Cultivable bacterial diversity and amylase production in three typical Daqus of Chinese spirits

Both culture‐dependent method and molecular technique were firstly used to simultaneously investigate the cultivable bacterial diversity and amylase production in three typical Daqus of Chinese spirits. The results showed that both cultivable bacterial diversity and amylase production were obviously different. The species of nine bacteria from Deshan, nine from Baisha and six from Wuling Daqus were identified. The total bacterial strains of 17, 15 and 14, and 9, 16 and 10 could produce α‐amylase and glucoamylase, respectively, from the Daqus, and the enzyme yields were different. Bacillus licheniformis, Bacillus subtilis and Bacillus amyloliquefaciens not only were dominant bacteria in the Daqus, but also possessed high activities of α‐amylase and glucoamylase. By comparison, Bacillus cereus and Bacillus oleronius were found to be another predominant bacterial species and good producers of α‐amylase and glucoamylase in Deshan and Wuling Daqus, respectively.     

新型糖化酶在淀粉制葡萄糖中的应用

在玉米淀粉双酶法制糖工艺中使用OPTIMAX4060VHP强效液体糖化酶,使工艺操作简单方便,生产更加稳定;降低可逆反应,提高糖液的葡萄糖含量;节约蒸汽;提高糖液透光率和糖液质量,具有良好的经济效益。     

戊二醛交联糖化酶的条件探索及协同实验教学分析

介绍了在生物工程实验中探索利用分组协同创新模式进行实验教学的成果。将一个教学自然班分成12个实验小组,每组同学3人。以可能影响实验结果的四个变量分解成四个独立又互相联系的实验,每个变量分别由三组学生负责研究,研究过程通过定期协调沟通对实验结果进行分析总结并不断优化实验设计,得出了优化实验工艺,同时也培养了学生独立思考和协作配合的精神。实验研究了戊二醛交联糖化酶的优化条件,考察了p H、戊二醛浓度、温度和时间四个变量对交联结果的影响。综合分析各实验小组的实验结果显示:酸性条件交联有利于酶活力及稳定性的保持;使用0.5%或更低的戊二醛浓度有利于酶活力的保持,但其稳定性提升不明显;较高温度下交联不利于酶活力的保持及稳定性的提升;随着交联时间的增加酶活力损失逐渐变大,但其使用稳定性却有所提升。     

Kinetics and thermodynamics of glucoamylase inhibition by lactate during fermentable sugar production from food waste

BACKGROUND: Glucoamylase hydrolysis is a key step in the bioconversion of food waste with complicated composition. This work investigated the effect of lactate on glucoamylase from Aspergillus niger UV‐60, and inhibition mechanisms of glucoamylase by lactate during food waste hydrolysis. RESULTS: For 125 min hydrolysis of food waste (10%, dry basis), reducing sugars produced in the absence of lactate were 15%, 26% and 56% more than those produced in the presence of 24 g L^?1 lactate at 60, 50 and 40 °C, respectively. Kinetic study showed that the type of glucoamylase inhibition by lactate was competitive, and K_m (Michaelis‐Menten constent), V_max (maximum initial velocity), K_I (inhibition constant) were 103.2 g L^?1, 5.0 g L^?1 min^?1, 100.6 g L^?1, respectively, for food waste hydrolysis at 60 °C and pH 4.6. Lactate also accelerated glucoamylase denaturation significantly. Activation energy of denaturation without inhibitor was 61% greater than that of denaturation with inhibitor (24 g L^?1 lactate). Half‐lives (t_1/2) without inhibitor were 7.6, 2.7, 2.6, 1.7 and 1.2 times longer than those with inhibitor at temperature 40, 45, 50, 55 and 60 °C, respectively. CONCLUSION: These results are helpful to process optimization of saccharification and bioconversion of food waste. Copyright © 2010 Society of Chemical Industry     

