固定化黑曲霉发酵玉米糖液生产柠檬酸的研究

利用PVA复合凝胶包埋黑曲霉的孢子及菌丝体。固定后的细胞经过一系列预培养,用于发酵玉米生产柠檬酸。试验确定的固定化细胞摇瓶发酵生产柠檬酸最适条件为：玉米糖液浓度10Bx,培养温度35℃,摇瓶转速250r/min。经此条件发酵64h,柠檬酸产率最高达到96g/L,通常稳定在90g/L左右。同时对柠檬酸连续批次发酵生产进行了初步研究,固定化黑曲霉可连续使用8批次以上,其柠檬酸产量稳定在86－92g/L之间,。这为柠檬酸连续发酵提供了有利的保证,并探讨了有关的工艺技术条件。     

固定化黑曲霉利用糖蜜发酵生产柠檬酸

利用海藻酸钙凝胶包埋黑曲霉W1-2的孢子及菌丝体,制成的固定化细胞经预培养后,用于发酵糖蜜制取柠檬酸。确定了固定化细胞摇瓶发酵生产柠檬酸的最佳条件:糖蜜浓度12%。初始pH值4.0,培养温度30℃等。在此条件下发酵12天,柠檬酸浓度达39 g/L。对分批发酵生产柠檬酸进行了初步研究。     

固定化黑曲霉发酵玉米糖液生产柠檬酸的研究*

利用PVA复合凝胶包埋黑曲霉的孢子及菌丝体。固定后的细胞经过一系列预培养 ,用于发酵玉米生产柠檬酸。试验确定的固定化细胞摇瓶发酵生产柠檬酸最适条件为 :玉米糖液浓度 1 0Bx,培养温度 35℃ ,摇瓶转速 2 5 0r/min。经此条件发酵 64h ,柠檬酸产率最高达到 96g/L ,通常稳定在 90g/L左右。同时对柠檬酸连续批次发酵生产进行了初步研究 ,固定化黑曲霉可连续使用 8批次以上 ,其柠檬酸产量稳定在 86～ 92g/L之间 ,这为柠檬酸连续发酵提供了有利的保证 ,并探讨了有关的工艺技术条件     

固定化丝状真菌细胞

丝状真菌是征税酶制剂,抗生素及甾体激素的重要微生物,随着固定化技术的发展,其细胞的固定比技术愈来愈受到重视。本文从固定化细胞的方法、载体及生物反应器等方面论述了国内外的现状。     

甲醛低温消毒对黑曲霉柠檬酸发酵影响的初步研究

在柠檬酸发酵中,加入较低浓度的甲醛后８５℃灭菌,可以灭活培养基中的杂菌,确保发酵正常进行,加甲醛灭菌后不仅不影响柠檬酸的产量,而且可能还有利于菌丝生长,在大生产中加甲醛低温灭菌还减少蒸汽用量,有明显经济意义。     

用黑曲霉发酵纤维素酶解液生产柠檬酸的研究

以麦草纤维素酶解液为原料,用黑曲霉发酵制备柠檬酸,研究了培养基组成、恒温发酵和周期变温发酵对柠檬酸发酵的影响,结果表明,适宜的培养基组成为NH4NO3 0.3%,KH2PO4 0.1%,Mg2+300×10-6,Fe2+10×10-6,此时,柠檬酸产量为10.52g/L,糖转化率为60.80%.研究还表明,添加低级醇如甲醇和乙醇有利于产酸,但添加甲醇的效果要好于添加乙醇的效果,适宜的甲醇量为2%.在恒温发酵过程中,0～8h为孢子萌发期,产酸较慢;8～24h为对数生长期,产酸增加;24h之后为菌体生长恒定期,但产酸继续增加;104h之后产酸降低.在周期变温发酵过程中,0～8h产酸较慢,8h之后产酸增加.通过对二者的比较可知,在0～16h,周期变温发酵的产酸量要高于恒温发酵的产酸量,但在16h之后,周期变温发酵的产酸量要低于恒温发酵的产酸量.     

