Enhancement Of Oxygen Transfer In Mycelia Fermentation System By Adding Oxygen-vectors

In this work, the study was carried out for the relatively low oxygen solubility in the Aspergillus Niger fermentation by adding some oxygen-vectors (organic phase) to enhance the acidic protease production and the oxygen transfer in oxygen-vector fermentation system was initially studied.1. The optimal fermentation medium, which was obtained by the single factor experiment and the uniform design test, was as following: soybean hydrolyzed liquidll.9%, maze syrup0.509%, NH4C10.632%, CaCl20.5%, Na2HPO40.475%, MgSO4 . 7H2O0.9825%, pH5.5-6.0, and under the optimal fermentation conditions, the highest enzyme activity reached to 1782.49U/ml.2. The optimal reactive conditions of the crude enzyme from the Aspergillus Niger were obtained with orthogonal test as follow: pH 3.0, substrate concentration 0.6% and the treatment temperature 40C. It was found that the temperature has the greatest effect on the hydrolysis reaction, and then is the substrate concentration, the system pH.3. Due to the significant oxygen requirement during acidic protease production and the relatively low solubility of oxygen in water, aeration is critical. Several oxygen-vectors, namely acetic ether, oleic acid, soybean oil, n-dodecane and Tween-80, in enhancing acidic protease accumulation were examined for the oxygen transfer process. Shake flask fermentation were conducted using different oxygen-vector concentrations. According to the price and safety, the addition of 2%(V/V) oleic acid was considered, which enhanced acidic protease accumulation, reduced residual glucose concentration and stimulated mycelial growth. Adding oleic acid had no adverse effects on the cells of Aspergillus Niger.4. During the single factor experiment, some factors, such as oxygen-vector concentration, fermentation medium pH and adding time, have great effect on the enzyme production and enhancement of the oxygen transfer. Jn order to acquire the optimal adding strategy, I designed the test with Response Surface Method(RSM) and analyzed the data with SAS statistic tool and finally obtained the following adding strategy: the oxygen-vector concentration of 2.64%, the adding time 36.99h, the fermentation medium pH3.74 and the fermentation is also carried out in 5L BIOSTAT瓸 fermenter.5. By the tank fermentation, the relationship between kLa and the stirring power N, the gas volume Vs, the volume of oxygen-vector , respectively, were obtained as follows:6. According to the cell hydrophobicity to the oil phase, I obtained the oxygen transfer process, as gas-water-cell and gas-oil-water-cell etc., in the oleic acid fermentation system. And the mechanism of oxygen vector enhanced oxygen transfer can be summered to reducing the gas membrane on the gas-liquid edge, increasing the specific area a and also receding the transfer coefficient kL from the gas to liquid phase. Additionally, the oil phase may have effects on the cell surface flocculation and it can increase the efficient of oxygen transfer as well.