for subsequent identification of varieties by RAPD PCR. Using these methods, and with the application of only one selected RAPD primer, we were able to differentiate sixteen rootstock varieties, including the seven varieties most commonly used in Germany. Problems commonly encountered with reproducibility of RAPD patterns were avoided by choosing primers with a dinucleotide sequence and a high G/C content that allowed a rather high annealing temperature of 45°C. Methods described here should also be useful for other horticultural crops, especially those with woody tissues rich in phenolic compounds and polysaccharides.     

An internet compendium of analytical methods and spectroscopic information for monomers and additives used in food packaging plastics

An internet website (http://cpf.jrc.it/smt/) has been produced as a means of dissemination of methods of analysis and supporting spectroscopic information on monomers and additives used for food contact materials (principally packaging). The site which is aimed primarily at assisting food control laboratories in the European Union contains analytical information on monomers, starting substances and additives used in the manufacture of plastics materials. A searchable index is provided giving PM and CAS numbers for each of 255 substances. For each substance a data sheet gives regulatory information, chemical structures, physico-chemical information and background information on the use of the substance in particular plastics, and the food packaging applications. For monomers and starting substances (155 compounds) the infra-red and mass spectra are provided, and for additives (100 compounds); additionally proton NMR are available for about 50% of the entries. Where analytical methods have been developed for determining these substances as residual amounts in plastics or as trace amounts in food simulants these methods are also on the website. All information is provided in portable document file (PDF) format which means that high quality copies can be readily printed, using freely available Adobe Acrobat Reader software. The website will in future be maintained and up-dated by the European Commission's Joint Research Centre (JRC) as new substances are authorized for use by the European Commission (DG-ENTR formerly DGIII). Where analytical laboratories (food control or other) require reference substances these can be obtained free-ofcharge from a reference collection housed at the JRC and maintained in conjunction with this website compendium.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

Tests of potential functional barriers for laminated multilayer food packages. Part I: Low molecular weight permeants

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 μm-thick oriented PP) into the food simulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.     

Chlorohydrins of bisphenol A diglycidyl ether (BADGE) and of bisphenol F diglycidyl ether (BFDGE) in canned foods and ready-to-drink coffees from the Japanese market

BADGE.2HCl and BFDGE.2HCl were determined in 28 samples of ready-to-drink canned coffee and 18 samples of canned vegetables (10 corn, 5 tomatoes and 3 others), all from the Japanese market. HPLC was used as the principal analytical method and GCMS for confirmation of relevant LC fractions. BADGE.2HCl was found to be present in one canned coffee and five samples of corn, BFDGE.2HCl in four samples of canned tomatoes and in one canned corn. No sample was found which exceeded the 1mg/kg limit of the EU for the BADGE chlorohydrins. However the highest concentration was found for the sum of BFDGE.2HCl and BFDGE.HCl.H₂O at a level of 1.5mg/kg. A Beilstein test confirmed that all cans containing foods contaminated with BADGE.2HCl or BFDGE.2HCl had at lest one part coated with a PVC organosol.     

European priorities for research to support legislation in the area of food contact materials and articles

A strong science base is required to underpin the planning and decision-making process involved in determining future European community legislation on materials and articles in contact with food. Significant progress has been made in the past 5 years in European funded work in this area, with many developments contributing to a much better understanding of the migration process, and better and simpler approaches to food control. In this paper this progress is reviewed against previously identified work-areas (identified in 1994) and conclusions are reached about future requirements for R&D to support legislation on food contact materials and articles over the next 5 or so years.     

Analysis of benzo[a]pyrene in spiked fatty foods by second derivative synchronous spectrofluorimetry after microwave-assisted treatment of samples

A simple, rapid and inexpensive method has been developed for the determination of benzo[a     

The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. II: Certification study

This paper describes the second part of a project undertaken to develop certified mussel reference materials for paralytic shellfish poisoning toxins. In the first part two interlaboratory studies were undertaken to investigate the performance of the analytical methodology for several PSP toxins, in particular saxitoxin and decarbamoyl-saxitoxin in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the certification exercise. Fifteen laboratories participated in this certification study and were asked to measure saxitoxin and decarbamoyl-saxitoxin in rehydrated lyophilized mussel material and in a saxitoxin-enriched mussel material. The participants were allowed to use a method of their choice but with an extraction procedure to be strictly followed. The study included extra experiments to verify the detection limits for both saxitoxin and decarbamoyl-saxitoxin. Most participants (13 of 15) were able to meet all the criteria set for the certification study. Results for saxitoxin.2HCl yielded a certified mass fraction of <0.07 mg/kg in the rehydrated lyophilized mussels. Results obtained for decarbamoyl-saxitoxin.2HCl yielded a certified mass fraction of 1.59+/-0.20 mg/kg. The results for saxitoxin.2HCl in enriched blank mussel yielded a certified mass fraction of 0.48 +/- 0.06 mg/kg. These certified reference materials for paralytic shellfish poisoning toxins in lyophilized mussel material are the first available for laboratories to test their method for accuracy and performance.     

Announcing a new international peer-reviewed journal:Food Science and Human Wellness now accepting manuscript submission in English

<正>We are pleased to announce the launch of a new international peer-reviewed journal-Food Science and Human Wellness,ISSN 2213-4530,which is an open access journal,produced and hosted by Elsevier B.V.on behalf of Beijing Academy of Food Sciences.Food Science and Human Wellness is an international peer-reviewed English journal that provides a forum for the dissemination of the