苹果渣基质柠檬酸高产菌株选育

分别以固态苹果渣、苹果渣固态酶解物、苹果渣酶解液和10%葡萄糖溶液为发酵基质研究了17株野生黑曲霉的柠檬酸产生能力,并对获得的4株柠檬酸高产菌进行了诱变育种。结果表明:17株黑曲霉在4种发酵基质中均能良好生长并发酵产生柠檬酸,不同菌株在同一发酵基质中产酸能力间存在差异。FG17、FG23、FG26、FG30等4株菌苹果渣基质柠檬酸产生能力较高,且在4种不同发酵基质中产酸性能稳定。4株菌分别经紫外线和60Co-γ射线诱变后得到的正向突变株柠檬酸产率均显著提高,突变株中FG26-15-4(UV)发酵苹果渣后柠檬酸产率最高,达11.32%,FG23-13-3(γ)发酵苹果渣酶解液后柠檬酸产率最高,达2.73 mg/mL,均高于现有研究报道,可作为不同类型苹果渣基质柠檬酸发酵用菌种。     

Citric acid production by Aspergillus niger on wet corn distillers grains

AIMS: To determine which citric acid-producing strain of Aspergillus niger utilized wet corn distillers grains most effectively to produce citric acid. METHODS AND RESULTS: Citric acid and biomass production by the fungal strains were analysed on the untreated grains or autoclaved grains using an enzyme assay and a gravimetric method respectively. Fungal citric acid production on the grains was found to occur on the untreated or autoclaved grains. The highest citric acid level on the grains was produced by A. niger ATCC 9142. The autoclaved grains supported less citric acid production by the majority of strains screened. Biomass production by the fungal strains on the untreated or autoclaved grains was quite similar. The highest citric acid yields for A. niger ATCC 9142, ATCC 10577, ATCC 11414, ATCC 12846 and ATCC 26550 were found on the untreated grains. Treatment of the grains had little effect on citric acid yields based on reducing sugars consumed by A. niger ATCC 9029 and ATCC 201122. CONCLUSIONS: It is feasible for citric acid-producing strains of A. niger to excrete citric acid on wet corn distillers grains whether the grains are treated or untreated. The most effective citric acid-producing strain of A. niger was ATCC 9142. SIGNIFICANCE AND IMPACT OF THE STUDY: The study shows that the ethanol processing co-product wet corn distillers grains could be utilized as a substrate for the commercial production of citric acid by A. niger without treatment of the grains.     

Citric and gluconic acid production from fig by Aspergillus niger using solid-state fermentation

The production of citric and gluconic acids from fig by Aspergillus niger ATCC 10577 in solid-state fermentation was investigated. The maximal citric and gluconic acids concentration (64 and 490 g/kg dry figs, respectively), citric acid yield (8%), and gluconic acid yield (63%) were obtained at a moisture level of 75%, initial pH 7.0, temperature 30°C, and fermentation time in 15 days. However, the highest biomass dry weight (40 g/kg wet substrate) and sugar utilization (90%) were obtained in cultures grown at 35°C. The addition of 6% (w/w) methanol into substrate increased the concentration of citric and gluconic acid from 64 and 490 to 96 and 685 g/kg dry fig, respectively. Journal of Industrial Microbiology & Biotechnology (2000) 25, 298–304. Received 15 April 2000/ Accepted in revised form 11 August 2000     

Gene Identification and Functional Analysis of Methylcitrate Synthase in Citric Acid-Producing Aspergillus niger WU-2223L

Methylcitrate synthase (EC 2.3.3.5; MCS) is a key enzyme of the methylcitric acid cycle localized in the mitochondria of eukaryotic cells and related to propionic acid metabolism. In this study, cloning of the gene mcsA encoding MCS and heterologous expression of it in Escherichia coli were performed for functional analysis of the MCS of citric acid-producing Aspergillus niger WU-2223L. Only one copy of mcsA (1,495 bp) exists in the A. niger WU-2223L chromosome. It encodes a 51-kDa polypeptide consisting of 465 amino acids containing mitochondrial targeting signal peptides. Purified recombinant MCS showed not only MCS activity (27.6 U/mg) but also citrate synthase (EC 2.3.3.1; CS) activity (26.8 U/mg). For functional analysis of MCS, mcsA disruptant strain DMCS-1, derived from A. niger WU-2223L, was constructed. Although A. niger WU-2223L showed growth on propionate as sole carbon source, DMCS-1 showed no growth. These results suggest that MCS is an essential enzyme in propionic acid metabolism, and that the methylcitric acid cycle operates functionally in A. niger WU-2223L. To determine whether MCS makes a contribution to citric acid production, citric acid production tests on DMCS-1 were performed. The amount of citric acid produced from glucose consumed by DMCS-1 in citric acid production medium over 12 d of cultivation was on the same level to that by WU-2223L. Thus it was found that MCS made no contribution to citric acid production from glucose in A. niger WU-2223L, although MCS showed CS activity.     

