The influence of the ion content of whey on the pH-activity profile of the β-galactosidase from Aspergillus oryzae

The pH-dependence of the reaction kinetics of lactase (β-galactosidase) from Aspergillus oryzae in different reaction media is presented in terms of a two-parameter model. The lactase from A. oryzae seems to have replaced the A. niger lactase on the market owing to a better activity/price ratio and may be utilised for lactose hydrolysis in acid as well as in neutral milk products. Its pH optimum is around pH 4.5. However, in the neutral pH-range its activity depended strongly on the salt content of the substrate solution. For example, its activity in whey (pH 6.5) fell to only 30% of its expected activity in a pure lactose solution at the same pH. The whey effect was the same for both soluble and immobilised lactase. The two parameter kinetic model, which included a term for competitive product inhibition gave excellent agreement with experimental data, and may thus be useful for the prediction of reactor performance with this enzyme.     

水稻白叶枯病菌受寄主诱导基因的鉴定

用一个具链霉素（Ｓｍ）抗性并含无启动子ＣＡＴ基因的广宿主启动子探针质粒ＰＩＪ３１００，用鸟枪法在ＣＡＴ基因上游的ＢａｍＨ１克隆位，或插入水稻白叶枯病菌（Ｘａｎｔｈｏｍｏｎａｓｏｒｙｚａｅｐｖ．ｏｒｙｚａｅ），用ＢａｍＨ１完全酶切的染色体ＤＮＡ片段，将重组质粒转化大肠杆菌ＥＤ８７６７在含链霉素的ＬＢ单板上筛选转化子。得到容量为６０００个转化子的克隆群体，其中２％的克隆含有水稻白叶枯病菌启动子活性片段，在平板上表现氯霉素（Ｃｍ）抗性。在帮助质粒ＰＲＫ２０１３的帮助下，通过三亲支配，将含有水稻白叶枯病菌启动子片段的重组质粒转移进野生型的水稻白叶枯病菌中去，在含链霉素的ＰＳＡ平板上筛选１６００个接合子，其中一个在平板上表现氯霉素抗性及含有组成表达的水稻白叶枯病菌启动子。随机选取２００个平板上对氯霉素敏感的接合子，接种用氯霉素处理的水稻感病品种金南风，得到１５个比对照明显致病的克隆。用其中一个含受水稻特异诱导启动子的重组质粒为探针，在水稻白叶枯病菌野生菌基因文库中筛选到２７个阳性克隆。     

转盘反应器固定米根霉的L－乳酸发酵

研究了米根霉的固定化方法，研制了用吸附法固定米根霉的生物转盘反应器，考察了在该反应器中培养基组成及其它操作条件对Ｌ－乳酸发酵的影响。实验结果表明，应用吸附法固定化的米根霉及生物转盘反应器进行Ｌ－乳酸发酵具有发酵速率快，Ｌ－乳酸得率高及既能用于连续发酵又能用于间歇发酵等优点     

米曲霉在牛乳中最适生长条件的研究

利用米曲霉对牛乳进行发酵,通过单因子及正交试验以菌丝体干重为指标对其在牛乳中的生长进行了研究．结果表明：接种量为4％,装液量为30mL,摇床转速为180r／min时菌丝体干重可达到最大．此外测得最大菌丝体干重时的蛋白质分解率可达35．6％．     

泸型大曲中根霉固态发酵产糖化酶条件研究

对泸型大曲中根霉菌株固态发酵产糖化酶的条件进行了研究。以糖化酶活力为评价指标,设计单因素实验,研究培养基水分含量、培养时间、培养温度对根霉产糖化酶的影响,在此基础上,利用Box—BenhnkenDesign的方法,对根霉菌株固态发酵产糖化酶的条件进行优化,结果显示泸型大曲中根霉菌株固态发酵产糖化酶的优化条件为培养温度29℃,培养基水分含量53％,培养时间164h,糖化酶的酶活力为2194．44U／g。     

