The Isolation And Screening Of A Thermostable α-Amylase-Producing Strain And The Studies On Its Fermentation Condition And Enzyme Characteristics

Amylases are consisted of a series of enzymes, which occupy 25% of the enzyme market. They are widely used in many fields such as the fabrication of wine and sugar, medicine, textile, prints and environment treatment etc. Now it is hoped thatα-amylase could be highly active at the high temperatures for better gelatinization and liquefaction in order to economize the costs. The thermostable alkaliphilic amylase can be highly active in the temperature range of 80℃~100℃and pH range of pH 8.0~pH 10.0. We have seriously investigated the growth characteristic of a bacterial strain which can produce thermostable amylase and the characteristic of this amylase that it produced. This strain was screened from hot spring of Dangxiong, Tibet. It was identified as Bacillus licheninformis and named as B. licheninformi LT after biochemistry, physiological tests and compared with the datas from GeneBank.We had also established the method for calculating the enzyme activity by ultraviolet-visible absorption spectroscopy. The cell growth and enzyme production conditions in the LB culture medium were tested and found that: The starch can stimulate the enzyme production. The maximal temperature for growth was 65℃, and the optimum temperature was 50℃; the optimal pH value for growth was 3.0~11.0, and at pH10.0 for enzyme production.This strain produced 65U amylase activity. After cultivated in the optimized medium (soy power 1.5, corn power 1.5, NaCl 1,K2HPO4 0.01, KH2PO4 0.01, CaCl2 0.4, span40 0.1,pH 10.0) at this condition (50℃,with shaking 180r/min) for 72 h in 100 mL erlenmeyer flask, the activity ofα-amylase obtained 105U. By centrifuge and precipitation, we have obtained about 3 g light yellow solid enzyme with a little pungent smell after the fermentation of 350 mL broth.The characteristics of the thermostableα-amylase were also discussed. The optimal temperature and pH for the enzyme were determined as 95℃and 10.0 respectively. 2 mmol/L Ca2+ can enhance the enzyme activity in the temperature range of 60℃~80℃. Over 80℃, Ca2+ effects as inhibitor. 4 mmol/L Ca2+ was totally inhibitor for the enzyme activity. We can also observe the same phenomenon for Mg2+. Its positive effect exists in the range of 60℃~90℃. The activity was enhanced by the presence of glycin,Li+,Fe2+,Sn2+,while strongly inhibited by Cu2+,Fe3+,Zn2+,Bi3+,Al3+, however, (NH3)3PO4,K2HPO4,Ba2+ had little influence on it. The kinetics measurements indicated that this enzyme reaction is substrate inhibition.At last, desizing technology for cotton fabric with amylase is researched, and influence factors on amylase desizing of amylase concentration, amylase temperature, pH value, metallic salts and processing time are discussed, and superior process of amylase desizing is defined. Compared with traditional alkali desizing, the feasibility for amylase desizing instead of alkali desizing in cotton fabric to reduce environment pollution is deduced.