Xu Ning, Liu Shixun, Xu Lijie, Zhou Jie, Xin Fengxue, Zhang Wenming, Qian Xiujuan, Li Min, Dong Weiliang, Jiang Min
1State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Puzhu South Road 30#, Nanjing, 211816 People's Republic of China.
2Jiangsu Key Laboratory for Biomass-based Energy and Enzyme Technology, Huaiyin Normal University, Huai'an, People's Republic of China.
Biotechnol Biofuels. 2020 Apr 24;13:80. doi: 10.1186/s13068-020-01716-w. eCollection 2020.
Rhamnolipids are the best known microbial-derived biosurfactants, which has attracted great interest as potential ''green" alternative for synthetic surfactants. However, rhamnolipids are the major contributors to severe foam problems, which greatly inhibit the economics of industrial-scale production. In this study, a novel foam-control system was established for ex situ dealing with the massive overflowing foam. Based on the designed facility, foam reduction efficiency, rhamnolipids production by batch and repeated fed-batch fermentation were comprehensively investigated.
An ex situ foam-control system was developed to control the massive overflowing foam and improve rhamnolipids production. It was found that the size of individual bubble in the early stage was much larger than that of late fermentation stage. The foam liquefaction efficiency decreased from 54.37% at the beginning to only 9.23% at the end of the fermentation. This difference of bubble stability directly resulted in higher foam reduction efficiency of 67.46% in the early stage, whereas the small uniform bubbles can only be reduced by 57.53% at the later fermentation stage. Moreover, reduction of secondary foam is very important for foam controlling. Two improved designs of the device in this study obtained about 20% improvement of foam reduction efficiency, respectively. The batch fermentation result showed that the average volume of the overflowing foam was reduced from 58-640 to 19-216 mL/min during the fermentation process, presenting a notable reduction efficiency ranging from 51.92 to 73.47%. Meanwhile, rhamnolipids production of batch fermentation reached 45.63 g/L, and the yield 0.76 g/g was significantly better than ever reported. Further, a repeated fed-batch fermentation based on the overall optimization was carried out. Total rhamnolipids concentration reached 48.67 g/L with the yield around of 0.67-0.83 g/g, which presented an improvement of 62% and 49% compared with conventional batch fermentation by using various kinds of defoamers, respectively.
The ex situ foam-control system presented a notable reduction efficiency, which helped greatly to easily solve the severe foaming problem without any defoamer addition. Moreover, rhamnolipids production and yield by repeated fed-batch fermentation obtained prominent improvement compared to conventional batch cultivation, which can further facilitate economical rhamnolipids production at large scales.
鼠李糖脂是最著名的微生物源生物表面活性剂，作为合成表面活性剂的潜在“绿色”替代品备受关注。然而，鼠李糖脂是严重泡沫问题的主要成因，极大地制约了工业规模生产的经济性。本研究建立了一种新型泡沫控制系统，用于异位处理大量溢出的泡沫。基于所设计的装置，全面研究了泡沫减少效率、分批发酵和重复补料分批发酵生产鼠李糖脂的情况。
开发了一种异位泡沫控制系统，以控制大量溢出的泡沫并提高鼠李糖脂产量。发现发酵前期单个气泡的尺寸比后期大得多。泡沫液化效率从开始时的54.37%降至发酵结束时的仅9.23%。这种气泡稳定性的差异直接导致前期泡沫减少效率更高，为67.46%，而后期发酵阶段小而均匀的气泡只能减少57.53%。此外，减少二次泡沫对泡沫控制非常重要。本研究中该装置的两种改进设计分别使泡沫减少效率提高了约20%。分批发酵结果表明，发酵过程中溢出泡沫的平均体积从58 - 640降至19 - 216 mL/分钟，减少效率显著，在51.92%至73.47%之间。同时，分批发酵的鼠李糖脂产量达到45.63 g/L，产率为0.76 g/g，明显优于以往报道。此外，基于整体优化进行了重复补料分批发酵。鼠李糖脂总浓度达到48.67 g/L，产率约为0.67 - 0.83 g/g，与使用各种消泡剂的传统分批发酵相比，分别提高了62%和49%。
异位泡沫控制系统具有显著的减少效率，有助于在不添加任何消泡剂的情况下轻松解决严重的泡沫问题。此外，与传统分批培养相比，重复补料分批发酵生产鼠李糖脂的产量和产率有显著提高，这可以进一步促进大规模鼠李糖脂的经济生产。