Effect of manganese deficiency on plasma-membrane lipid composition and glucose uptake in Aspergillus niger

Abstract Plasma membranes were isolated by means of the concanavalin A technique from protoplasts of manganese deficient (< 10⁻⁸ M Mn²⁺) and sufficient (10⁻⁵ M Mn²⁺) grown mycelium. The membranes differed with respect to their quantitative contents of fatty acids, sterols and phospholipids. These changes did not influence the glucose transport system, as shown by kinetic investigations using intact mycelia.     

Increases in Gene-Targeting Frequencies Due to Disruption of kueA as a ku80 Homolog in Citric Acid-Producing Aspergillus niger

Low efficiencies of gene targeting hamper functional genomics in industrially important strains of Aspergillus niger. To generate strains showing high gene-targeting frequencies in A. niger WU-2223L producing citric acid, disruption of kueA encoding Ku80 homolog was performed. Disruption of kueA increased gene-targeting frequencies to 70%, and had no effect on citric acid production.     

利用固定化黑曲霉单宁酶制备没食子酸的研究

用海藻酸钙载体包埋单宁酶,制备出转化五倍子单宁成没食子酸能力较好的固定化酶。研究了固定化条件和固定化单宁酶的部分性质,结果表明：最佳固定化条件为海藻酸钠90mg包埋单宁酶546u(3mL,182u/Ml),在1%～2%CaCl₂中作硬化处理;固定化单宁酶的最适温度为45℃,在10～50℃范围内稳定;其最适Ph值为6.5,在Ph5～7之间基本稳定;在此基础上,进行了没食子酸实验室克量级酶法制备实验,3次实验没食子酸产品的平均产率达到61%。和目前所用工业生产没食子酸的硫酸水解法相当,具有潜在的工业开发价值。     

An Experimental Study on Citric Acid Production by Aspergillus niger Using Gelidiella acerosa as a Substrate

Citric acid (CA) is the most important commercial product which is produced by using various sugar substrates in the terrestrial environment. The present study made an attempt to produce citric acid by the fungal strain Aspergillus niger from red seaweed Gelidiella acerosa is the best alternative to sugar substrate in the marine environment. In this study three types of production media were prepared including control (sucrose) by following standard fermentation conditions. The acid production was indicated by the reduction of pH levels. The control medium gave the highest yield of 80 g/l at pH 1.5 and the medium containing crude seaweed powder and other compositions gave the yield of 30 g/l at pH 3.5 whereas the medium containing crude seaweed and 10% sucrose gave the yield of 50 g/l at pH 3.0. When calculating the benefit cost ratio, crude seaweed powder and 10% sucrose yielded 50 g of citric acid at the lower cost of Rs. 35, whereas the other two media gave the yield of 80 and 30 g respectively with the cost of Rs. 77 and 28. In economic point of view, the medium containing seaweed and 10% sucrose showed more benefit with lower cost.     

Citric acid production by solid state fermentation using sugarcane bagasse

A solid state fermentation (SSF) method was used to produce citric acid by Aspergillus niger DS 1 using sugarcane bagasse as a carrier and sucrose or molasses based medium as a moistening agent. Initially bagasse and wheat bran were compared as carrier. Bagasse was the most suitable carrier, as it did not show agglomeration after moistening with medium, resulting in better heat and mass transfer during fermentation and higher product yield. Different parameters such as moisture content, particle size, sugar level and methanol concentration of the medium were optimised and 75% moisture level, 31.8 g sugar/100 g dry solid, 4% (v/w) methanol and particles of the size between 1.2 and 1.6 mm were found to be optimal. Sucrose and clarified and non-clarified molasses medium were also tested as moistening agents for SSF and under optimised conditions, 20.2, 19.8 and 17.9 g citric acid /100 g of dry solid with yield of 69.6, 64.5 and 62.4% (based on sugar consumed) was obtained in sucrose, clarified and non-clarified molasses medium respectively, after 9 days of fermentation.