Effects Of Soybean Oil On The Fermentation Of GA3 Produced By Gibberella Fujikuroi 978

Gibberellic acid (GA3) is a commercially important plant growth hormone, which is produced by submerged fermentation using the fungus Gibberella fujikuroi. However, the poor titer of fermentation has restricted its use to preclude application for plant growth promotion, except for certain high value plants. To improve the yield of GA3 produced by Gibberella fujikuroi 978, several means of soybean oil used in the process of GA3 fermentation were studied. The work will be greatly helpful for the industrial production of GA3.Firstly, the role of vegetable oils in the starch used as the main carbon source of fermentation was studied based on the starch medium. The concentration and time of soybean oil added were important to the titer of GA₃ fermentation, which was proved by the investigation of the soybean oil added to the starch medium. Soybean oil increased the yield of GA3 when it was added at the storage phase of the fermentation and was utilized perfectly by the fungus. The titer of GA3 could be increased by 21 % in flask and by nearly 20 % in 10 L fermenter compared with that of the control, when 1.0 % (W/V) soybean oil was added to the starch medium as the control after 60 h cultivation. Further, the effect of added-batch soybean oil on the GA3 fermentation also was tested, and the importance of the concentration and time of soybean oil added was similarly acquainted. The results showed that the production of GA3 were improved respectively by 26 % and by 29 % when both of 0.5 % (W/V) soybean oil was added to the starch medium after 60 h and 108 h cultivation in flask and in 10 L fermenter.Then the soybean oil used as the main carbon source of fermentation was researched. The DO value of broth was affected markedly by the concentration of soybean oil, and the biomass of the fungus and the titer of GA3 would be impacted by the DO. The rational soybean oil medium including 6.0 % (W/V) soybean oil and 1.2 % peanut powder with adding 0.001mol/L MnSO₄ and 0.1 % PEG, which other ingredients were same as the starch medium, could increased the titer of GA3 by 32 % in flask and by nearly 30 % in 10 L fermenter compared with the starch medium. The influenced of added-batch soybean oil on the GA3 produced by the oil as the carbon source was significant, especially the concentration and time of soybean oil added. The results showed that the production of GA3 was effectively improved by 38 % when 3.0 % (W/V) soybean oil acted as the original carbon source and added 2.0 % soybean oil and 1.0 % one after 60 h and 108 h cultivation in flask. But themechanism of the added-batch fermentation about GA3 production should be research in order to guide the reasonable added-batch means.The results in the experiments of offering different mainly carbon source in the different phase showed: the means of fermentation, which starch acted as the initial carbon source with an appropriate concentration of soybean oil in order to induced and maintained lipase activity and added soybean oil based the trend of residual glucose and lipase activity of the broth, would produce the perfect biomass of the fungus then obtain the fine titer of GA3 and avoid the residual oil in the end of the fermentation. Adding 1.0 % (W/V)soybean oil in the medium of the initial 4 % corn starch which the concentration of sugar be required at about 22 g/L and feeding 4.0 %(W/V)of soybean oil after 60 h cultivation was established. The GA3 yields could be increased by 32 % in flask and nearly 38 % in 10 L fermenter compared with that of the control. In the experiments of fed-batch oil, the results indicated the oil should be fed in the storage phase of the fermentation which can ensure oil to be sufficiency utilized. In flask, the yield of GA3 higher by 40 % than the control in the condition that 2.0 %(W/V) would be each fed to the optimal initial medium after 60 h and 108 h cultivation.