6328A He-Ne激光对黑曲霉的作用

本文报道了6328AHe-Ne激光对黑曲霉作用的对照实验研究。实验结果表明,照射剂量为2×10~(-3)～2×10~(-2)J/cm~2时,He-Ne激光对黑曲霉孢子有提高存活率的趋势;照射剂量为3.5×10~(-2)～8×10~(-2)J/cm~2时,He-Ne激光对黑曲霉孢子有抑制作用。     

PURIFICATION AND PARTIAL CHARACTERIZATION OF AN ENDO-POLYGALACTURONASE FROM ASPERGILLUS NIGER

A pectinase was identified and isolated from a commercial Aspergillus niger pectinase preparation. The crude enzyme preparation, which was prepared by precipitation of the water extract of the culture of A. niger with ammonium sulfate, was further fractionated by three steps of chromatography, i. e., cation exchange, hydrophobic interaction and onion exchange, to obtain an electrophoretically homogeneous pectinase. The molecular weight of the purified enzyme was estimated by SDS‐PAGE to be about 40.4 kDa under both nonreducing and reducing conditions, with the optimum pH at 5.0 and the optimum temperature at 36C. The enzyme was stable at temperatures below 35C. The partial N‐terminal ammo acid sequence data analysis of the first 19 amina acids of the obtained pectinase revealed 94.7% and 89.5% homology with two reported pectinases from A. niger.     

黑曲霉2277菌株产纤维素酶最佳液体发酵条件的研究

对黑曲霉2277菌株产纤维素酶最佳液体培养条件进行了研究。结果表明,黑曲霉2277最适液体培养条件为:稻草粉(碳源)6%,豆饼粉(氮源)1%,初始pH6.0～6.5,培养温度28℃～30℃,一级培养时间120h,二级培养时间76h～84h,接种量10%,250mL三角瓶装液量75mL,摇床转速150r/min。在最适培养条件下,以DNS法对酶活进行定量分析,测得发酵液中CMC酶活达92.1μg/mL·min;以滤纸崩溃度对酶活进行定性分析,滤纸在94h内完全分解。     

黑曲霉液态发酵生产果胶酶的工艺条件初探

选用鲜苹果渣作为碳源,通过试验探索了黑曲霉液态发酵生产果胶酶的工艺条件。确定最适发酵培基的组成为:麸皮2.5g,鲜苹果渣1.5g,硫酸铵1.0g,K2HPO40.05g,KCl0.025g,MgSO4·7H2O0.025g,Na2SO40.025g,FeSO4·7H20微量,蒸馏水50mL;最佳发酵条件为:发酵时间5d,发酵温度30℃,起始pH2.0,接种量2.0%,装瓶量50mL,在250mL三角瓶中进行摇床振荡培养,最终果胶酶平均酶比活力达到37.91单位/mL。     

麦麸发酵生产混合酶制剂的培养基条件优化

采用SAS软件中的Plackett-Burman及响应曲面中心点组合实验设计对发酵生产阿拉伯木聚糖酶和阿魏酸酯酶混合酶制剂的培养基条件进行优化。使用Plackett-Burman设计评价了8个培养基因素对混合酶制剂产量的影响,得到主要影响因素;以此为基础,采用响应曲面中心点组合设计确定了麦麸发酵生产混合酶制剂的最佳培养基条件:麦麸10%、NH4NO30.28%、KH2PO40.2%、MgSO·47H2O0.08%、NaNO30.31%、pH5.5。     

HYDROLYSIS OF PHYTATE IN BROWN RICE-ADDED BREAD BY ADDITION OF CRUDE AND PURIFIED ASPERGILLUS NIGER PHYTASE PREPARATIONS DURING BREAD MAKING

Brown rice-added breads were prepared with and without crude and purified Aspergillus niger phytase preparations. By adding 30% (w/w) brown rice flour and no phytase preparation, the phytate (myo-inositol hexaphosphate; IP₆) content of the bread was increased and the loaf volume was reduced. The direct addition of a food-additive grade phytase preparation (3,000 U) resulted in a significant decrease in the IP₆ content. However, it collapsed the bread crust. The crude phytase preparation had significant protease and amylase activities. A simple chromatographic method for the separation of phytase activity from the protease and amylase activities was developed. By using purified phytase, the IP₆ content was reduced without any adverse effects on the rising of the bread, which indicates that protease and amylase may be responsible for the collapse of the crust by the commercial phytase preparation.

PRACTICAL APPLICATIONS

Phytate in unrefined cereals and beans lowers bioavailability of minerals. On the other hand, these materials are rich in health-promoting components. To reduce the phytate in them during processing, some commercially available phytase preparations are now used. However, we found that such preparation contains significant amylase and protease activities, which may cause adverse effect on the appearance and textural properties of final products. To solve these problems, a simple and inexpensive procedure for separation of phyatase from amylase and protease was developed in the present study. The purified phytase can reduce phytate in brown rice-added bread without adverse effect on rising of bread. These results would encourage prepare the phytase preparation in high purity in an industrial scale to improve nutritional value of unrefined cereal- and bean-based functional foods.     

