Isolation and partial characterization of alkaline feruloyl esterases from Aspergillus niger CFR 1105 grown on wheat bran

Feruloyl esterases (FAEs) of a strain of Aspergillus niger (CFR 1105) grown in solid state (ssf) and submerged fermentations (smf) using wheat bran both as carbon source and inducer of the enzyme were studied. The feruloyl esterase activity was maximum after 4 days in solid state as well as in submerged fermentations (32.5 and 31.5 U/g dry weight of wheat bran respectively) and the enzyme titers were comparable. The specific activity was maximum on day 2 in ssf (12.8 U/mg protein) and it decreased thereafter, whereas specific activity was maximum on day 3 (11.7 U/mg protein) in smf and it remained constant up to 5 days. Two isoenzymes of feruloyl esterases were isolated and purified to homogeneity by conventional protein purification methods from the day 5 culture filtrate of A. niger grown in smf. On a DEAE-cellulose column, two enzyme activity peaks designated as FAE-1 and FAE-2 were eluted with 0.3 and 0.35 M NaCl, respectively. They were monomeric glycoproteins with approximate molecular weights of 50 kDa (FAE-1) and 55 kDa (FAE-2), respectively. FAE-1 showed a temperature optimum of 40°C whereas FAE-2 showed a wider temperature optimum of 40–50°C. FAE-1 and FAE-2 exhibited pH optima of 9 and 6, respectively, and both were stable over a pH range of 6–9. The ability of the enzyme to be active in alkaline pH may be advantageous in biotechnological applications.     

Glucoamylase production by Aspergillus niger on rice bran is improved by adding nitrogen sources

Corn steep liquor, peptone or NH _inf4 ^sup+ salts increased the yield of glucoamylase from Aspergillus niger growing in a solid-state fermentation on rice bran up to 360 IU/g dry substrate over 96 h at 30°C.The authors are with the Biotechnology Unit, Regional Research Laboratory, CSIR, Trivandrum-695 019, India;     

Enhanced polygalacturonase production by Aspergillus niger NRRL-364 grown on supplemented citrus pectin

Enhanced levels of extracellular polygalacturonase activity were obtained when Aspergillus niger NRRL-364 was grown on pectic substances as sole carbon sources in a submerged culture. Among the factors affecting enzyme production those of carbon source concentration, nitrogen source, initial pH and time of cultivation were found to be the most important ones. Under optimum growth and activity conditions yields as high as 14.5 U (measured as reducing groups) ml^-1 of growth medium were obtained, comparing favourably with those reported for fungi grown under similar conditions and used in food processes.     

Oxalic acid production by Aspergillus niger

Aspergillus niger is able to produce a quite high concentration of oxalic acid using sucrose as carbon and energy source. Operating at pH higher than 6 and an enriched N and P medium is necessary in order to conduct the fermentation towards oxalic acid production. A pH?shift technique, operating at acid pH?in the first two days and then setting pH?to 6, allowed the productivity to slightly increase in shaking flasks cultures up to 3.0?kg/m³?·?d, with a final oxalic acid concentration of 29?kg/m³. When operating at more controlled conditions, in a stirred tank, both productivity and oxalic acid concentration were improved (4.1?kg/m³?·?d and 33.8?kg/m³, respectively). However the main drawback of this fermentation is the low yield attained (about 0.3?kg oxalic acid/kg sucrose) because most of glucose, resulting from the hydrolysis of sucrose by the extracellular enzymes secreted at the beginning of the fermentation, is very quickly oxidised to gluconic acid, a process which is favoured at a pH?close to 6. Milk whey was proved to be a very good substrate as it allows oxalic acid to be produced with a similar productivity (2.5?kg/m³?·?d in shaking flasks) giving excellent yields of almost 0.6?kg oxalic acid/kg lactose.     