微波辐射下双酶催化淀粉水解的动力学研究

以玉米淀粉为反应底物,研究了α-淀粉酶和糖化酶分别在微波辐射和水浴加热条件下水解玉米淀粉的动力学特性。考察了pH、温度、底物质量浓度、酶用量对玉米淀粉水解反应速率的影响。结果表明,微波辐射条件下的平均反应速率比水浴加热提高了20%以上。以米氏方程为基础,研究了两种加热方式下的米氏常数Km、最大反应速率νm和抑制常数Ki。结果表明,微波辐射下α-淀粉酶的Km=3 922.76 g/L,νm=1.72×10-3mol/(mL.min),糖化酶的Km=173.31 g/L,νm=3.289×10-5mol/(mL.min);水浴加热条件下α-淀粉酶的Km=312.03g/L,νm=1.21×10-4mol/(mL.min),糖化酶的Km=16.14 g/L,νm=3.89×10-6mol/(mL.min);微波辐射下糖化酶的抑制常数(Ki)低于水浴加热的抑制常数。     

Construction of a brewing yeast expressing the glucoamylase gene STA1 by mating

Standard brewing yeast cannot utilize larger oligomers or dextrins, which represent about 25% of wort sugars. A brewing yeast strain that could ferment these additional sugars to ethanol would be useful for producing low‐carbohydrate diabetic or low‐calorie beers. In this study, a brewing yeast strain that secretes glucoamylase was constructed by mating. The resulting Saccharomyces cerevisiae 278/113371 yeast was MAT a/α diploid, but expressed the glucoamylase gene STA1 . At the early phase of the fermentation test in malt extract medium, the fermentation rate of the diploid STA1 strain was slower than those of both the parent strain S. cerevisiae MAFF113371 and the reference strain bottom‐fermenting yeast Weihenstephan 34/70. At the later phase of the fermentation test, however, the fermentation rate of the STA1 yeast strain was faster than those of the other strains. The concentration of ethanol in the culture supernatant of the STA1 yeast strain after the fermentation test was higher than those of the others. The concentration of all maltooligosaccharides in the culture supernatant of the STA1 yeast strain after the fermentation test was lower than those of the parent and reference strains, whereas the concentrations of flavour compounds in the culture supernatant were higher. These effects are due to the glucoamylase secreted by the constructed STA1 yeast strain. In summary, a glucoamylase‐secreting diploid yeast has been constructed by mating that will be useful for producing novel types of beer owing to its different fermentation pattern and concentrations of ethanol and flavour compounds. Copyright © 2017 The Institute of Brewing & Distilling     

双酶法水解橡子淀粉工艺研究

为掌握中温α-淀粉酶和糖化酶联合水解橡子淀粉的工艺条件,该研究在单因素试验的基础上,运用正交试验设计方法对橡子中的淀粉水解工艺进行了研究和优化。结果表明,橡子淀粉最佳液化工艺条件为中温α-淀粉酶添加量30 U/g,液化温度70 ℃,CaCl2添加量0.3%,液化pH 7.5,液化时间120 min,葡萄糖当量（DE）值为27.79%;最佳糖化工艺条件为糖化酶添加量300 U/g,糖化温度50 ℃,糖化pH 4.5,糖化时间120 min,DE值为48.13%。     

交联糖化酶聚集体的制备

为了克服游离糖化酶的部分缺点,将游离糖化酶用合适的沉淀剂沉淀后,再用戊二醛作为交联剂进行交联,制备了新型的固定化糖化酶-交联糖化酶聚集体。研究结果表明,糖化酶最适聚集条件为:pH5.6,20℃,5g/L的糖化酶液中加入叔丁醇沉淀,可获得比较理想的糖化酶聚集体;最适交联条件为:向糖化酶聚集体中加入10%戊二醛水溶液交联120min,再经离心、洗涤数次后即得交联糖化酶聚集体,酶活力为游离糖化酶的40.4%。     

黑曲霉产糖化酶固态发酵营养条件优化研究

实验以黑曲霉作为出发菌株,采用单因素试验确定黑曲霉固态发酵的最佳的碳源和氮源添加量,选取正交试验L9(33),确定该菌株产糖化酶最佳营养条件.结果表明,糖化酶固态发酵最佳营养条件为麸皮/玉米粉2∶1; (NH4)2SO4 1.0％; K2HPO4 0.2％;水50％.在该最佳营养条件下及发酵温度30℃、发酵5d后,该菌株产糖化酶的活力为11282U/g,比原始培养基提高了21％,本研究可以为工业固态发酵生产糖化酶提供一定的技术依据.