Piedrahíta-Aguirre C A, Bastos R G, Carvalho A L, Monte Alegre R
Department of Food Engineering, College of Food Engineering, State University of Campinas, P.O. Box 6121, Campinas, SP, 13083-862, Brazil,
Bioprocess Biosyst Eng. 2014 Aug;37(8):1569-76. doi: 10.1007/s00449-014-1129-1. Epub 2014 Feb 7.
The strain Bacillus iso 1 co-produces the lipopeptide iturin A and biopolymer poly-γ-glutamic acid (γ-PGA) in solid-state fermentation of substrate consisting of soybean meal, wheat bran with rice husks as an inert support. The effects of pressure drop, oxygen consumption, medium permeability and temperature profile were studied in an aerated packed bed bioreactor to produce iturin A, diameter of which was 50 mm and bed height 300 mm. The highest concentrations of iturin A and γ-PGA were 5.58 and 3.58 g/kg-dry substrate, respectively, at 0.4 L/min after 96 h of fermentation. The low oxygen uptake rates, being 23.34 and 22.56 mg O2/kg-dry solid substrate for each air flow rate tested generated 5.75 W/kg-dry substrate that increased the fermentation temperature at 3.7 °C. The highest pressure drop was 561 Pa/m at 0.8 L/min in 24 h. This is the highest concentration of iturin A produced to date in an aerated packed bed bioreactor in solid-state fermentation. The results can be useful to design strategies to scale-up process of iturin A in aerated packed bed bioreactors. Low concentration of γ-PGA affected seriously pressure drop, decreasing the viability of the process due to generation of huge pressure gradients with volumetric air flow rates. Also, the low oxygenation favored the iturin A production due to the reduction of free void by γ-PGA production, and finally, the low oxygen consumption generated low metabolic heat. The results show that it must control the pressure gradients to scale-up the process of iturin A production.
菌株芽孢杆菌iso 1在以豆粕、麦麸和稻壳为惰性载体的底物固态发酵中共同产生脂肽伊枯草菌素A和生物聚合物聚γ-谷氨酸（γ-PGA）。在一个直径为50 mm、床高为300 mm的曝气填充床生物反应器中研究了压降、氧气消耗、培养基渗透性和温度分布对伊枯草菌素A生产的影响。发酵96小时后，在0.4 L/min的条件下，伊枯草菌素A和γ-PGA的最高浓度分别为5.58和3.58 g/kg干底物。在所测试的每个空气流速下，低氧气吸收率分别为23.34和22.56 mg O2/kg干固体底物，产生了5.75 W/kg干底物，使发酵温度升高了3.7℃。在24小时内，0.8 L/min时的最高压降为561 Pa/m。这是迄今为止在曝气填充床生物反应器固态发酵中产生的伊枯草菌素A的最高浓度。这些结果对于设计在曝气填充床生物反应器中扩大伊枯草菌素A生产工艺的策略可能是有用的。低浓度的γ-PGA严重影响了压降，由于随着体积空气流速产生巨大的压力梯度，降低了该工艺的可行性。此外，低氧合作用有利于伊枯草菌素A的产生，因为γ-PGA的产生减少了自由空隙率，最后，低氧气消耗产生了低代谢热。结果表明，在扩大伊枯草菌素A生产工艺时必须控制压力梯度。