OPTIMIZATION STUDY FOR THE PRODUCTION OF CITRIC AND GLUCONIC ACID FROM FIG WATER EXTRACT BY ASPERGILLUS NIGER IN SURFACE FERMENTATION

The production of citric and gluconic acid from fig extract by Aspergillus niger ATCC 10577 and A. niger B60 in surface fermentation was investigated. The strain 10577 gave higher concentration of citric and gluconic acid than strain B60. A maximum citric and gluconic acid concentration (20.5 and 97.0 g/L, respectively), citric acid yield (12%), biomass dry weight (18.5 g/L), and sugar utilization (85%) was achieved at an initial sugar concentration of 200 g/L and a pH of 7.0. On the other hand, the highest gluconic acid yield (79.7%) was obtained in culture grown at initial sugar concentration 100 g/L. The addition of 4% (v/v) methanol in the fig extract increased the concentration of citric and gluconic acid from 20.5 and 97.0 g/L to 30.7 and 145.5 g/L, respectively. Citric acid was separated from the gluconic acid by extraction with diethyl ether or ethyl acetate.     

MACERATION ACTIVITY OF AN ENDOPOLYGALACTURONASE FROM CANDIDA MACEDONIENSIS

The yeast Candida macedoniensis produces constitutively an extracellular pectinolytic enzyme with a high maceration activity; the culture filtrate is free from foreign enzyme activity. The enzyme formation is optimal under strictly anaerobic conditions with N₂ gassing. The culture medium for optimal enzyme recovery is a nutrient solution containing 1% yeast extract, 2% peptone and 10% sucrose, at pH 3, 28°C. Characterization of the enzyme showed it to be an endopolygalacturonase. The pH and temperature optima of the enzyme differ for pectic acid cleavage and maceration activity, these being 4.5 and 50—53°C and 2.5 and 40°C, respectively. The enzyme activities could not be separated from one another by protein chemical methods (analytical and preparative isoelectric focussing). Dialysis of the enzyme-containing culture filtrate did not decrease the enzyme activity. The endopolygalacturonase from Candida macedoniensis leads to the release of plant cells from the tissue, without destroying the cells by lysing the cell walls. After two hours incubation of the substrate (carrot slices), the tissue mass consisted of cell clumps of up to 15 cells.     

ASPERGILLUS FUMIGATUS AND ASPERGILLUS AMSTELODAMI AS CAUSES OF GUSHING

Malt that has caused gushing of beer was found to be contaminated with several storage fungi. The dominating species were Aspergillus fumigatus and Aspergillus amstelodami. These fungi were found to cause gushing in beers when they were added to the steeping water.     

黑曲霉诱变方法比较研究

黑曲霉A3为出发菌株,采取两种方法对其进行诱变处理,第一种是利用紫外线进行物理诱变,第二种是利用紫外线和亚硝酸进行复合诱变,以得到产木聚糖酶较高的菌种,利用其产木聚糖酶来降解小麦麸皮中木聚糖得到低聚木糖.通过对诱变处理后菌种所产木聚糖酶活的比较得出,单纯的紫外线诱变的效果优于复合诱变的效果.     

产果糖基转移酶米曲霉菌株的选育

通过紫外线、紫外线和氯化锂复合、微波、微波和氯化锂复合4种诱变方法，对米曲霉GX-0010菌株进行了诱变，选育得到果糖基转移酶酶活高于GX-0010菌株的突变株8株，其中UVLi-3突变株的酶活最高，比GX-0010菌株高45．4％。     

THERMAL STABILITY OF A NEUTRAL PROTEASE OF ASPERGILLUS ORYZAE

The thermal stability of the neutral protease of Aspergillus oryzae was measured by differential scanning calorimetry. The activation energy, preexponential factor and the reaction rate constant calculated by means of the dynamic method are similar to those obtained for denaturation of other proteins. Half life (t_1/2) calculated by using the above-mentioned parameters permitted estimation of the amount of native enzyme remaining after different thermal treatments. Complete denaturation occurred above 60C. The presence of substrate stabilizes the enzyme. The behavior of flour samples treated with the neutral protease was studied as well. A tendency to shift towards higher temperatures when flour was treated with the enzyme was observed for both the T_p (DSC peak maximum temperature) corresponding to gelatinization of starch and the dissociation of the amylose-lipid complex.     

RELATIONSHIP OF ASEXUAL DEVELOPMENT TO AFLATOXIN PRODUCTION IN ASPERGILLUS PARASITICUS

The association between asexual development and aflatoxin production in Aspergillus parasiticus is reviewed. Aflatoxin does not appear to be a product of asexual development. The ability to sporulate and to produce aflatoxin are not mutually exclusive of each other. The environment regulates the asexual development and aflatoxin production. The initial inoculum level will affect the competence time and the time of initiation of aflatoxin production. The time of initiation of aflatoxin production is independent of the initial composition of the medium, in contrast to the onset of sporulation which is dependent on the medium.     

INHIBITION OF ASPERGILLUS PARASITICUS GROWTH AND TOXIN PRODUCTION BY GARLIC

Mycelial growth and toxin production by Asperigillus parasiticus were inhibited by garlic concentrations of 0.3–0.4%. When the fungus was grown in broth, aflatoxin B₁ production was inhibited at a garlic concentration of 0.3% while aflatoxin G₁ production was inhibited by 0.25% garlic. When growth on rice, aflatoxin B₁ was detected at garlic concentrations of up to 2.5%. Aflatoxin G₁ was detected at 1.25% garlic concentration but not above this level.