Enhanced rhamnolipids production using a novel bioreactor system based on integrated foam-control and repeated fed-batch fermentation strategy

Abstract

Background: 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. Results: 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. Conclusions: 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

Evaluation of the Antimicrobial Efficacy of N-Acetyl-l-Cysteine, Rhamnolipids, and Usnic Acid—Novel Approaches to Fight Food-Borne Pathogens

“…In this work, three types of natural substances (NAC, RLs, and UA) were tested for their ability to inhibit bacterial growth, prevent biofilm formation, and reduce biofilm mass of four selected bacterial food-borne pathogens (Gram-positive L. monocytogenes, S. aureus, and Gram-negative E. coli, S. enterica Infantis, and Enteritidis). Information regarding the antimicrobial efficacy of NAC, RLs, and UA against food-borne pathogens is sparse; however, all the substances previously showed promising antimicrobial efficacy against other pathogens [15][16][17][18][19][22][23][24][25][26][27][28][29][30][31][32][33].…”

“…coli , S. enterica Infantis, and Enteritidis). Information regarding the antimicrobial efficacy of NAC, RLs, and UA against food-borne pathogens is sparse; however, all the substances previously showed promising antimicrobial efficacy against other pathogens [ 15 , 16 , 17 , 18 , 19 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ].…”

“…This strongly suggests that additional, potentially less conventional approaches are needed to control biofilm formation in food industry settings. One possible strategy is to employ natural substances, such as N -Acetyl -l- cysteine (NAC), rhamnolipids (RLs; R90), and (+)-usnic acid (UA), all of which previously showed promising antimicrobial efficacy against important clinical pathogens [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Other benefits of these substances are their solubility, affordability, and chemical stability.…”

“…While RLs can be produced by diverse organisms [ 23 , 24 , 25 , 26 ], the best-studied ones were isolated from cultures of Pseudomonas aeruginosa [ 23 , 26 ]. They have been utilized in a wide range of applications, including medicine (anticancer and antibiofilm agents), cosmetics (cosmetic formulations), the food industry (additives and antimicrobial agents), biofuels, and in bioremediation of pesticides and heavy metals [ 24 , 25 , 26 , 27 ]. Although the mechanism of action is not completely understood, it is supposed that RLs may disturb membrane structure through interactions with phospholipids and membrane proteins [ 23 , 28 ].…”

Uncoupling Foam Fractionation and Foam Adsorption for Enhanced Biosurfactant Synthesis and Recovery

“…In this context, an in situ extraction with a biocompatible and low-priced solvent followed by solvent recycling was recently presented by Demling et al [ 42 ]. Proven mechanical systems to prevent or limit surfactant mediated foaming are specific gassing membranes for bubble-free aeration or foam destruction by compression or centrifugation [ 14 , 40 , 43 , 44 , 45 , 46 ]. Such installations cannot avoid inhomogeneities in the reactor headspace and external pipelines.…”