酱油曲菌的选择及酱油发酵条件

研究了日本酱油生产菌AspergillusoryzaeJP DQ 1,AspergillusoryzaeJP W和我国酱油生产菌AspergillusoryzaeAS3.951的酶系。结果表明:3种菌在浓酱油曲和白酱油曲培养基上均可产生α 淀粉酶、糖化酶、纤维素外切酶、果胶酶、酸性蛋白酶和中性蛋白酶;JP W是较好的白酱油生产菌,JP DQ 1是较好的浓酱油生产菌。还对酱油酵母的生理特性进行了部分研究,发现食盐浓度对酱油酵母生长影响较大,酱油发酵过程的盐浓度不宜超过3mol／L,低于2mol／L更佳。酱油酵母的较适生长pH为4.5～5.5。     

Construction of the mutant strain in Aspergillus oryzae 3.042 for abundant proteinase production by the N+ ion implantation mutagenesis

Because of secreting large amounts of enzymes, Aspergillus oryzae was widely used in the fermentation of soy sauce in many Asian countries. Here, N⁺ ion implantation mutagenesis was applied to improve the ability of A. oryzae to secrete acid protease. Several mutants were screened using three kinds of plates (Casein medium, Czapek’s medium and carboxymethyl cellulose medium agar plates). Compared with the other mutants, the mutant A100‐8 could secrete the most protease. Acid protease activity of A100‐8 was enhanced about 44.1% at 36 h by koji fermentation test. In addition, A100‐8 was stable by periodically subculturing and maintaining on the agar slant. The mRNA expression levels of two kinds of acid protease (serine carboxypeptidase and aspartyl protease) were measured by RT‐PCR at different periods. Serine carboxypeptidase and some kinds of aspartyl protease of A100‐8 were significantly (P < 0.01) expressed higher than the control at all times.     

Co-Production of Fungal Biomass Derived Constituents and Ethanol from Citrus Wastes Free Sugars without Auxiliary Nutrients in Airlift Bioreactor

The potential of two zygomycetes fungi, Mucor indicus and Rhizopus oryzae, in assimilating citrus waste free sugars (CWFS) and producing fungal chitosan, oil, and protein as well as ethanol was investigated. Extraction of free sugars from citrus waste can reduce its environmental impact by decreasing the possibility of wild microorganisms growth and formation of bad odors, a typical problem facing the citrus industries. A total sugar concentration of 25.1 g/L was obtained by water extraction of citrus waste at room temperature, used for fungal cultivation in shake flasks and airlift bioreactor with no additional nutrients. In shake flasks cultivations, the fungi were only able to assimilate glucose, while fructose remained almost intact. In contrast, the cultivation of M. indicus and R. oryzae in the four-liter airlift bioreactor resulted in the consumption of almost all sugars and production of 250 and 280 g fungal biomass per kg of consumed sugar, respectively. These biomasses correspondingly contained 40% and 51% protein and 9.8% and 4.4% oil. Furthermore, the fungal cell walls, obtained after removing the alkali soluble fraction of the fungi, contained 0.61 and 0.69 g chitin and chitosan per g of cell wall for M. indicus and R. oryzae, respectively. Moreover, the maximum ethanol yield of 36% and 18% was obtained from M. indicus and R. oryzae, respectively. Furthermore, that M. indicus grew as clump mycelia in the airlift bioreactor, while R. oryzae formed spherical suspended pellets, is a promising feature towards industrialization of the process.     

Characteristics of L-lactic Acid Production byRhizopus oryzae mutant RL6041

A high-yield mutant strain Rhizopus oryzae RL6041 induced by ions implantation was used in the present study. L (+)-lactic acid was generated by RL6041 grown on liquefied corn starch as a substrate. With optimal conditions (Liquefied corn starch 150g/L, (NH₄)₂SO₄ 2.0g/L, MgSO₄·7H₂O 1.0g/L, ZnSO₄·7H₂O 2g/L, KH₂PO₄ 0.2g/L, CaCO₃ 8%, medium size 20/250Ml, seed age 6h, fermentation temperature 38° C), the yield of L (+)-lactic acid in shake-flask reached 133～136g/L after 36h, indicating that the conversion rate was as high as 88%～91%, and the productivity was 3.75g/L·h. There was almost a 70% increase in lactic acid production compared with the original strain RE3303.