Mechanism Study on the Severe Foaming of Rhamnolipid in Fermentation

Abstract

Although the biosurfactant rhamnolipid has been previously characterized as having low foam ability, its fermentation is largely impeded by severe foaming. Hence, the investigation of this paradox is critically important for improving the mass production of rhamnolipid. Unexpectedly, the hydrophobic cell, instead of rhamnolipid, has been claimed to explain such severe foaming in rhamnolipid fermentation. This study tried to systematically investigate the severe foaming in fermentation, aiming to propose an effective strategy for foam control. The overflowing foam sustained a super high stability in terms of half‐time for over 30 min. The major product of rhamnolipid largely contributed to the severe foaming in the fermentation process whereas other products like cells elicited much more limited effects. Furthermore, the foam stability of the fermentation broth increased with rhamnolipid concentration and noticeably increased with agitation speed. In the classic Bikerman foam test system without stirring, rhamnolipid showed foam stability as low as Tween 20 which is well known for its poor foam stability. However, in a stirring Bikerman system, rhamnolipid exhibited a foam stability almost as high as sodium dodecyl sulfate (SDS) at 10 g/L and even surpassed SDS at a higher concentration of 20 g/L. Hence, the extraordinarily increased foam stability of rhamnolipid with both agitation and concentration could explain the severe foaming at its late‐stage fermentation when rhamnolipid‐rich solution is mechanically agitated.

Extraction Separation of Rhamnolipids by n‐Hexane via Forming Reverse Micelles

“…Pseudomonas aeruginosa ZJU211 was inoculated into 30 mL of the culture medium in a 150 mL flask and cultured in a shaking incubator (ZWY-2102C, Zhicheng, Shanghai, China) at 37 C and 220 rpm for 48 h. Then, the culture was inoculated at 3% (v/v) into 100 mL of culture medium in a 500 mL flask and grown for 48 h as the seed for batch fermentation of RL in a 10 L bioreactor (GUJS-10C, Eastbiotech, Zhenjiang, China) (Long et al, 2016). The fermentation was performed under an agitation speed of 300 rpm at 37 C for 96 h.…”

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

“…Currently, rhamnolipid production on the large scale was still limited due to its low yields and high production costs [4]. Especially, the extreme foaming problem in aerobic fermentation was thought to be a main challenge [5,6]. Severe foaming inhibits cell growth and product accumulation by reducing the working volume, bioavailability of substrates, mass transfer efficiency of oxygen and other adverse physical or biological effects [7,8].…”

“…Considering these, fed-batch fermentation was considered as more efficient in maintaining the biomass growth rate and rhamnolipid productivity [19,[21][22][23]. However, rhamnolipid is both the target product and major contributor to severe foam problems, and more rhamnolipid production would cause more severe form problem, which need more efficient foam controlling strategy [6].…”

Enhancing rhamnolipid production and exploring the mechanisms of low-foaming fermentation under weak-acid conditions

“…However, despite their potential, the industrial application of rhamnolipid was restricted seriously since the cost of rhamnolipid production was approximate ten times that of synthetic surfactant [11]. One of the major reasons was due to the severe foaming in fermentation [12][13][14]. Although a large quantity of fermentation strategies, including anaerobic [15,16] and solid fermentation [14,17,18] have attempted to solve the severe foaming, submerged liquid fermentation still seems to be the sole approach for the high-yield production of rhamnolipid at present [19].…”

“…Although a large quantity of fermentation strategies, including anaerobic [15,16] and solid fermentation [14,17,18] have attempted to solve the severe foaming, submerged liquid fermentation still seems to be the sole approach for the high-yield production of rhamnolipid at present [19]. Therefore, to reduce foaming behavior in submerged liquid fermentation of rhamnolipid have become an urgent requirement for the large-scale production and application of rhamnolipid [13]. In this respect, some fermentation strategies such as fermentation-defoaming tandem system, foam fractionation fermentation [20,21] and foam adsorption fermentation [22,23] have been carried out, but all of these fermentation strategies were ex-situ and caused some problems such as loss of culture uid, high contamination risk and increasing cost of equipment.…”