Oxalic acid production by Aspergillus niger

Oxalic acid is formed by Aspergillus niger at nearly neutral pH values. In this study the applicability of milk whey as a carbon source was investigated, both in shaking flask experiments and in a stirred tank reactor. The influence of pH on oxalic acid formation showed that the maximum production rate and higher concentration of the product are observed at pH 6. At pH 7 the same production rate was obtained although at a lower oxalic acid concentration. The process was shown to be inhibited by product from an oxalic acid concentration of about 10?kg/m³ and its behaviour was fitted by Luong's equation. In a 10-dm³ strirred tank ferment the stirrer speed was varied in a range from 100 to 600 rpm. At values between 200 and 400 rpm, maximum production rates of oxalic acid of 6.8?kg/m³·d and 6.5?kg/m³·d were reached, respec-tively. A final concentration of 41.4?kg oxalic acid/m³ was reached operating at 400 rpm.     

Citric acid production by Aspergillus niger grown on orange peel medium fortified with cane molasses

Citric acid production (CAP) by Aspergillus niger was obtained following culture on an orange peel medium (OPM) fortified with cane molasses. The key physico-chemical parameters influencing CAP, such as bed loading, moisture levels, volume and age of inoculum, initial pH, incubation temperature and duration, agitation rate, sugar concentration, addition of nitrogen and phosphorus sources, treatment of molasses and the addition of different low levels of alcohols, were assessed. The suitability of molasses to increase the concentration of sugar in the fermentation medium without previous treatments with EDTA or ferro-cyanide was indicated. Maximum amounts of CA (640 g/kg orange peel) were obtained after 72 h of incubation on an OPM moisturized to 65 %?w/v, with bed loading of 20 %, an initial pH of 5, a temperature of 30 °C, an agitation rate of 250 rpm, with fortification of the medium with molasses at a final sugar concentration of 14 % in the presence of 3.5 % methanol.     

黑曲霉固态发酵及酶解玉米皮

以玉米提取淀粉后的玉米皮渣为主要原料,采用黑曲霉固态发酵法产酶再酶解的二步法降解玉米皮中纤维素类物质。经Plackett-Burman法及响应面设计优化发酵条件得:温度30℃,接种量10%,初始水分体积分数60%,物料厚度2.47 cm,初始pH 5.79,发酵时间6 d;滤纸比酶活可达11.01 U/g,较原始酶活提高了40.61%;产酶结束后加入pH 4.8醋酸-醋酸钠缓冲液,置于50℃下酶解144 h,中性洗涤纤维与酸性洗涤纤维降解率分别为46.09%、48.82%,还原糖质量分数达到9.02%。     

Heterologous expression of two Aspergillus niger feruloyl esterases in Trichoderma reesei for the production of ferulic acid from wheat bran

Bioprocess and Biosystems Engineering - Feruloyl esterase (FAE)-encoding genes AnfaeA and AnfaeB were isolated from Aspergillus niger 0913. For overexpression of the two genes in Trichoderma...     

Gluconate production by spores of Aspergillus niger

Spores of Aspergillus niger obtained by solid state fermentation on buckwheat seeds produced gluconic acid from glucose with a high yield, near 1.06 g gluconic acid/g glucose, close to the stoichiometric value. The reaction itself could be carried out either with purified biocatalyst or with the whole buckwheat medium resulting from spore production process. 200 g gluconic acid/L were obtained in 200 h with sequential feedings of glucose up to 190 g/L.     

Rock phosphate solubilization by Aspergillus niger grown on sugar-beet waste medium

Solubilization of rock phosphate by Aspergillus niger was studied in solid-state fermentation on sugar-beet waste. This combination was selected after testing three agroindustrial waste materials, namely rice hulls, sugar-beet waste and alperujo. Sugar-beet waste was the best substrate for fungal growth with 69% mineralization, followed by rice hulls and alperujo. The fungus was successfully cultivated on sugar-beet waste supplemented with 3.0 g/l rock phosphate, acidifying the medium and thus decreasing the pH to 3–3.5. Solubilization of insoluble phosphate increased during the first half of the process, reaching a maximum of 292 g phosphate/ml, although a part of it was probably consumed by the mycelium.     

Release of ferulic acid from wheat bran by a ferulic acid esterase (FAE-III) from Aspergillus niger

Ferulic acid was efficiently released from a wheat bran preparation by a ferulic acid esterase from Aspergillus niger (FAE-III) when incubated together with a Trichoderma viride xylanase (a maximum of 95% total ferulic acid released after 5 h incubation). FAE-III by itself could release ferulic acid but at a level almost 24-fold lower than that obtained in the presence of the xylanase (2 U). Release of ferulic acid was proportional to the FAE-III concentration between 0.1 U and 1.3 U, but the presence of low levels of xylanase (0.1 U) increased the amount of ferulic acid released 6-fold. Total sugar release was not influenced by the action of FAE-III on the wheat bran, but the rate of release of the apparent end-products of xylanase action (xylose and xylobiose) was elevated by the presence of the esterase. The results show that FAE-III and the xylanase act together to break down feruloylated plant cell-wall polysaccharides to give a high yield of ferulic acid.     

Hydrolase production by Aspergillus niger in solid-state cultivation

Summary A production of macerating enzymes which liquefy and hydrolyze the mandarin orange peel was studied in a solid state cultivation of Aspergillus niger on wheat bran substrate. Solid state cultivation in a 2 drum fermenter capable of interchangeable operation under dynamic or static conditions were carried out maintaining the moisture content of the substrate at 32, 39, 46, 56, 67, and 74%. Biomass grown on the solid substrate was estimated on the basis of a constant value of glucosamine content of A. niger, 50 mg glucosamine/g cell. A linear relationship between oxygen uptake rate and growth rate observed in all the experiments gave an oxygen growth yield, Y_X/O, of 28.5 g cell/mol O₂. The rate of macerating enzyme formation was also in proportion to the growth rate irrespective of the difference of the moisture content of the substrate.The enzyme accumulation on the solid substrate, the growth rate and oxygen uptake rate were maximum when the moisture content of the substrate was maintained at ca. 56% ascending from 32 to 56 and descending from 56 to 74.     

Citric acid production by Aspergillus niger immobilized on polyurethane foam

Summary Citric acid was produced using Aspergillus niger immobilized on polyurethane foam in a bubble column reactor. Most of the adsorbed cells remained on the support and, as a result, high oxygen tension was maintained during the reactor operation. However, uncontrolled growth of the pellets made continuous reactor operation difficult. The citric acid productivity obtained from 15 vol.% foam particles containing immobilized cells was 0.135 g/l per hour. This productivity of immobilized cells was almost the same as that of free cells. The oxygen level dropped to half saturation in 5 days in the immobilized cell culture in contrast to 2 days in the free cell culture.     

Ochratoxin A production by strains of Aspergillus niger var. niger.

In a survey of the occurrence of ochratoxin A (OA)-positive strains isolated from feedstuffs, two of the 19 isolates of Aspergillus niger var. niger that were studied produced OA in 2% yeast extract-15% sucrose broth and in corn cultures. This is the first report of production of OA by this species.     

Lipid production by a cellulolytic strain of Aspergillus niger

Studies on lipid formation by a cellulolytic mould. Aspergillus niger AS-101, were carried out in shake flasks. The maximum amount of lipid accumulated comprised 17% and 14·9% of the mycelial dry weight on glucose and cellulose media, respectively. Unsaturated fatty acids comprised around 80% of the total fatty material, with linoleic acid predominating.     

A comparison of factors influencing citric acid production by Aspergillus niger grown in submerged culture and on filter paper

Summary A filter paper surface cultivation method (previously described as a tool for strain selection by Röhr et al. 1979) was adopted as a cultivation system for citric acid production on a small scale and compared with submerged cultivation. Citric acid production in the submerged system was optimal at defined low concentrations of zinc, ferrous and manganese ions, defined phosphate and nitrogen concentrations and within a defined initial pH. In constrast, citric acid production in the filter paper system was not at all influenced by any of these variables. On the other hand, optimal citrate production in both systems required a high (10%–14%, w/v) sucrose concentration. This identifies sugar concentration as a most significant parameter for citrate production, whereas all other nutritional effects are related to the cultivation system used.